Prepared in cooperation with the Colorado Geological Survey for the

United States Department of Agriculture Forest Service

Development of Industrial Minerals in Colorado

U.S. Department of the Interior

U.S. Geological Survey

Circular 1368

Development of Industrial Minerals in Colorado

By Belinda F. Arbogast, Daniel H. Knepper, William H. Langer, Jr., James A. Cappa, 

John W. Keller, Beth L. Widmann, Karl J. Ellefsen, Terry L. Klein, Jeffrey E. Lucius, 

and John S. Dersch

Prepared in cooperation with the Colorado Geological Survey for the United 

States Department of Agriculture Forest Service

Circular 1368

U.S. Department of the Interior

U.S. Geological Survey
U.S. Department of the Interior

KEN SALAZAR, Secretary

U.S. Geological Survey

Marcia K. McNutt, Director

U.S. Geological Survey, Reston, Virginia: 2011

For more information on the USGS—the Federal source for science about the Earth, its natural and living resources, 

natural hazards, and the environment, visit http://www.usgs.gov or call 1-888-ASK-USGS

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Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement 

by the U.S. Government.

Although this report is in the public domain, permission must be secured from the individual copyright owners to 

reproduce any copyrighted materials contained within this report.

Suggested citation:

Arbogast, B.F., Knepper, D.H., Langer, Jr., W.H., Cappa, J.A., Keller, J.W., Widmann, B.L., Ellefsen, K.J., 

Klein, T.L., Lucius, J.E., and Dersch, J.S., 2011, Development of industrial minerals in Colorado: U.S. Geological Survey 

Circular 1368, 87 p.

Library of Congress Cataloging-in-Publication Data

Development of industrial minerals in Colorado / Belinda F. Arbogast ... [et al.].

 p. cm. -- (Circular ; 1368)

 “Prepared in cooperation with the Colorado Geological Survey for the United States Department of 

Agriculture Forest Service.”

 Includes bibliographical references.

 ISBN 978-1-4113-3118-1 (pbk.)

 1. Mines and mineral resources--Colorado. I. Arbogast, B. F. (Belinda F.) II. Colorado Geological Survey. 

III. Geological Survey (U.S.) 

 TN24.C6D48 2011

 338.2’309788--dc23

 2011023893
iii

Contents

Prologue ..........................................................................................................................................................1

Introduction.....................................................................................................................................................1

The Need for Industrial Minerals.......................................................................................................1

Definition and Characteristics of Industrial Minerals ....................................................................2

Competing Land Uses and Industrial Minerals................................................................................4

Central Colorado Assessment Project .......................................................................................................5

Regulation of Mining for Industrial Minerals ............................................................................................8

Overview.................................................................................................................................................8

Regulation Outside the United States ...............................................................................................9

International Laws and Agreements ........................................................................................9

Best Management Practices Outside the United States ....................................................10

Federal Regulations............................................................................................................................11

Locatable Minerals....................................................................................................................11

Leasable Minerals .....................................................................................................................13

Saleable Minerals......................................................................................................................13

Mineral Specimens Sought by Collectors .............................................................................13

USDA Forest Service and Bureau of Land Management Regulations .............................14

State Regulations................................................................................................................................15

Municipal and County Regulations..................................................................................................18

Production of Industrial Minerals .............................................................................................................18

Overview...............................................................................................................................................18

Care of Physical and Cultural Landscapes.....................................................................................24

Exploration Activities..........................................................................................................................26

Marketing Study.........................................................................................................................26

Geological and Geophysical Exploration...............................................................................26

Sampling and Analysis..............................................................................................................26

The Physical Environment—Geotechnical Concerns ..................................................................28

Acid Mine Drainage ..................................................................................................................28

Air Pollutants and Noise...........................................................................................................28

Erosion and Slope Stability ......................................................................................................29

Water Management ..................................................................................................................31

The Biological Environment—Flora and Fauna.............................................................................31

The Visual Environment—Measuring Landscape Quality...........................................................34

Visual Analysis ...........................................................................................................................34

User Analysis..............................................................................................................................35

USDA Forest Service and Bureau of Land Management Visual Assessment ................37

Other Visual Assessment Methods.........................................................................................37

The Socioeconomic Environment—Efficiency, Equity, and Acceptability................................41

Reclamation and Postmining Use ....................................................................................................42

Colorado Industrial Minerals—Occurrence, Use in Colorado, Mining, and Production.................47

Introduction..........................................................................................................................................47

Clays and Shale...................................................................................................................................47

Classification by Use.................................................................................................................48
iv

Geology of Colorado Clay and Shale Deposits .....................................................................49

Mining and Production .............................................................................................................49

Sand and Gravel (Construction) .......................................................................................................51

Geology of Colorado Sand and Gravel Deposits ..................................................................52

Mining and Production .............................................................................................................52

Silica Sand (Industrial).......................................................................................................................53

Geology of Colorado Silica Sand Deposits............................................................................53

Mining and Production .............................................................................................................53

Crushed Stone.....................................................................................................................................54

Geology of Colorado Crushed Stone Deposits......................................................................54

Mining and Production .............................................................................................................55

Limestone.............................................................................................................................................55

Geology of Colorado Limestone Deposits..............................................................................55

Mining and Production .............................................................................................................56

Gypsum.................................................................................................................................................56

Geology of Colorado Gypsum Deposits..................................................................................56

Mining and Production .............................................................................................................57

Lightweight Aggregates—Pumice, Scoria, Perlite, and Vermiculite.........................................59

Classification of Lightweight Aggregates..............................................................................59

Geology of Colorado Lightweight Aggregate Deposits .......................................................59

Mining and Production .............................................................................................................60

Dimension Stone.................................................................................................................................60

Classification by Rock Groups.................................................................................................61

Geology of Colorado Dimension Stone Deposits..................................................................63

Mining and Production .............................................................................................................65

Feldspar and Mica..............................................................................................................................65

Geology of Colorado Feldspar and Mica Deposits ..............................................................67

Mining and Production .............................................................................................................67

Sulfur.....................................................................................................................................................67

Geology of Colorado Sulfur Deposits .....................................................................................68

Mining and Production .............................................................................................................68

Barite.....................................................................................................................................................68

Geology of Colorado Barite Deposits .....................................................................................69

Mining and Production .............................................................................................................69

Diamonds, Gemstones, and Mineral Specimens ..........................................................................69

Classification by Mineral Variety ............................................................................................69

Geology of Colorado Gemstone and Hand Specimen Dep osits........................................72

Mining and Production .............................................................................................................73

Fluorspar...............................................................................................................................................73

Geology of Colorado Fluorspar Deposits ...............................................................................73

Mining and Production .............................................................................................................74

Nahcolite..............................................................................................................................................74

Geology of Colorado Nahcolite Deposits...............................................................................75

Mining and Production .............................................................................................................75

Titanium ................................................................................................................................................76

Geology of Colorado Titanium Deposits.................................................................................76
v

Mining and Production .............................................................................................................76

Zeolite ...................................................................................................................................................77

Geology of Colorado Zeolite Deposits....................................................................................77

Mining and Production .............................................................................................................78

References Cited..........................................................................................................................................78

Figures

1. Photograph of stone villages at Mesa Verde National Park, southwestern Colorado.....2

2. Cartoon showing estimated lifetime use of minerals, metals, and fuels.............................2

3. Photographs of industrial minerals being mined or in use....................................................3

4. Photographs showing urban growth in Colorado ...................................................................5

5. Map of Colorado showing area of Central Colorado Assessment Project.........................6

6. Map of Federal land, major mining districts, counties, and cities in Colorado..................7

7–27. Photographs showing the following:

7. Gravel pit, Seattle, Wash., 1907.........................................................................................8

8. Mitigation methods used at open-pit mines....................................................................9

9. Glensanda granite quarry, coastal Scotland ................................................................10

10. Recycled asphalt and concrete, Denver, Colorado.....................................................11

11. Thirteenth-century Puebloan structure in Canyons of the Ancients National 

Monument, southwestern Colorado...............................................................................14

12. Mine sites or quarries preserved for recreational use...............................................17

13. Extraction of granite and of sand and gravel................................................................22

14. Landscapes that contain natural and manmade features..........................................25

15. Gravel tip and rocky outcrops, Wind River Reservation, Wyoming..........................25

16. Geologists collecting seismic data.................................................................................27

17. Deteriorated concrete bridge pillars..............................................................................27

18. Rock face in an industrial sand pit..................................................................................30

19. Wood fiber netting used to prevent erosion until grass is established....................30

20. Sedimentation pond at a coal mine site near Craig, Colorado ..................................31

21. Columbian sharp-tailed grouse and reclaimed mine land near Craig, Colorado....32

22. Revegetation of mined lands ...........................................................................................33

23. Arid-region rock coatings ................................................................................................33

24. Gay Head Cliffs, Martha’s Vineyard, Massachusetts..................................................35

25. Disparate uses of water in England and Spain ............................................................36

26. Landscape in Yellowstone National Park......................................................................36

27. Natural landscape features that mimic manmade features ......................................40

28. Wood block print of mineral beneficiation in the 1500s.......................................................41

29–37. Photographs showing the following:

29. Before and after quarry restoration, Arkansas ............................................................43

30. Reclamation work at Howe pit, Colorado......................................................................43

31. Natural and manmade camouflage of a gravel pit, Colorado ....................................44

32. Restored mined areas.......................................................................................................44

33. Reclaimed mined land that serves community needs.................................................45
vi

34. Quarries used to educate the public about mining......................................................46

35. Large reclamation art works............................................................................................46

36. Reclaimed land that provides wildlife habitat ..............................................................46

37. Landscapes incorporating historical mining structures.............................................47

38. Sketch of clay cliff, Colorado....................................................................................................48

39–61. Photographs showing the following:

39. Fire clay, sandstone, and shale in Dakota Sandstone hogback................................50

40. Poor drainage on bentonite, Albany County, Wyoming ..............................................50

41. Stockpiles at a sand and gravel mine ............................................................................52

42. Hydraulic mining of industrial sand................................................................................53

43. Limestone quarries............................................................................................................56

44. Gypsum-containing construction materials and a gypsum mine..............................57

45. Gypsum quarry, Colorado.................................................................................................58

46. Raw and heat-expanded vermiculite .............................................................................60

47. Dimension stone being processed and in use..............................................................61

48. Granite used as building facing and sketch of granite outcrop. ...............................62

49. Yule Marble quarry, Colorado..........................................................................................63

50. Lyons Sandstone in outcrop and in use.........................................................................64

51. Contact between Sawatch Quartzite and Pikes Peak Granite ..................................65

52. Mica in outcrop and in scanning electron micrograph ..............................................66

53. Scientists working underwater at a reef.......................................................................68

54. Diamond fields in Arkansas .............................................................................................70

55. Sawatch Range, Colorado................................................................................................70

56. Rhodochrosite specimen..................................................................................................72

57. Nelly E garnet mine, Colorado.........................................................................................74

58. Fault zone between Tertiary rhyolite tuff and Precambian rocks .............................75

59. Nahcolite plant, Colorado.................................................................................................76

60. Zeolite as seen in a scanning electron micrograph ....................................................77

61. Small zeolite production pit, Oregon ..............................................................................78

Tables

1. Preliminary population forecasts for Colorado by region, 2000–2030 .................................4

2. Typical Federal conservation laws or policies and their implications for mining............12

3. Typical State policies and their implications for mining ......................................................16

4. Typical county or municipal policies and their implications for mining ............................19

5. Principal industrial minerals of Colorado—uses and source areas..................................20

6. Average unit price of and industry efforts to conserve deposits of certain mineral 

commodities ................................................................................................................................23

7. Volumes of six pollutants released by various industries....................................................29

8. Clay processing operations by type of clay ...........................................................................51
vii

Conversion Factors

Multiply By To obtain

kilometer (km) 0.6214 mile (mi)

meter (m) 3.281 foot (ft) 

meter (m) 1.094 yard (yd) 

centimeter (cm) 0.3937 inch (in.)

micrometer (μm) 3.937 inch (in.)

Abbreviations Used in This Report

Abbreviated units used in this report

Ga giga-annum; billions of years ago

Ma mega-annum; millions of years ago

μm micrometer (1 millionth meter)

cm centimeter or centimeters

ft Foot or feet

in. inch, inches

lb pound

m meter, meters

mm millimeter, millimeters

Abbreviated terms used in this report

B.C.E. Before Common Era

BLM U.S. Bureau of Land Management

USDA U.S. Department of Agriculture

USGS U.S. Geological Survey

ISO International Organization for Standardization

Prologue

Humans use technology to alter nature and landscapes in 

order to survive, express themselves, and suit their activities. 

The natural landscape changes, whereas we seek stability. We 

shape the landscape through science and art; through mining, 

managing national forests, constructing water reservoirs, and 

urban development. The societal values we attach to various 

resources reflect our culture, experience, education, and many 

other factors. Both culture and society’s approach to resource 

management change over time.

Natural landscapes face competition through increasing 

human populations and pressures from agriculture, housing, 

recreation, and mineral extraction. Humans have the capacity 

to create a wide variety of environments. We can create landscapes that satisfy our basic need for food, minerals, timber, 

and even wilderness.

Technology and engineering have helped make mining 

safer and cleaner for both humans and the environment. Inevitably, mineral development entails costs as well as benefits. 

Developing a mine is an environmental, engineering, and planning challenge that must conform to many Federal, State, and 

local regulations. “The mining legacy in the Rocky Mountain 

region, though sometimes environmentally destructive in the 

past, left ‘simple and powerful structural forms [that] continue 

to inspire new designs’” (U.S. Department of Agriculture Forest Service, 2001, p. 163).

Community collaboration, creative design, and best management practices of sustainability and biodiversity can be 

positive indicators for the mining industry. A better understanding of aesthetics, culture, economics, geology, climate, 

vegetation and wildlife, topography, historical significance, 

and regional land planning is important in resolving land-use 

issues and managing mineral resources wisely. Ultimately, the 

consuming public makes choices about product use (including 

water, food, highways, housing, and thousands of other items) 

that influence operations of the mineral industry. Land planners, resource managers, earth scientists, designers, and public groups have a responsibility to consider sound scientific 

information, society’s needs, and community appeals in 

making smart decisions concerning resource use and how 

complex landscapes should change.

An effort to provide comprehensive geosciences data for 

land management agencies in central Colorado was undertaken in 2003 by scientists of the U.S. Geological Survey 

and the Colorado Geological Survey. This effort, the Central 

Colorado Assessment Project, addressed a variety of land-use 

issues in the Colorado Front Range, North Park, Middle Park, 

and South Park, and in the Gore Range, Mosquito Range, 

Sawatch Range, and Sangre de Cristo Mountains. Among the 

goals of the project was an understanding of the availability 

of industrial and metallic rocks and minerals, the geochemical and environmental effects of historic mining activity on 

surface water and groundwater, and the geologic controls on 

the availability and quality of groundwater.

For instance, large tracts of U.S. Department of Agriculture (USDA) Forest Service lands, which compose the majority of Federally administered lands in the Central Colorado 

Assessment Project, are underlain with sand and gravel or 

stone resources that could be used for construction purposes. 

The USDA Forest Service and other land management agencies have the opportunity to contribute to the sustainable 

management of natural aggregate and other mineral resources 

through the identification and selective development of mineral resources and the reclamation of mines on lands that they 

administer. The information in this Circular will help them 

carry out that task.

Introduction

The Need for Industrial Minerals

If you are reading this publication, you are using industrial minerals. Clay and chemicals made from other industrial 

minerals are used to make paper and ink. Without industrial 

minerals, there would be no roads, rail lines, or airports to 

deliver oranges from Florida or salmon from Alaska. There 

would be no foundations for our homes, schools, and commercial buildings, no insulated walls to keep out the cold, no 

paint, no bike paths, no rubber tires, and certainly no computers. Without industrial minerals, society as we know it would 

cease to exist.

Development of Industrial Minerals in Colorado

By Belinda F. Arbogast,1 Daniel H. Knepper,1 William H. Langer,1 Jr., James A. Cappa,2 John W. Keller,2

Beth L. Widmann,2

 Karl J. Ellefsen,1 Terry L. Klein,1 Jeffrey E. Lucius,1 and John S. Dersch3

1

U.S. Geological Survey, MS 973, Box 25046, Denver, CO 80226

2

Colorado Geological Survey, 1313 Sherman Street, Denver, CO 80203

3

USDA Forest Service, POB 25127, Lakewood, CO 80225
2 Development of Industrial Minerals in Colorado

On a small scale even prehistoric cultures and preindustrial Native Americans mined and used industrial minerals. In 

Colorado, Clovis period sites (dated between 11,200 and 10,900 

Before Common Era (B.C.E.)) have yielded projectile points 

and tools crafted from fine-grained rock and bone (Stone, 1999). 

At the Black Dumps site in the mountains of the San Isabel 

National Forest, Chaffee County (Prasciunas, 2003), Ancestral 

Puebloan and other peoples mined clay and sand for dwellings, 

pots, and decorative items; turquoise for trade, jewelry, and 

art; and cryptocrystalline quartz (flint or chert) for tool making 

(Murphy and Modreski, 2002). Obsidian, chalcedony, and other 

forms of glassy silica were quarried and used to manufacture 

tools and weapons. Crystalline igneous and metamorphic rocks 

were used as grinding implements. Prehistoric stone tools made 

from Colorado rocks have been found throughout the Rocky 

Mountain region (T. McMahon, written commun., 2003). 

Colorado’s first national park, Mesa Verde (west of Durango), 

was created in 1906 to preserve ancient Native American cliff 

dwellings built of stone (Noel and others, 1994) (fig. 1).

a major economic factor in the development of construction 

materials. Sand, gravel, and crushed stone are construction 

materials that typically undergo little or no processing before 

being used. Larger blocks of resistant stone (riprap) are 

needed to protect riverbanks, harbors, or shorelines from 

erosion. Smaller rocks are needed for railway ballast. Clay or 

ground shale can be formed and kiln dried into bricks used 

for construction (fig. 3). Other construction materials require 

additional processing, such as the sawing and polishing of 

granite for countertops.

Definition and Characteristics of Industrial 

Minerals

Minerals are natural inorganic substances that are “* * * the 

raw material on which all economic activity and life itself ultimately depend” (Daly and Farley, 2004, p. 74). Society requires 

certain minerals used in industry that are mined, quarried, or 

extracted from the Earth’s surface. The term “industrial mineral” 

applies to economically valuable geologic materials that are 

neither metals nor fuels; these minerals may be used for construction (such as sand and gravel or stone), agriculture (such as 

phosphate in fertilizers and insecticides), or industrial processes.

Mineral aggregates are valuable because of characteristics 

such as their bulk, weight, durability, compressive strength, lack 

of chemical reactivity, uniform composition, and other special 

features such as color, insulating value, and texture (McCarl, 

1994). The most useful mineral aggregates are free of chemically reactive constituents, especially the following: cement 

alkalis and unstable or noncrystalline forms of silica that react 

with each other to form an alkali-silica gel that may accelerate 

deterioration of concrete structures; zeolites and clays formed 

in weathered or hydrothermally altered rocks; and unstable iron 

minerals, particularly in the aggregate used in concrete, that 

oxidize and cause the concrete to develop rust stains, change 

volume, and lose strength (Christie and others, 2001a).

Figure 1. Elaborate stone villages built in sheltered alcoves of

canyon walls at Mesa Verde National Park, southwestern Colorado. 

Archeological sites range from pit houses built during the 500s to 

cliff dwellings of the 1200s. Courtesy of National Park Service.

Today, we depend on a staggering amount of industrial 

minerals. On average, in a year each American makes use 

of 12,695 pounds (lb) of stone, 8,945 lb of sand and gravel, 

895 lb of cement, 361 lb of phosphate, and 304 lb of clay, 

among other minerals (Dorr and Paty, 2002) (fig. 2). Moreover, the largest user of industrial minerals, the construction 

industry, continues to grow in the United States. It accounts 

for most of the consumption of clay, cement, glass, sand and 

gravel, crushed and dimension stone, and steel (U.S. Geological Survey, 2004). For example, crushed stone and sand and 

gravel produced in the United States has increased from about 

58 million tons in 1900 to 2.3 billion tons in 1996 (Tepordei, 1999). Tepordei (1999) expected that by 2020 United 

States production of crushed stone will increase by more than 

20 percent while sand and gravel will increase by 14 percent. 

Relatively small amounts of material from demolished buildings are recycled because construction aggregate is usually 

abundant and inexpensive to produce. Transportation costs are 

573,056 lbs.

Coal

32,810 lbs.

Iron Ore 849 lbs.

Lead

5.78 million cu. ft.

of Natural Gas

29,336 lbs.

Salt

772 lbs.

Zinc

1.55 million lbs.

Stone, Sand, & Gravel

4,864 lbs.

Bauxite

(Aluminum)

21,848 lbs.

Phosphate Rock

20,226 lbs.

Clays

65,543 lbs.

Cement

81,518 gallons

Petroleum

Every American Born Will Need . . .

3.6 million pounds of minerals, metals, and fuels in a lifetime

© 2004 Mineral Information Institute Golden, Colorado

+48,096 lbs.

Other Minerals

& Metals

 1,390 lbs.

Copper

1.279 Troy oz.

Gold

Figure 2. Estimated amounts of minerals, metals, and fuels used 

in a lifetime in the United States. Natural resources are developed 

to meet this need. Courtesy of © Mineral Information Institute, 

Golden, Colo.
Introduction 3

Figure 3 (continued next page). Industrial 

minerals in use in and around Denver, Colo. 

A, Clay from the Chieftain Mine is used to 

produce bricks. The grass area beyond 

the mine was reclaimed from previous 

mining activity. Courtesy of Robinson Brick 

Company. B, Coors Field baseball stadium 

was built with 1.2 million bricks made 

from Colorado clay. The street contains 

aggregate and asphalt, itself made from 

crude oil. Photograph by John Keller.

A

B
4 Development of Industrial Minerals in Colorado

Competing Land Uses and Industrial Minerals

Between 1900 and 2003, the population of Colorado 

grew from 539,700 to approximately 4.55 million people 

(U.S. Census Bureau, 2004). The State was projected to 

have 5.19 million people by 2025. Colorado’s Front Range 

urban corridor, which stretches about 350 km (217 mi) north 

and south of Denver—to Pueblo in the south and to the 

Colorado-Wyoming border in the north—is one of the fastest 

growing regions in the western United States (table 1). This 

population growth puts pressure on resources and has created 

many land management controversies for local, State, and 

Federal agencies. Growing public demand for outdoor recreation, scenery, and open space will compete with resource 

demands (Bastian and others, 2002).

The Front Range urban corridor experience has been true 

elsewhere (fig. 4). Nearly four out of every five people in the 

United States live in one of 273 metropolitan regions (Daniels, 1999), and these regions tend to be the locus of conflicts 

between land use and mining. The public desires amenities 

that contain industrial minerals, but it also wants mining 

operations to be located away from their communities.

The public good and protection of the environment is best 

served by sound scientific methodologies, current technology, 

and effective communication. Scientists, through research 

and increasingly comprehensive databases, attempt to provide 

land-use planners and resource managers a variety of information at a variety of scales: site (for example, a mine’s effect on 

nearby flora and fauna), local (for example, its effect on roads 

or air quality in the surrounding neighborhood), and regional 

(for example, its effect on a watershed). Land planners and 

managers, workers in the mineral industries, regulators, and 

the general public all have a responsibility to be informed 

about the development of industrial minerals.

Table 1. Preliminary population forecasts for Colorado by 

region, 2000–2030 (modified from Colorado Department of Local 

Affairs Division of Local Government, 2005).

Regions Estimated

2000

Projected

2010 2020 2030

Front Range 3,538,770 4,226,658 4,993,836 5,803,275

Western Slope 468,388 586,216 763,681 942,525

Central Mountains 126,191 154,016 209,123 272,104

San Luis Valley 46,435 52,124 58,169 62,996

Eastern Plains 159,024 177,387 210,903 244,238

Figure 3 (continued). Industrial minerals in use in and around 

Denver, Colo. Shoreline of a reclaimed sand and gravel pit at 

South Platte Park (southwestern Denver metropolitan area) before 

(C) and after (D) riprap (coarsely broken rock) was set in place to 

prevent erosion. Photographs C and D by Raymond Sperger.

C

D
Central Colorado Assessment Project 5

environmental effects of historic mining activity on surface 

water and groundwater, and the geologic controls on the availability and quality of groundwater.

Large tracts of USDA Forest Service lands, which compose the majority of Federally administered lands in the Central Colorado Assessment Project, are underlain by sand and 

gravel or by rock suitable for construction. These resources 

could be used for applications such as polished or rough-cut 

dimension stone, landscaping materials, and concrete—a mixture of cement, fine aggregate (such as sand), coarse aggregate 

(such as gravel), and water. The USDA Forest Service and 

other land management agencies have the opportunity to contribute to the sustainable management of natural aggregate and 

other mineral resources through the identification and selective 

development of mineral resources, followed by appropriate 

reclamation of lands that they administer.

The USDA Forest Service is responsible for managing 

191.6 million acres in the national forest system, about 

8.3 percent of the land in the United States (USDA Forest 

Service, 2005). This report is a first step in opening a discussion 

about the need for and use of industrial minerals in the Rocky 

Mountain region’s national forests and public lands (fig. 6). 

The terms “public land” and “public domain” can be used 

interchangeably; both terms refer to land owned by the Federal 

government for the benefit of citizens.

The original public domain contained lands that were 

turned over to the Federal Government by the colonial States 

and the areas acquired later from native Indian nations or 

Figure 4. Urban growth in 

Colorado; such growth increases 

the demand for industrial minerals. 

A, Housing will soon compete with 

a clay pit for land use in Golden, 

2002. B, Edwards, a bedroom 

community about 13 miles west 

of Vail, viewed from Interstate 

Highway 70. A sand and gravel 

operation is in the foreground. 

Aggregate mining is necessary for 

the construction of infrastructure 

in Edwards, the fastest growing 

community in Eagle County. 

Photographs by B. Arbogast, 2004.

A

Central Colorado Assessment Project

An effort to provide comprehensive geosciences data for 

land management agencies in central Colorado was started 

in 2003 by scientists of the U.S. Geological Survey and the 

Colorado Geological Survey. This effort, the Central Colorado 

Assessment Project, addressed a variety of land-use issues in 

the Colorado Front Range, in North Park, Middle Park, and 

South Park, and in the Gore Range, Mosquito Range, Sawatch 

Range, and Sangre de Cristo Mountains (fig. 5). Among the 

goals of the project were an understanding of the availability—in terms of balancing competing uses desired for a given 

parcel of land—of industrial and metallic rocks and minerals 

used by industry and in construction, the geochemical and 

B
6 Development of Industrial Minerals in Colorado

Figure 5. Colorado showing area of the Central Colorado Assessment Project (outlined in black).

Trinidad

Fort Collins

Greeley

Colorado Springs

Pueblo

Craig

Steamboat

Springs

Glenwood

Springs

Marble

Crested

Butte

Creede

Westcliff

Canon

City

Salida

Hartsel

Fairplay

Boulder

DENVER

Georgetown

Vail

Castle Rock

Durango

South

Park

Wet Mountains

Sangre de Cristo Range

San Juan Moutains

Sawatch Range

Gore Range

Mosquito Range

FRONT

RANGE

24

50

50

24

25

25

76

36

40

285

San Luis 

 Valley

North Table Mountain

Gem Park

Wilson Park

Glen Cove

Pikes Peak

Crystal Peak

Devils Head

Tappan Mountain

 Topaz

Mountain

Phantom Canyon

Monarch Pass

Mount Antero

Ruby Mtn

Browns Canyon

Herring Park

Perry Park

Coal Creek

 Canyon

Ralston Butte

 Harris Park

 Rocky Flats

 Valmont Dike

Summitville

Dotsero

Volcano

 Italian

Mountain

Mount White

 Willow Peak

Coon Gulch South Table

Mountain

 Gobbler Knob

 Black Forest

North

 Park

Middle

 Park

Chieftain

Mine

Jamestown

Northgate

State Line District

Powderhorn

Sweet Home Mine

Owl Canyon

 Quarry

Kelsey Lake

Aberdeen

Quarry

Trapper Mine

39°

40°

38°

108° 107° 106° 105° 104°

70 70

133

149

160 25

69

285

285

160

50

40

550

84

EXPLANATION

National monuments and parks

Other National Forests

San Isabel National Forest

Pike National Forest

Pawnee National Grasslands

Major mineral districts

Boundary of Central Colorado

 Assessment Project

0 25 50 MILES
Figure 6. Federal land, major mining districts, counties, and cities in Colorado. Gray border, boundary of Central Colorado Assessment Project.

WASHINGT

LOGAN

LINCOLN

CROWLEY

OTERO

BEN

LAS ANIMAS

COSTILLA

HUERFANO

ALAMOSA

RIO GRANDE

CONEJOS

MINERAL

SAGUACHE

HINSDALE

MONTEZUMA LA PLATA

DOLORES

SAN MIGUEL

OURAY

MONTROSE

GUNNISON

DELTA

MESA

EAGLE

PITKIN

LAKE

CHAFFEE

FREMONT

TELLER

PARK

GARFIELD

RIO BLANCO

MOFFAT

ROUTT

JACKSON

GRAND

LARIMER

BOULDER

GILPIN

CLEAR

CREEK

SUMMIT JEFFERSON

DENVER

BROOMFIELD

ARAPAHOE

ELBERT

DOUGLAS

EL PASO

PUEBLO CUSTER

SAN

JUAN

ARCHULETA

MORGAN

WELD

ADAMS

Sterl

Limon

La Junta

Trinidad

Fort Collins

Greeley

DENVER

Colorado Springs

Pueblo

Cortez

Grand Junction

Craig Steamboat

Springs

Glenwood

Springs

Marble

Rifle

Crested

Butte

Creede

Westcliff

CanonCity

Salida

Hartsel

Fairplay

Boulder

Georgetown

Vail

Castle Rock

Durango

SouthPark

0 

Wet Mountains

Sangre de Cristo Range San Juan Moutains

Uncompahgre Plateau

Sawatch Range

Gore Range

Mosquito Range

FRONT

RANGE

Roan Plateau

70

24

50

50

24

25

25

76

36

36

287

40

285

34

7

San Luis  Valley

North Table Mountain

Gem Park

Wilson Park

Glen Cove

Pikes Peak

Crystal Peak

Devils Head

Tappan Mountain

 TopazMountain

Phantom Canyon Monarch Pass

Mount Antero

Ruby Mtn

Browns Canyon

Herring Park

Perry Park

Coal Creek

 Canyon Ralston Butte

 Harris Park

 Rocky Flats

 Valmont Dike

Summitville

Dotsero

Volcano

 ItalianMountain

Mount White

 Willow Peak

Coon Gulch South Table

Mountain

 Gobbler Knob

 Black Forest

North Park

Middle Park

Chieftain

Mine

Jamestown

Northgate

State Line District

Powderhorn

Sweet Home Mine

Owl Canyon Quarry

Kelsey Lake

AberdeenQuarry

Trapper Mine

39°

40°

38°

109° 108° 107° 106° 105° 104° 10

70

70

133

149

160

25

69

160

285

285

160

666

50

350

40

40

550

84

 Piceance Basin
8 Development of Industrial Minerals in Colorado

foreign powers (U.S. Department of the Interior National Atlas 

of the United States, 2005). Overall, the Federal government 

owns approximately one-third of United States land; Federal 

lands account for as much as 86 percent of the land in certain 

Western States. Some Federal land is close to major metropolitan areas or to rural communities. The agencies managing 

most of the Federal land are as follows:

• USDA Forest Service

• Bureau of Land Management 

• Fish and Wildlife Service

• National Park Service

• Bureau of Indian Affairs 

• Bureau of Reclamation

• Army Corps of Engineers

“Use of the public lands has changed throughout our 

Nation’s history and continues to evolve. Originally viewed 

as the Great American Desert, these [Western] lands over time 

came to be regarded primarily as a source of livestock forage, 

timber, and energy and mineral resources. Today, the public lands are valued more and more for their environmental 

resources, the recreational opportunities they offer, the cultural 

resources they contain, and, in an increasingly urban world, their 

vast open spaces” (U.S. Bureau of Land Management, 1997).

Regulation of Mining for Industrial 

Minerals

Overview

Mineral resources, along with land and water, once 

seemed to be inexhaustible commodities, and there appeared 

to be little concern about environmental damage (fig. 7). 

Today, the law, environmental regulations, and best management practices mitigate damaging effects of mining. The 

General Mining Act of 1872 encouraged mineral exploration 

and development on vacant public lands but excluded lands in 

Figure 7. Gravel pit, Summit Avenue near Pine Street, Seattle, Wash., 1907. Photograph by N.H. Darton. Courtesy of USGS 

Photographic Library.
Regulation of Mining for Industrial Minerals 9

national parks, national monuments, and Indian reservations, 

except where specifically authorized by law (U.S. Bureau of 

Land Management, 1964). Although the earliest State legislation regulating surface mining was passed in 1939 (in West 

Virginia), the failure of some States to protect their natural 

resources eventually led to a large body of Federal, State, and 

local environmental laws that govern mineral exploration, 

mine development, and site reclamation.

Mining requires natural science and social science information, environmental studies, and dialogue between the mining company and the local community that allow community 

concerns to be stated and addressed. Adjacent communities’ 

desired use for the land, societal values (overall quality of life, 

influenced in part by the mine’s visual effect), mitigation of 

nuisances associated with mining (noise, dust, traffic), laws, 

and regulatory bodies influence mining operations and treatment of the environment (fig. 8).

State agencies that regulate mining, air quality, and 

water quality, as well as other agencies such as wildlife and 

geological surveys and local governments that determine 

zoning requirements and other infrastructure issues, all might 

have a role in granting a mining permit. When a company 

proposes a quarry or mine, contact with local citizen and 

neighborhood groups is important so that relationships can 

be built early to resolve problems that may develop. The 

mining industry is expected to apply the best environmental management standards available and abide by current 

regulations pertaining to mining and production sites. And 

in a world where cross-border operations are becoming the 

norm, international law will play a larger and larger role in 

the conduct of mining operations.

Regulation Outside the United States

International Laws and Agreements

In an increasing global market and industry, governments now tend to focus on an international paradigm of 

sustainable development and international environmental law 

(Pring, 2003). Mineral resources are unevenly distributed, 

and sea trade between industrial countries grows steadily: 

aggregate has been exported from Scotland to Texas (fig. 9), 

gypsum from Mexico to California, talc from Montana to 

Belgium, potash from Saskatchewan to the corn belt of the 

United States, soda ash from western United States ports to 

the Pacific Rim, and bentonite from Wyoming to oil rigs all 

over the world (Kuzvart, 2003).

Mining is increasingly subject to international law but 

relies on political will for enforcement (United Nations, 

2003a). Nevertheless, “* * * it [international environmental 

law] is growing in both scope and enforceability and becoming a force that can no longer be prudently ignored” (Pring, 

2003, p. 3). For example, Yellowstone National Park and the 

Grand Canyon are sites protected in perpetuity and included 

as part of the world heritage through the 1972 United Nations 

Educational, Social, and Cultural Organization (UNESCO) 

Figure 8. Two dust mitigation methods. A, Water sprayed on a 

rock face during active mining to reduce airborne dust. Courtesy 

of North Carolina Geological Survey. B, Seedlings airlifted into 

an active quarry will be planted to begin reclamation of minedout regions of the quarry. Courtesy of Western Mobile Company, 

Golden, Colo.

A

B
10 Development of Industrial Minerals in Colorado

Convention for the Protection of the World Cultural and 

Natural Heritage (Pring, 2003). The mining industry has also 

developed International Organization for Standardization 

(ISO) 9000 Quality Management System standards and ISO 

14000 Environmental System standards to enhance product 

requirements and minimize harmful environmental effects 

(Pring, 2003).

International regulatory documents such as treaties and 

standards treat a broad range of economic, social, and cultural 

situations affected by the industrial-mineral industry: sustainable development, safety and health, corporate social responsibility, human rights, rights of indigenous peoples, labor rights, 

public participation, transboundary effects (movement across 

country borders that results in another action—such as pollution of air or of watershed systems), hazardous substances 

(for example, mill tailings), land degradation, protection of 

wild animal species and their habitat, World Heritage sites (as 

defined by the United Nations), and the marine environment 

(United Nations, 2003a).

Mineral resources and lands are best managed in a sustainable fashion, just as forest resources are (United Nations, 1992), 

to meet the social, economic, ecological, cultural, and spiritual 

needs of present and future generations. These needs include 

not only mineral products but also shelter and employment.

The Bureau of Land Management and USDA Forest Service have accepted sustainable development of minerals and 

forests as a foundation for their own public policy (Anderson 

and others, 2002). The agencies note that principles underlying sustainable development (such as product recycling, social 

well being, environmental health, and economic prosperity) 

apply to mining operations (fig. 10). Sustainable development 

entails the mining industry’s use of best practice environmental management to protect biological diversity; sustain ecological processes over the long term; develop sound, scientifically 

based approaches to land planning; and work with stakeholders to achieve a balance of interests. Sustainable 

development also “represents an evolution from impact 

analysis (mitigation of damage) to contribution analysis 

(ensuring net benefits)” (Chadwick, 2004, p. 2). Sustainability 

is inherently complex and multifaceted, and it extends beyond 

site-based issues (Perry, 2004).

Best Management Practices Outside the United 

States

Implementing best management practices may be costly, 

but it produces long-term gains for the industry, the community, and the environment (Environment Australia, 2002). 

Best-management practices include the following:

• Open and effective communication with the local community and other interested parties

• Adapting risk analysis by taking into account environmental factors, engineering, and planning needs

• Maximizing efficiency (for example, minimizing 

waste, improving mine design and management 

practices (Environmental Mining Council of British 

Columbia, 2004)

• Substituting renewable materials for nonrenewable 

minerals and recycling

• Adopting best practices even if not required by regulation

• Returning the land to a desirable postmining form

• Applying the Precautionary Principle (“* * * the lack 

of full scientific certainty should not be used as a reason for postponing a measure to prevent degradation 

of the environment where there are threats of serious 

or irreversible environmental damage” (Environment 

Australia, 2002, p. 3).

Figure 9. Glensanda coastal granite quarry in Argyll, Scotland. The mining industry serves local, regional,

and international markets. Glensanda transports granite only by ship to markets in the United Kingdom and 

Europe. Image courtesy of Aggregate Industries Yeoman Glensanda.
Regulation of Mining for Industrial Minerals 11

The European Union in 2001 agreed that environmental 

decisionmaking requires the involvement of a community’s 

citizens and responsibility for stewardship of the environment 

(Meredith, 2004). The question raised is how to ensure fair 

public participation in an anticipatory rather than reactive 

mode. Mineral development and reclamation are most successful when mining operators work cooperatively with regulators 

at all levels, land planners, and the public.

Federal Regulations

All Federal, State, and private lands in the United States 

(including USDA Forest Service and BLM lands) are subject 

to Federal regulations such as the Clean Air, Clean Water, 

Endangered Species, National Historic Preservation, and 

National Environmental Policy Acts. Such Federal regulations affect treatment of landscapes and promote public 

health and safety as well as monetary, physical, aesthetic, 

and spiritual values (table 2). Environmental policies of the 

1990s (such as legislation to protect biodiversity, establish 

protected habitats, and improve waste management) have not 

created burdensome economic costs (Organization for Economic Co-operation and Development, 2001). Reclamation 

costs are minimal if reclamation is planned from the outset 

(Norman and Lingley, 1992).

The Mining and Minerals Policy Act of 1970 (84 Stat. 

1876; 30 U.S.C. 21a) and the National Materials and Minerals Policy Research and Development Act of 1980 encourage 

the orderly economic development of domestic resources on 

public lands. The policies assure that the nation’s industrial, 

security, and environmental needs are satisfied while the land’s 

productivity is maintained for other uses and to support biodiversity (USDA Forest Service, 2010a,b).

Minerals as treated under the mining laws are recognized as such when found in public lands in quantity and 

quality sufficient to render the lands valuable (U.S. Bureau 

of Land Management, 1964). Potentially valuable minerals 

on Federal lands are classified according to a “disposition 

class” as locatable, leasable, or saleable. Mineral disposition classes are broad, and deposits of a given mineral may 

fall into more than one class depending upon their location, 

geologic setting, composition, and other factors such as case 

law. For example, clays and zeolite can be considered locatable, leasable, or saleable. Pumice, depending upon its type, 

may be considered locatable or saleable (pumicite, volcanic 

ash, volcanic dust, and scoria) or it may be considered saleable only (for example, volcanic cinders). Gypsum may be 

considered locatable or leasable (in the form of rock gypsum 

or anhydrite) or it may be saleable only (if it is gypsite) (U.S. 

Bureau of Land Management, 1994). The Bureau of Land 

Management or USDA Forest Service District Office can 

provide specific information regarding disposition classes 

that apply to a specific site.

Locatable Minerals

The term “hard-rock minerals” is widely used as a 

synonym for “locatable minerals” (National Academy of 

Sciences, 1999). These minerals are principally the base and 

precious metal ores (such as copper, lead, zinc, magnesium, 

molybdenum, nickel, and tungsten, gold, silver, and platinum), 

ferrous metal ores, and certain classes of industrial minerals:

Figure 10. Recycled asphalt and concrete north of Denver, Colo. These materials are available for other projects as part 

of sustainable construction. Steel pipe, used oil, and scrap tires can also be recycled. Photograph by B. Arbogast, 2002.
12 Development of Industrial Minerals in Colorado

• Nonmetallic minerals such as asbestos, barite, bentonite, borax, cement-grade limestone, ceramic clay, 

feldspar, fluorspar, gypsum, mica, and zeolite

• Rare earth elements such as uranium or thorium

• Gemstones such as diamonds, sapphires, and rubies

• Industrial stones such as garnet, diamond, and quartz 

sand. (Although some varieties of garnet may be locatable, common varieties of garnet and other relatively 

hard minerals used as abrasives may be considered 

saleable by the USDA Forest Service.)

• Uncommon varieties of sand, gravel, stone, pumice, 

pumicite, and cinders. (Uncommon varieties of stone 

are building or decorative stones such as marble, highgrade limestone or dolomite, and some granitic rocks.)

The Multiple Use Mining Act of 1955 (69 Stat. 368, as 

amended; 30 U.S.C. 611–615) details the classification of 

locatable minerals (USDA Forest Service, 2010b). Mining of 

locatable minerals on Federal lands is subject to the General 

Mining Law of 1872 (17 Stat. 91, as amended; 30 U.S.C. §22 

et seq.) (Nichols, 1999; USDA Forest Service, 2010b). When 

a valuable mineral deposit is found, a mining claim (a lease 

that allows the extraction of minerals) may be patented (U.S. 

Bureau of Land Management, 2004). (A patent gives the successful mining claimant title to both the surface land and to the 

underlying mineral deposit.) Acquisition is accomplished first 

by staking the mining claim (marking its surface location, also 

called “locating”) over a deposit and then by acquiring the 

permits necessary before exploration or mining. The Bureau 

of Land Management approves any plan of operations that 

disturbs more than five acres of public land (U.S. Bureau of 

Land Management, 2004). All mining activities that disturb 

Table 2. Typical Federal conservation laws or policies and their implications for certain aspects of mining (modified from Arbogast, 2002).

Issue Conservation law or policy Intent or effect on mining operations

Air quality Air Quality Act of 1967

Clean Air Act of 1970

Addresses airborne pollutants at their source, such as emissions from vehicles, 

mine processing facilities, and dust that accompanies mining operations.

Archaeological or 

historical 

significance of land

Antiquities Act of 1906

Historic Sites Act of 1935

National Historic Preservation 

Act of 1966

Establishes sites of archaeological, historic, and scientific interest.

Blasting or other 

noise; health and 

safety

Noise Pollution and Abatement 

Act of 1970

Federal Mine Safety and Health 

Act of 1977

Provides for control of noise that is detrimental to the human environment

Establishes mandatory health and safety standards; regulates blasting.

Grading and control 

of erosion

Surface Mining Control and 

Reclamation Act of 1977

Requires that land mined for coal be returned to its approximate original contour

After mining and reclamation, land required to be equal to or better than the 

same land as used before mining.

Mining proposal National Environmental Policy 

Act of 1969

Requires an environmental impact statement for any major Federal action that 

may significantly affect the environment.

Requires public comment on any proposed action that triggers an environmental 

impact statement.

Visual quality of area 

during and after 

mining

The Federal Land Policy and 

Management Act of 1976

Requires all practicable means to assure aesthetic and culturally pleasing 

surroundings during and after mining.

Waste material Resource Conservation and 

Recovery Act of 1976

Regulates the transport and disposal of solid/hazardous wastes. Regulation of 

high-volume, low-hazard mining wastes is exempt under this Act and is the 

responsibility of the states.

Water quality and 

quantity

Federal Water Pollution Control 

Act of 1972

Safe Drinking Water Act of 

1974

Clean Water Act of 1977

Coastal Zone Management 

Act of 1972

Federal or state permit for major “point source” of pollutants that are discharged 

into surface waters.

Regulates disposal of mining-related water, storm runoff, and the pumping of 

water to the surface.

Effects of mining on aquifers and well water assessed.

Regulates development of offshore mineral and petroleum resources.

Wetlands River and Harbor Act of 1899 Permit issued by U.S. Army Corps of Engineers.

Wildlife and habitat Endangered Species Act of 1973 Minerals development may not jeopardize any listed species or its critical habitat.
Regulation of Mining for Industrial Minerals 13

the land surface and that are on USDA Forest Service lands 

on which a claim may be staked (lands available for “mineral 

entry”) take place in accordance with Title 36 of the Code of 

Federal Regulations, Part 228–A (Nichols, 1999). Operators 

carry reclamation bonds to ensure that the site is reclaimed 

after mining ends (USDA Forest Service, 2010a).

Leasable Minerals

Leasable minerals may be leased from the Federal government but may not be claimed; that is, the leaseholder may 

extract the underlying mineral, but the leaseholder does not 

own the surface land over the mineral deposit. Leasable minerals are as follows:

• Fossil fuels such as coal, oil and gas, oil shale

• Geothermal resources (heat derived from the Earth)

• Nonenergy leasable minerals—Fertilizer and feedstock 

(for chemical processes) such as phosphate, potassium, 

and sodium. This category contains chlorides, sulfates, 

carbonates, borates, silicates, and nitrates of potassium 

or sodium.

• Native asphalt and solid and semisolid bitumen

• Sulfur on public lands in Louisiana and New Mexico, 

and silica deposits in certain parts of Nevada (U.S. 

Bureau of Land Management, 1964).

• Leasable minerals are those commodities that may be 

acquired on Federal public lands under the Mineral 

Land Leasing Act of 1920, as amended; the Geothermal Steam Act of 1970, as amended; or the Acquired 

Lands Act of 1947, as amended (National Academy 

of Sciences, 1999). The Mineral Leasing Act of 1920 

gives authority to the USDA Forest Service to manage leasable minerals on national forest system lands 

(USDA Forest Service, 2010b).

On USDA Forest Service lands, oil, gas, and fertilizer 

resources are managed in three stages: leasing, exploration, and 

development. Land must go through a competitive bid, held 

by the Bureau of Land Management, for a lease to be obtained 

(USDA Forest Service, 2010a). “Leases are issued for specific 

periods of time, and the lessee pays a rental fee and royalties 

on the minerals produced. * * * After public lands are leased, 

applications to conduct exploration, drilling, and productionrelated activities are reviewed to ensure technical competence, 

environmental protection, and mineral resources conservation” 

(U.S. Bureau of Land Management, 2004).

Saleable Minerals

Saleable minerals are the common varieties of construction materials and aggregates, such as sand, gravel, and 

cinders and roadbed and ballast material. Common-variety 

minerals do not possess any special quality, quantity, character, or location that makes them of unique commercial value 

(National Academy of Sciences, 1999). Saleable minerals may 

also be common varieties of pumice, pumicite, and ordinary 

clay. These minerals may be obtained under the Mineral Materials Act of 1947, as amended (30 U.S.C. 602–604, 611–615) 

(National Academy of Sciences, 1999).

“Common landscaping and construction materials * * * are 

available through material sales at fair market value or through 

free use permits and government agencies and nonprofit organizations” (U.S. Bureau of Land Management, 2004). Free use 

permits are no-fee permits with special provisions; for example, 

the resource obtained may not be sold or exported from the 

State. Small tonnages that can be easily removed are sold over 

the counter through a noncompetitive process. Larger tonnages 

or the contents of known deposits of common-variety minerals 

may be sold either competitively or noncompetitively (Nichols, 

1999). In a competitive sale, the material bid on goes to the 

highest bidder. The operator posts reclamation bonds to ensure 

site reclamation (USDA Forest Service, 2010a).

Various instances of case law and mineral estates (which 

have a distinct set of legal rights pertaining to owning land 

with mineral rights) can change the administrative regulations for these commodities. The appropriate Bureau of Land 

Management or USDA Forest Service field office can provide 

more detailed and up-to-date information regarding Federal 

regulations and definitions.

In the Rocky Mountain region, the USDA Forest Service’s Mineral Materials Program is ranked as the tenth largest 

producer of saleable minerals (primarily aggregate) in the 

United States (USDA Forest Service, 2010a). Saleable mineral materials mined on public lands in Colorado are mainly 

sand and gravel for concrete aggregate and fill, and rock for 

aggregate, riprap, and decorative purposes (flagstone and moss 

rock) (U.S. Bureau of Land Management, 2009).

Mineral Specimens Sought by Collectors

Rock hounding and collecting mineral specimens 

(activities such as gold panning or digging out a few quartz 

crystals) are considered to be hobbies or personal activities if 

they involve only the occasional removal of small amounts of 

material by hand from surface exposures (Nichols, 1999).

“Rocks, mineral specimens and semi-precious 

gemstones, petrified wood, * * * may be collected 

on public lands without charge or permit in reasonable amounts [see reference cited for definitions] 

as long as the specimens are for personal use and 

are not collected for sale or barter to commercial 

dealers. Collectors should note that there are some 

restrictions [including prohibited areas and locations 

encumbered with un-patented mining claims] and 

a BLM permit may be required, depending on the 

amount of material you collect, how you collect it, 

where or when you collect, and whether the material 
14 Development of Industrial Minerals in Colorado

will be used commercially. * * * [Approved] Collection and removal cannot be aided with motorized or 

mechanized equipment including but not limited to: 

tractors, bulldozers, plows, power shovels, semitrailers or other heavy equipment is not authorized. 

Undue or unnecessary degradation of the public 

lands is not allowed during the removal of rocks, 

minerals, gemstones, or fossils” (U.S. Bureau of 

Land Management, 2009).

USDA Forest Service and Bureau of Land 

Management Regulations

The USDA Forest Service manages the land surface in 

national forests. The Bureau of Land Management, as the 

“keeper of the mineral estate,” regulates subsurface mining on 

both Bureau of Land Management and USDA Forest Service 

lands. The Bureau also sets national policies and processes for 

extraction of solid minerals (that is, nonpetroleum resources) 

under Federal jurisdiction: coal and nonleasable minerals, 

hard-rock minerals on acquired lands, locatable minerals, and 

saleable minerals. In addition, it is the custodian of publiclands records for the United States Government (U.S. Bureau 

of Land Management, 1997).

USDA Forest Service and Bureau of Land Management regulations provide procedures for the exploration, development, and disposal of mineral resources 

from national forests and other public lands. In order to 

understand information regarding mining on national forest lands, one must first understand terms that describe 

mineral-estate status (Nichols, 1999).

Applications for prospecting permits and leases are 

required for hard-rock minerals on “acquired status” forest lands. Acquired status refers to national forest lands and 

minerals purchased, donated, or received in exchange for 

purchased or donated lands and minerals.

• “Public domain” status refers to land and minerals withdrawn or reserved for use as part of national 

forests or national grasslands; those lands have never 

left Federal ownership or been received in exchange 

for land of the same status. Mining claims for locatable 

minerals can be sited only on public-domain-status forest lands. In all cases, a reclamation bond sufficient to 

insure full site reclamation is required to be submitted 

by the operator.

• Not all Bureau of Land Management and USDA Forest 

Service lands are available for mineral prospecting and 

mining. Various categories of these lands have been 

withdrawn to meet other public purposes. Chief among 

these withdrawn lands are congressionally designated 

wilderness areas (National Academy of Sciences, 1999); 

others are national parks, national monuments, Indian 

reservations, most reclamation projects, military reservations, scientific testing areas, and lands designated 

for the National Wilderness Preservation System or the 

Wild and Scenic Rivers System (U.S. Bureau of Land 

Management, 1996) (fig. 11). Other exempt lands are 

national forest system lands, those currently staked by 

a mining claim, or Bankhead-Jones lands, principally 

national grasslands. (The Bankhead-Jones Farm Tenant Act of 1937 authorized the Federal government to 

acquire damaged farm lands in order to rehabilitate and 

use them for various purposes (U.S. Senate, 2003)). The 

Act also allows limited discretion for disposal of mineral 

materials on land acquired under this act provided development does not interfere with the primary purpose of 

the land (USDA Forest Service, 2010b).

Regulations specifically allow mining, but they also protect the mineable resource and the environment. The authority for these regulations for both agencies is the Materials 

Act of July 31, 1947, as amended. USDA Forest Service 

regulations are found in 36 CFR Subpart C entitled “Disposal of Mineral Materials” and the Bureau of Land Management regulations are located in 43 CFR Part 3600 entitled 

“Mineral Materials Disposal.” The Resources Planning Act 

of 1974, the National Forest Management Act of 1976, the 

Federal Land Policy and Management Act of 1976, and the 

Public Rangelands Improvement Act of 1978 give the USDA 

Forest Service and Bureau of Land Management specific 

planning and management responsibilities. Both agencies 

are to balance public values of outdoor recreation and open 

space with traditional uses such as timber harvesting, mining, 

Figure 11. A 13th century Puebloan structure in the Canyons of 

the Ancients National Monument, southwest Colorado. Activity 

on two existing mining claims in the national monument will be 

regulated in order to protect the purpose of the monument, and no 

new claims will be permitted. Photograph courtesy of Bureau of 

Land Management.
Regulation of Mining for Industrial Minerals 15

or livestock grazing. Decisions on conflicting uses are made 

on a case-by-case basis.

The Materials Act of July 31, 1947, as amended, defines 

mineral materials such as petrified wood and common varieties of sand, stone, pumice, pumicite, cinders, clay, and similar 

materials. USDA Forest Service regulations have further 

defined the deposits that are used for agriculture, animal 

husbandry, building, abrasion, construction, and landscaping. 

The policy of both agencies is to (1) sell the mineral material 

resources at not less than fair market value, (2) permit Federal, 

State, and local government entities and nonprofit organizations free use for qualified purposes, (3) protect both the 

mineral resources and the environment and minimize damage 

during mining, (4) prevent unauthorized removal of mineral 

materials, and (5) require purchasers and permittees to be 

accountable for their actions.

Resources deemed to be a mineral material can be 

acquired through a special-use permit or mineral-materials 

contract through the USDA Forest Service or Bureau of 

Land Management. The permits or contracts themselves 

can be obtained by competitive sales, negotiated contracts, 

preference-right negotiated sale, or free-use and agency-force 

account. Each method will have volume and acreage limitations. The length of contract may not exceed one year unless 

an extension is authorized.

All mining operations are governed by an approved 

Operating Plan (USDA Forest Service) or Mining and 

Reclamation Plan (Bureau of Land Management). These 

documents state (1) who will direct the mining operation, 

(2) how the resource will be mined, (3) when mining will 

occur, (4) where the quarry is to be located and how it will 

be accessed, and (5) how the site will be reclaimed either 

during mining or when the project is completed. Any proposed structures or building occupancy on the site is required 

to be described on the plan. A map of the proposed mine area 

and location of the resource and access roads to it is required 

to be attached to the plan. An environmental assessment is 

conducted for the proposal.

An authorized officer completes the award of a contract. 

The award depends on the submittal of an acceptable bid, 

the ability to perform in a timely fashion, and receipt of an 

approved bond. The authorized officer ensures that an environmental analysis is completed for all planned mining.

The bond is required to be sufficient to assure payment 

(rent on the lease and royalties on the material extracted) 

and timely reclamation of the mining site. Moreover, regular 

inspections are required of all stockpiles of mined material. 

Production records are used to determine volumes removed 

and verify the correct payments—and they may serve as a 

deterrent to theft of stockpiled material. Acceptable bond 

forms are outlined in agency manuals.

Poor administration or inattentiveness by the parties can 

result in theft of mineral materials. Regular inspections are 

required of all mineral material resource disposals. Production records are necessary to determine volumes removed and 

verify the correct payment for the resource.

State Regulations

State law does not take precedence over Federal law, 

and States differ greatly in their regulations regarding mine 

reclamation and in their definitions of a mineral. A minerals agreement is a contract between lessor and lessee that 

states the right to explore for specified minerals and the 

obligation to develop or to produce (or both) those minerals during a specified length of time. States require a 

minerals agreement if Federal lands or Indian Tribal lands 

within the State are to be mined, and the mining company 

must comply with the terms of State, county, and municipal approvals and permits. In addition, State regulations 

and policies that govern mine reclamation may address the 

following topics:

• Public comment—Required during the development 

of new regulations, review of permits, and release of 

bonds after reclamation, and when citizen complaints 

are presented

• Financial assurances—Permit fees, fines, penalties, and 

performance bond

• Pre-mining environmental data—Hydrology, geology, 

plant coverage, air and water quality, wetlands, land 

use or zoning, historic value

• Mining and reclamation standards—Topsoil (its 

salvage, maintenance, and redistribution), grading 

and stabilization of slopes, soil analysis, revegetation (density, species richness, use of native species), fugitive dust, noise, protection of surface water 

and groundwater, wildlife habitat, visual screening, 

disposal of waste (including mill tailings), drainage 

from the mined area (surface runoff, construction of 

diversion structures) (table 3).

State agencies involved in regulating the industry 

may be concerned with public health, public safety, natural 

resources, wildlife, engineering practices, transportation, 

labor, historical preservation, and revenue. These agencies 

ensure compliance with State and Federal standards governing water and air quality and with regulations concerning 

archeological or historical sites. Historical cultural landscapes may include farms, ranch lands, mining districts, 

transportation corridors, irrigation systems, parks, and prehistoric sites (Colorado Historical Society Office of Archaeology and Historic Preservation, 2001) (fig. 12). More than 

100 mining-related properties are listed in the Colorado State 

Register of Historic Properties (Colorado Historical Society 

Office of Archaeology and Historic Preservation, 2003). 

The National Register of Historic Places (U.S. Department 

of the Interior National Park Service, 2004) lists a number 

of mining districts in Colorado that are administered by the 

National Park Service: for example, Lake City (in the heart 

of the San Juan Mountains of south-central Colorado), Littlejohn mine complex (near Granite), Vicksburg and Winfield 
16 Development of Industrial Minerals in Colorado

Table 3. Typical State policies and their implications for certain aspects of mining.

Aspect Requirement of state policy

Air quality Compliance with State and Federal regulations.

Archaeological or historical significance of a site Compliance with State and Federal regulations.

Blasting or other noise, health and safety Compliance with State and Federal standards that set permissible noise levels.

On-site standards and inspections to regulate the health and safety of employees and 

visitors.

Drill or auger holes Plugged with noncombustible material; prevent polluting drainage.

Geologic hazards Require assessment of geochemical stability and characteristics of the site and a 

geologic report.

Grading or control of erosion Final topography (slope angle and shape, drainage) appropriate for proposed land use 

after mining and similar to surrounding landforms. Affected land protected from 

slides; surface areas stabilized; specified ratios for lakes or pond slopes.

Seeding, mulches, and careful location of drainage and water-control systems.

Mineral transportation Set load limits and truck safety standards (except for Federal highways, which are 

administered by the Federal government).

Mining proposal Demonstrate state permit and compliance with local county and municipal approval 

for mining operations. May include legal description, index map, pre-mining plan 

of affected lands, mining plan (existing topography, hydrology), reclamation plan 

(subsequent land use, sequence of excavation and reclamation, designation of 

overburden storage areas), and public notice.

Overburden and backfill Map of general type, thickness, and distribution of soil. Topsoil preserved and 

segregated from spoil.

Site location Permit or minerals agreement required, as are maps and cross sections of site. 

Impermeable pit floors may need to be blasted so that water can drain from the site. 

Water sources may be included in the design of a post-mining pond or wetland.

Vegetation Premining inventory of vegetation. Plan for post-mining vegetation (a diverse, 

effective, and long-lasting vegetative cover capable of self-regeneration and at 

least the equivalent of cover in the surrounding area). Specification and location of 

ground cover and trees to be planted. Irrigation schedule if necessary.

Visual quality Visual impact study. Proper siting and location, reduction of unnecessary disturbance 

and visibility.

Waste material Location, stabilization, and reclamation of waste rock piles and overburden. Refuse 

disposed of in a proper manner.

Water quality and quantity Compliance with Federal, State, and county regulations. Map of existing watercourses, streams, rivers, ponds and wetlands. Covers nonpoint-source pollution, 

water rights. Hydraulic project approval, drainage controls.

Wetlands Stream channel reconstruction. Federal dredge-and-fill permit.

Wildlife Compliance with Federal and State regulations. Wildlife on site protected; diverse 

habitat encouraged; endangered species protected.

mining camps (northwest of Buena Vista), Crystal mill 

(southeast of Marble), Ore Processing mill and dam (Georgetown), and the Argo tunnel and mill (Idaho Springs). (Some 

of these historic places are also on national forest lands: the 

Littlejohn mine complex, the Vicksburg and Winfield mining 

camps, and the Crystal mill.) The Mineral Belt Trail around 

the outskirts of Leadville winds through the mining district, 

historic structures, and mining artifacts.

Beyond required Federal regulations that are enforced 

at the State level, States differ in which particular minerals 

or aspects of mining are regulated and to what extent. 

Generally, State laws are directed at problems most pressing 

in that State (Toy and Hadley, 1987). For example, in Colorado the ponding of water and its subsequent evaporation led 

to a court ruling: mine operators that expose groundwater to 

the atmosphere must obtain a permit from the State Engineer 

to do so, and the operator must make up for injurious evaporation losses through a plan to replenish the lost groundwater 

(Brown, 1989).

All mining and reclamation in Colorado is directed by the 

Colorado Mined Land Reclamation Board. The Board oversees 

the Division of Minerals and Geology, which issues mining and 
Regulation of Mining for Industrial Minerals 17

Figure 12. Remains of historical landscapes preserved for the future. A, View 

from the top of Mt. McClellan, Colo., 1940, showing the towns of Silver Plume in the 

foreground, founded in the 1860s by prospectors looking for silver, and Georgetown 

in the right-hand middle ground. Mine dumps and trails can be seen on the hillsides. 

The Georgetown–Silver Plume area was declared a national historic landmark 

district in 1966. Image by C.L. McClure, courtesy of Arthur Lakes Library, Colorado 

School of Mines. B, In 1865, the James Sawyers Wagon Road Expedition camped on 

this site near Gillette, Wyo. A coal company, the public, and the local history museum 

joined to preserve the Belle Ayr mine site’s historical integrity. Courtesy of Chuck 

Meyers, Office of Surface Mining, Washington, D.C. C, Plan view of Fossil Park 

project, Sylvania, Ohio, a mine site of scientific interest. D, People enjoy hunting for 

Devonian fossils in the five-acre rock quarry, Fossil Park. Images C and D courtesy of 

The Collaborative Inc. and the Olander Park System.

BUS PARKING

(6 STALLS)

CONNECT TO

EXISTING TRAIL

FOSSIL CENTER

(+ 15,000 S.F.)

PARKING AREA

(135 STALLS)

ADA ACCESSIBLE

ENTRY PATH DIG SITES

FOSSIL QUARRY

RESTROOM

AMPHITHEATRE

PRAIRIE GRASS

PICNIC SITE (TYP)

OPEN AIR

SHELTER

SCULPTIAL

ELEMENT

SCULPTIAL

ELEMENT

ENTRY

DRIVE

RECREATION

TRAIL SAFETY

FENCE

B C

D

A
18 Development of Industrial Minerals in Colorado

reclamation permits, within the Colorado Department of Natural 

Resources. The Minerals Program of the Office of Mined Land 

Reclamation (a part of the Colorado Division of Minerals and 

Geology) reviews mine permit applications; it is funded largely 

through permit fees paid by mine operators.

Before mining operations begin, the State of Colorado 

requires three items: 

• A performance bond—A promise that the mining 

operation will reclaim the land; it gives the State the 

authority to pursue reclamation costs from operations 

that fail to reclaim

• A reclamation bond—A financial warranty that equals 

the cost the State would incur to reclaim the site should 

the mining operation fail to reclaim the site

• A permit―With minor exceptions, all mine operators 

must obtain a State permit for extraction of minerals and disturbance of soils (U.S. Environmental 

Protection Agency, 1995a). Exceptions are made for 

extraction where material is not sold or hauled offsite, 

foundation excavation with an approved building 

permit, or excavation for tunnels that will carry water 

or roads.

• Copies of Colorado’s laws and regulations are located in 

the Colorado Revised Statutes at certain public libraries 

(called government repository libraries); they are also 

available for a small fee from the Division of Minerals 

and Geology (Department of Natural Resources, 1313 

Sherman Street, Denver, Colo., 80203).

Municipal and County Regulations

Through land-use regulations and zoning, local governments (municipalities, counties, special districts, and regional 

authorities) usually have the greatest control over how land 

is used. Such regulations and laws commonly are carefully 

evaluated at the time a mine site is selected. Restrictive 

zoning requirements in some jurisdictions may prohibit any 

industrial activity. Local agencies may determine the land 

use, both before and after a mining application is submitted, 

and establish additional regulations to protect the environment (commonly, limits on noise and on traffic and requirements controlling aesthetics—the visual appearance of the 

mine site). Municipalities that include citizens in the decisionmaking process, zoning changes, mine permitting, and 

environmental impact studies give the public a way to influence where mine operations are sited.

Municipal or county zoning powers have been used 

in three ways to allow mining (Werth, 1993). First, special 

extraction districts can be created; mining is then considered the highest and best use of land in the district. Second, 

areas underlain by mineral resources can be shown as an 

overlay on a zoning map; the jurisdiction then determines 

where mining will create the least conflict. Third, mineral 

deposits are mapped into existing use districts (such as 

agriculture, open space, or industrial; mining is allowed as 

a special exception).

Applicants for mining in Colorado are required to 

notify the local county government, municipalities within 

2 miles, and all landowners within 200 feet (ft) of the mine’s 

affected land, and they publish a weekly notice in a local 

newspaper for two weeks before an application hearing. 

Colorado counties differ in their approaches to mineral 

development. Boulder County Land Use Department (2008) 

prepared a comprehensive plan that contains a mineral 

resource areas map and geologic hazards and constraint 

areas map. Mineral resource areas do not overlap lands 

defined and mapped as critical wildlife habitat, agricultural 

lands of national or statewide importance, or designated 

natural landmarks and natural areas. Clear Creek County 

created a special extraction district and paired it with an 

ordinance considering mining the highest and best use of 

land in that district. The Jefferson County Mineral Extraction Policy Plan (Jefferson County, Colorado, Planning and 

Zoning, 1977) established a point system for evaluating 

mine sites according to their ability to conform to county 

goals. Table 4 lists potential mining issues and how they 

may be addressed from a local perspective.

Production of Industrial Minerals

Overview

In 2003, Colorado produced $672 million worth of 

nonfuel minerals, principally construction sand and gravel, 

Portland cement, molybdenum concentrates, gold, and crushed 

stone (U.S. Geological Survey, 2004). Colorado possesses 

numerous deposits of several essential industrial minerals, 

such as sand and gravel, stone, nahcolite (used to manufacture 

sodium bicarbonate or baking soda), gypsum, and limestone. 

The Colorado mineral belt, an elongate zone containing high 

concentrations of metallic minerals, extends from Boulder 

in the northeast diagonally across the State to the San Juan 

Mountains in Colorado’s southwestern corner. Many of these 

mineral deposits are located in or near national forests and 

national grasslands (see fig. 5).

National forests in the western United States come in all 

sizes, shapes, climates, environments, and geologic settings. 

Although few forests are underlain by base or precious metal 

deposits or energy resources, nearly all forests are underlain by 

at least one industrial mineral (table 5). Even though industrial 

minerals have never been (or no longer are) produced in some 

forests, changes in technology or in economic or political 

views could encourage development of these resources. Consequently, if the stewards of our national forests understand the 

potential industrial mineral resources in their jurisdictions, then 

they can effectively evaluate proposed mineral development 

and manage any development in an informed manner.
Production of Industrial Minerals 19

Table 4. Typical county or municipal policies and their implications for certain aspects of mining.

Aspect Requirements of county and municipal policy

Air and water quality Preservation and conservation of groundwater and air quality; meet and maintain 

state and county water and air quality standards. 

Archaeological or historical significance of site Historic resources, archeological resources, and paleontological study.

Blasting or other noise; health and safety Noise impact criteria, noise and blasting study, fire protection study, radiation 

study, safety fencing. Buffer zones and reclamation setbacks. Hours of operation 

regulated.

Drill or auger holes Core drilling sample report.

Geologic hazards Geologic report.

Grading, control of erosion Restrictions on post-mining uses and grading plans for final land contours.

Mineral transportation Site access map, traffic impact study, road access requirements, hours of operation 

limited. Detouring, paving, and speed control may be included.

Mining proposal Mining permit, reclamation plan, environmental impact statement, and public 

notice.

Overburden and backfill Sufficient arable soil for spreading over excavated areas.

Site location County and land use permits, building permits. Federal and State permits may be 

required for mining operation.

Vegetation Vegetation study, soil report, revegetation plan, specifications for landscaping. 

Topsoil retained.

Visual quality Protect and preserve natural landmarks, visual impact study (visibility mapping 

and visualization techniques), and open-space-resources study, screening 

requirements. Create slopes that fit in with surrounding landforms.

Waste material On-site sewage disposal.

Wetlands Wetland conservation, tie into natural drainage.

Wildlife Wildlife study, wildlife impact report, conservation of critical habitats.

Mining of industrial minerals may be as simple as using 

a front-end loader to excavate a gravel deposit or as complex as the meticulously planned blasting and processing 

techniques required to liberate tungsten or molybdenum ore 

(fig. 13A). Extraction may occur in open pits or quarries; along 

streambeds, valley bottoms, or river terraces; under lakes or 

in underground mines. All forms of mining entail dust, noise, 

traffic, erosion, changes to landscapes, and displacement of 

flora and wildlife. These considerations are discussed in more 

detail later.

Processing may use mechanical operations, termed beneficiation, that separate the desired mineral from waste rock 

(fig. 13B). For example, beneficiation may sequentially use 

crushing, grinding, washing, screening, pulverizing, sizing, 

and magnetic or centrifugal separation (or both). The extraction of some minerals may require further processing, such 

as physical separation according to specific gravity; chemical separations such as leaching with acids, bases, or oxides; 

electrolysis; or distillation. Some treatments, such as heating, 

take place in both the beneficiation and manufacturing stages. 

Some very fine grained material (such as mine tailings) is 

commonly considered waste. The tailings may need to be 

dewatered and revegetated as part of mine operations. Treatments range from passive drying in surface tailings ponds 

to highly technological methods that produce high-density 

slurry and paste backfills. Increasingly, waste material is being 

reused as raw material for some other product. For instance, 

cement or concrete projects may use recycled granular mine 

tailings and recovered mineral components (such as those in 

coal fly ash, the residue from coal combustion), thereby preventing waste and saving energy.

The estimated value of minerals changes with time 

owing to the economy (which in turn depends on consumer 

confidence, retail sales, industrial production, home starts, 

and inflation), regulations and trade agreements, technological 

improvements, research to reduce production costs, and new 

uses for byproducts (U.S. Geological Survey, 2004). Transporting the material from the mine to a point of use or sale is 

often the most costly phase of the resource supply line. Deposits of natural aggregates (rock materials in their natural state, 

such as sand and gravel, in contrast to artificial aggregate such 

as slag or expanded clay) near large population centers, such 

as Denver, have a high economic value. Such construction 

materials are usually readily available in large quantities and, 

therefore, have low unit value—the cost of a ton or truckload 

of the material is relatively small.

Other industrial minerals are less common than sand and 

gravel or building stone and have more technical industrial 

applications (table 6). Because of their relative scarcity, some 

industrial minerals have a higher economic unit value than 
20 Development of Industrial Minerals in Colorado

Table 5. Principal industrial minerals of Colorado, their uses and source areas (modified from Keller and Widmann, 2002; Mineral 

Information Institute, 2004).—Continued

Commodity Main uses Other uses Principal sources in Colorado

Barite Drilling mud for petroleum 

exploration, filler in food

Automotive paint, chemicals, 

and radiological applications

Vein deposits in Boulder County and in the Wet 

Mountains of Fremont and Custer Counties. 

Not currently mined in Colorado, 

Clays and shale Bricks, tiles, ceramics, 

porcelain, paper-making 

(kaolin only)

Lightweight aggregate, paint, 

paper-making, drilling mud, 

cat litter, tires, plastics, 

fiberglass, wire insulation

Currently mined mainly in eastern Colorado, along the 

flank of the Front Range in Fremont, Jefferson, and 

Pueblo Counties.

Diamond Industrial abrasive, cutting 

and grinding applications. Drill bits for 

drilling water, oil, and 

natural gas

Jewelry, mineral specimens More than 100 kimberlite pipes and dikes along the 

Colorado-Wyoming border in Larimer County, 

northwest of Ft. Collins.

Feldspar A main ingredient in 

manufactured glass and 

ceramics

Sandblasting agent, abrasives, 

soap, and filler in textiles 

and paper

Numerous granitic pegmatites in mountainous areas, 

especially in Boulder, Chaffee, El Paso, Fremont, 

Gunnison, Larimer, Jefferson, and Park Counties. 

No longer mined in Colorado.

Fluorspar 

(fluorite)

Reacts to form hydrofluoric acid, which is used 

to make fluorocarbon 

chemicals (contained in 

most air conditioners and 

refrigerators); aerosols

Aluminum smelting, steelmakingBoulder and Jackson Counties and in Browns Canyon 

in Chaffee County. Fluorspar was at one time 

Colorado’s most economically important industrial 

mineral. No mines currently operating in the United 

States, which imports fluorspar, mainly from China.

Gypsum Wallboard (drywall) and 

building plaster

An additive in cement, a soil 

conditioner, and a slope 

stabilizer

Large mine in Eagle county for wallboard; smaller 

mines in Fremont and Larimer Counties for other 

uses.

Limestone Crushed stone for highway construction and 

maintenance projects, 

dimension stone, and as 

a source of quicklime in 

cement production

Food products, soil conditioner, 

water and sewage treatment, 

and acid-waste neutralization 

in environmental remediation

Fremont and Larimer Counties, where it is mined for 

cement; occurs in many locations in the state.

Mica House paint, drywall joint 

compound, and insulators 

in electric motors

Insulation material in toasters, 

adds “sparkle” or “shimmer” 

in cosmetics

 Pegmatites (often with feldspar), especially in Fremont County. Currently very little production in the 

United States.

Nahcolite Source of sodium bicarbonate (baking soda) for 

use in food. Also used 

in animal feed, cleaning 

products, pharmaceuticals, and other chemicals. 

Has been mined to make 

soda ash, which is used 

to make glass, soap, 

detergents, and other 

chemicals. 

Sodium bicarbonate is used to 

treat water, in fire extinguishers, as a paint-blast medium, 

and in several other products.

 Bedded deposits within the Green River Formation; nahcolite is mined from solution wells in Rio 

Blanco County. 
Table 5. Principal industrial minerals of Colorado, their uses and source areas (modified from Keller and Widmann, 2002; Mineral 

Information Institute, 2004).—Continued

Commodity Main uses Other uses Principal sources in Colorado

Perlite Used as lightweight 

concrete construction 

aggregate and in acoustic 

ceiling tiles when 

expanded by high heat

Used in plant potting mixtures to 

keep soil loose

Formerly mined near Rosita in Custer County. Now 

most United States production is in New Mexico.

Pumice and 

scoria 

(volcanic 

cinders)

Lightweight construction 

materials such as cinder 

blocks

Abrasives, cleaners, horticulture, 

landscaping, and barbeque 

grill rocks

Basaltic cinders are mined in Eagle County for making cinder blocks. Scoria was formerly produced 

from a cinder cone in the southern San Luis Valley. 

Pumice is not currently mined in Colorado. Small 

quantities were mined in the past in Grand, La 

Plata, and Mineral Counties (Argall, 1949). 

Sand & gravel 

(construction)

Construction aggregate 

(concrete and asphalt), 

road base and fill

Golf course sand traps, troutspawning habitat for 

hatcheries

All areas of the state along rivers and major creeks 

and in former glacial valleys.

Sand 

(industrial)

Gravel packs for groundwater monitoring wells, 

hydro-fracturing of oil 

and gas wells

Ceramics, stucco, optical fiber, 

nonskid flooring, steel 

foundry sand, fiberglass

Eolian sand deposits in Colorado Springs area and El 

Paso County are quarried.

Stone

crushed)

Construction aggregate 

(concrete and asphalt), 

road base and fill

Barbecue grill rock (volcanic 

cinder), decorative stone for 

landscaping

Granite and metamorphic rock in the Front Range and 

other mountains; volcanic rock in southwest and 

south-central Colorado; limestone, sandstone, and 

quartzite in eastern Colorado; marble in Chaffee 

County; volcanic cinder in Costilla and Eagle 

Counties.

Stone 

(dimension)

Building construction and 

decoration, paving stones

Countertops, statuary, 

monuments

Marble (Gunnison County), sandstone (Boulder, El 

Paso, Fremont, Larimer, and Pueblo Counties), 

granite (Chaffee, Fremont, Gunnison, Larimer, and 

Teller Counties), rhyolite (Douglas and Fremont 

Counties), travertine (Fremont County).

Sulfur Manufacture sulfuric acid, 

fertilizers, petroleum 

refining

Elemental sulfur is used in 

synthetic rubber production, 

fungicides

Formerly, small mines in Delta, Gunnison, and Mineral Counties. Most United States sulfur is 

now produced as a byproduct of petroleum refining. 

No longer mined in Colorado

Titanium Used in its oxidized form as 

white pigment in paints, 

plastics, and paper

Titanium metal is used in jet 

engines and airplane frames, 

very light bicycle frames, and 

golf clubs

Large potential resources in southern Gunnison 

County and on the eastern plains near Limon, 

in Elbert County. No mines currently operate.

Vermiculite Similar to perlite, useful 

when greatly expanded 

by heat; used as fireproof insulation material 

and as a soil conditioner

Protective base material for 

swimming pools

Only in Precambrian and Cambrian rocks in the 

mountains of Colorado. Best deposits in Chaffee, 

Custer, Fremont, Gunnison, Jackson, and Pueblo 

Counties. Not presently mined in the state. 

Zeolites 

(clinoptilolite 

and other 

minerals)

Because of its capacity for 

cation-exchange, used in 

water treatment plants. 

Removes ammonia, 

arsenic, radon, and other 

impurities

Used in pet litter to remove odor 

and in nuclear plant effluent to 

remove radioactive ions

In the past, clinoptilolite occurred in Moffat County 

in Tertiary alkaline lake-bed deposits; it was mined 

from an altered volcanic ash layer near Creede in 

Mineral County. 

Production of Industrial Minerals 21
22 Development of Industrial Minerals in Colorado

Figure 13. Extraction of granite and of sand and gravel. Extraction is usually followed by beneficiation, which generates some waste. 

A, A drill is used to size blocks of granite to be extracted from a quarry. Photograph by William Langer. B, After extraction, sand and 

gravel may be crushed, screened to classify by size, and stored at the mine site. Photograph by B. Arbogast.

A

B
Production of Industrial Minerals 23

Table 6. Average unit price of, reliance on imports of, recycling of, and substitutes for certain industrial minerals (modified from U.S. 

Geological Survey, 2004, except as noted).—Continued

Industrial

mineral

Average price

dollars per ton Percentage imported1 Products recycledby industry

Substitutes for certain 

applications

Barite 29 81 None Celestite, ilmenite, iron ore, and 

synthetic hematite.

Generally, the substitutes are 

less satisfactory (Brobst, 

1994).

Clays

Ball clay

Bentonite

Common clay

Fire clay

Fuller’s earth

Kaolin

42

45

6

23

90

119

Net exports Insignificant Calcium carbonate and talc. 

Diamond

Industrial Stone

Dust, grit, powder

12,000,000

144,000

80

39

Diamond bort, grit, dust, 

powder

Synthetic diamond, cubic boron 

nitride, fused aluminum 

oxide, and silicon carbide.

Feldspar 55 Net exports Insignificant Nepheline syenite, clays, 

electric furnace slag, 

feldspar-silica mixtures, 

pyrophyllite, spodumene, 

or talc.

Fluorspar

Acid grade 2136–141

100 Synthetic fluorspar from 

uranium enrichment

Fluorides and hydrofluoric acid 

from smelting operations 

Olivine or dolomite.

Gypsum

Crude

Calcined

7

20

23 Gypsum waste from wallboard 

manufacture or installation 

and from building demolition

Cement, lime, lumber, 

masonry, and steel.

Lime

Quicklime

Hydrate

61

92

3

 <0.5 Paper mills, municipal water 

treatment plants, carbide 

industry

Limestone (slower reacting), 

calcined gypsum, cement and 

lime kiln dust, fly ash. 

Limestone (soda ash) 69–130 Net exports No recycling by limestone 

producers

Producers of glass containers 

using rejects from glass 

manufacturing and bottle 

banks, thereby reducing 

consumption of soda ash

Caustic soda (or sodium 

hydroxide).

Mica

Scrap, flake

Ground 

Sheet

120

200–1,000

2–60

7

100

None Lightweight aggregates, talc, 

and silica sand for ground 

mica.

Acrylic, scrap mica, and a number of registered 

products for sheet mica.

Perlite 37 28 Not available Diatomite, expanded clay and 

shale, pumice, slag, 

vermiculite.

Pumice, pumicite

24

29 Not available Crushed aggregates, 

diatomite, and expanded clay 

and shale.
24 Development of Industrial Minerals in Colorado

Table 6. Average unit price of, reliance on imports of, recycling of, and substitutes for certain industrial minerals (modified from U.S. 

Geological Survey, 2004, except as noted).—Continued

Industrial

mineral

Average price

dollars per ton Percentage imported1 Products recycledby industry

Substitutes for certain 

applications

Sand, gravel 

(construction) 5

<0.5 Asphalt road surfaces, 

cement concrete surfaces 

and structures

Crushed stone.

Sand (industrial) 20 Net exports Foundry sand and recycled 

cullet (pieces of glass)

Chromite, olivine, staurolite, 

and zircon sands.

Stone (crushed) 6 <0.5 Road surfaces of asphalt and 

crushed stone, cement 

concrete surfaces

Sand and gravel, slag, clay 

and shale, perlite, 

vermiculite.

Stone (dimension) 4

Marble 

Granite

865

1013

86 Small amount by restorers Aluminum, brick, ceramic 

tile, glass, plastics, resinagglomerated stone, concrete 

and steel.

Sulfur 25 20 Spent sulfuric acid from 

petroleum refining

Few are satisfactory.

Titanium mineral 

concentrates 5

Ilmenite

Rutile

93

430

70

None Ilmenite, leucoxene, rutile, slag, 

synthetic rutile, ground and 

precipitated calcium carbonate, kaolin, and talc.

Titanium dioxide:

Rutile 1,800

Net exports

Vermiculite 143 28 Insignificant Perlite, clay, shale, slate, slag, 

fiberglass, peat, sawdust, 

bark, and other synthetic soil 

conditioners.

Zeolite 6

Natural

Synthetic

85–140

500–600

Minimal6 A process catalyst Synthetic zeolite, clays, 

dolomite, diatomite and 

pumice, activated carbon.7

1

 Percentage imported = imports – exports + adjustments for Government and industry stock changes; stock changes assumed to be zero.

2

 Miller (2001); average U.S. Gulf port price for Chinese acid grade.

3 Miller (2004a).

4

Obtained from European Union; for a ton of processed natural stone, North American buyers pay 50 percent more than European Union 

buyers pay (KD Resources, 2003).

5

 Titanium mineral concentrates in bulk, “freight on board” from Australian ports.

6

 Virta (2003).

7

 Christie and others (2002); synthetic zeolite is detergent grade.

the construction materials. Barite, diamond, fluorspar, mica, 

nahcolite, silica sand, titanium oxides, and zeolite minerals 

all have a high unit value. These special industrial minerals 

are used in the manufacture of chemicals, abrasives, paint, 

specialty ceramics, glass, semiconductors, refractories (heatresistant products such as the lining of furnaces used to make 

steel), fertilizers, absorbents, insulating materials, and even 

prepared foods.

The materials considered to be industrial minerals 

(table 5) are fairly common in nature, but their occurrence in 

concentrations and volumes large enough to be of economic 

value requires that a combination of geologic processes 

operate under the right conditions, sometimes for millions 

of years. Some industrial minerals, such as crushed stone, 

are extremely abundant and virtually inexhaustible in central 

Colorado. Others, such as barite, are in much more limited 

supply. In chapter 4, each commodity’s use, geologic origin in 

Colorado, mining, and production is discussed.

Care of Physical and Cultural Landscapes

Long-term planning, management, and reclamation of pits 

and quarries are encouraged in response to concerns about the 

visual, physical, biological, and socioeconomic environments 
Production of Industrial Minerals 25

Figure 15. Gravel tip and rocky outcrops on the Wind River 

Reservation, Wyo., 2005. The establishment of native plants to 

reclaim sand and gravel pits is important to Eastern Shoshone and 

Northern Arapaho tribes. The tribes retain traditional values, and 

many plants in the sagebrush ecosystem are used as medicines 

and in ceremonies. Photograph by B. Arbogast.

surrounding the development of industrial mineral resources. 

Exploration and production activities can have considerable 

effect on the site and the surrounding community. The contrast between excavated and unexcavated areas, alterations in 

topography and landform, changes in vegetative cover, disturbance of local fauna, and response to regional resource needs 

may need careful consideration. Careful planning and design 

can address potential effects from an engineering, ecosystem, 

visual, and socioeconomic perspective. Proper site investigation, planning and location, reduction of unnecessary disturbance (such as minimizing road widths and restoring vegetated 

areas as soon as possible), making the site less visible (such as 

retaining as much existing vegetation as possible and screening the operation from public view), and sensitivity to the site’s 

ecoregion character (defined by its soil, hydrologic function, 

climate, and natural processes) all help mitigate a project’s 

immediate effects (U.S. Bureau of Land Management, 1984).

The cultural landscape contains both natural and manmade components (fig. 14). “A natural landscape or ecosystem is one that developed by natural processes and that is 

self-organizing and self-maintaining” (Society for Ecological 

Restoration, 2004). Special scenic areas, unique geologic 

landscapes, and critical habitat may be declared off-limits to 

mineral development. Remote areas that are intended to be 

used by backcountry campers may not be as suitable for mineral development as areas that are already built up with roads 

and other facilities. Careful environmental assessment and 

collaborative planning can establish preferred mining sites.

Preserving religious or archaeological sites respects 

the cultural needs of Native peoples (fig. 15). Lafarge North 

America considered mining a 120-acre site, which includes an 

old pumice mine, adjacent to ancestral lands of the Santa Clara 

Pueblo in Rio Arriba County, N. Mex. In 2005, the company 

Figure 14. Landscapes can contain both natural and manmade features. A, An 1800s lime kiln near St. Louis, Mo., contributes to a 

picturesque scene. Photograph by B. Arbogast, 2002. B, Carved out of an old clay quarry, Fossil Trace Golf Club is owned by the city of 

Golden, Colo. The crane was used to remove clay units between sandstone layers. Courtesy of Fossil Trace Golf Club.

A B

instead donated the land and a sum of money for its reclamation to the pueblo (Lafarge North America, 2005).

Literature discussing the prediction and management of 

environmental issues in mining can be found in publications 

from a variety of sources:
26 Development of Industrial Minerals in Colorado

• Academia (for example, Darmer, 1990, Landscape and 

surface mining—Ecological guidelines for reclamation)

• Industry (for example, National Stone Association, 

1995, Environmental management guide)

• State and Federal agencies (for example, Buttleman, 

1992, A handbook for reclaiming sand and gravel 

pits in Minnesota; Norman and others, 1997, Best 

management practices for reclaiming surface mines 

in Washington and Oregon; Colorado Department of 

Natural Resources Division of Minerals and Geology, 

1998, In-stream aggregate extraction and reclamation 

guidance document; Environment Australia, 2002, 

Overview of best practice environmental management 

in mining; and Wright and White, 2004, The practical 

guide to reclamation in Utah)

• Scientific journals (for example, Journal of Environmental Management; Landscape Research; and Landscape and Urban Planning) 

• World Wide Web sites sponsored by the Environmental 

Protection Agency, U.S. Geological Survey, USDA 

Forest Service, Bureau of Land Management, and 

Office of Surface Mining, such as the following:

• http://www.epa.gov/epahome/scitech.htm

• http://www.usgs.gov/pubprod/

• http://www.fs.fed.us/publications

• http://www.blm.gov/nhp/index.htm

• http://www.osmre.gov/resources/Ref/References.shtm

Exploration Activities

Exploration for additional industrial minerals proceeds by 

stages (Bates, 1969; Peters, 1978).

Marketing Study

First, a marketing study inventories known resources and 

deposits on the basis of written reports, small-scale regional 

geologic maps (U.S. Geological Survey 1° × 2° geologic 

maps are particularly useful), aerial photographs, a site visit, 

and visual assessment. If this marketing study supports the 

venture, a detailed project plan of the mine or quarry is then 

prepared. Exploration field work follows, using techniques 

such as random sampling and field checks of known occurrences; exploration by grid pitting, trenching, and drilling; and 

laboratory testing of samples (discussed in the next section).

A second-stage feasibility study will contain results 

of these exploration studies. The report evaluates geologic, 

economic, and environmental aspects of mining the property: 

mineral reserves, composition, and characteristics; location, 

access, and transport; mineral, water, and surface rights; water 

and energy supply; mining method, manpower, and production 

capacity; and protection of the environment (Kuzvart, 2003).

Geological and Geophysical Exploration

Geologic examination, usually by mapping, can determine the areal extent of a mineral occurrence and those soil 

and bedrock properties that indicate difficult or unstable 

ground conditions. On a microscopic scale, geologic examinations of the rocks can yield information about the type, size, 

shape, and proportions of mineral grains, their interlocking 

nature, and the amount and interconnectedness of pores and 

fractures in the rocks. Such attributes determine rock strength 

and stability. Mapping has little or no effect on the land surface, but drilling, trenching, and pitting (discussed in the next 

section) will disturb the land surface. Usually the changes are 

small and are straightforward to reclaim.

Geophysical techniques can be used to determine the 

subsurface characteristics of a mineral deposit and complement the geological mapping. For example, geophysical 

investigations can be used to measure the depth of overburden, 

map sedimentary strata, and help determine the structural 

or geological stability of mine faces. It can also determine 

anomalies (local distortions within the overall pattern) or 

structures that may affect the mining of the deposit (such as 

geologic faults, cavities, or old mineshafts). Which of the 

many geophysical techniques are used depends on the type 

of information sought, the local geology, and features such as 

roads or buildings that may skew certain kinds of geophysical 

measurements. Surveys can be run from the ground or from 

the air, depending on the scale and objectives of the investigation. Airborne methods have no environmental effect other 

than the brief passage of an airplane or helicopter. Active 

methods transmit energy into the Earth; passive methods do 

not. Passive geophysical exploration methods—gravity, radiometric, and magnetic surveys— measure natural properties 

of sediments and rocks. Like geological mapping, they have 

essentially no environmental effect.

Active methods include most electrical and seismic 

surveys (fig. 16). Electrical methods measure various electrical properties and generally have a very limited environmental 

effect. Seismic surveys measure the properties of waves that 

pass through the Earth and may cause limited environmental 

effects. Small-scale site surveys commonly use a sledgehammer, a portable steel plate, and a recording device; consequently they leave few traces in the environment. On the other 

hand, large-scale regional seismic surveys, such as those used 

in petroleum exploration, use trucks to move specialized equipment across the land surface. These surveys commonly cause 

some environmental damage that may require reclamation.

Sampling and Analysis

The feasibility of any mining project depends chiefly 

on the size of the deposit (its thickness and depth) and the 

quality or grade of the deposit (its ratio of useful to useless 
Production of Industrial Minerals 27

components). Well-designed sampling programs, which usually go hand in hand with calculations of size or reserves, 

can determine quality or grade. Sampling can be as simple as 

grab samples (hand-sized samples) from selected outcrops or 

exposures such as road cuts. Or, a gridded sampling program 

may sample densely enough to record all the variability in a 

deposit. Sampling programs may combine large samples taken 

from various points in the deposit to produce a composited or 

bulked sample that may range from a few hundred pounds to 

several tons. The most ambitious investigations combine bulk 

sampling with a pilot plant on the mine site to test the planned 

recovery process.

Drilling is one way of physically sampling the subsurface 

of a deposit. Not only does the drilling program provide information on the lithological variation of a deposit, but samples 

can also be analyzed for other chemical and physical properties. Depending on the samples required, the drilling program 

might use core-drilling machines or rotary or hammer drills, 

which provide chips and fragments. Drilling programs may 

construct drill pads, access roads, pits for water storage, and 

other temporary facilities. If the drilling and sampling program 

is unsuccessful in delimiting a mineable deposit, then the drill 

sites and roads will be reclaimed.

Other types of sampling can cause limited to moderate 

effects on the land surface. Bulk sampling usually requires 

use of trenching, blasting, and haulage equipment on the site. 

Some reclamation work is usually required. A pilot plant is 

usually a scaled-down version of the final proposed plant and 

mine. Environmental effects, depending on the size of the 

operation, can differ; however, most pilot plant operations 

are a precursor to actual full-scale mining, and the repair and 

reclamation of environmental changes are generally completed 

as part of the approved mine plan.

Analysis of a deposit’s chemical or physical properties 

is almost always required before the economic viability of 

the deposit can be determined. Geochemical or petrologic 

sampling and analysis can distinguish the physical attributes 

of the deposit (such as composition, abundance of elements in 

the mineral, grain size, texture, and lithology). A geochemical 

analysis might determine the calcium carbonate content of a 

limestone or chemical impurities in a gypsum deposit. Very 

pure and treatable industrial minerals are needed for certain 

manufactured materials—such as composites, special ceramics, superconductors, and optical fibers—but such deposits 

or reserves are usually small (Kuzvart, 2003). Knowing the 

physical properties of raw materials is important, given the 

common need for large volumes of a uniform product that 

meets stringent specifications. In order to lay the highly 

durable asphalt pavements called “Superpave,” for example, 

highway engineers specify aggregate that meets criteria for 

angularity of coarse aggregate, uncompacted voids in fine 

aggregate, flat and elongated particles, clay content, and gradation parameters (Pavement Interactive, 2008). Moreover, 

aggregate should be free of certain types of impurities, such 

as opalescent quartz, which may react with lime in cement 

and cause the concrete to disintegrate (U.S. Environmental 

Protection Agency, 1995a) (fig. 17).

The feasibility studies and mineral exploration program 

are followed by detailed project drawings of the mine or 

quarry and its buildings and infrastructure. Mapping, sampling, drilling, and geophysical programs provide the raw 

data needed to develop a mine plan. Computer programs 

can manipulate data on grade and size of an ore deposit and 

develop a mining plan that allows for efficient mining of the 

resource. Once the mine plan has been determined and all 

permits have been acquired, the deposit can be developed.

Figure 16. Geologists collecting shallow seismic data to help 

assess aggregate deposit thickness and character. Photograph by 

J.E. Lucius.

Figure 17. Deteriorated concrete bridge pillars. Unstable silica

in the aggregate reacted with alkali in the cement; the resulting 

alkali-silica gel may have contributed to the deterioration of the 

concrete. Photograph by William Langer.
28 Development of Industrial Minerals in Colorado

The exploration program is a small but important part 

of the development and production of a mineral deposit. The 

design and implementation of the exploration program can 

influence not only the eventual mine plan but also the environmental changes that take place during mine operation and 

eventual reclamation.

The Physical Environment—Geotechnical 

Concerns

During a mining operation that causes the physical disturbance of a landscape sound engineering and geologic decisions 

ensure public safety and proper processing of mineral ore, disposal of waste rock, and reclamation. The chief concerns during 

earthwork and grading are promoting safety and reducing erosion (Wright and White, 2004). Short-term minor to moderate 

adverse effects of mining include surface runoff (flow of water 

over the land), dust, noise, and land disturbance. All of these 

issues exist at any construction site (even residential building 

sites) or during road repair and timber harvesting.

Acid Mine Drainage

The general public may be familiar with environmental 

problems associated with toxic reagents (such as the leakage of 

cyanide-bearing solutions from the Summitville open-pit gold 

mine in Colorado) or the formation of acidic and metal-bearing 

soils and waters from mining activity (termed “acid mine drainage”) (King, 1995). When certain rock types and mine wastes 

containing sulfide minerals are exposed to air and water, those 

minerals (such as the iron sulfide minerals pyrite (FeS2) and pyrrhotite (Fe1–xS)) can oxidize and produce highly acidic waters 

with elevated metal concentrations (Alpers and others, 1994). 

The likelihood that acid drainage will form increases during 

mining, because the rates of mineral weathering increase greatly 

during mining and mineral processing (Alpers and others, 

1994). Acid rock drainage that is not contained or mitigated (as 

by buffering with excess limestone or other calcium-bearing 

rock obtained from cement operations) may contaminate surface 

water, groundwater, and vegetation. Acid mine drainage is more 

commonly associated with abandoned hard-rock metal mines 

(those that recovered gold, copper, lead, or zinc ore) or coal 

mines rather than industrial mineral mines. Typically, mines that 

recover industrial minerals have fewer engineering problems 

compared with metal mines. Processing is simple, and relatively 

benign waste is produced. However, gaseous and particulate 

pollutants, blasting with explosives, slope stability, and water 

quality are concerns in any mining operation.

Air Pollutants and Noise

Dust typically is a byproduct of the production and processing of minerals (U.S. Environmental Protection Agency, 

1995c). It is generated by drilling, blasting, front-end loaders handling and transferring material, trucks on haul roads, 

mechanical processing (crushing, screening, and grinding) of 

minerals, and wind erosion of storage piles.

Dust can be difficult to eliminate entirely but usually can 

be reduced out-of-doors by wet suppression (spraying roads, 

sites of blasting, stockpiles, and exposed surfaces with water 

and a surfactant), by covering or enclosing open operations, 

and by planting windbreaks and other vegetation. Magnesium 

chloride can be sprayed to reduce dust on dirt roads and tailings (U.S. Environmental Protection Agency, 1995a). Truck 

wheels can be cleaned before they move from the mine site to 

public highways and paved roads.

Indoor operations can avoid sending dust to the atmosphere by using hoods and fans to collect dust (dry collection). 

Most kilns have some sort of dust control, such as fallout 

chambers, cyclone separator, fabric and gravel bed filters, wet 

scrubbers, and electrostatic precipitators (U.S. Environmental Protection Agency, 1995c). Machinery such as crushers, 

vibrating screens that separate crushed material according to 

size, and conveyor belts can be enclosed.

More serious than the nuisance aspect of dust is occupational exposure, through inhalation, to dust that contains crystalline silica—a kind of dust present in many industries, such 

as mines and quarries, metal foundries, construction sites, and 

sites where sandblasting is used. Overexposure to respirable 

crystalline silica may result in silicosis, a disabling, nonreversible, and sometimes fatal lung disease (U.S. Department of 

Labor, 2002). A comprehensive program to protect the respiratory health of workers who work with materials that contain 

crystalline silica contains the following (National Industrial 

Sand Association, 1997):

• Warning and training workers concerning hazards

• Sampling of crystalline-silica dust

• Engineering controls (such as improved wet drilling, prevention of contamination, removal by exhaust ventilation, 

dilution with uncontaminated air, and remote handling)

• Good housekeeping

• Medical surveillance of workers’ respiratory health.

“Many minerals or rocks of commercial value contain 

varying amounts of crystalline silica. Silica can be a predominant constituent or be present only as a minor accessory mineral with minerals of commercial value” (National Industrial 

Sand Association, 1997). Most industrial rocks and minerals 

are mined from deposits containing crystalline silica (U.S. 

Bureau of Mines Branch of Industrial Minerals, 1992). Such 

rocks and minerals include barite, beach sand, bentonite, calcite, crushed stone, clay, feldspar, granite, gypsum, industrial 

sand, kaolin, limestone, mica, rutile, sandstone, vermiculite, 

and zeolite (U.S. Bureau of Mines Branch of Industrial Minerals, 1992; National Industrial Sand Association, 1997).

The U.S. Environmental Protection Agency (1995a) 

lists the air emissions of particular chemicals, such as carbon 

monoxide, nitrogen dioxide, total particulates, sulfur dioxide, 

and volatile organic compounds, according to industry sector 
Production of Industrial Minerals 29

(table 7). Carbon monoxide, nitrogen dioxide, and sulfur 

dioxide gases are commonly products of combustion from 

coal- and petroleum-driven furnaces or dryers. Gasoline- and 

diesel-powered vehicles used during mining activities are 

another major source of air emissions. If natural gas is used 

for fuel, the emittable pollutants resulting from combustion are 

fewer in volume and number than those from the combustion 

of any other fossil fuel (U.S. Environmental Protection Agency, 

1995c; U.S. Energy Information Administration, 1998).

Explosives are used to displace rock from the quarry face 

and reduce the size of rock fragments. Larger quarries may 

blast once a day and smaller operations once or twice a week. 

The use of explosives and detonators is regulated by Federal 

and State agency regulations, including those of the Bureau of 

Alcohol, Tobacco, and Firearms. Selective blasting is used to 

modify rock benches in mines or quarries, reduce the steepness of walls to make them more stable, and blend highwalls 

with the surrounding landform.

The intensity of ground vibrations and air overpressure 

(pressure waves in the atmosphere sensed as noise or concussion (or both)) may not exceed certain limits set by the Environmental Protection Agency. Relations with nearby communities 

proceed more smoothly when those communities are notified 

of proposed explosive work well beforehand, haul trucks 

have effective mufflers, and machinery is fitted with silencers 

and acoustic housing. Efficient, controlled blasting obtains 

maximum energy from smaller explosive charges (that do not 

produce an appreciable air blast) and limits the range of flyrock. 

Seismographs, laser profilers, and velocity-of-detonation 

measuring systems can monitor results of blasting. Buffer zones 

may be needed between the blasting area and surrounding 

areas—especially those areas where “natural quiet” is required. 

Tree belts and berms can reduce noise levels and screen 

activities between a mine site and the surrounding community.

Table 7. Volumes (short tons per year) of six pollutants released by industry (modified from the U.S. Environmental Protection 

Agency, 1995a).

Industry Carbon

monoxide

Nitrogen

dioxide

Total

particulates

Sulfur

dioxide

Volatile organic 

compounds

Nonmetal mining 4,525 28,804 167,948 24,129 1,736

Motor vehicles, 

bodies, parts, and 

accessories

35,303 23,725 12,853 25,462 101,275

Stone, clay, glass and 

concrete

58,043 338,482 171,853 339,216 30,262

Petroleum refining 419,311 380,641 36,877 648,153 309,058

Pulp and paper 624,291 394,448 113,571 341,002 96,875

Iron and steel 1,518,642 138,985 83,017 238,268 82,292

Erosion and Slope Stability

One of the most commonly encountered engineering 

problems is maintaining the stability of slopes in quarry 

walls and waste dumps. Some earth scientists claim that 

erosion control is the major goal of reclamation (Toy and 

Hadley, 1987).

Mining (as well as urbanization, agriculture, and forestry) 

increases the runoff of water, which in turn increases erosion. 

The erodibility of a particular area is controlled mainly by the 

nature of the underlying bedrock, the climate, and the steepness of slopes. Generally, igneous and metamorphic rocks 

and tightly cemented sedimentary rocks are more resistant to 

physical erosion. Harder rocks such as granite typically form 

more-stable slopes than do softer rocks such as shale, clay, 

or gypsum. Shale along Colorado’s Front Range weathers to 

clays that produce gently curving hillslopes, whereas granite 

weathers to sand and gravel and commonly produces steeper 

hillslopes (Wohl, 2001).

However, even rocks that may be strong as long as they 

are underground may weather and become softer or less stable 

once mining exposes them to air. Site engineers and geologists 

are interested in identifying the physical and chemical character of the rock or mineral to be mined, the stability of natural 

slopes (which determines the mining technique to be used), and 

the extent of the area disturbed by mining in order to predict 

the effects of that disturbance (fig. 18). Landslides are of particular concern during the rainy season in mountainous regions.

Minimizing the disturbed area, reducing the time newly 

exposed surfaces are left untreated, and constructing earth 

walls and spillways can reduce erosion. Extreme surface roughening (pocking, ripping, or gouging) creates a network of many 

small pits that trap sediment (Wright and White, 2004). Stabilizing the soils that rim a pit or quarry may help to stabilize 
30 Development of Industrial Minerals in Colorado

standard activities in reclaiming the mined land and reducing 

erosion as soon as possible.

The height, length, and steepness of mine faces (highwalls) or the slopes of mine-waste piles strongly influence 

their stability. Mine engineers and geologists monitor potential hazards such as rock falls or landslides from mine faces or 

the collapse of mine-waste piles. Highwalls also impinge on 

the visual landscape. Guidance on appropriate slope gradients 

and bench heights differs according to regulatory authorities 

and is influenced by the erodibility of the material in question and local hydrologic processes. In order to prevent slope 

failure, safety regulations may forbid highwall slopes greater 

than 45° or even less if the slopes might be unstable (Wright 

and White, 2004). In an arid environment, slopes may be 

constructed with a gradient of no greater than 20° and with 

benches every 7–10 m (approximately 23–33 ft) of vertical 

height (Gratzfeld, 2003).

Mine wastes may be used as backfill against a mine wall 

to minimize the problem of surface disposal of the waste 

elsewhere and minimize surface subsidence by filling in 

underground voids (U.S. Environmental Protection Agency, 

1995a). However, backfilling consumes energy, precludes 

mining reserves, and may destroy wildlife habitat created 

by the excavated pit. Each mine site will have its own set of 

engineering requirements.

their underlying slopes. Limiting surface mine operations 

during high winds or intense rainfall and using mulches, cover 

crops, liquid sprays, and geotextiles may help to stabilize soils 

and thus slopes (fig. 19). Ditches and catchment ponds may be 

constructed to collect effluents and sediment.

Setting a mine face to a slope angle and slope length that 

approaches natural slopes can also help reduce erosion. A natural surface slope has a convex or concave profile that merges 

with a flat section at the toe of a slope and is thought to generally yield less sediment than a straight or uniform slope (Toy 

and Hadley, 1987). Hill slopes in arid regions tend to be shorter 

and steeper and have a smaller radius of curvature of the convex 

element than those in humid areas, and south-facing hill slopes 

are longer but less steep than their north-facing counterparts. As 

land is reclaimed, the intended postmining land use will influence the design of the final landform. Flat areas are suitable for 

playing fields but are unnecessary for forests or grazing. Reduction of back slopes, replacement of topsoil, and revegetation are 

Figure 19. Wood-fiber netting at Glenharold mine, North Dakota. 

The netting helps prevent erosion until grass is established. Courtesy 

of Chuck Meyers, Office of Surface Mining, Washington, D.C.

Figure 18. Geologists examine rock face in an industrial sand pit 

near Tamms, Ill. Photograph by B. Arbogast, 2002.
Production of Industrial Minerals 31

Water Management

Water is nearly everywhere in mining operations. It is 

naturally present as groundwater in many mines; it is used 

during mining and in the processing of industrial minerals. A 

comprehensive water management plan characterizes aquifers 

and monitor surface water and groundwater. Rainwater and 

water used in processing are commonly stored in a recycling 

pond. Dewatering of mines to lower the water table within the 

site may be necessary through pumping or dewatering wells 

(for temporary withdrawal of groundwater or to drain water 

from an upper aquifer into a lower one). In order to prevent 

or minimize erosion as well as retain water on the mine site, 

storm-water runoff may be controlled by best management 

practices such as retention ponds, storm-water conveyances 

(for example, gutters and sewer), diversion dikes or berms 

(structures that block runoff), silt traps in drainage areas, 

graded areas, and vegetation (fig. 20). Effective control 

measures result from careful consideration of drainage areas, 

runoff patterns, and discharge points.

When water is withdrawn from a well, groundwater 

may form an inverted cone of depression around the well 

that locally lowers the water table (Bates and Jackson, 1987). 

Similarly, dewatered mines can also lower the water table 

around them. On the other hand, mine pits can be flooded 

by overbank river water and by groundwater. Careful hydrologic studies and mine siting can conserve water resources 

and decrease the risk of water pollution. Creating vegetated 

areas and wetlands onsite can help to filter waste and increase 

groundwater recharge.

Some geologic environments, such as karst areas and 

active stream channels, are particularly apt to be disrupted by 

mining. Karst landforms are produced in humid regions when 

rainwater (enriched in carbon dioxide from organic soils) dissolves subsurface limestone and thus produces sinkholes, cave 

systems, and valleys in which no streams flow on the surface. 

Karst topography is more common in the eastern United States 

than in the West. Gypsum can also be dissolved and removed 

in groundwater, but ground subsidence in gypsiferous rocks is 

less common than ground subsidence in limestone. In active 

stream channels, aggregate can be extracted from riparian 

zones triggering upstream incision, which can undermine 

banks and destroy riparian and aquatic habitat, even if the 

hydrological regime that created those zones is restored. In 

Colorado, the ground subsidence of greatest concern is associated with sedimentary rocks over abandoned coal and clay 

mines (Colorado Geological Survey, 2004a).

Flotation is a common method of separating a higher density target mineral from a lower density waste rock. “Processes 

used to remove mineral impurities can be a major source of 

water contamination. Flotation, a wet method used to refine 

certain nonfuel, nonmetallic minerals (sand and gravel, kaolin, 

potash, phosphate rock) is a potential source of water pollution 

due to the chemicals used to separate impurities from the mineral. Flotation involves placing minerals in an acidic or basic 

bath of chemicals where pH modifiers such as sulfuric acid, 

ammonia, and hydrofluoric acid are used to control pH levels 

in order to separate impurities from the target mineral. Additional materials may be added to the flotation bath to assist in 

removing impurities, including frothers, conditioning agents, 

sulfonated oils, and heavy alcohol” (U.S. Environmental 

Protection Agency, 1995c). Sensors on flotation equipment can 

reduce the amount of flotation reagents needed (U.S. Environmental Protection Agency, 1995c). Alternative procedures that 

use organic chemicals to separate minerals of interest from 

waste remain under development; such procedures may make 

processes such as acid leaching and heavy media separation 

safer for the operator and for the environment.

Mine operations may pollute groundwater or surface 

water by accidental spills of fuels, oils, or solvents and of 

nitrates or ammonium used in blasting. Hazardous materials, such as petroleum in tanks, are commonly stored within 

a bermed or diked area to contain any spills, and ponds into 

which tailings are fed may be impounded.

The Biological Environment—Flora and Fauna

The development of mineral resources and conservation 

of biodiversity need not conflict. Embracing environmental 

fitness (healthy, self-organizing systems) may satisfy both aesthetic and functional landscape needs (Carlson, 2001). Federal 

agencies are required to ensure that mining activities do not 

adversely affect the habitat of a Federal- or State-listed threatened or endangered species (U.S. Environmental Protection 

Figure 20. Sedimentation pond at a coal mine site near Craig, 

Colo. Sedimentation ponds allow sediment to settle from water 

so that only clear water flows from mine site. Courtesy of Chuck 

Meyers, Office of Surface Mining.
32 Development of Industrial Minerals in Colorado

Figure 21. The Columbian sharp-tailed grouse (A) is a Colorado 

native species of State special concern and was reestablished at 

the Trapper Mine on reclaimed land (B) near Craig, Colo. Courtesy 

of Minerals Information Institute.

A B

threatened species). Although the Columbian sharp-tailed 

grouse (Tympanuchus phasianellus columbianus, a species of 

State special concern) population has declined over most of its 

western range, its numbers are increasing on reclaimed mined 

land at Trapper Mine, a surface coal mine in northwestern 

Colorado (Raabe, 2002) (fig. 21).

In arid and semiarid lands of the western United States, 

the scarcity of water may limit revegetation, and irrigation 

is an essential component of plans for establishing seedlings (National Academy of Sciences, 1974) (fig. 22). High 

altitude and a short growing season also make revegetation 

difficult. Moreover, disturbed land—such as around mining 

operations—may create new niches for nonnative invasive 

plants that also compete for scarce water.

Avoiding the spread of noxious weeds is always a goal in 

reclamation work. Concurrent reclamation practices, reestablishing vegetation on all bare ground as soon as possible, minimizing the creation of bare soil and removal of trees (particularly on 

south-facing aspects), and removing seed sources (for example, 

pressure washing mining equipment to remove dirt and plant 

material before transporting that equipment to the mining site, 

mowing or treating noxious weed plants, using weed-free mulch) 

may help to preclude introduction of nonnative vegetation into 

high-ecological-risk areas.

Ecosystems are much easier to restore if local topsoil 

and plant species have been retained. Collecting native seeds, 

using cuttings, establishing transplants, removing invasive 

species, reproducing local norms of minimum plant density, 

and controlling potential damage to new plantings by wildlife 

or livestock are all a part of establishing new vegetation. Much 

research is needed to define seed mixtures that will produce 

diverse, adapted plant communities. Optimum vegetative stability requires slopes of less than 25 percent (Toy and Hadley, 

1987). “Small or long, linear disturbances, such as roads or 

pipelines, can revegetate naturally without seeding if good 

Agency, 1995a). Forest managers may take into account the 

best available science to protect air, water, wildlife, and other 

natural resources that make up a landscape.

Federal agencies undertaking a Federal action (such as a 

BLM review of proposed mining operations) are required to 

consult with the U.S. Fish and Wildlife Service, which may 

require an environmental impact assessment. If certain critical 

habitats are identified, mining operations may be relocated or 

they may be suspended during seasonal migrations or breeding. Or, the protected species may be relocated. For example, 

near Orlando, Florida, Tarmac America’s Center Sand facility 

captured and relocated a protected species, the burrowing 

gopher tortoise (Gopherus polyphemus) (Mineral Information 

Institute, 2004).

In Colorado, the Federal and State lists of endangered 

or threatened species and list of animals of special concern 

contain 23 species of fish, 7 of amphibians, 10 of reptiles, 2 of 

mollusks, 19 of birds, and 13 of mammals (Colorado Department of Natural Resources Division of Wildlife, 2003). Properly planned mine sites may help with the recovery of some 

species. Underground mines have been secured for bat habitat. 

Around reservoirs and wetlands reclaimed from mined-out 

sand and gravel pits, mudflats could become nesting areas for 

the endangered whooping crane (Grus americana); sandy or 

pebbly beaches could become nesting habitat for the endangered least tern (Sterna antillarum) and the threatened piping 

plover (Charadrius melodus). The creation of quiet, warm 

backwaters could help the spawning of Colorado pikeminnow 

fish (Ptychocheilus lucius, a Federal endangered and State 
Production of Industrial Minerals 33

Mining operations may cause the loss of desert varnish, a 

coating on exposed rock surfaces in certain arid regions. The 

varnish is a thin brown to black patina formed during thousands of years by bacteria cementing windborne deposits of 

clay, iron, and manganese oxide minerals (fig. 23A). Coating 

vertical mine surfaces with certain oxidizing agents can simulate the colors of natural desert varnish. Cryptobiotic crusts 

may also be important in arid and semiarid plant communities 

(Belnap, 2003) (fig. 23B). These soil crusts, which are dominated by cyanobacteria, lichens, and mosses, intercept rainfall, 

stabilize surfaces, and contribute fertility to dryland ecosystems (Belnap, 2003). Recovery times for disturbed biological 

crusts are generally measured in decades or centuries (Belnap, 

2003). It may help to separately salvage the top inch of dry 

crust material from topsoil and spread it as thinly as possible 

over topsoil storage piles to keep the piles active (Wright 

A

B

Figure 22. Revegetation of mined lands depends on the local soil 

types, nutrient status, and climate conditions. A, Field checking 

vegetation established in a former sand and gravel pit, Wren 

Pit project, Fort Collins, Colo., 1996. Photograph by B. Rolle. B, 

At a North Dakota coal mine, reclaimed land is seeded in native 

grasses in late spring or early summer. After two or three growing 

seasons local ranchers begin to graze their livestock. Courtesy of 

Chuck Meyers, Office of Surface Mining.

Figure 23. Two types of coatings on arid-region rock faces. 

A, Native American peoples used stone tools to cut line drawings 

(petroglyphs) through dark desert varnish on a rock face outside 

Moab, Utah. Photograph by B. Arbogast, 2005. B, Cryptobiotic 

crusts (foreground) on the Colorado Plateau. Photograph by 

Jayne Belnap.

A

B

topsoil handling techniques are practiced” (Wright and White, 

2004, p. 89). Research by Colorado State University, the Colorado Division of Minerals and Geology, the Colorado Division 

of Wildlife, the U.S. Soil Conservation Service, and the USDA 

Forest Service continue to improve techniques for seeding, 

replacing topsoil, and other aspects of revegetation.
34 Development of Industrial Minerals in Colorado

and White, 2004). However, large disturbed areas may never 

recover although, under the best circumstances, a thin veneer 

may return in 5 to 7 years (Belnap, 2003).

Mine reclamation is most successful when those in 

charge recognize the role of time and space in working with 

processes such as vegetative succession or soil sedimentation 

and erosion. Plant communities reestablished on bare ground 

take time to develop high diversity. Because most people are 

aware of only those landscape changes that take place within 

a few decades, they commonly do not recognize landscape 

changes that may have occurred during longer periods of 

time (Wohl, 2001). For example, Front Range rivers appear 

relatively natural now partly because few people know how 

the rivers may have looked 200 years ago (Wohl, 2001). Few 

people recognize former mines within the Denver, Colo., 

metropolitan area, now that the sites have been reclaimed for 

water storage, wildlife or greenbelt space, multipurpose reservoirs, or uses such as light industrial districts or residential 

housing (Arbogast and others, 2000).

“Cumulative impact” is the impact on the environment 

which results from the incremental impact of the action 

when added to other past, present, and reasonably foreseeable future actions regardless of what agency (Federal 

or non-Federal) or person undertakes such other actions. 

Cumulative impacts can result from individually minor but 

collectively significant actions taking place over a period of 

time” (40 CFR Sec. 1508.7). For example, one mine may 

not be noticeable on a landscape but as the number of mines 

increases over time, the effect may become noticeable in a 

broad area. The most effective mitigation plans are based on a 

development scenario for the entire area, not just for one mine 

at a time (U.S. Bureau of Land Management, 1986a).

Spatial patterns within a mined area can differ markedly 

depending upon the scale of the assessment. A minimum of 

three or four scales is usually adequate for simple analysis and 

understanding of ecosystem behavior (USDA Forest Service, 

1995; Steinhardt and Volk, 2001). For example, at a larger scale 

are drainage basins produced by a region’s climate, lithology, 

tectonic history, and physiography, which operate during time 

scales of more than 10,000 years (Petts and Amoros, 1996; 

Wohl, 2001). A smaller scale may be evaluated for mesohabitats 

(such as gravel patches, sand bars, or tree roots) that persist during a time scale of 0.01 to 10 years (Petts and Amoros, 1996).

Mining activities can alter the amounts of water and 

sediment entering rivers or destabilize valley slopes (Wohl, 

2001). Taking into account fluvial geomorphic principles in 

reclaiming disturbed drainage basins and stream channels may 

promote long-term stability of the land, and a variety of slope 

aspects and lengths may provide a greater diversity of vegetation (Bugosh, 2002; Wright and White, 2004).

In the early 21st century, some mining companies are 

considering the environment more holistically, and they 

are integrating ecological studies with landscape character, 

historic land use, and local culture. Local identity remains 

important in rural areas that are faced with urban sprawl. 

In Europe the norm is to restore the cultural landscape, 

whereas in North America the norm is to restore pristine 

landscapes (Society for Ecological Restoration, 2004). Few 

places on Earth are unaffected by human activity. Natural 

or wild untouched areas have vanished from most parts of 

the world today (Krönert and others, 2001). Many Europeans include the capacity for human use in their models of 

“natural” environments and development. For example, the 

Dutch view landscapes and culture as interrelated; building construction in existing ecological zones and creation 

of new wildland environments in urbanized areas are both 

considered “natural” (Scott, 2002). The Dutch, as have most 

Europeans, have been living in cities, dealing with the loss 

of natural habitat, and running out of space for a much longer time than North Americans.

If humans are to be accepted as part of the ecosystem, 

changes in the appearance of landscapes are inevitable, and 

if biodiversity is to be a goal, then a forward-looking mining industry probably will welcome citizen participation, 

understand the complexity of evolutionary processes, and 

move away from managing single species. For example, 

forested ecosystems may change slowly owing to long-term 

drought or more quickly owing to fire and manmade development. We may want to consider what we want from our 

forests, how to improve forest health, and which land uses to 

promote or discourage.

The Visual Environment—Measuring Landscape 

Quality

Of our six senses, sight is the one that we use the most in 

our Western culture. Hearing, smell, taste, touch, and balance 

influence our perceptions of mining, but the visual effect of 

mining may raise public concerns quickly, especially near residential or, conversely, less developed areas. Visual assessment 

early in the planning stages may assist in extraction operations 

fitting within the natural and social environments. Given that 

mining may disturb the landscape, a mine is best sited where it 

offers the least amount of contrast and can be subordinated to 

the natural landscape.

Many visual-assessment methodologies evaluate natural 

or rural landscapes where recreation or tourism is increasingly 

important. Most simply, one can evaluate the landscape by a 

descriptive inventory of its features (called a visual analysis), 

by compiling viewers’ emotional response to or experience of 

a landscape (called a user analysis), or by combining the two 

approaches for a more holistic evaluation.

Visual Analysis

The inventory approach identifies visual elements in a 

landscape and their interrelationships. On the basis of the 

character of a given landscape, government agencies may 

deny permits for a mining operation in a scenic area or a 

widely visible landscape, or they may remove certain lands 

from mineral development because the lands contain critical 
Production of Industrial Minerals 35

wildlife habitat, agricultural lands of importance, or officially 

designated scenic vistas, backdrops, and views. Natural areas 

of unique beauty, geology, vegetation, or historical significance may also be excluded. The capacity of a landscape to 

accommodate change commonly is considered as well as the 

opportunity for new development.

Aspects of the physical landscape (such as significant 

geologic features, historic sites, vegetation, rare species, land 

use) or design elements (such as form, line, color, and texture) 

may be inventoried, usually by an expert, to help establish 

a landscape baseline that provides a basis for predicting the 

potential effects of mining operations. The whole landscape is 

assumed to be defined and explained by the sum of its parts, 

and scenic beauty is assumed to be a physical attribute. The 

visual analysis methodology, the traditional method of choice, 

is descriptive, versatile, and relatively low cost. This approach, 

however, fails to take into account the users’ or observers’ 

perception of scenic beauty (a perception that may differ from 

place to place) or economic tradeoffs, and it assumes that 

landscapes are objects rather than systems. Thus, the method 

may favor a certain type of landscape and is subjective in the 

physical attributes selected.

Scenic attractiveness has come to include intangibles 

(such as scenic vistas, natural quiet, sounds of nature, clear 

night skies, and human psychological well being) as well as 

the tangibles (such as unique landform, water, animal species, 

geologic features, and historic sites) (fig. 24). Indirect effects 

associated with mineral development (such as new roads, 

signage, transmission lines) and longer term effects (such as 

housing that builds up later around a mine site) are of concern 

but hard to address in detail (Landscape Institute and Institute 

of Environmental Management and Assessment, 2002).

Figure 24. Gay Head Cliffs (now known as the Aquinnah Cliffs), on

the western tip of Martha’s Vineyard, Mass. The cliffs, a national 

natural landmark, contain multicolored clays and sands that formed 

about 100 million years ago. Photograph by B. Arbogast, 2005.

The Natural Resources Management Reference Manual 

used by the National Park Service (U.S. Department of Interior 

National Park Service, 2001, p. 2) does not address “* * * aesthetics in the context of the built or cultural environment* * *” 

but considers viewsheds, photographic visibility, weather data, 

air quality, sociological studies (to evaluate visitor preferences 

and aesthetic effects) and ethnographic research (to document 

the aesthetics, preferences, and concerns of Native American 

and other communities). Old Man Mountain, on the east side of 

Rocky Mountain National Park, Colo., is an example of a sacred 

landscape used for vision quests for more than 3,000 years 

(Stone, 1999). Increasingly, Federal agencies may be expected 

to include Native Americans in the consultation process for historic preservation and in construction and development projects 

in or near Native American lands (Banks, 1999).

A more inclusive understanding of landscape is based 

on experiential appreciation and what a landscape does 

rather than just the Western appreciation of scenery for how 

it looks (Makhzoumi, 2002). The English design philosophy 

of landscape, so often expressed in the United States as an 

ideal, includes green grass on a vast scale, irregular form, 

a concern with form rather than content, and a character of 

greatness (Jellicoe and Jellicoe, 1987) (fig. 25A). The United 

States expresses that desire for bigness and green grass with 

reclamation in arid and semiarid lands that requires water 

and fertilizer. In contrast, the form of certain Middle Eastern 

cultural landscapes can express an almost indistinguishable 

relationship between inside and outside living spaces. “The 

spaces are mathematically proportioned, human in scale, and 

in principle imaginatively unconfined” (Jellicoe and Jellicoe, 

1987, p. 41) (fig. 25B).

Landscape quality does not refer solely to the physical 

landscape in front of your eyes. Landscape is also a psychological vision that exists in the mind and may trigger an emotional response. Our past experiences, socioeconomic profile 

(including factors such as age, ethnic identity, income level, 

and education), and rapidly changing world view influence 

our visual values and aesthetic traditions (Zongyu and others, 

2002). People in many cultures share a craving for aesthetic 

satisfaction in order to maintain physical and psychological health (Kellert and Wilson, 1993). This craving includes 

preferences for nature, water, and mountains (fig. 26); a mix 

of open landscape and forest; a focal point, distant views 

to the horizon, and moderate complexity (Zube and others, 

1975; Ulrich, 1977, Porteous, 1996).

User Analysis

The user analysis approach evaluates individual preferences (the observer’s or user’s point of view), requires surveys, is subjective, assumes that good feelings are produced 

by a scenic landscape, and relies upon the totality of human 

experience. Of all landscape assessment methods, psychophysical methods have been subjected to the most rigorous 

evaluation (Daniel and Vining, 1983). Such models do not 

classify landscapes but rather predict scenic preference or 
36 Development of Industrial Minerals in Colorado

visual quality. Psychophysical models are developed specifically for a given landscape type and observer population 

(Buyhoff and others, 1994). Psychological variables used 

in determining visual quality (such as legibility, coherence, 

prospect, drama, and mystery) have been related to physical viewshed properties (such as breadth and depth of view, 

characteristics of the horizon or skyline, surface shape, and 

relief) by use of geographic information systems (Baldwin 

and others, 1996; Meitner and Daniel, 1997).

Discussions, correspondence, public meetings, and 

workshops—in which these psychological preferences can 

be expressed—typically use considerable time and money. 

Survey and questionnaire costs may be lowered and efficiencies increased through the use of the World Wide Web; 

chat rooms can increase the opportunity for public participation (Wherrett, 2000). Virtual geographic environments 

are being proposed so that the public can participate in 

the analysis of spatial data and in environmental planning 

(Lin and others, 2002). The prototype system allows public 

participation in visual impact assessment through online, 

three-dimensional virtual worlds and three-dimensional 

representations of participants.

Critics point out that people don’t necessarily perceive a natural landscape as scenic. For instance, grand 

landscapes, such as those in Yellowstone National Park, 

once were favored over dry landscapes such as those in 

Pawnee or Comanche National Grasslands in northeastern 

Figure 26. Sylvan Lake, Yellowstone National Park. Courtesy of 

National Park Service.

A

B

Figure 25. Use of water in two cultures. A, Estate lawn 

in England, where rainfall is plentiful. B, Court of the Lions, 

Alhambra, Spain, where water is scarce. Columns are alabaster, 

an industrial mineral. Photographs by B. Arbogast.
Production of Industrial Minerals 37

Colorado. The grasslands at one time would have been 

considered a wasteland. Figure 27 demonstrates that it is 

not always easy to distinguish and appreciate what is the 

ecologically valuable in contrast to unhealthy disturbed 

landscapes; determining the physical characteristics of 

the landscape remains essential (fig. 27). Basic aspects 

of analysis remain uncertain: the nature of an appropriate 

sample size or location, and whether the individual rater or 

the group average is the more appropriate unit of analysis 

(Zongyu and others, 2002).

Both the visual analysis (or inventory method) and the 

user analysis (or preference method) have proven effective 

in assessing natural landscapes, but they are not considered 

reliable for urban landscapes (Zongyu and others, 2002). The 

urban landscape can appear chaotic (owing to noise, signage, 

and traffic), rigid (owing to massive steel, concrete, or glass 

structures), geometric (owing to the street grid commonly 

produced by our land survey system), and sterile (owing to 

insufficient natural landscape). Urban views are commonly 

linear (along streets or highways) and foreshortened, much as 

a mine site appears during operation. Wise planning, design, 

and reclamation can mitigate such visual problems.

USDA Forest Service and Bureau of Land 

Management Visual Assessment

Two visual analysis methods developed by Federal 

agencies are the Visual Resource Management system 

(U.S. Bureau of Land Management, 1984), and the Scenery 

Management system (USDA Forest Service, 1995). Both 

methods attempt to identify and protect visually valuable 

public lands. Bureau of Land Management and USDA Forest Service manuals or handbooks provide a means of comparing, in a decisionmaking process, the value of scenery 

with the value of other resources such as forestry, wildlife, 

recreation, highways, or development such as oil, gas, or 

wind energy. The U.S. Bureau of Land Management (2001) 

and USDA Forest Service (1995) incorporate geographic 

information systems and image processing technologies 

to improve on existing expert-based descriptive systems. 

Both systems

• were developed because of conflict between a new land 

use (such as timber harvesting, energy development, or 

mineral development) and existing scenic uses;

• treat the visual landscape as a basic resource;

• value diversity and harmony in the landscape;

• assume that natural-appearing landscapes are the most 

valued and that most people find certain elements (for 

instance, clear air and clean water, unique and varied 

wildlife) intrinsic to scenic attractiveness;

• assess landscape integrity or contrast for the amount of 

deviation in form, line, color, and texture between the 

existing and proposed landscape;

• assess landscape visibility through key observation 

points or distance zones; and

• encourage an interdisciplinary approach.

The USDA Forest Service handbook for scenery management “presents a vocabulary for managing scenery and 

a systematic approach for determining the relative value 

and importance of scenery in a national forest” (USDA 

Forest Service, 1995, p. 5). This system identifies landscape 

character, analyzes existing scenic integrity, and determines 

inherent scenic attractiveness, landscape visibility, and scenic 

classes. The process combines user analysis (people’s values 

and expectations) and visual analysis (physical attributes) 

in the broad context of ecosystem management. This system 

allows for changes in the natural system and accepts the 

cultural landscape.

The Bureau of Land Management system inventories 

visual resources and applies a visual resource contrast-rating 

tool in the context of a resource management plan for public lands (U.S. Bureau of Land Management, 1986a,b). The 

Bureau of Land Management visual management objectives 

are developed through the Resource Management Plan process 

for all Bureau lands (U.S. Bureau of Land Management, 

1984). “To maintain the health of the public lands, the agency 

is taking a ‘big picture’ or landscape approach to land management. This promotes both biological diversity on the public 

lands and sustainable development of their resources” (U.S. 

Bureau of Land Management, 1997). The Bureau’s mandate 

under the Federal Land Policy and Management Act of 1976 is 

to manage the public lands for multiple use, while protecting 

the long-term health of the land.

Other Visual Assessment Methods

There are other landscape evaluation methods. Ecological models are sensitive to the natural environment and 

emphasize species of plants and animals and geomorphologic 

processes. These models assume that all natural landscapes 

are of scenic beauty; that landscape quality is related to its 

“naturalness” and its diversity; and that natural landscapes 

take precedence over manmade structures and cultural 

landscapes. However, people are not always able to distinguish between natural and cultural landscapes―for instance, 

landscapes that contain reclaimed mine sites, cleared forests, 

hedgerows, and canals (Magill, 1992). Observers also tend 

to base their landscape preferences upon land use rather than 

beauty (Arthur and others, 1977).

Scotland, England, and Wales have descriptive systems 

for classifying the countryside on a national scale, and those 

countries map landscape character and natural zones to aid 

in landscape protection and management. Their map system 

allows for a holistic view illustrating the natural and cultural 

characteristics of the countryside on the basis of biodiversity 

and landscape without making judgments about their relative 

worth (Landscape Institute and Institute of Environmental 

Management and Assessment, 2002).
A

Figure 27. Which features are natural and which manmade? A, Marble terrace at Mammoth Hot Springs, Yellowstone National Park, Wyo., 1922. Pho

Courtesy of USGS Photographic Library.
B

Figure 27. (continued) Which features are natural and which manmade? B, Gypsum quarry and mill, Nephi County, Utah. Photograph by E.F. Burchar

Photographic Library.
40 Development of Industrial Minerals in Colorado

C D

E

F

Figure 27. Which features are natural and which

manmade? C, Cut rock slope with edges in silica mine, 

Pacific, Mo. D, Similar view, silica mine, after reclamation. 

Photographs C and D by B. Arbogast. E, Aggregate mining 

operation along the Gunnison River at Curecanti National 

Recreation Area, Colo. Courtesy of National Park Service. 

F, Great Owl lava tunnel in basalt flow, Craters of the Moon 

National Monument, Butte County, Idaho, 1952. Photograph 

by H.R. Cornwall. Courtesy of USGS Photographic Library.
Production of Industrial Minerals 41

An interdisciplinary approach is recognized as the 

best approach in landscape evaluation. That means including the technical engineering aspects of mining development when one assesses a landscape’s ability to absorb 

change and treating the landscape as a complex system 

rather than an object. The USDA Forest Service requires 

independent audits of forest plans, using a process that it 

says accounts for changing forest conditions while emphasizing science and public involvement. Mining development has come a long way since Georgius Agricola (1556) 

published the first Western manual of mining techniques 

(fig. 28).

The Socioeconomic Environment—Efficiency, 

Equity, and Acceptability

Our Western industrialized society consumes natural 

resources in order to build and maintain our manmade environment and indeed our civilization. However, global patterns 

of production and consumption are uneven (United Nations, 

2003b) and, in addition, the mining industry today tries to 

avoid the boom-and-bust character of past mining operations. 

More weight is given in mineral investigations to the concept of societal needs (such as public health or the costs and 

benefits of land-use alternatives), risk assessment, and land 

values (the effect of mineral production on price per acre and 

the secondary value of the land after extraction) (Moss, 1977). 

The public weighs the value of mineral development, whether 

an immediate need for mineral resources that lie within a 

national forest or the regional needs of large cities, against 

other considerations. Courts have upheld that considerations of 

economic cost and technical feasibility are secondary to considerations of public health (Moss, 1977). Mineral industries 

are required to ensure the health and safety of their employees 

and of the local community.

Beliefs about mining are quite susceptible to change on the 

basis of new information (Bingham, 2000). When the fears of a 

community about to become neighbors with a mining operation 

and the importance of mineral resources in daily life are both 

acknowledged and understood, communication between the 

public welfare and industry may progress. “Mine site development is often responsible for significant changes in the local 

social and economic conditions in an area” (Robertson and Shaw, 

2004, p. 7). Multiple accounts analysis has been used to weigh 

the costs and benefits of a new mine in terms of the project’s 

technical, economic, environmental, and socioeconomic accounts 

(Shaw and others, 2001), sustainability value, aesthetics, stability, 

and safety (Robertson and Shaw, 2004). The mining industry in 

Colorado (excluding oil and gas production) contributed about 

$8 billion to the State’s economy both directly and indirectly in 

2008, and miners are the highest paid industrial workers in 

Colorado—average annual earnings in 2008 were $77,920 

(Colorado Mining Association, 2008).

Marketing factors play into mining decisions. Natural 

components of the ore that may be considered contaminants 

by potential buyers and transportation costs can increase 

production and market costs enough to eliminate a mining 

operation. Proximity to rail lines or waterways able to haul 

bulky material with a low unit value can improve the overall 

economics of a site. Investment in United States mining operations is falling as the nation’s dependence on foreign minerals 

is rising, and the United States already imports 100 percent 

of 16 major minerals (U.S. Geological Survey, 2004; Western 

Governors’ Association, 2010). Two of those commodities are 

the industrial minerals fluorspar and sheet mica, both of which 

have been mined in Colorado.

Land itself can be viewed as fixed and taxable, an input 

for production, space for amenities, and as an asset (Xu and 

others, 1993). The demand for amenities such as scenery, 

Figure 28. Wood block from Georgius Agricola’s “De Re 

Metallica” (1556) illustrates mineral beneficiation during the 

1500s. Courtesy of Stephen Henley. Image downloaded at 

URL http://www.mining-heritage.com
42 Development of Industrial Minerals in Colorado

recreation, wildlife habitat, and open space is expected to 

grow as populations continue to migrate into less urban areas 

(Bastian and others, 2002). The Rocky Mountain region 

has a “strong public expectation for ‘wilderness experience’” (USDA Forest Service, 2001, p. 165) and access to 

mountain climbing, backpacking, hiking, and bike trails. 

Sequential land use is an approach that takes into account 

the undeveloped aggregate resource and allows redevelopment only after the resource has been extracted. Mined lands 

near metropolitan areas may be redeveloped for residential, 

commercial, industrial, recreational (such as fishing, boating, 

swimming, and hiking), or water storage uses, and that land 

can be sold for a higher price than paid when the land was 

originally acquired for mining (Fong, 2005). In the Denver 

metropolitan area, for example, the city of Aurora offered to 

pay $17 million to the Central Colorado Water Conservancy 

District for a gravel pit near Brighton, which will be used for 

a new reservoir with a capacity of just more than 1 billion 

gallons of water (Fong, 2005). The higher resale value of 

depleted sand and gravel mining sites, along with more efficient mining and processing equipment and larger operating 

units, has been instrumental in maintaining adequate production of sand and gravel (Goldman, 1994).

Pricing a scenic view is difficult, but attempts have been 

made to do so by use of the following methods (Macaulay 

Land Use Research Institute, 2005): 

• Hedonic price method—Measures people’s willingness 

to pay to live in a particular type of landscape

• Travel cost method—Asks visitors to a site questions 

about their journey, costs incurred, and sociodemographic characteristics

• Contingent valuation techniques—Estimates dollar 

value on the basis of landscape component scores and 

public-preference techniques

• Willingness-to-pay studies—Attempts to value the 

benefits which visitors and residents might derive from 

landscapes today or in the future.

Cultural, political, and moral points of view all affect 

the balance between conservation and resource development. 

(Bennett, 1993). Traditional economics may not have taken 

into account public concern over aesthetics or clean air and 

water, but today doing so is the norm. Ecological economics 

recognizes economics as part of the global ecosystem; sustainability, distribution, and allocation are key issues (Daly 

and Farley, 2004). The supply of mineral resources is finite, 

and the supply that is of sufficient quality and extractable is 

even more limited. “At a given point in time * * * we can 

think of mineral resources as rival goods within a generation, but as partially nonrival between [future] generations, 

depending on how much is wasted and recycled. * * * we 

could not sustain existing populations or levels of economic 

production in the absence of these minerals” (Daly and Farley, 2004, p. 86–87).

Sustainability concepts are being applied to mineral 

resources in many countries of the world at local, regional, 

and national levels, and from the perspectives of governments, 

citizens, and industry. Ecosystems have been managed for 

mineral resources in the past, but community and industry 

planners, when making decisions, now consider values in 

addition to production and consumption. Taking environmental issues into account means addressing the inherent value 

of species diversity and ecosystem processes. Sustainability 

includes reusing and recycling mineral materials and planning for cleanup and reclamation of the mine site. The costs 

and benefits of mining and reclamation are likely to become 

more quantified and scrutinized as conflicts about land use and 

demand for industrial minerals continue.

Reclamation and Postmining Use

Reclamation of disturbed sites is a requirement after 

completion of exploration and mining (U.S. Bureau of Land 

Management, 1996). Reclamation in the context of mining has 

a variety of definitions: 

• Avoiding or correcting damage to the lands and waters 

of the mine site (also termed mitigation)

• Making the surface-mined landscape productive 

(sometimes called rehabilitation)

• Returning the mined land to a beneficial use

• Making the mined land visually attractive.

In North America, reclamation also includes public safety, 

terrain stabilization, aesthetic improvement, and revegetation 

(Society for Ecological Restoration, 2004). Reclamation is a 

broad term that begins with minimizing the effects of exploration 

and extends to extraction, mineral processing, site decommissioning, and postmining land use (fig. 29). It also means considering 

community wants and needs. On forest lands, structures and roads 

should not disturb ecological integrity and should respect the 

landscape’s character (USDA Forest Service, 2001). Reclamation 

of mined lands on national forest lands, which is required by the 

Forest Service at the operator’s expense, has created ecological 

niches, wildlife openings, wildlife ponds, dispersed group camping, and even a shooting range. Effective reclamation aims for 

proper hydrologic requirements, the best ecologic conditions for 

the land-use objectives, and the most pleasing aesthetic experience for the viewer (National Academy of Sciences, 1974).

Restoration in the early 21st century is more ecological 

and includes the reestablishment of preexisting native habitat and blending the landscape into the greater surrounding 

community. People tend to be more concerned with safety or 

revegetation than with restoration of sound ecosystems (Tapsell, 1995). It is important to reclaim the land with respect to 

its geomorphology and natural processes. Land so reclaimed 

will have long-term stability, lower long-term costs, greater 

diversity, and visual harmony (Trimble, 1997; Bugosh, 2002). 

Reclamation and ecological restoration projects that anticipate 
Production of Industrial Minerals 43

unwanted effects and work with natural processes are more 

likely to be successful from a social, economic, and environmental objective (Trimble, 1997; Bugosh, 2002).

Projects successful in the long run aim for an ecosystem that is restored to a historic trajectory (that is, one that 

describes the broad developmental pathway of an ecosystem 

through time), not a particular narrow and specific historic 

state (Society for Ecological Restoration, 2004; Winterhalder 

and others, 2004). Determining the historic trajectory of a 

disturbed site may be difficult in practice owing to the highly 

complex nature of the entire ecosystem (Winterhalder and 

others, 2004). One thing that most planners and scientists 

agree on is that reclamation planning is best begun well before 

excavation can start.

Mining operations may follow any of four reclamation 

strategies: progressive, segmental, interim, or postmining 

(Norman and Lingley, 1992) depending on the site’s location, 

type of mineral resource, and State or local laws. Progressive 

reclamation immediately follows the removal of overburden 

and the mined material. It is preferred by the public but may 

be wasteful or impractical for those operations that blend 

compositions or grain sizes (Norman and Lingley, 1992). 

Segmental reclamation follows the removal of minerals in 

designated sections of the mine. It is cost efficient, establishes 

final slopes as part of the mining operation, and works well 

in homogenous deposits (fig. 30). Interim reclamation meets 

temporary goals in order to stabilize disturbed areas with fastgrowing grasses or legumes. Postmining reclamation does not 

begin until the entire mine has been exhausted. Postmining 

reclamation may lead to deterioration of soils and take longer 

to revegetate, and bond liability may be high.

The final land use of a mine site is influenced by surface topography, elevation above or below the water table, 

proximity to other development, and needs of the local 

population. Plans for reclaiming mine sites generally use 

at least one of nine design approaches (Arbogast and others, 2000): natural, camouflage, restoration, rehabilitation, 

mitigation, renewable, education, art, and integration. The 

best-managed reclamation operations commonly incorporate 

several design approaches such as camouflage, mitigation, 

renewable, and education. Some highly successful mine 

reclamation projects achieve uses that the public may not 

associate with mined-out land.

Visitors to national forests expect to see landscapes 

that appear natural (USDA Forest Service, 2001). Natural 

reclamation allows nature to reclaim the mine site with no 

or little human influence. At a minimum, the topography is 

restored to blend with surrounding landforms and at least 

30 cm (12 in.) of topsoil is replaced within 5 years. To protect farmland soils, the subsoil may be salvaged to a depth 

of 1.2 m (4 ft) (Wright and White, 2004). Preferably, when 

soil is removed from an active area of the mine, it is immediately spread over graded overburden (Wright and White, 

2004). If necessary, the topsoil is stored in stockpiles no 

more than 1 m (3.2 ft) high to retain the maximum amount of 

microbial (mycorrhizae) activity (Norman and Lingley, 1992; 

Gratzfeld, 2003). Mycorrhizae are formed by a symbiotic 

Figure 29. Mine site restored to approximate its original state. A, A quartz crystal mine, Womble Ranger District, Ouachita National 

Forest, Ark. B, Same view approximately three years after reclamation. Courtesy of J.C. Nichols, Ouachita National Forest.

A B

Figure 30. Reclamation work at the Howe pit, north of Denver, 

Colo. Such work requires moving earth. Photograph by B. Arbogast.
44 Development of Industrial Minerals in Colorado

association of fungus with a root or rhizome of a higher plant 

(Bates and Jackson, 1987). Because mycorrhizae spores 

are distributed by wind, most reclaimed sites are inoculated 

naturally within a year (Wright and White, 2004). Inoculua 

for small sites can also be collected from nearby soil and fine 

roots. In some instances, topsoil may not be replaced in order 

to encourage the emergence of plants that don’t germinate in 

topsoil, such as piñon pine and mountain mahogany (Mineral 

Information Institute, 2004). Rocks and boulders can be salvaged in order to mimic the surroundings, diversify habitat, 

and reduce surface soil erosion.

Camouflage is a superficial and immediate treatment of 

the landscape to hide the operation, usually around the perimeter of the site. Buffer zones, reclamation setbacks, rock outcrops, natural topography, fences, vegetation, and earth berms 

may be used to screen views (fig. 31). Slightly darker color 

schemes that use colors in the local landscape may reduce the 

prominence of structures such as water towers or fuel storage 

tanks. Technology can help reduce the contrast between the 

existing landscape and mine surfaces. For example, microorganisms can be sprayed on exposed limestone to more quickly 

start natural ecological processes (for example, weathering) 

(Courtney, 2001).

A restoration approach has been used in landscapes 

as varied as prairie, woodland, orchards, farmland, stream 

and riparian, and beach. Former quarries and pits have been 

restored to habitats of high biodiversity value that shelter 

threatened or endangered species. Many sand and gravel 

quarries support a large number of breeding water birds 

(English Nature and others, 1999). Butterflies, bats, frogs, 

and toads are among the wildlife that can be attracted to a 

former quarry (fig. 32). A bentonite mine operated by Wyo 

Ben Inc. in the Big Horn Basin, Wyo., was the recipient of 

Figure 32. Postmining land restoration in Colorado. A, Butterfly 

at South Platte Park, near Denver, formerly mined for aggregate. 

Photograph by Bill Bevington. Courtesy of South Suburban Park 

and Recreation District, Littleton, Colo. B, Settling ponds that once 

were part of a gravel pit near Boulder. C, The same pit, now called 

the Marshall Pit Wetland, after reclamation. Photographs B and C

courtesy of Mineral Information Institute.

A

B

C

Figure 31. Visual screens and buffers help to camouflage a 

mining operation. Topography and an earth berm conceal an 

aggregate mining and production facility south of Morrison, Colo. 

Painting the storage tank in the left middle ground an earth color 

would reduce the visual contrast. Photograph by B. Arbogast.
Production of Industrial Minerals 45

the 1999 Wyoming Game and Fish Department Mine Reclamation and Wildlife Stewardship Award (Mineral Information Institute, 2004).

Mine sites in urban areas tend to be rehabilitated. The 

exhausted mine site may be used for public amenities such as 

amphitheatres, botanic gardens, swimming areas, or soccer 

and baseball fields; hiking, bicycle, and horse trails; or golf 

courses (fig. 33). An operating sand and gravel pit in Moab, 

Utah, is slated to become a community pit (“collect the 

aggregate yourself”) as part of the reclamation plan. The pit 

will continue to provide sand and gravel for the public once 

commercial extraction has ceased. A jail, housing, and industrial development occupy former clay and shale quarries in 

West Virginia.

When a mine site requires extensive repair (usually 

because it has been abandoned) or scientific input to protect 

the environment from degradation, a mitigation approach may 

be required. Sand and gravel quarries have improved the value 

of rivers for biodiversity by widening the river or regrading its 

banks (English Nature and others, 1999). Copeland Sand and 

Gravel of Grants Pass, Ore., which had been mining aggregate 

from pits adjacent to the Applegate River, took advantage of 

a 1997 flood. The flood redeposited tons of river rock and 

changed the course of the Applegate River. The company 

worked with the Oregon Department of Fish and Wildlife and 

Department of Geology and Mineral Industries to enhance fish 

habitat and decrease erosion along the river while excavating 

the aggregate (Mineral Information Institute, 2004). Gravel 

with smooth pebbles is also used to line ponds at fish hatcheries so that spawning fish aren’t injured when laying their eggs 

(Keller and Widmann, 2002).

Reclaiming land in a renewable fashion implies sustainability and ecological management. Reducing the amount of 

minerals removed from the land and efficient use of the appropriate material for a given manufactured product extend the 

availability of mineral resources. Mine sites have been used 

for composting, forestry, groundwater recharge, wastewater 

treatment, and recycling of glass, concrete, and macadam.

Educative reclamation projects include nature trails, 

boardwalks, viewing areas, and signage that explain the area’s 

natural history and historical significance (fig. 34). In an educative approach, mining information is communicated through 

outreach so citizens can make informed choices about future 

land use and learn about environmental responsibility.

An artistic approach celebrates the site as a work of 

beauty and unique experiences; the earth becomes outdoor 

sculpture (fig. 35). Projects may be ephemeral in nature and 

associated with natural processes and geology.

Finally, an integrated approach combines art and science, fulfilling aesthetic, utilitarian, recreational, cultural, and 

ecological needs (fig. 36). Such works can repair the damage 

done by past engineering works. With an increased demand 

for multifunctional space, the integrated design approach is 

being increasingly used. The Owl Canyon Quarry Project is on 

the eastern slope of the Rocky Mountains in northern Colorado, at more than 1,800 m (6,000 ft) in elevation. The design 

Figure 33. Community needs controlled how these mined lands

were reclaimed. A, A future underground storage facility at 

Bussen’s quarry near St. Louis, Mo., 2002. B, An amphitheater 

built within a stone quarry, Santa Cruz University campus, 

California. Courtesy of Mineral Information Institute. C, Bowling 

alley, the Gravel Pit Lanes, built in a former sand and gravel pit, 

Moab, Utah, 2005. Photographs A and C by B. Arbogast.

B

A

C
46 Development of Industrial Minerals in Colorado

Figure 35. Two large reclamation art works have a similarity to art minimalism. Earth works as land art are primarily concerned with 

the environment. A, Nancy Holt’s “Up and Under” and B, Agnes Denes’ “Tree Mountain” projects at gravel pits near Pinsi, Finland. At 

Tree Mountain, 10,000 trees were planted by 10,000 people. The land is protected and will be maintained for 400 years. Photographs by 

B. Arbogast, 2001.

A B

A

Figure 36. Two reclamation projects that used a holistic approach to 

create multipurpose space. A, Quarry Cove (Yaquina Head Outstanding 

Natural Area, Newport, Ore.) is a manmade tidal zone developed by the 

Bureau of Land Management. Formerly an abandoned basalt quarry, 

the tidal-zone cove provides wildlife habitat, research opportunities 

for marine biologists, educational opportunities for visitors, and scenic 

views. Photograph by B. Arbogast. B, White-tailed deer forage for food 

on a newly reclaimed area of the Owl Canyon Quarry, Colo. The diverse 

landscape accommodates both grazing and wildlife interests. Courtesy 

of Mineral Information Institute.

Figure 34. Two quarries opened to the public that educate the public about mining. A, Temple Quarry nature trail, near Little 

Cottonwood Canyon, southeast of Salt Lake City, Utah. The granite from this former granite quarry was used to build the Salt 

Lake Temple. Photograph by B. Arbogast, 1999. B, Park-like setting serves as staging area for open houses and quarry tours, 

Fox River Stone Company, South Elgin, Ill. The active quarry is visible in the background. Courtesy of Mineral Information 

Institute.

A B

B
Colorado Industrial Minerals—Occurrence, Use in Colorado, Mining, and Production 47

accommodates grazing and wildlife interests, a variety of landscaped slopes, some intact highwall faces to attract raptors, 

and small canyons and talus slopes to resemble the existing 

hogback formations (Mineral Information Institute, 2004).

In Colorado, many former sand and gravel pits have 

become water reservoirs, recreational lakes for fishing and 

boating, wildlife protection areas; others assume “hidden” 

uses. Hidden landscapes are reclamation projects that people 

may not realize were once active mines. Former pits and quarries across the country are now in use as an amphitheater, golf 

course, shopping center, residential housing area, farmland, 

nature center, riparian habitat, and tidal pool.

Practical, economic, environmentally and culturally 

sensitive reclamation plans commonly are flexible and 

emphasize process (for example, sustainability, maintenance 

issues, or monitoring of best management practices). Opportunities exist for mine sites to create habitat and improve 

biodiversity, support educational and recreational use, fulfill 

community needs, and provide industrial mineral products 

for society.

As anthropomorphic agents, humans can work to make 

landscapes sustainable, diverse, and profitable, and we can 

choose whether the landscape appears “natural” or “manmade” (fig. 37).

Colorado Industrial Minerals—

Occurrence, Use in Colorado, Mining, 

and Production

Introduction

The geology of Colorado is conducive to the occurrence 

of numerous types of industrial minerals. The State contains 

industrial minerals associated with igneous, metamorphic, and 

sedimentary rocks. Some common industrial minerals, such as 

sand and gravel, crushed stone, and dimension stone, continue 

to be fundamental to the economy of the State. Others, such as 

fluorspar and nahcolite, once formidable commodities in the 

State, are no longer produced, while large deposits of titanium 

have never been produced.

Clays and Shale

Clay has been used in sun-dried bricks for possibly 

10,000 years and in earthenware for at least 9,000 years 

(Christie and others, 2001b). The term derives from the Old 

English clāēg, akin to the Latin glus or glue (MerriamWebster, 2009).

Clays and clay minerals are found mainly on or near the 

surface of the Earth (fig. 38). The term “clay” has two meanings. In its size sense, clay is any very fine grained material 

(grains having a diameter less than 1/256 millimeters (mm) 

or 4 micrometers (μm) or 0.00016 in., the upper size limit of 

particles that can show colloidal properties (Bates and Jackson, 

Figure 37. Two industrial landscapes in Colorado with historical 

value. A, Old mine in Peru Creek, east of Montezuma. B, Tram 

tower from mine in Peru Creek. Photographs by Anna Wilson.

A

B

1987)). In its compositional sense, clays are minerals rich in 

alumina (Al2O3), silica (SiO2), and water in various combinations (U.S. Environmental Protection Agency, 1995c). Clay 

minerals commonly are clay sized. What is commonly called 

“clay” may be a mixture of fine-grained clay minerals (hydrous 

aluminum silicates) and clay-sized grains of quartz or minerals 

that contain carbonate or metal oxides (Foley, 1999).
48 Development of Industrial Minerals in Colorado

Classification by Use

Six groups of clay were recognized by the U.S. Bureau 

of Mines (U.S. Environmental Protection Agency, 1995c), 

and each has specific uses. The groups are ball clay, bentonite, fire clay, fuller’s earth, kaolin, and common clay and 

shale. Materials commercially referred to as pottery clay 

(clay used for pottery and stoneware) are principally kaolin 

or ball clay; refractory clay (clay that has a high melting 

temperature) may be kaolinite, flint clay, plastic fire clay, or 

ball clay, or it may be various calcined materials (Arkansas 

Geological Survey, 2009).

Ball Clay

The name “ball clay” reflects the early English tradition 

of extracting clay in cubical blocks that became rounded during handling and storage. Ball clay is sedimentary in origin 

and usually contains kaolinite, mica, and quartz (Industrial 

Minerals Association North America, 2004). Its characteristic 

high plasticity, strength, and light or white color after firing 

make it an excellent clay to use for floor and wall tiles and 

sanitary ware such as sinks or toilets (Virta, 2004).

Bentonite

Bentonite is formed by the devitrification and chemical 

alteration of volcanic ash, tuff (that is, consolidated pyroclastic 

rock), or glass; other igneous rocks; or rocks of sedimentary 

origin. It consists predominantly of smectite, a group of clay 

minerals (also called montmorillonite group clay minerals) 

(Industrial Minerals Association North America, 2004). Two 

categories of bentonite, swelling and nonswelling, are recognized. Sodium bentonite, the swelling clay, can absorb water 

many times its original dry volume and possesses a high 

dry-bonding strength, whereas calcium bentonite, the “nonswelling” type, swells to a much lesser degree when wet and 

usually possesses greater adsorptive characteristics (Dumont, 

2004). The largest swelling-bentonite deposits, which are in 

Wyoming, Montana, and South Dakota, are commonly called 

Western-type bentonite (Elzea and Murray, 1994).

Bentonite is used as pet waste absorbent in cat litter, 

as a binder in animal feed pellets, in drilling muds, iron 

ore pelletizing, sand molds for metal casting, wastewater 

purification, detergents, paper manufacture, and as a sealing material or liner for landfills.

Fire Clay

Fire clay is composed primarily of kaolinite with a high 

content of alumina and silica and few impurities that lower the 

fusion point of the clay. The clays are refractory (resistant to 

heat) and withstand temperatures of 1,500°C (2,700°F) before 

melting (U.S. Environmental Protection Agency, 1995c). For 

this reason, fire clays are used in heat-resistant products such as 

glass furnaces, foundries, kilns, and crucibles.

Figure 38. Sketch of clay cliff near mouth of Fraser River, Middle Park, Colo. Drawing by W.H. 

Holmes, 1873, U.S. Geological and Geographical Survey of the Territories (Hayden Survey) Sheet 

no. 39. Courtesy of USGS Photographic Library.
Colorado Industrial Minerals—Occurrence, Use in Colorado, Mining, and Production 49

Fuller’s Earth

“Fuller’s earth” traditionally was used by textile workers 

(fullers) for whitening, degreasing, or fulling (shrinking and 

thickening) wool by kneading it in a clay-water mixture (Bates 

and Jackson, 1987). It may also be called natural bleaching 

clay. The term is used for any fine-grained material with absorbent and bleaching properties (Elzea and Murray, 1994).

The clays in fuller’s earth are similar to those in bentonite, but they are typically high in magnesia and able to adsorb 

impurities (U.S. Environmental Protection Agency, 1995c). 

Fuller’s earth is formed by the alteration of volcanic ash or by 

direct chemical precipitation of the clay mineral montmorillonite in shallow marine basins (Dumont, 2004).

Applications include pharmaceuticals designed to absorb 

toxins, bacteria, and alkaloids and to treat dysentery; it is also 

used to remove contaminants from water and drycleaning 

fluids; in the manufacture of wallpaper; and as an extender or 

filler for plastic, paint, and putty (Dumont, 2004).

Kaolin

The word kaolin is derived from the Chinese kauling, meaning high ridge where clay deposits were worked 

thousands of years ago (WBB Minerals, 2005). Kaolin is a 

fine, usually white, china clay consisting of pure kaolinite, 

(OH)8Al4Si4O10, or related clay minerals. Kaolin minerals are 

generally derived from the alteration or weathering of alkali 

feldspars and micas (Bates and Jackson, 1987). Kaolin is 

one of the purest clays and is used in porcelain, rubber tire 

manufacturing, inks, paints, plastics, and medicines, and as a 

main ingredient in glossy paper.

Common Clay and Shale

Common clay and shale are composed mainly of illite or 

chlorite, but they may also contain kaolin and montmorillonite. 

Common clay has a vitrification point below 1,100°C (2,000°F) 

(U.S. Environmental Protection Agency, 1995c). Shale is a 

fine-grained laminated sedimentary rock in which the original 

constituents were clay and silt-size particles. Shales composed 

predominantly of clay minerals easily split into thin flat plates 

or sheets (Arkansas Geological Survey, 2009). Shale that has 

hardened in response to heat and pressure is slate, a metamorphic rock used in building construction.

Some clays (and also shales, slates, and fine-grained mine 

wastes) will, when fired, expand (“bloat”) into a frothy mass 

with closed cellular texture. Those materials are thus desirable 

for making lightweight aggregate (Arkansas Geological Survey, 

2009). Shale and slate are also used in the manufacture of building materials such as paving bricks, tile, and Portland cement and 

as an impermeable liner in ponds or wastewater impoundments.

Geology of Colorado Clay and Shale Deposits

Clay generally forms in one of two ways: at the surface 

during the chemical weathering of aluminum-silicate minerals 

by carbonic acid or in the subsurface by the alteration activity 

of acidic hydrothermal fluids circulating through fault systems and porous rock. Clays may be found in soil horizons, 

continental and marine sediments, geothermal fields, volcanic 

deposits, and weathered rock formations (Foley, 1999). Clays 

generally swell when wet and shrink when dry. The physical properties that determine the commercial value of clays 

include firing temperature, percentage of shrinkage or swelling 

on firing, plasticity index, bloating characteristics, fired color, 

fired strength, and percentage of fines (slack) produced upon 

crushing (Arkansas Geological Survey, 2009).

Many times during the Cretaceous Period, 145–65 megaannum (Ma or millions of years ago), an inland sea advanced 

and retreated across central Colorado. Where advancing seas 

were deepest, marine shales were deposited; as the coastline 

moved back and forth across the region, sandstones were 

deposited near shore. Several central Colorado marine shales 

are clay rich and are suitable for brick, fire, or pottery clays 

(fig. 39). In eastern Colorado, Cretaceous shales of the Glencairn Shale Member of the Purgatoire Formation and the Dry 

Creek Member of the Dakota Sandstone form the largest 

economic clay deposits (Waage, 1953), although clay has also 

been mined from the Graneros, Niobrara, and Pierre shales and 

the Laramie Formation and Fox Hills Sandstone. In addition, 

shales contained in the Permian Lykins Formation, Jurassic 

Morrison Formation, and Tertiary Dawson Formations have 

been mined for their clays. Even Pleistocene loess was mined 

for manufacturing bricks (Patterson, 1964). In western Colorado, the major clay-producing units are the Mancos and Lewis 

shales, the Mesaverde Group, the Dakota Sandstone, and some 

Jurassic shales (Waage, 1953). Uplift and erosion has removed 

these units from much of the mountainous areas that underlie 

central Colorado’s national forests, but where they have been 

preserved along mountain fronts clay resources may exist.

In addition to sedimentary processes, clays can also form 

when hydrothermal fluids (generated during the emplacement of felsic to intermediate volcanic magmas and shallow 

intrusive magmas) alter preexisting rocks. Rocks containing 

abundant feldspar minerals are particularly susceptible to 

hydrothermal alteration. Depending on the composition and 

acidity of the hydrothermal fluids, a smectite clay, such as 

montmorillonite, or kaolinite and halloysite may be formed 

(Hosterman and Orris, 1998a,b). Deposits of hydrothermally 

altered clays tend to be small, although a few attain economic 

volumes―such as those in porous volcanic tuffs at Westcliffe, 

Silver Cliff, and Creede, Colo. (Patterson, 1964).

Mining and Production

Most domestic clay and shale deposits are mined from 

open pits by heavy machinery such as draglines, power shovels, 

and bulldozers.

Ball clay is extracted from quarries and then blended with 

other raw clay to obtain specific characteristics. Processing 

includes shredding the clay into golf-ball-sized pieces, drying, and 

grinding (Industrial Minerals Association North America, 2004).
50 Development of Industrial Minerals in Colorado

Fire clay is more apt to be mined underground because 

higher quality fire clay is found at depth (Pickering and Murray, 1994; U.S. Environmental Protection Agency, 1995c). 

Fire clay is mined, transported to a processing plant, and 

stockpiled (sometimes for 6 to 12 months to produce smaller 

weathered particles and improve plasticity) (U.S. Environmental Protection Agency, 1995c). The clay is then crushed, 

ground, and dried.

Kaolin is washed by high-pressure water jets (hydraulic 

mining) from the surrounding rock into a clay suspension. 

Mechanical systems remove any unwanted quartz and mica 

before the suspension is pumped into large tanks where the 

clay settles. Excess water is drained and the slurry is pumped 

out to be filtered, dried, and blended.

Some materials―for example, kaolin―will receive 

further processing (table 8). Grit (mostly quartz and feldspar) may be removed from kaolin solely by dry mechanical processes (“dry processing,” which yields a lower 

quality product) or by mechanical, electromagnetic, and 

chemical processes (“wet processing,” which yields a purer 

product) (U.S. Environmental Protection Agency, 1995a,c; 

Christie and others, 2001b). Kaolin may also be processed 

into a slurry (by “blunging”); the slurry can then be transported by pipeline. This process lowers costs, allows better 

quality control, keeps heavy trucks off the roads, and can 

reuse old mine pits in the area to dispose of impurities 

(Pickering and Murray, 1994).

In 2003, Colorado produced an estimated 236,000 tons 

of common clays valued at $1.26 million (Cappa and others, 

2003); in 2004, it produced 289,000 tons valued at $1.4 million 

(Cappa and others, 2004).

Figure 40. Alkali pond on Benton Shale, which drains poorly 

owing to a high bentonite content, 1 mi west of Howell, Albany 

County, Wyo., 1905. Photograph by N.H. Darton. Courtesy of USGS 

Photographic Library.

Because bentonite is so slippery, deposits generally 

can’t be worked in wet weather; well-drained deposits are 

worked in dry, warm weather and poorly drained ones in 

dry cold weather (Dumont, 2004) (fig. 40). Most bentonite and some fuller’s earth deposits are selectively mined 

(Dumont, 2004) to obtain a relatively high-grade product (at a somewhat higher cost). Various grades of clay 

are mined and stockpiled separately and then blended to 

obtain desired physical properties. If necessary, bentonite 

is activated with the addition of soda ash (Na2

CO3) (Industrial Minerals Association North America, 2004). Bentonite 

is then dried and either sieved (into a granular form), or 

milled (into powder) according to its end use.

Figure 39. Fire clay, plant-bearing sandstone, and shale in Dakota Sandstone hogback, 3 mi 

south of Golden, Jefferson County, Colo., 1922. Photograph by W.T. Lee. Courtesy of USGS 

Photographic Library.
Colorado Industrial Minerals—Occurrence, Use in Colorado, Mining, and Production 51

Sand and Gravel (Construction)

Sand and gravel have been used since ancient times for 

construction. The oldest paved road known was built more 

than 5,700 years ago to ease the transport of granite blocks to 

the pyramids in Egypt (Christie and others, 2001a).

“Sand and gravel is defined as continuously graded 

unconsolidated material (sediment) present on the Earth’s 

surface as a result of the natural disintegration of rocks. * * * 

It is composed predominantly of the mineral quartz, although 

gravel may also consist of various resistant rock types, such as 

novaculite, chert, and sandstone” (Arkansas Geological Survey, 

2009). The manmade equivalent of sand and gravel is crushed 

stone, broken by mechanical means into smaller fragments.

The Wentworth scale (Wentworth, 1922) is the common 

scale used by geologists to describe the size of rock particles. 

Rounded rocks that are 0.08–2.5 inches (in.) (2–64 mm) 

in diameter are called pebbles; those that are 2.5–10 in. 

(64–250 mm) diameter are called cobbles, and those larger 

than 10 in. (250 mm) diameter are called boulders. Pebbles and 

cobbles are collectively known as gravel. Sand grains are those 

smaller than 2 mm (0.08 in.). Particles smaller than 1/16 mm are 

called silt and those smaller than 1/256 mm are called clay. “In 

the aggregate-producing industry, gravel consists predominantly 

of particles larger than 4.75 mm (retained on a U.S. Standard 

No. 4 sieve), whereas sand consists of particles predominantly 

between 4.75 mm and 75 [as in the original report; should be 

0.075] mm (passes through a No. 4 sieve but is mostly retained 

on a No. 200 sieve” (Christie and others, 2001a, p. 6).

Fine aggregate (sand) and coarse aggregate (gravel 

and crushed stone) are used in the construction of nearly all 

buildings and public works projects and are the main filtering agent of water and sewage filtration systems. Nearly half 

of all construction sand and gravel produced each year is 

used in concrete aggregate and concrete products (such as 

block, bricks, and pipe). The remainder is used for asphalt, 

road-base material, railroad ballast, snow and ice control, 

and water filtration. The use of recycled aggregate, mostly 

from concrete surfaces, structures, and asphalt pavements, is 

increasing (Bolen, 2004a).

Worldwide, more sand and gravel is mined annually than 

any other industrial material; yet domestic shortages of construction sand and gravel are expected to increase in urban and 

industrialized areas (Bolen, 2004a). Few deposits meet the 

construction ideal of 60 percent gravel and 40 percent sand—

enough gravel for use as road base or bituminous aggregate and 

enough sand for use in concrete (Goldman, 1994). The construction of one mile of a typical four-lane interstate highway requires 

85,000 tons of aggregate. Germany uses twice that amount of 

material in building one mile of its autobahn. Construction of 

an average six-room house in the United States requires 90 tons 

of aggregate, larger ones claim as much as 400 tons (Keller 

and Widmann, 2002), and an average-sized school or hospital 

requires about 15,000 tons (Langer and Glanzman, 1993).

Table 8. Clay processing operations by type of clay (modified from U.S. Environmental Protection Agency, 1995c).

[--, not applicable]

Process Ball clay Bentonite Common clay 

and shale Fire clay Fuller’s earth Kaolin

Mining X X X X X X

Stockpiling X X X X X X

Crushing X X X X X X

Grinding X X X X X X

Screening -- -- X X X X

Mixing X -- X -- -- X

Blunging1 -- -- X -- X X

Air flotation X -- -- -- -- X

Slurrying X -- -- -- -- X

Extruding -- -- X -- X --

Drying -- X X X X X

Calcining -- -- -- X -- X

Packaging X X -- X X X

Other2 X X -- X X X

1

Blunging—Wet processing of kaolin which produces a slurry that can be piped to its destination.

2

Other processes include water fractionation, magnetic separation, acid treatment, bleaching, shredding, pulverizing,weathering, blending, cation exchange, 

granulating, air classifying, and dispersing.
52 Development of Industrial Minerals in Colorado

Geology of Colorado Sand and Gravel Deposits

Thick, extensive sand and gravel deposits in central 

Colorado occur in five basic Quaternary geologic settings: 

alluvial fans, high-elevation dissected terraces, intermediateelevation terraces, low-elevation terraces, and floodplains 

(Lindsey and others, 2005). They may also be found in older, 

partially cemented and hardened, conglomerates. High-energy 

streams carrying material eroded from the crystalline rocks of 

nearby mountains lose carrying capacity after the streams exit 

the mountains and the stream gradients decrease; the streams 

then deposite their sediment load.

Terraces and floodplains are found along major streams 

that drained the mountain uplifts during the Quaternary; the 

different elevations represent deposits of different ages. High 

terraces contain the oldest deposits and low terraces and 

floodplains the youngest. These deposits contain outwash 

transported during wetter periods of the Pleistocene. Some of 

the deposits are glacial outwash, but some deposits formed in 

drainage basins that were not glaciated.

The floodplains and low terraces are the principal source 

of high-quality sand and gravel in central Colorado. Older 

gravels of the intermediate and high terraces are not commonly used for high-specification aggregate because they 

contain boulders, cobbles, and pebbles that are soft and friable 

owing to weathering. Mountain-front alluvial fans are also 

avoided because the deposits are poorly sorted, and processing 

typically produces large amounts of fine waste products. In 

addition, older Pleistocene alluvial fans may be highly weathered (Lindsey and others, 2005). Nevertheless, as environmental concerns make it more difficult to mine gravels along major 

ephemeral streams, alluvial fans may provide an alternative 

source. Sand has been commercially exploited in the San Luis 

Valley and at Rocky Flats south of Boulder, Colo.

Another potential alternative source of sand and gravel 

is unconsolidated to partially consolidated Tertiary conglomerates, mainly of Miocene and Pliocene age, exposed in various portions of central Colorado. These rocks accumulated as 

alluvial fans along the borders of downfaulted blocks related 

to the Rio Grande rift zone and in the floodplains of major 

late Tertiary drainages (for example, Dry Union Formation 

in the upper Arkansas River Valley, north of Salida (Van 

Alstine, 1969).

Mining and Production

Many prime sand and gravel deposits are located in 

or adjacent to flowing streams and rivers (fig. 41A). If the 

water table is low or can be regulated, the deposits may 

be extracted from the ground by front-end loaders, power 

shovels, or draglines. Otherwise, the deposits are dredged. 

Dredges are mounted on boats or barges and remove sand 

and gravel by suction. Dredging also loosens fine sediment 

along with the sand and gravel, which increases the turbidity 

of water downstream. Sediments are collected and agitated 

with the aid of slurry pumps that dewater the load.

Once collected, the sand and gravel is passed across a 

series of screens and split into size increments ranging from 

dust to boulders (fig. 41B). Larger fragments may be used 

for erosion control, reclamation, and other uses, or they may 

be crushed (U.S. Environmental Protection Agency, 1995c). 

Sized material may be sold directly or may be blended with 

other size fractions to meet the aggregate specifications of 

a given customer. Specimens of chalcedony, agate, jasper, 

and petrified wood may be recovered from certain gravel and 

sand pits (Sinkankas, 1988).

In some cases, sand and gravel are washed to remove 

excess calcium carbonate, clay, organic impurities, or other 

surface coatings that may degrade the binding properties of 

the material.

Figure 41. Stockpiles at sand and gravel mines. Large amounts of

sand and gravel are extracted and processed in the United States. 

A, Sand and gravel mine along the Colorado River near Rifle, Colo. 

B, Sand and gravel are sorted using screens and belt conveyors. 

In 2005, this processing facility in Missouri produced more than 100 

products from aggregate and rock. Photographs by B. Arbogast.

A

B
Colorado Industrial Minerals—Occurrence, Use in Colorado, Mining, and Production 53

In 2003, Colorado produced 41 million tons of sand and 

gravel valued at $205 million (Cappa and others, 2003); in 

2004, it produced about 45.5 million tons of sand and gravel 

valued at $238 million (Cappa and others, 2004).

Silica Sand (Industrial)

The word silica is derived from the Latin silex, meaning flint or quartz (Merriam-Webster, 2009). Silica (SiO2 ) is 

abundant in rocks, and the weathering of those rocks can free 

it. It also forms minerals (varieties of quartz) that contain 

only silicon, oxygen, and traces of other elements. Silica can 

be so fine grained that it is called cryptocrystalline or amorphous; examples are chert, chalcedony, or flint, and diatomite, which is biological in origin. Or, it may be crystalline, 

as in quartz.

Silica sand deposits, which are less common than 

construction sand and gravel deposits, meet stringent quality 

requirements (National Industrial Sand Association, 1997). 

Almost half of all silica sand produced in the United States 

today is used to manufacture glass (Zdunczyk and Linkous, 

1994). Crystalline silica was used for glass manufacture 

more than 5,000 years ago in Egypt (U.S. Bureau of Mines 

Branch of Industrial Minerals, 1992). Silica sand is invaluable in the production of metal casting (foundry molds), 

metallurgy, chemical production, building products, paint, 

ceramics and refractories, water filtration, abrasive and 

grinding materials, oil and gas recovery (as hydraulic fracturing sand), and recreation (athletic fields and golf courses) 

(Zdunczyk and Linkous, 1994; Industrial Minerals Association North America, 2004).

Geology of Colorado Silica Sand Deposits

The durability of sand, a common product of the erosion 

of bedrock, causes large quantities to remain in stream channel, terrace, and alluvial fan deposits. Common sand deposits, however, contain many mineral impurities such as clay, 

feldspar, and iron oxides and typically are poorly sorted—that 

is, they contain a wide range of particle sizes. Treating this 

material to produce industrial-grade sand is costly; sand that 

has been naturally sorted and cleaned is much more economical. Extensive deposits of nearly pure quartz (SiO2

) 

sand formed near the shores of shallow seas during much of 

Phanerozoic time (Ketner, 1973). In Colorado these deposits 

are represented by numerous widespread sandstone units that 

accumulated where wave and current action thoroughly broke 

down softer minerals and washed their debris away, leaving a 

sand composed mostly of quartz. The Permian Lykins Formation and the Cretaceous Dakota Sandstone that crop out along 

the eastern flank of the Front Range and Wet Mountains have 

provided the majority of the industrial sand in Colorado. Other 

units that have been mined on a small scale for industrial 

sand include the Cambrian Sawatch Quartzite, the Ordovician 

Harding Sandstone, the Devonian Parting Quartzite member of the Chaffee Formation, the Pennsylvanian Fountain 

Formation, the Permian Lyons Sandstone, the Jurassic Morrison Formation, the Cretaceous Lytle Sandstone Member 

of the Purgatoire Formation, Codell Sandstone Member of 

the Carlile Shale, Trinidad Sandstone, Fox Hills Sandstone, 

and Laramie Formation, and the Tertiary Dawson Formation 

(Carter, W.D., 1964).

Mining and Production

High quality industrial sand above the water table is 

mined from open pits; below the water table it is dredged. 

Shallow-water dredges may be hydraulic (fig. 42) or mechanical (such as draglines or clamshells). Some sands need only 

to be screened in order to meet a buyer’s specifications, but 

others first undergo blasting and crushing. Beneficiating 

(for example, washing, screening, scrubbing, drying, and 

blending) of the ore may be necessary to increase the silica 

Figure 42. Extraction of industrial sand by hydraulic mining, which

is limited to a depth of 60 m (about 200 ft). A, Sand is recovered by 

strong jets of water and transported underground to a beneficiation 

plant. B, Closeup of operation. Photographs by B. Arbogast.

A

B
54 Development of Industrial Minerals in Colorado

content and obtain the optimum size for a given purpose. Acid 

leaching may be required to produce high-purity industrial 

silica sand (Zdunczyk and Linkous, 1994). Froth flotation 

may be used to remove mica, feldspar, or iron-bearing 

minerals (U.S. Environmental Protection Agency, 1995c). 

Froth flotation uses chemical reagents, followed by agitation 

and aeration, to create a foam that takes advantage of differences in minerals’ surface characteristics; some minerals are 

caught in the foam whereas others sink. The process is said 

to have been invented by a miner who watched the process 

happening while washing dirty work clothing in his home 

washing machine (Denver Mineral Engineers, Inc., 2005).

The industrial sand and gravel industry is concerned with 

safety and health regulations and environmental restrictions 

(Dolley, 2004). Prolonged and excessive exposure to crystalline silica (but not noncrystalline, or amorphous, silica) dust 

can cause silicosis, a noncancerous lung disease (U.S. Bureau 

of Mines Branch of Industrial Minerals, 1992). Studies in the 

1980s suggested that crystalline silica was also a carcinogen. 

Businesses that use materials containing 0.1 percent or more 

crystalline silica are regulated under Federal guidelines concerning worker training and ensuring that workers understand 

on-the-job hazards (U.S. Bureau of Mines Branch of Industrial 

Minerals, 1992).

In 2003, Colorado produced about 69,000 tons of industrial sand and gravel; the dollar value is not public information (Cappa and others, 2003); in 2004, it produced just over 

77,000 tons valued at $3 million (Cappa and others, 2004).

Crushed Stone

Crushed stone is aggregate that is derived by crushing 

bedrock. Although the crushed stone used in concrete and 

asphalt must meet rigid specifications, many rock types are 

suitable for producing crushed stone. Crushed stone suitable 

for construction is resistant to abrasion and to disintegration 

from repeated freezing and thawing (soundness) and meets 

other standards governing permissible range of grain size 

(gradation), deleterious materials, color, fines, specific gravity, 

water absorption, particle shape, concrete strength, and skid 

resistance (Herrick, 1994).

Generally, any rock (igneous, metamorphic, or sedimentary) that is strong and resistant to rough handling, physically 

stable under wet and dry conditions, stable through freeze or 

thaw cycles, and not chemically reactive with cement can be 

used for crushed stone if a large enough volume of the rock 

is available (Knepper, 2002). In addition, a potential source 

of crushed stone must meet strength and durability specifications; contain a volume that will allow at least 10 year and 

preferably 20 or more years of production; have an adequate 

market, a competitive transportation cost, and an acceptable 

environmental effect; and be acceptable to agencies that 

grant needed permits (Herrick, 1994; Arkansas Geological 

Survey, 2009).

Limestone and dolomite account for 71 percent of all 

crushed stone produced in the United States (Tepordei, 1999). 

The majority of crushed stone, 84 percent, is used for highway construction and maintenance projects (Tepordei, 2004). 

The use of crushed stone as an alternative to sand and gravel 

is increasing across the United States because stone quarries 

typically operate within a smaller area and can be located 

farther from urban areas and visually sensitive river valleys 

(Cappa and others, 2004).

Geology of Colorado Crushed Stone Deposits

A variety of igneous, metamorphic, and sedimentary 

rocks in Colorado have been used to produce crushed stone, 

including granite, gneiss, sandstone, limestone, and volcanic 

rock (Langer and Glanzman, 1993). Most granite that is not 

deeply weathered, hydrothermally altered, or strongly foliated 

makes good crushed stone regardless of its age. Precambrian 

granites, such as the Pikes Peak Granite and the Silver Plume 

Granite, are exposed over large areas of central Colorado and 

may be excellent sources of crushed stone. Some Precambrian 

metamorphic rocks have also been used for crushed stone. 

Metamorphic gneiss is the primary source rock for the quarries providing crushed stone to the metropolitan Denver area 

(Knepper, 2002). Metamorphic Precambrian quartzites, such 

as those exposed in Coal Creek Canyon on the east flank of 

the Front Range and in Phantom Canyon and Wilson Park near 

Cañon City, make excellent crushed stone because of their 

chemical stability and hardness, but they have not been widely 

used because their limited occurrences are not in convenient 

locations and because they cause excessive wear and tear on 

mechanical crushers. Marble, a metamorphosed limestone or 

dolomite rock, has the physical and chemical properties to 

make good crushed stone, but it is usually more valuable as 

dimension stone.

Volcanic rocks, especially darker varieties such as basalt, 

make good sources of crushed stone. For example, the basaltic 

flow rock that caps North Table Mountain and South Table 

Mountain east of Golden produces high-quality crushed stone. 

The feeder vent (dike) that fed volcanic flows to the surface 

is exposed at Ralston Butte to the north, and similar rock in 

the Valmont dike near Boulder are good examples of volcanic 

rock used to produce high quality crushed stone in Colorado 

(Colton and Fitch, 1974; Knepper, 2002). Lighter colored 

(felsic) volcanic rocks that do not contain critical amounts of 

microcrystalline quartz—which reacts with cement to weaken 

concrete—can also make excellent crushed stone aggregate if 

the deposit is large enough. Abundant felsic volcanic rocks in 

central and southwestern Colorado that formed from superheated ash and lava (welded tuffs and ash flow tuffs; see 

Dimension Stone) commonly contain too much microcrystalline quartz to be used for concrete aggregate, but they do make 

good road base.

Although most sandstones, siltstones, and shales in the 

study area are too soft to make good crushed stone for concrete aggregate, some can be used for fill and road base. The 
Colorado Industrial Minerals—Occurrence, Use in Colorado, Mining, and Production 55

most common source of crushed stone nationally is limestone 

or dolomite (Tepordei, 2004). Many carbonate units in Colorado could provide crushed stone for concrete aggregate, such 

as the Ordovician Manitou Dolomite and Fremont Limestone, 

the Mississippian Leadville Limestone, many limestones in 

the thick Pennsylvanian and Permian sedimentary section, and 

several Cretaceous limestones. Many of these units briefly 

provided crushed stone from small quarries (Lindvall, 1964). 

Longer term crushed-stone operations worked Ordovician 

carbonate units in the Cañon City, Colorado Springs, and Fort 

Collins areas. Well-indurated, silica-cemented sandstone, such 

as the Ordovician Harding Sandstone in some areas of Colorado, can also make good crushed stone.

Mining and Production

Drill holes are meticulously laid out on mine benches and 

are filled with explosive charges. Detonation of the charges 

fractures the rock and creates a loose rubble. Diesel-powered 

hydraulic shovels load haul trucks that then carry the rubble to 

a primary crusher. Conveyor belts transport the crushed stone 

for screening and secondary or tertiary crushers where it is 

broken down further to meet customer specifications.

Depending upon the type of stone, types of contaminants in the stone, and availability of pond space and water 

(Herrick, 1994), crushed stone may be processed by wet or 

dry methods. It may be washed to remove unwanted material 

and the waste water is then sent to settling ponds. Wet plants 

do not have the dust problems that may be associated with dry 

processing, but other methods may be used to suppress dust.

In 2004, about 10.4 million tons of crushed stone (valued 

at $59.5 million) was produced in Colorado, an increase of 

1 percent as compared with 2003 (Cappa and others, 2004).

Limestone

Limestone is a sedimentary rock that can originate in 

two ways: biologically, as shells and skeletons of marine 

organisms that accumulate in sediment (for example, chalk) 

and chemically, as CaCO3 (calcium carbonate or calcite) that 

precipitates from water and accumulates as limestone or 

travertine. The word calcium is derived from the Latin calx, 

meaning lime (Merriam-Webster, 2009). Limestone can also 

be physically altered by metamorphism to marble. The rock 

must contain at least 50 percent calcite (CaCO3) to be classified as limestone (U.S. Environmental Protection Agency, 

1995c). When the rock is a mixture of calcite and the mineral 

dolomite, CaMg(CO3)2, and dolomite makes up at least half 

of the rock, then the entire rock is referred to as dolomite 

(Bates, 1969; Eckel, 1997). Although the terms limestone and 

dolomite are often used interchangeably, limestone is not a 

suitable replacement for dolomite in its most important use—

the manufacture of refractory dolomite and the preparation of 

heat-insulating materials (Arkansas Geological Survey, 2009).

Although limestone (including marble) can be used as 

a dimension stone and for rock fill and riprap, the bulk of 

crushed limestone is used as road base, concrete aggregate, and 

agricultural limestone. Limestone is also used in steel making, 

to treat water and sewage, and to neutralize acid waste.

Quicklime (CaO, calcium oxide) is another important 

product manufactured from crushed limestone. Archeological discoveries in Turkey indicate that quicklime was used 

as a mortar as early as 7,000 years ago (Mineral Information Institute, 2004). Quicklime is used in metallurgy, paper 

manufacture, water and sewage treatment, building materials, and ceramic products. Although limestone can substitute 

for lime in many applications, such as agriculture, fluxing, 

and sulfur removal, limestone is slower to react than quicklime and may have other disadvantages depending on the 

application (Miller, 2004a).

Reacting lime (calcium) with water forms hydrated or 

slaked lime, also known as calcium hydroxide or Ca(OH)2

. 

Slaked lime is used to neutralize acid and to precipitate 

certain soluble or gaseous impurities such as acids and 

heavy metals.

Geology of Colorado Limestone Deposits

Most carbonate rocks in central colorado are sedimentary 

marine limestones formed primarily from the calcite shells 

and skeletons of marine organisms. Because magnesium can 

be added while sediment is converted to rock (diagenesis), the 

dominant mineral may change from calcite to dolomite. Thus, 

a single mapped formation may be a limestone in one geographic area and a dolomite in another.

In central Colorado, the thickest and most widespread 

carbonate units were deposited in a shallow sea during the 

Ordovician (Manitou Dolomite and Fremont Limestone) 

and the Mississippian (Leadville Limestone). The Leadville 

Limestone was quarried for decades at Monarch Pass and 

elsewhere by the Colorado Fuel and Iron Corporation for 

use as flux in making steel in Pueblo (Carter, D.A., 1964). 

Abundant thinner limestone beds have been mapped in the 

marine Pennsylvanian and Permian formations west of the 

Front Range (Minturn and Maroon Formations) and are a 

potential resource. One of these units, the Permian Ingleside Formation, was quarried in Larimer County to provide 

limestone for refining sugar by the Great Western and Holly 

Sugar factories; Leadville Limestone was also quarried near 

Glenwood Springs and Salida for use in sugar refining (Berlin, 1964). Relatively pure limestones and dolomites suitable 

for producing reagents (metallurgical limestone) occur in the 

Cretaceous Fort Hays Member of the Niobrara Formation, 

the Ordovician Fremont Limestone, and the Mississippian 

Leadville Limestone (Carter, D.A., 1964). Limestone for 

making cement is found in the Cretaceous Niobrara Formation, especially the Fort Hays Limestone Member, where it 

is exposed along the eastern flank of the Front Range and the 

Wet Mountains. Although the Leadville Limestone usually 

contains some dolomite, the formation is locally pure enough 

to be used to produce cement in the western part of the State 

(Wolfe, 1964).
56 Development of Industrial Minerals in Colorado

Mining and Production

Limestone is quarried from open pits and underground 

mines (fig. 43). Limestone that is to be used for ornamental 

purposes is extracted from the bedrock by saws and wedges. 

The rock is then either cut or carved to its final shape and polished. To obtain crushed limestone, the rock face is drilled and 

blasted; the stone is then crushed, dried if necessary, screened 

into various sizes, and washed to remove fines. Certain industrial and agricultural applications may call for further air classification (winnowing or air tabling) and milling followed by 

storage in enclosed silos and bins (Carr and others, 1994). To 

manufacture quicklime, crushed ore is heated at high temperature to drive off carbon dioxide and form calcium hydroxide 

(the ore is “calcined”). The U.S. Environmental Protection 

Agency has set limits that reduce toxic air pollutants from lime 

plants (Miller, 2004a).

In 2002, Colorado produced an estimated 4.6 million 

tons of crushed limestone valued at $30.9 million (U.S. Geological Survey, 2003a), most of which went into cement. In 

2004, Colorado produced about 2.6 million tons of cement, 

an increase of more than 50 percent as compared with the 

1.7 million tons produced in 2003 (Cappa and others, 2004).

Gypsum

The word gypsum is derived from the Greek gypsos, 

meaning plaster (Merriam-Webster, 2009) or chalk. Gypsum 

(CaSO4·2H2O, calcium sulfate dihydrate) occurs principally 

as selenite crystals, massive alabaster, and fibrous satin spar, 

all of which are soft enough to be scratched by a fingernail. 

Gypsum ore was first mined in North America, in Nova Scotia, 

in 1770; it was shipped to the eastern seaboard of the United 

States for use as fertilizer (Adams, 1993).

Almost 90 percent of gypsum is manufactured into 

wallboard (gypsum sandwiched between two layers of heavy 

paper) and plaster products (Olson, 2004a) (fig. 44). Gypsum 

is used for molds such as those that form dental prostheses, 

plate glass, and car parts; in plaster of Paris, match heads, soil 

conditioners, and fertilizer; and as a retarder (a component that 

slows down reactions) in Portland cement.

About a quarter of the total domestic supply comes from 

synthetic gypsum—gypsum that has been recovered from 

coal-fired generating stations by desulphurization of flue gas 

(Olson, 2004a). Near Florence, Fremont County, Colo., synthetic gypsum is produced from flue gas at a Holcim cement 

plant. This gypsum is then added to the cement later in the 

manufacturing process.

Geology of Colorado Gypsum Deposits

As sulfur-bearing rocks weather at the Earth’s surface, 

gypsum is commonly produced; it is especially abundant 

around exposed sulfide mineral veins and mine dumps in central Colorado. However, economically extractable amounts of 

gypsum are found only in thick sedimentary rock units formed 

by the evaporation of shallow marine brines (fig. 45). This 

type of gypsum belongs to a family of rocks called evaporites, 

which also includes anhydrite, salt, dolomite, and salts of 

potassium and magnesium. A single evaporite stratigraphic 

sequence may contain each of these rock types, reflecting the 

changing composition of the brine with time.

The primary source of commercial gypsum in central 

Colorado is the Eagle Valley Evaporite. In Pennsylvanian 

time, a shallow sea occupied a narrow northwest-trending 

basin (the Central Colorado trough) between the Ancestral 

Front Range and Uncompahgre uplifts. Along the edge of 

the trough adjacent to the uplifts, a thick sequence of coarse 

clastic sediments accumulated (now the Maroon and Minturn 

Formations), whereas evaporation of the shallow sea toward 

Figure 43. Two limestone quarries. A, Walls in Fort Hays 

(formerly Timpas) Limestone quarry show thickness of beds 

and interbedded layers of shale, southeast of La Junta, Otero 

County, Colo., 1904. Photograph by N.H. Darton. Courtesy of USGS 

Photographic Library. B, Tower Rock stone quarry near Saint 

Genevieve, Mo., a large limestone open pit, 2002. Photograph by 

B. Arbogast.

B

A
Colorado Industrial Minerals—Occurrence, Use in Colorado, Mining, and Production 57

Figure 44. Two types of gypsum-containing construction materials used by the construction industry. A, Wallboard, which is made 

from gypsum, stacked at a home-improvement warehouse store. B, Building with stucco exterior. Stucco is a traditional building 

material in New Mexico. It was historically made from hydrated or slaked lime, water, and sand, to which straw or animal hair was 

added. Gypsum has largely replaced lime in contemporary stucco work. C, Gypsum mine in Eagle County, Colo. (Centex Construction 

Products, Inc.). The Eagle Valley Evaporite formation of Pennsylvanian age contains thick beds of gypsum. Photographs A and C by John 

Keller, Colorado Geological Survey. Photograph B by B. Arbogast.

A B

C

the center of the trough (Eagle Valley Basin) formed the 

deposits of bedded gypsum, anhydrite, halite (salt), and 

traces of potash salts of the Eagle Valley Evaporite sequence 

(Lovering and Mallory, 1962; Mallory, 1971). The transition 

between the clastic and evaporite sediments was uneven, 

such that gypsum locally occurs in the Minturn Formation 

and was mined along the Arkansas River southeast of Salida 

(Withington, 1964). Elsewhere in central Colorado, conditions were locally favorable for the formation of bedded gypsum during the Permian (Lykins Formation) and the Jurassic 

(Morrison and Ralston Creek Formations) (Vanderwilt, 1947; 

Withington, 1964). These deposits are relatively small and 

have been of only minor economic importance.

Mining and Production

In Colorado, gypsum is mined in open pits by large 

mobile grinders (mechanical rotomills) similar to the ones 

used to grind and recycle asphalt during highway repaving. 

Explosives are used on occasion to break apart more competent layers within the deposit. The ground gypsum is 

transported by front-end loader to a plant where it is further 

crushed and graded to specification. In a separate process, 

gypsum is ground up, boiled, and dehydrated (calcined), 

becoming the fine powder known as plaster of Paris or stucco.

In 2003, Colorado produced about 590,000 tons of 

gypsum (Cappa and others, 2003); in 2004 production 

increased to 645,000 tons (Cappa and others, 2004).
Figure 45. Panoramic photograph of a gypsum quarry, Colorado Portland Cement Company, Coaldale, Fremont County, Colo., undated. Photograph by USGS Photographic Library.
Colorado Industrial Minerals—Occurrence, Use in Colorado, Mining, and Production 59

Lightweight Aggregates—Pumice, Scoria, 

Perlite, and Vermiculite

Lightweight aggregates have properties similar to those 

of natural aggregate, but they are less dense and therefore have 

lighter unit weights—for example, pumice, volcanic cinders, 

expanded shale, or expanded perlite and vermiculite. The use 

of lightweight aggregates speeds handling and can save money 

by replacing structural steel in foundations (Bates, 1969). In 

some applications, strength is greater than it would have been 

if heavier rock aggregate had been used (Arkansas Geological Survey, 2009). Lightweight aggregates are also used for 

hydroponics, soil conditioners, insulation, and filler.

Classification of Lightweight Aggregates

The lightweight aggregates are categorized as follows 

(U.S. Environmental Protection Agency, 1995b, p. 1) :

1. Natural lightweight aggregate materials—Prepared by 

crushing and sizing rock materials such as pumice and 

volcanic cinders

2. Manufactured structural lightweight aggregates—Prepared 

by heating certain types of shale, clay, or slate so the 

material expands into a porous product

3. Manufactured “ultralightweight” aggregates used for 

insulation—Prepared by heating ground vermiculite, 

perlite, and diatomite to extremely high temperatures

4. Byproduct lightweight aggregates—Prepared by crushing and sizing foamed and granulated slag, cinders, and 

coke breeze (fine-grained coke generated during iron and 

steel production).

In Colorado, pumice, scoria, perlite, and vermiculite 

deposits are of interest as sources of lightweight aggregate.

Pumice

The word pumice is from the Latin pumex, meaning foam 

(Merriam-Webster, 2009). All types of volcanic magma (basalt, 

andesite, dacite, and rhyolite) will form pumice (U.S. Geological Survey, 2000). Pumice appears frothy and full of bubbles 

owing to the escape of volcanic gases as the volcanic material 

solidified; it can be light enough to float on water. It is inert and 

does not react with components of concrete or steel. Pumicite, 

or volcanic ash, is finer grained than pumice; grains are generally less than 2 or 3 mm (0.08 in.) diameter (Bates, 1969).

Pumice is considered by some to be an environmentally 

benign product because no harmful production processes are 

involved and the waste matter generally is recovered. The 

overburden, reject ore, and mineral fines produced during mining and processing of pumice are used to reclaim the minedout areas (Bolen, 2004b).

In commerce and for practical uses, a distinction is made 

between pumice blocks and pumice powder (Stellman, 1998). 

Seventy-five percent of pumice and pumicite is used to make lightweight construction materials such as concrete block and concrete; 

the remainder is used in abrasive cleaners, soaps, polishes, potting 

soil, and solutions used to wash new blue jeans before sale (U.S. 

Geological Survey, 2003a; Mineral Information Institute, 2004).

Scoria

The word scoria is from the Greek scoria, meaning excrement (Merriam-Webster, 2009). Scoria, or volcanic cinder, is 

similar to pumice. It is usually heavier, darker, and more crystalline than pumice (Bates and Jackson, 1987), and it is also 

less porous. Scoria is used in road base owing to its hardness 

and porosity, in cinder blocks and gas barbeque grills, and as 

the common landscaping material called lava rock.

Perlite

The word perlite is from the French perle, meaning pearl 

(Merriam-Webster, 2009). Perlite is a silica-rich volcanic glass 

that contains trapped water, which when heated escapes and 

expands the mineral 4 to 20 times its original volume (U.S. 

Environmental Protection Agency, 1995c). Perlite continues to 

be used as a substitute for vermiculite despite concerns about 

trace amounts of crystalline quartz (Breese and Barker, 1994; 

Hindman, 1994). Perlite is used as a lightweight aggregate in 

concrete and plaster and in potting soil, acoustical tiles, and 

thermal insulating materials.

Vermiculite

The term vermiculite comes from the Latin word vermiculus, meaning little worm (Merriam-Webster, 2009). It 

alludes to a worm-like (or accordion-like) shape produced by 

heating, which expands the material 6 to as much as 30 times 

its original thickness (fig. 46). In exfoliated form, vermiculite has the low density and biological inertness of expanded 

perlite (Hindman, 1994). These characteristics make it useful 

in absorbents and textured paints; in lightweight insulating 

fireproofing, concrete, and masonry fill; in horticulture as a 

growth medium, for bioremediation, and in animal feed.

Vermiculite has one drawback: it commonly contains 

other minerals, one of which may be asbestos. Asbestos is 

a very minor contaminant, and only a few ore deposits are 

known to contain more than trace amounts of asbestos minerals. However, exposure to airborne asbestos particles is linked 

with respiratory ailments and with cancer (U.S. Environmental 

Protection Agency, 2010).

Geology of Colorado Lightweight Aggregate 

Deposits

Both scoria and pumice are pyroclastic volcanic rocks 

composed largely of volcanic glass explosively erupted from 

gas-charged viscous silicic volcanoes (Vanderwilt, 1947; 

Bates, 1969). Frothy lava at or near the surface is explosively 

erupted into the air, rapidly cooled to volcanic glass, carried 
60 Development of Industrial Minerals in Colorado

downwind, and deposited on land or in lakes forming deposits of tuff. During this process, particles are sorted by size as 

a function of distance from the vent, fine particles traveling 

farther. If sufficient heat is maintained, the glass fragments 

can be totally or partially welded together forming a light, 

porous rock. Otherwise, the particles are unconsolidated or are 

indurated only by secondary cement at a later time. Since the 

volcanic glass begins to devitrify to quartz and clay minerals relatively quickly, pumice is most common in deposits of 

Quaternary and Tertiary age. The scoriaceous cinder deposits 

of Gobbler Cone (Pliocene) and Dotsero and Willow Peak 

volcanoes (Holocene) in Eagle and Garfield Counties, Colo., 

are examples of sources suitable for lightweight aggregate 

(Streufert and others, 1997).

Perlite is also a silicic volcanic rock composed of glass. 

Originally it was thought that perlite was a primary volcanic 

rock formed by the rapid chilling of lava erupting onto the 

Earth’s surface. Lack of a pumice outer shell and a crystalline 

core in perlite deposits suggested that the perlite may have been 

intruded at shallow depths that provided sufficient pressure to 

prevent the formation of pumice. More recently, it has been 

proposed that perlite is not a primary rock type but is formed 

by hydration of obsidian or rhyolite (Bates, 1969).

Vermiculite forms from the weathering of micas, chiefly 

biotite and phlogopite, by contact with surface water or groundwater in the zone of groundwater circulation (Bush, 1976; Van 

Gosen and others, 2002). Commercial quantities of vermiculite 

typically are produced where mica crystals are abundant and 

fairly large. Commercial vermiculite deposits form in a range 

of igneous and metamorphic rocks. In central Colorado, vermiculite is associated with Proterozoic gneisses, granodiorite, 

and granite; Cambrian diabase and alkalic plutonic rocks; and 

Tertiary volcanic rocks (Van Gosen and Bush, 2001). However, 

safe development proceeds cautiously because a preliminary 

reconnaissance study by the U.S. Geological Survey found 

amphibole asbestos minerals in at least two Colorado vermiculite districts (Van Gosen and others, 2002).

Mining and Production

Pumice, scoria, perlite, and vermiculite are usually mined 

by simple open pit methods such as bulldozers and front-end 

loaders but may be mined with traditional drilling and blasting 

methods. Crushing and screening to specification follows. Beneficiation generally does not alter the nature of the mineral itself 

other than by reducing or enlarging particle size. Wastes produced during beneficiation typically are merely unneeded sizes, 

such as clays (U.S. Environmental Protection Agency, 1995b).

Perlite or vermiculite may be selectively mined in 

deposits of variable quality (Breese and Barker, 1994; 

Hindman, 1994). Vermiculite may be processed by dry 

or wet methods. Dry beneficiation includes drying, dust 

collection, screening, and air classification (by winnowing or air tabling); wet beneficiation includes froth flotation, heavy media separation, and dewatering (Hindman, 

1994). Expansion of perlite and vermiculite ore by high 

heat, a process called exfoliation, follows at processing 

plants commonly located away from the mines and close to 

consumers owing to the higher shipping costs of expanded 

ore (Breese and Barker, 1994; Hindman, 1994). Dust and 

sludge are among the mineral processing wastes generated; 

kiln drying and sifting produce the largest amounts of dust 

requiring control (Stellman, 1998). According to the U.S. 

Environmental Protection Agency (1995b), in 1995 all 

facilities used dry dust collection systems.

Pumice, perlite, and vermiculite are not presently 

mined in Colorado (John Keller, Colorado Geological 

Survey, oral commun., 2006). Volcanic cinder or scoria 

is currently mined in Colorado but the mining companies 

have withheld production information to avoid disclosing proprietary data (U.S. Geological Survey, 2003a; John 

Keller, Colorado Geological Survey, oral commun., 2006).

Dimension Stone

Dimension stone is indurated bedrock that is shaped 

into useful sizes for construction purposes such as tiles, 

paving stones, countertops, and walls. Any type of bedrock 

that is hard and durable and that can be cut or broken into 

useful forms can be used as dimension stone. The stone’s 

ability to be polished and its color, grain texture, durability, and strength are important. The dimension stone 

industry classifies dimension stone as granite, marble, 

sandstone, or slate. Decorative or ornamental stone is more 

broadly defined by geologists as any stone used primarily 

for its color, texture, and general appearance rather than 

for its strength or durability (Barker and Austin, 1994). 

Crushed stone and rounded cobbles can also be considered 

decorative stone.

0

0

1 INCH

2 CENTIMETERS

Figure 46. Raw vermiculite (left) and heat-expanded vermiculite

(right). Vermiculite heated to 800–1,100°C expands because water 

contained in its crystal structure converts to steam that pushes 

crystal layers apart. Photograph from Van Gosen and others 

(2002, p. 5).
Colorado Industrial Minerals—Occurrence, Use in Colorado, Mining, and Production 61

A finished piece of building stone is an expensive 

product owing to labor costs (fig. 47A). A large proportion 

of dimension stone is transported overseas by ship for cutting and finishing. Dimension stone is used in monuments, 

statuary, flooring, stairs, and the decorative cladding of 

buildings. Dimension stone used in buildings must meet 

standards (set by the American Society for Testing and 

Materials) for absorption, bulk specific gravity, modulus 

of rupture, compressive strength, and resistance to abrasion (Panagapko, 2003). In other words, a good building 

stone is dense, strong, hard, and not porous. “Soundness 

or freedom from flaws is one of the most critical factors in 

evaluating a dimension stone deposit and one of the most 

difficult to determine” (Power, 1994, p. 1000). Failure to 

eliminate stone of inferior quality at the quarry can hasten 

structures’ deterioration (fig. 47B,C).

Early Denver buildings typically were faced with locally 

quarried granite, rhyolite tuff, marble, travertine, or sandstone 

(Murphy, 1995). Sandstone, marble, and granite are still quarried in Colorado for use as dimension stone.

Figure 47. Dimension stone being processed or in use. It is 

required in new construction and later as replacement material. 

A, Granite processing at a plant near Salt Lake City, Utah. 

Photograph by William Langer. B, Ivy Chapel, Fairmount Cemetery, 

Denver, Colo. Natural weathering is one of the greatest threats 

to historic buildings. In 1890, building material of unknown origin 

was used to construct this chapel. C, Weathered building material 

at the front entrance of Ivy Chapel, 2005. Paint was applied in an 

attempt to slow decay. Photographs B and C by D. Knepper, Jr.

A

C

Classification by Rock Groups

Granite and Rhyolite

Granite is an intrusive igneous rock that solidified 

slowly at great depth; it is composed principally of coarse 

crystals of quartz, feldspar, mica and, usually, hornblende. 

The term granite is from the Italian granire, to granulate, and 

the Latin granum, grain (Merriam-Webster, 2009). It is an 

excellent building material because it can withstand thousands of pounds of pressure and weathers slowly (fig. 48) 

(U.S. Geological Survey, 2003b). Most fresh, unweathered 

granite can be cut into usable building stone, but some colors, textures, and crystal sizes are more attractive than others 

and some granite is more uniform and yields larger volumes 

of homogeneous stone. The term rhyolite is from the Greek 

rhyax, meaning stream of lava (Merriam-Webster, 2009). 

Rhyolite is the fine-grained equivalent of granite; an extrusive igneous rock, it cooled rapidly at the Earth’s surface. 

Rhyolite is also rich in silica and aluminum.

B
62 Development of Industrial Minerals in Colorado

B

A

Figure 48. Granite used to face buildings in Denver, Colo., and 

in outcrop. Granite is one of the oldest and most durable building 

materials. A, Gray granite from the Aberdeen Quarry, South Beaver 

Creek, Gunnison County, was used to construct the Colorado State 

Capitol in 1888. The War Memorial in the foreground constructed 

from Colorado sandstone. Photograph by John Keller, Colorado 

Geological Survey. B, Sketch of granite dikes in black schistose 

rock, Colorado. By W.H. Holmes, 1873. U.S. Geological and 

Geographical Survey of the Territories (Hayden Survey) Sheet 15. 

Courtesy of USGS Photographic Library.

Marble and Travertine

Commercially, marble is a rock composed primarily of calcium carbonate (CaCO3

, calcite), dolomite 

(CaMg(CO3)2), or serpentine (a hydrated calcium, magnesium, and silica oxide) that is capable of taking a polish 

(Power, 1994). Marble commonly is a crystalline, compact 

metamorphosed limestone. Although marble is abundant 

throughout the world, very few deposits are of high enough 

quality to be quarried (Sinkankas, 1988). The Beulah 

marble of Pueblo County was used on the interior walls 

and pillars of the Colorado State Capital building (Keller 

and Widmann, 2002). Yule marble, a lustrous, pure white 

marble quarried near the community of Marble, in Gunnison County, is the Colorado State rock (fig. 49). It is used 

as facing stone in the Lincoln Memorial and the Tomb of 
Colorado Industrial Minerals—Occurrence, Use in Colorado, Mining, and Production 63

the Unknown Soldier in Washington, D.C., in municipal 

buildings in New York City and San Francisco, and in the 

central post office and Federal Reserve Bank in downtown 

Denver (Pearl, 1972).

Travertine is a variety of limestone formed by precipitation of calcite from mineralized spring water, commonly 

hot or warm. Commercially valuable travertine is hard and 

dense, and banding and streaking of colors and textures 

make it an attractive building stone. Travertine deposits 

in central Colorado are relatively small, but the stone has 

been widely used in buildings in Colorado and elsewhere 

(Keller and Widmann, 2002).

Sandstone

Sandstone is a sedimentary rock composed of sandsized grains (usually fragments of quartz) cemented by clay, 

silica, carbonate, or iron oxide (fig. 50). The most widely 

used dimension stone in Colorado is the tan to reddishbrown flagstone mined from the Permian Lyons Sandstone 

in Boulder and Larimer Counties. Many of the buildings at 

the University of Colorado in Boulder were built with Lyons 

Sandstone, as well as many buildings, patios, walls, and 

other structures in the metropolitan Denver area. Although 

not as popular as the Lyons Sandstone, the Cretaceous 

Dakota Sandstone and the Ordovician Harding Sandstone 

have been used locally as building stone.

Slate

Rocks composed of cemented particles finer than sand 

are called shales. Slate is the harder metamorphic equivalent 

of shale (Sinkankas, 1988). It splits readily into slabs and is 

used for roofing and pavements. “Beds of differing composition that form color stripes on cleaved surfaces are called 

ribbons” and are considered deleterious in high-grade slate 

(Power, 1994, p. 992).

Geology of Colorado Dimension Stone Deposits

Heat that emanated from nearby shallow intrusive 

igneous rocks recrystallized Mississippian limestone and 

dolomite strata, thus forming the marble near Marble, 

Colo. A thick travertine deposit has been quarried at 

Wellsville (east of Salida) in Fremont County (Murphy, 

1995). Deposits near Cañon City are capable of supplying 

large amounts of specimen travertine and have furnished 

large blocks for Federal buildings throughout the country 

(Pearl, 1972).

Granite, a common coarse-grained, colorful, intrusive 

igneous rock, is widely used as dimension stone. Several 

common granites in central Colorado have been quarried 

for building stone, including the large bodies of the Pikes 

Peak and Silver Plume granite (fig. 51). Along the Front 

Range, large masses of gray or pink Precambrian granitic 

rocks can be found west of Boulder, near Silver Plume 

(Clear Creek County) (Murphy, 1995).

Figure 49. Yule marble quarry. Yule marble is prized world wide 

for its high quality and white color. A, Marble blocks outside 

quarry area, Gunnison County, Colo. B, Interior space of the Yule 

marble quarry. The walls of the quarry show saw marks made 

as stone was extracted. Photographs by John Keller, Colorado 

Geological Survey.

A

B
64 Development of Industrial Minerals in Colorado

Figure 50. Multicolored Lyons sandstone in outcrop and in use. A, Lyons sandstone outcrops on 

the east side of Colorado’s Front Range. Photograph by E.D. McKee. Courtesy of USGS Photographic 

Library. B, Building on the University of Colorado campus, Boulder. Sandstone from the Lyons Formation 

in Boulder and Larimer Counties used to construct most buildings on this campus. Cement sidewalk 

(made from limestone, sandstone, and aggregate) and decorative crushed stone in foreground. 

Photograph by Beth Widmann.

A

B
Colorado Industrial Minerals—Occurrence, Use in Colorado, Mining, and Production 65

The Wall Mountain Tuff (called Castle Rock Rhyolite 

in the mineral industry) is used as dimension stone in central 

Colorado. It is an eruptive volcanic rock with the same chemical composition as granite. The tuff was erupted as superheated, gas-charged lava and ash that moved rapidly across 

the countryside. When the superheated lava and ash came to 

rest, the materials welded together and formed a dense, hard 

stone suitable for construction. High-quality rhyolite tuff is 

quarried from mesa tops in the Castle Rock area, Douglas 

County (Murphy, 1995).

Mining and Production

Dimension stone may be extracted from above or below 

ground. Ornamental, building, and statuary stone is extracted 

by use of minimal blasting and then cut, processed, and 

transported with care to prevent damage.

Quarrying methods may use various combinations 

of diamond saws, wire saws, chain saws, channeling and 

drilling machines, wedges, and broaching tools (used to 

remove blocks after drilling a row of holes) to isolate a mass 

of rock by cutting it free from the main mass on all sides but 

one. The isolated block is then lifted or separated from the 

parent mass by breaking it free with wedges, high-pressure 

air or water bags, or by undercutting it with a wire or chain 

saw. First-cut blocks tend to be massive and may be several 

tens of feet long, as much as 6 m (20 ft) high, and less than 

3 m (10 ft) wide. These massive quarried blocks are then 

subdivided into smaller blocks of a certain size and shape 

that can be sold or sent to a mill for further finishing. Explosives may be used to access different or higher grade parts of 

the deposit but are other-wise rarely used because they can 

damage the structural integrity of the stone.

Processing may produce specialty surfaces such as 

those that are polished or have a roughened flame texture; 

tumbling, leaching, scabbing (shaping and squaring of 

blocks for shipping and storage), and sandblasting may also 

be needed (Barker and Austin, 1994). The large quantities of 

dust produced during the mining, quarrying, and processing 

of dimension stone can be controlled by moist methods or 

by exhaust ventilation (Stellman, 1998).

In 2003, Colorado produced 4,600 tons of dimension 

stone (Beth Widmann, Colorado Geological Survey, written 

commun., 2006). In 2004, it produced about 5,800 tons 

valued at $1.5 million (Cappa and others, 2004).

Feldspar and Mica

The word feldspar comes from the German feld, 

meaning field, and spath meaning any of various nonmetallic but usually cleavable and lustrous minerals 

(Merriam-Webster, 2009). Feldspar is not a mineral with a 

single chemical composition but rather a group of related 

minerals of similar structure whose composition varies: 

its formula is MAl(AlSi)3O8, where M may be K, Na, Ca, 

Ba, Rb, Sr, or Fe (Bates and Jackson, 1987). Feldspar 

is abundant in rocks in the Earth’s crust and in coarsegrained bodies (pegmatites) associated with granitic igneous rocks. In 2004, seventy percent of domestic feldspar 

was used in glass manufacture (Potter, 2005). Feldspar 

provides alumina that increases the hardness, durability, 

and resistance to chemical corrosion of ceramic and glass 

products. Rarely, feldspar forms large, bright bluish-green, 

gem-quality crystals called amazonite (Austin, 1995). 

Amazonite is found at a few places in the Precambrian 

Pikes Peak Granite in central Colorado (Eckel, 1961); it is 

prized by mineral collectors.

The term mica is akin to the Greek word micros, 

meaning small and the Latin word micare, to gleam or 

sparkle (Stellman, 1998; Merriam-Webster, 2009). The 

micas are a group of crystalline phyllosilicate minerals 

possessing platy habit, excellent cleavage, and resistance 

to heat. Natural mica is most commonly found in the form 

of flakes, scales, shreds, and books (books split into thin 

sheets) (fig. 52).

Figure 51. Sawatch Quartzite resting on smooth erosional 

surface on Pikes Peak Granite. Ute Pass, near Manitou Springs, 

El Paso County, Colo., 1914. Photograph by N.H. Darton. Courtesy 

of USGS Photographic Library.
66 Development of Industrial Minerals in Colorado

Figure 52. Mica rosettes in outcrop 

and scanning electron micrograph of 

mica. A, Mica mine, 8 mi (13 km) south of 

Grand Junction, Mesa County, Colo., 1911. 

Rosettes of mica and tourmaline in wall. 

Photograph by D.B. Sterrett. Courtesy of 

USGS Photographic Library. B, Scanning 

electron micrograph of mica mass. Bar 

length, 2 μm (0.0002 cm). From Northrop 

and Whitney (Brockport, NY: International 

Committee on Natural Zeolites, 1987, p. 5).

A

B
Colorado Industrial Minerals—Occurrence, Use in Colorado, Mining, and Production 67

Thin sheets of mica called isinglass, taken from large 

crystals that occur in extremely coarse grained granitic rocks 

(pegmatites), were once used as windows in ovens and gas 

lanterns because of mica’s translucence and resistance to heat. 

Today it is used principally in the electronic and electrical 

industries, which import most sheet mica because of the higher 

cost to mine and process it in the United Sates (Hedrick, 

2004). Built-up mica is produced by overlapping mica sheets 

and alternate layers of binders, then pressing them under high 

heat; it is used as an insulating material (for example, between 

copper wires or in electric motors).

Scrap mica is a byproduct of the beneficiation of feldspar, 

kaolin, and industrial sand, a reversal of earlier times when 

feldspar was considered waste in the search for mica (Anglin, 

2002; Hedrick, 2004). Mines that produce pure, high-quality 

mica also produce feldspathic sand (used for stucco and golf 

course sand) as a byproduct.

The majority of domestic scrap and flake mica is ground 

to a coarse powder (Hedrick, 2004) that is used as a filler and 

reinforcement in plastics, joint compound, additive in oil-well 

mud, paint, roofing felts, and rubber products.

Geology of Colorado Feldspar and Mica Deposits 

In central Colorado, feldspar and mica have been produced from several Precambrian pegmatites. Pegmatites are 

relatively small igneous bodies of granitic composition distinguished by their extremely large crystals; it is not unusual to 

find individual crystals in pegmatites measured in feet. They 

form during the late, relatively water-rich stages of crystallization of large bodies (batholiths) of granitic rocks. Such large 

granite bodies were emplaced in Proterozoic metamorphic 

country rocks of central Colorado: the Routt Plutonic Suite, 

which includes the Boulder Creek Granite, 1.7 billion years 

ago (Ga); the Berthoud Plutonic Suite, which includes the 

Silver Plume Granite, 1.4 Ga, and the granitic rocks of the 

Pikes Peak batholith,1.0 Ga (Tweto, 1987). The pegmatites lie 

within the batholithic rocks and in the metamorphic country 

rocks (Lovering and Goddard, 1950).

The essential minerals in pegmatites are potassium feldspar 

(microcline) and quartz. Common accessory minerals include 

muscovite, biotite, plagioclase, and other minerals found in 

granites. In addition, pegmatites may contain beryl, columbitetantalite, lepidolite, topaz, tourmaline, and other exotic minerals 

but generally not in commercial quantities. Although the shapes 

of pegmatite bodies are highly irregular, they usually have a 

broad concentric zoning: the core contains very coarse grained 

microcline or quartz, or both; an intermediate zone of less 

coarse grained muscovite and albite plagioclase, and an outer 

zone of even less coarse grained quartz, potassium feldspar, and 

muscovite (Lovering and Goddard, 1950). In iron-rich pegmatites emplaced in the Pikes Peak batholith, iron-bearing biotite 

mica crystallized instead of muscovite (Simmons and Heinrich, 

1980). The once commercially valuable deposits of feldspar and 

mica came primarily from the core and intermediate zones of 

the pegmatites (Vanderwilt, 1947).

Mining and Production

Conventional open-pit mining methods and some 

hydraulic dredging are used to remove overburden and to 

drill, blast, and haul feldspar ore, which then is crushed. 

A froth flotation process is commonly used to concentrate 

feldspar (U.S. Environmental Protection Agency, 1995c). 

An amine collector floats off mica after sulfuric acid, pine 

oil, and fuel oil are added. After dewatering the discharge 

(usually by rotary dryers), sulfuric acid is added to lower the 

pH and petroleum sulfonate is added to remove iron-bearing 

minerals. Magnetic separation may be used to remove any 

iron minerals. The discharge is dewatered again, and a cationic amine is used for collection as the feldspar is floated 

away from quartz in hydrofluoric acid. Further milling and 

refining may be necessary depending upon its end use. Feldspar is ground to about 20 mesh for glassmaking and to 200 

mesh or finer for most ceramic and filler applications. Some 

processors are able to recover mica and silica sand from 

feldspar ores (Potter, 2005).

To reduce the environmental and health concerns of working with acids, new flotation reagents are being tested (in 2005) 

as are high-intensity magnetic separators. The primary pollutant of concern that is emitted from feldspar processing is particulate matter (U.S. Environmental Protection Agency, 1995c). 

Health hazards posed by this particulate matter may include 

exposure to substantial amounts of free silica (Stellman, 1998).

Although flake mica is mined by conventional open-pit 

methods, sheet mica typically is mined by the hard-rock mining techniques of drilling and blasting. Sheet mica is quarried 

by open pit or underground mining, which requires careful 

blasting to keep the crystals intact. The mined crystals are 

trimmed of rock (cobbed) and sorted by thickness and quality 

into blocks, thin leaves (splittings), and scrap. Dry grinding or 

dewatering, pneumatic separation, and screening may follow. 

Mica scrap is ground into mica flakes or powder.

Static electricity can be generated during the processing 

of mica; engineering techniques can discharge it harmlessly. 

Dusts that contain quartz, feldspar, and silicates are generated 

and must be controlled (Stellman, 1998). No environmental 

concerns are associated with the manufacture and use of mica 

products (Hedrick, 2004).

Feldspar and mica are not presently mined in Colorado 

(John Keller, Colorado Geological Survey, oral commun., 2006).

Sulfur

The term sulfur is from the Latin sulpur and Middle 

English sulphur, meaning brimstone, “the stone that burns” 

(Merriam-Webster, 2009). Early humans used sulfur as a colorant for cave drawings and as a fumigant, the Egyptians used 

it to bleach fabrics as early as 2000 B.C.E., and the ancient 

Greeks used sulfur in warfare to produce suffocating gases and 

as a disinfectant (Wilburn and others, 2001; Ober, 2002). Sulfur 

was also important because of its use in early gunpowder, discovered by the Chinese in the 9th century (Buchanan, 2006).
68 Development of Industrial Minerals in Colorado

Today, 90 percent of sulfur in the United States is converted to sulfuric acid (H2

SO4) for the processing of phosphate 

rock into phosphoric acid (H3PO4) and other phosphate fertilizers, in petroleum refining, and in metal industry processes 

(Ober, 2004). Sulfur is also used in rubber, insecticides, 

medicine for skin diseases, and pellets for direct application as 

an agricultural soil supplement.

In 1996, the Louisiana Department of Wildlife and 

Fisheries created the world’s largest artificial reef from the 

Freeport sulfur mine off Grand Isle, La. (Kasprzak, 2000) 

(fig. 53). The mile-long sulfur mine platform (including bridge 

supports) provides habitat to many coastal fishes. Annually, 

the Department’s marine laboratory staff attaches recreational 

mooring buoys to the sulfur mine reef site.

Geology of Colorado Sulfur Deposits

Sulfur is abundant in central Colorado, but very little 

has actually been produced. Most of the sulfur is in sulfide 

and sulfate minerals and in deposits of petroleum and natural 

gas. The abundant hydrothermal mineral deposits of Colorado 

contain sulfide minerals of Pb, Zn, Fe, Cu, and Mo. In the 

past, smelters produced unwanted sulfur as a waste byproduct 

of processing these ores. The natural oxidation of sulfide 

minerals releases sulfur into water moving through sulfide-rich 

deposits, producing sulfuric acid, or through the mine workings of the exploited deposits, producing acid mine drainage. 

A second source is the large quantity of sulfur locked up in the 

voluminous sedimentary deposits of gypsum and anhydrite 

in evaporite deposits of late Paleozoic and Mesozoic age in 

central Colorado.

Mining and Production

Sulfur and sulfuric acid are produced from three sources: 

combined sulfur, recovered sulfur, and formed sulfur (U.S. 

Environmental Protection Agency, 2002). Combined sulfur 

occurs in minerals such as iron pyrite (FeS2), copper sulfides, 

and gypsum (calcium sulfate). Combined sulfur can be recovered from sulfur dioxide emissions produced during the smelting of metal sulfides (U.S. Environmental Protection Agency, 

2002). Recovered sulfur is produced—and then captured—as a 

byproduct of oil refining, natural gas processing, and air pollution control. Formed sulfur is elemental sulfur cast or pressed 

into particular shapes.

Sulfur is mined by underground, surface, and Frasch 

mining methods. Open pit and underground mining extract 

elemental sulfur and pyrite deposits not amenable to the Frasch 

process. High- to medium-grade ore from these deposits can 

be roasted and the resulting SO2

 gas converted to sulfuric acid. 

To produce elemental sulfur, low-grade ores are treated by 

processes such as direct melting, distillation, agglomeration, 

solvent extraction, and flotation.

The Frasch process, a solution mining method, was used 

to extract underground deposits of sulfur such as those in 

limestones around the Gulf of Mexico. A mixture of compressed air and superheated water was pumped into deposits 

containing sulfur. The hot water melted the sulfur and the 

pressurized air drove the liquid sulfur to the surface. The 

liquid sulfur was treated to remove organic impurities and 

then either was sold as a liquid or cooled and solidified for 

the market. Domestic mining of elemental sulfur by use of 

the Frasch process ended in 2000 because of environmental 

concerns; all sulfur now produced in the United States is 

recovered from the refining of sulfur-bearing natural gas and 

crude petroleum and from coking plants (Ober, 2002).

The Claus process, which uses thermal and catalyticconversion reactions, was the first process for recovering 

sulfur from hydrogen sulfide (H2

S) in oil and gas production 

(Wilburn and others, 2001). Sulfur is considered a sustainable 

industrial mineral for the foreseeable future, and recovered 

sulfur tonnages are expected to continue from petroleum refineries, as sulfur emissions are strictly controlled by government 

regulations (Ober, 2004).

Barite

The term barite comes from the Greek barites, meaning 

weight (Merriam-Webster, 2009). Barite, the principle ore of 

barium, is a heavy, nonmetallic mineral consisting of barium 

sulfate (BaSO4). Barite is relatively insoluble, a property that 

keeps the heavy metal barium (Ba) from entering surface 

waters (Hammarstrom and Smith, 2002).

About 95 percent of barite in the United States is used 

as a weighting agent in gas-well and oil-well drilling fluids 

(Searls, 2004). Pulverized barite is added to the drilling fluid 

(a clay-water mixture called mud) to control the escape of 

gas from the reservoir and prevent blowouts (Bates, 1969). 

Figure 53. Scientists record data on the biota of an artificial reef. 

Courtesy of Louisiana Department of Wildlife and Fisheries.
Colorado Industrial Minerals—Occurrence, Use in Colorado, Mining, and Production 69

Barium compounds are also used in medical x-ray examinations, automobile brake and clutch pads, golf and tennis 

balls, optical glassware, radiation shields around nuclear 

reactors, faceplates for television sets and computer monitors, and cement vessels that contain radioactive materials 

(Searls, 2004).

Beginning in 1981, importing ore from overseas sources 

became less expensive than extracting, processing barite ore, 

and shipping it long distances in the United States. Twentyseven years later, however, increased oil-field drilling and a 

shortage of inexpensive foreign ores could make barite an 

economically attractive mineral commodity again (Arkansas 

Geological Survey, 2009). In 2005, 82 percent of the barite 

used in the United States was imported (U.S. Geological 

Survey, 2006).

Geology of Colorado Barite Deposits

Barite occurs as a gangue (undesired part of an ore) mineral in some hydrothermal veins associated with base and precious metal deposits in central Colorado, especially within the 

Colorado mineral belt. The veins cut Cretaceous and Tertiary 

plutons, nearby Precambrian igneous or metamorphic rocks, 

or Paleozoic country rocks. However, none of these hydrothermally altered country rocks contain barite in a quantity that 

can be mined economically today.

In the northern Wet Mountains, barite occurs in quartzbarite-thorite veins and fracture zones associated with the 

intrusion of alkalic rocks of the Gem Park area, including the 

McClure Mountain and Democratic Creek complexes and 

associated dikes (Armbrustmacher, 1988). The age of these 

rocks is about 520 Ma, or Early Cambrian (Olsen and others, 

1977). The veins and fracture zones cut Proterozoic igneous and 

metamorphic rocks as well as the Cambrian alkalic rocks of the 

complexes.

Barite occurs at the surface today in tailings at abandoned 

mines in Boulder County, in the Wet Mountains, and probably in many other mine dumps in the region. Barite crystals 

have been found on Federal land (Pawnee National Grassland) 

and throughout a wide region of Weld and Logan Counties 

(Workman, 1964). Most of the barite crystals are on State and 

privately owned land (P. Modreski, U.S. Geological Survey, 

oral commun., 2004). Of note are the large blue barite crystals 

found southwest of Hartsel, Park County, Colo. (Pearl, 1972).

Mining and Production

Barite ore is crushed and stockpiled. Some barite ores are 

ground to the user’s specifications (Brobst, 1994); barite from 

other deposits may be washed and separated by various techniques—moving screens up and down in water, heavy media, 

tabling, flotation, and magnetic (Searls, 2003).

“The barite industry has no especially difficult ecological problems other than those attendant upon the mining and 

beneficiation of ores [for example, water quality and dust suppression]” (Brobst, 1994, p. 132). Although barite contains the 

heavy metal barium it is not thought to be toxic, as defined in 

Section 313 of the Emergency Planning and Community Rightto-Know Act of 1986, owing to its insolubility (Searls, 2003).

Barite is not presently mined in Colorado (John Keller, 

Colorado Geological Survey, oral commun., 2006).

Diamonds, Gemstones, and Mineral Specimens

Gemstones are minerals or other natural materials (such 

as pearl, amber, and coral) with superior color and clarity that 

are durable for ornamental purposes. “Collector or specialty 

gems are rare, unusual, or unique gems that are not normally 

seen by the gem buying public. The stones may be gem materials that are common to the market place, but are unusual or 

unique because of their large size or unusual color” (Austin, 

1995, p. 7). They range in value from a few tens of dollars per 

carat to more than $1,000 per carat.

Although gems are not usually considered industrial 

minerals, certain gem minerals, such as diamond or garnet 

that do not meet gem standards may be used primarily as 

abrasives and are termed “industrial.” In addition, some 

mineral specimens have economic value. “Aside from a 

few regions such as the Alps of Europe or the granite areas 

of Colorado west of Colorado Springs * * * virtually all 

[mineral] specimens enter the market as byproducts of mines 

operated for metallic ores or industrial or gem minerals” 

(Sinkankas, 1988, p. 328). Specimens are sold mostly to 

tourists, museums, schools, and private collectors domestically and abroad (Arkansas Geological Survey, 2009). 

Collecting mineral specimens is a popular recreation activity 

(fig. 54).

Gemstones found in Colorado that are of commercial importance include amazonite, aquamarine, diamond, 

gypsum (fine-grained alabaster and fibrous satin spar types), 

lazurite, several varieties of quartz, rhodochrosite, topaz, and 

turquoise (Scott, 1964; Murphy and Modreski, 2002). Colorado’s quartz gemstones include fine quality jasper, agate, 

petrified wood, and agatized dinosaur bone on both sides of 

the Continental Divide (Austin, 1995).

Diverse gemstones and mineral specimens can be collected in Colorado. Edwin Eckel’s book, “Minerals of Colorado,” (1997), describes the chief occurrences of all known 

or reported Colorado minerals; refer to it for additional 

localities. Many of Colorado’s prolific mineral localities 

are on public land (Pearl, 1972). A number of examples are 

given below.

Classification by Mineral Variety

Amazonite

Amazonite (or amazonstone) is a green to blue-green 

variety of the mineral microcline (KAlSi3O8, potassium 

feldspar); it is commonly mistaken for jade. It is fairly hard 

(Mohs hardness of 6–6.5). The Pikes Peak region is an 

important source of amazonite, smoky quartz, topaz, and 
70 Development of Industrial Minerals in Colorado

Ruby Mountain, south of Buena Vista (Chaffee County), is 

popular with mineral collectors for its black obsidian, 

garnet, and topaz specimens.

Aquamarine

The term aquamarine is from the Latin aqua marina, 

meaning seawater (Merriam-Webster, 2009). It is a 

transparent blue, green, or blue-green gem variety of the 

mineral beryl (Be3Al2Si6O18) with a Mohs hardness of 7.5–8. 

The color is caused by iron impurities. Aquamarine has been 

found in Egyptian and Greek tombs and is Colorado’s official 

State gemstone. Aquamarine and smoky quartz are known to 

occur in the Mount Antero area (part of San Isabel National 

Forest) and Mount White area (in the Sawatch Range at about 

4,300 m (14,000 ft) of central Chaffee County (fig. 55).

Figure 55. The Sawatch Range, southern Colorado Rocky Mountains, is famous for gems and views. A, Sawatch Mountains. 

B, Close-up of the Mount Antero–Mount White area, Chaffee County, Colo. The area is known for its mineral resources. Photographs by Jim 

Shannon. Courtesy of Colorado School of Mines.

A B

amethyst (Pearl, 1972). The region includes the Crystal Peak 

area in Park and Teller Counties (north of Florissant) and 

along the Tarryall Mountains from Topaz Mountain to Tappan Mountain (west of Manitou Springs, El Paso County) 

(Pearl, 1972; Murphy and Modreski, 2002). The Crystal 

Peak area “* * * is the most productive source of gem and 

specimen quality amazonite in Colorado, if not in the world” 

(Eckel, 1997, p. 323).

Apache Tears

Small black stones of obsidian, called Apache tears, are 

natural volcanic siliceous glass formed by rapidly cooled 

magma. Obsidian has a Mohs hardness of 5.0–5.5. Stone-age 

people sought obsidian for its ability to break and give sharpedged tools. Today, the stones are used in the souvenir trade. 

Figure 54. Crater of Diamonds State Park, near Murfreesboro, Ark. A, Prospectors of all ages at this tourist attraction access 

the diamond search area through the park visitor center. Here interpretive exhibits and an audiovisual program explain the area’s 

geology and give tips on recognizing diamonds in the rough. B, Diamonds from the State park; they can be any color in the rainbow. 

Raw diamonds have a shiny metallic look. Courtesy of Crater of Diamonds State Park.

A B
Colorado Industrial Minerals—Occurrence, Use in Colorado, Mining, and Production 71

Diamond

Diamond, one of the hardest materials known, is composed of pure crystalline carbon (C). Only about 20 percent of 

all diamonds mined meet gem standards. The rest are classified as natural industrial grade and used in tool and die stones, 

drilling material, grits, and powders (Reckling and others, 

1994) and as heat sinks in electronic compounds, infrared 

windows in heat detectors, and surgical instruments (Arkansas 

Geological Survey, 2009). Synthetic manufactured diamonds 

have replaced more than 90 percent of the natural industrial 

diamonds once used in the United States (Olson, 2004b).

Primary diamond deposits are found in unusual igneous 

intrusive bodies known as kimberlite and lamproite pipes 

that formed at great depth, whereas secondary deposits are 

found in sand and gravel of alluvial streambeds. Mining of 

diamonds within the United States has been limited to Arkansas and to Larimer County in northern Colorado (Colorado 

Geological Survey, 1999).

Gypsum

The three mineral varieties of gypsum (CaSO4·2H2O, 

calcium sulfate dihydrate) are all sought by mineral collectors: 

selenite is a colorless to translucent form with a pearl luster, 

satin spar has a fibrous, satiny look, and alabaster is a finegrained massive material. Selenite and satin spar are of less 

economic importance than alabaster (Bates, 1969). The largest 

alabaster quarry in the United States is located in eastern 

Larimer County, north of Fort Collins; alabaster is one of the 

Colorado ornamental minerals best known from a commercial standpoint (Pearl, 1972). Gypsum localities such as Coon 

Gulch, south of Golden, Jefferson County; Perry Park, Douglas County; and areas near Colorado Springs, El Paso County, 

are of interest to collectors (Eckel, 1997).

Lazurite

Lazurite is the blue component of the gemstone lapis 

lazuli, once used as the pigment ultramarine when ground 

to a powder for tempera and oil paint. The ancient city of 

Ur, near the Euphrates River in lower Iraq, had a thriving 

trade in lapis as early as 4,000 B.C.E. (Bancroft, 2000). 

Lazurite is a feldspathoid mineral of the sodalite group—

(Na,Ca)78(Al,Si)12(O,S)24[SO4,Cl2(OH)2]2 (Bates and Jackson, 

1987). Lazurite occurs on Italian Mountain in the Sawatch 

Range, north of Crested Butte, Gunnison County, Colo., one 

of the few sources in the world of high quality lapis lazuli 

(Pearl, 1972; Eckel, 1997).

Peridot

Pliny tells of the first recorded peridot specimen, which 

was presented to a Theban queen of Lower Egypt about 

300 B.C.E. (Bancroft, 2000). It is also known as the “evening 

emerald” and as chrysolite. Peridot is the transparent gem 

variety of a common rock-forming mineral called olivine. It 

is a magnesium iron silicate, (Mg,Fe)2

SiO4, and has a Mohs 

hardness of 6.5–7. Peridot occurs within the San Isabel 

National Forest on a fairly remote basalt-capped mesa near the 

southwest edge of South Park (on the border of Fremont and 

Park Counties in the vicinity of Herring Park, Colo.) (Murphy 

and Modreski, 2002).

Pyrite

“Fools gold” is a common name for pyrite (FeS2, iron 

sulfide), a shiny brass-yellow mineral with a Mohs hardness 

of 6–6.5. Pyrite was mined for its sulfur content during World 

War II. It is a common mineral, but unique pyrite clusters can 

be found near Florence, Fremont County, Colo.

Quartz

Cryptocrystalline quartz (SiO2, silicon dioxide) includes 

chalcedony, agate, jasper, flint, hornstone, and chert. Around 

2.5 million years ago, Paleolithic humans used flint to make 

tools. Agate and jasper are found throughout Colorado (Eckel, 

1997). Gem quality or collectible crystalline quartz occurs in 

many varieties; Eckel (1997, p. 399–405) summarizes Colorado quartz occurrences.

• Rock—Colorless, found throughout the Colorado 

mineral belt and most abundantly in Chaffee, Ouray, 

and San Juan Counties (Eckel, 1997)

• Amethyst—Purple, a low- to moderate-temperature 

variety of quartz. Found in the Pikes Peak batholith 

(Douglas, Jefferson, El Paso, Park, and Teller Counties)

• Citrine—Yellow

• Rose—Colored by trace amounts of titanium, iron, 

or manganese. Found in Chaffee, Clear Creek, and 

Fremont Counties

• Smoky—Tan to brown to black coloring, formed 

through natural irradiation of clear quartz that contains 

aluminum. Found in granitic pegmatites in the Pikes 

Peak batholith and the Mount Antero Granite, including Chaffee, Douglas, Jefferson, El Paso, Park and 

Teller Counties

• Milky—Found in the San Juan region, Ouray County, 

southwestern Colorado

• Rutilated—Quartz that encloses needlelike crystals of 

rutile.

Topaz

Topaz (Al2SiO4(F,OH)2, an aluminum silicate mineral) 

(Eckel, 1997) has a hardness of 8 on the Mohs scale. The 

name topaz is incorrectly applied to citrine, which is yellow quartz. The best known sources of gem-quality topaz 

are pegmatites in the Pikes Peak batholith including Pike 

National Forest (the area of Devils Head, south of Sedalia, 

Douglas County); Harris Park, Park County; Crystal Peak 
72 Development of Industrial Minerals in Colorado

(near Florissant), Teller County; Glen Cove, Teller County; 

and the Tarryall Mountains, Park County (Eckel, 1997). 

The Devils Head area offers more long-range possibilities 

for mineral collecting than any other place in Colorado, 

according to Pearl (1972).

Rhodochrosite

Rhodochrosite (MnCO3, manganese carbonate), the Colorado State mineral, is a pink to red mineral, but its inherent 

softness (Mohs hardness 3.5–4.0) discourages its use in jewelry. It was mined by the Incas probably more than a thousand 

years ago in Argentina (Bancroft, 2000). It was once ground 

up for face powder, and in the early mining days of Colorado, 

miners discarded the red mineral as waste while they mined 

silver- and gold-bearing sulfide veins. Rhodochrosite is found 

in eighteen of Colorado’s counties associated with gold, 

silver, lead, zinc, and molybdenum ores (Colorado Geological 

Survey, 2004b). Translucent red crystal specimens are prized 

the world over. One of the finest rhodochrosite sources was 

the Sweet Home mine in Park County, west of Alma (Austin, 

1995; Murphy and Modreski, 2002) (fig. 56). The Sweet 

Home mine closed in 2004 after many years of operation.

Turquoise

Turquoise (CuAl6(PO4)4(OH)8·4H2O, hydrated copper 

aluminum phosphate) is probably one of the oldest gemstones 

known, worn by pharaohs, Aztec kings, and Native Americans 

(Austin, 1995). The Anasazi and Hohokam mined turquoise 

throughout the Southwest. Its Mohs hardness is 5–6. In the 

United States, the aluminum (Al) in “turquoise” is partially 

replaced by iron (Fe) and thus, strictly speaking, the mineral 

is chalcosiderite, not turquoise (Schumann, 2007). Turquoise 

has been recovered near Leadville, Lake and Eagle Counties; 

near Colorado Springs, El Paso County; and near Villa Grove, 

Saguache County (Austin, 1995). Although total production 

is small, turquoise is one of the most valuable gemstones 

produced in Colorado (Eckel, 1997).

Geology of Colorado Gemstone and Hand 

Specimen Deposits

The majority of Colorado’s gemstone and crystal specimens is found in pegmatites rather than hydrothermal deposits 

(Murphy and Modreski, 2002). One exception, rhodochrosite, 

occurs in moderate- to low-temperature hydrothermal ore 

veins, particularly those containing silver, lead, zinc, and copper, as well as in high-temperature metamorphic deposits.

Crystal specimens of amazonite, aquamarine, beryl, and 

topaz are found in pegmatites in the Pikes Peak batholith, 

central Colorado, and are commonly accompanied by quartz, 

mica, and feldspar crystals. Pegmatites have the same basic 

mineralogic composition as granite but are extremely coarse 

grained. Pegmatites generally formed within a trapped pocket 

of magma that cooled very slowly in a relatively water-rich 

fluid that allowed very large crystals to form.

Lapis lazuli usually occurs in crystalline limestones as a 

result of contact metamorphism. Alabaster, like other forms of 

gypsum, forms by evaporation of seawater.

Pyrite forms large bodies in moderate- to high-temperature 

hydrothermal deposits and in contact metamorphic ore deposits, is an accessory in many igneous rocks, and is common in 

sedimentary beds and metamorphosed sediments.

Widespread deposits of petrified wood are found in the 

Tertiary Dawson Arkose throughout an area extending from 

south and east of Denver to the Black Forest area northeast of 

Colorado Springs, including parts Arapahoe, Douglas, Elbert, 

and El Paso Counties (Eckel, 1997).

Turquoise is formed by the percolation of groundwater 

through aluminous rock in the presence of copper. For this 

reason, it is often associated with copper deposits as a secondary mineral, most often in copper deposits in arid, semiarid, or 

desert environments (Austin, 1995).

Diamonds occur in an unusual igneous rock called kimberlite. Kimberlites are found in pipe-like structures extending from the upper part of the mantle through the crust to 

the surface. These pipes, called diatremes, are formed by the 

violent eruption of carbon dioxide (CO2

) in melted mantle 

(magma), which entrains pieces of mantle rock and crust 

(xenoliths) and crystals precipitated out of the melt (phenocrysts). Chunks of wall rock dragged into the mobile kimberlite magma contain rock types typical of the upper mantle 

(peridotite and eclogite, which may contain diamonds), of 

the lower crust (granitic and metamorphic rocks), and of 

the near-surface crust (sedimentary rocks entrained during 

Figure 56. Specimen containing rhodochrosite (red), quartz (white),

tetrahedrite (black), chalcopyrite (gold), and fluorite (pale purple). 

Sweet Home mine (formerly a silver mine), Alma, Colo.; specimen 

8 x 8 cm. Courtesy of Fabre Minerals http://www.fabreminerals.com. 

Rhodochrosite is the official State mineral of Colorado.
Colorado Industrial Minerals—Occurrence, Use in Colorado, Mining, and Production 73

an eruption). The most common mineral crystals found in 

unweathered kimberlite are ilmenite, garnet, olivine, clinopyroxene, and orthopyroxene. Alteration and weathering usually destroy most primary minerals and textures, producing 

a soft rock composed largely of secondary minerals such as 

serpentine, carbonate minerals, and iron and titanium minerals (Coopersmith and Schulze, 1996).

Kimberlite rocks were identified in the Colorado Front 

Range in 1965 near the Colorado-Wyoming border. Since 

then, about 100 kimberlite intrusions have been identified in 

the Front Range between Boulder, Colo., and southern Wyoming. It wasn’t until 1975 that a diamond was discovered in a 

rock sample from one kimberlite near the Colorado-Wyoming 

State line. Approximately 40 kimberlite occurrences have 

since been identified in this area, known as the State Line 

kimberlite district (Colorado Geological Survey, 1999). Virtually all of the State Line kimberlites contain diamonds, but 

only the largest bodies in a cluster near Kelsey Lake have been 

mined commercially (Thompson, 1996).

Mining and Production

Overall, gemstone production in Colorado was estimated 

to be $359,000 in 2004 (Cappa and others, 2004), an increase 

of 31 percent as compared with the 2003 estimated value of 

$274,000 (production in tons not available) (U.S. Geological 

Survey, 2003a). Kelsey Lake diamond mine, Larimer County, 

Colo., was not mined during 2003. Its reserve is estimated at 

18.7 million tons grading at 3.4 to 4.6 carats per 100 tons of 

kimberlite ore (Cappa and others, 2003).

Diamonds

Diamond-bearing kimberlite deposits are mined in 

open pits that are excavated by use of blasting, shovels, and 

bulldozers and underground with a method termed block 

caving. In Canada, some diamond mines are under water, 

so the kimberlite-bearing pipes are surrounded by dikes and 

then drained. Approximately 25 tons of rock are mined and 

processed to obtain 1 gram (5 metric carats) of diamonds 

(Reckling and others, 1994).

Alluvial mining can be as simple as a shovel and a pan 

that is filled with water and sediment and swirled to allow diamonds to settle to the bottom. Larger operations use equipment 

to move both ore and waste alluvium to a process plant, where 

the ore is crushed and screened, and scrubbers remove fine 

waste material. A heavy-medium separation further separates a 

diamond concentrate from the crushed ore. Diamonds and other 

high-density minerals sink to the bottom of cones whereas 

lighter minerals float to the top. Cyclones swirl the heavy minerals to the conical wall, while waste minerals are sucked up 

from the center of the vortex. Finally, x-ray fluorescence sorters 

or a vibrating grease table are used to extract diamonds from 

the residual waste. When exposed to x rays, diamonds fluoresce 

and thereby activate a jet of air that deflects the diamonds into 

a storage bin. The recovered diamonds are washed in acid or 

boiled in water and sorted.

Minerals Sought by Collectors

Old prospect pits and mine dumps may offer mineral specimens in weathered rock. For example, dumps at the Sedalia copper mine, north of Salida, Chaffee County, Colo., have produced 

large specimen-grade garnets (Pearl, 1972; Austin, 1995).

Collectors may dig shallow pits with simple hand 

tools, such as a shovel, pick, or hammer (fig. 57). Mineral 

specimens may be washed out of debris with a large hose 

and screened. Specimens are cleaned with water, chemical 

solutions, or mechanical methods (such as sharpened tools, 

ultrasound, and tumbling), trimmed, repaired, and preserved 

(Sinkankas, 1988). Gemstones may be irradiated, heat 

treated, or coated to enhance color.

Fluorspar

Fluorspar (the industrial name applied to the impure ores 

of fluorite) is a transparent to translucent mineral composed 

of calcium fluoride (CaF2) (Eckel, 1997). Fluorspar is found 

in various colors (commonly blue or purple) and has a Mohs 

hardness of 4 (Bates and Jackson, 1987). The mineral has been 

used for centuries as a flux in various metallurgical processes; 

its name is derived from the Latin fluere, to flow (Encyclopedia Britannica, 2004a).

No domestic fluorspar was mined in 2003; all fluorspar was imported (Miller, 2004b). All domestic fluorspar is 

derived from sales of material from the U.S. Department of 

Defense National Defense Stockpile and from a small amount 

of synthetic fluorspar produced from industrial waste streams 

(Miller, 2004b).

Approximately 80 percent of fluorspar consumed in the 

United States is used to produce hydrofluoric acid and aluminum fluoride (AlF3

) (Miller, 2004b). Hydrofluoric acid is used 

in the manufacture of all fluorine-bearing chemicals. Fluorspar 

is also used to make iron and steel and in refrigerants, solvents, toothpaste, and anesthetics. Fluorosilicic acid (H2

SiF6), 

which is recovered from phosphoric acid plants that process 

phosphate rock, is used primarily in water fluoridation (Miller, 

2004b). Legislation to reduce emissions of fluorinated gases in 

the European Union may reduce the demand for fluorspar and 

flurochemicals (Miller, 2004b).

Geology of Colorado Fluorspar Deposits

Most fluorspar deposits in central colorado are veins or 

replacements along faults and in fault breccia (rock along fault 

planes that was broken up during fault movement) that formed 

in tertiary time (fig. 58). Fluorspar is also a gangue mineral 

found in metalliferous veins in some mining districts in central 

colorado, where it is considered a waste mineral. The major 

fluorspar veins and replacement deposits (Jamestown, Northgate, and Browns Canyon districts) are all epithermal deposits 

formed by warm dilute aqueous solutions, probably of hot 

springs origin, moving through open faults and fault breccias 

at shallow depths. The temperatures at which these deposits 
74 Development of Industrial Minerals in Colorado

formed were probably in the range of 50–200°C (Van Alstine, 

1969). The deposits are characterized by fluorite and microcrystalline to chalcedonic quartz forming layered coatings on 

vein walls and around breccia fragments, as well as lining or 

filling vugs (small cavities in a vein or rock).

Mining and Production

Fluorspar veins may be mined in open pits with draglines, scrapers, or power shovels, or they may be extracted 

by underground mining techniques. Fluorspar is obtained 

by drilling and blasting the rock, followed by crushing and 

screening to remove waste. Additional beneficiation (such as 

concentration by gravity processes, froth flotation, and washing) may be needed to meet market specifications (Fulton 

and Montgomery, 1994).

Waste material is disposed of in tailing ponds or used 

as a cemented backfill in underground mining. “The disposal of mill tailings creates a problem because, even after 

impoundment and clarification, the liquid effluents may 

contain traces of chemicals that are in violation of environmental standards” (Fulton and Montgomery, 1994, p. 521). 

Safe working conditions during mining of fluorspar require 

careful dust control (such as wet drilling, watering of loose 

rock, and general ventilation) (Stellman, 1998).

Fluorspar mining in Colorado ended in the 1970s (John 

Keller, Colorado Geological Survey, oral commun., 2006).

Nahcolite

Nahcolite is one of only a few minerals whose name 

also gives its chemical composition. The name nahcolite 

(NaHCO3, naturally occurring sodium bicarbonate) is formed 

by changing the subscript 3 to the common mineral suffix 

“lite.” Nahcolite is one source of soda ash (Na2CO3, sodium 

carbonate); it can also be refined from the mineral trona 

(Na2CO3·NaHCO3·2H2O), brines of soda ash, or synthetic 

chemical processes (Kostick, 2004; Mineral Information Institute, 2004). Synthetic soda ash is the least desirable source; 

it is more costly to produce and generates environmentally 

deleterious wastes (Kostick, 2004).

Soda ash has applications in glass production, flue 

gas desulfurization, soaps and detergents, water treatment 

(by adjusting pH), and pulp and paper production. Sodium 

Figure 57. View looking north towards the Nelly E garnet mine, 2.5 mi (4 km) south of Cañon City, Colo., 1910. 

Most gems found in the pit where mine owner J.D. Endicott stands. Photograph by D.B. Sterrett. Courtesy of USGS 

Photographic Library.
Colorado Industrial Minerals—Occurrence, Use in Colorado, Mining, and Production 75

bicarbonate (baking soda) is used in food products, animal 

feed, cleaning products, and pharmaceuticals.

The world’s second-largest known soda ash resource 

is in the Piceance Basin, Rio Blanco County, northwest 

Colorado (Kostick, 1994; Eckel, 1997; Keller and Widmann, 

2002), and the world’s largest buried trona resource is in the 

Green River Basin of southwestern Wyoming (Mineral Information Institute, 2004).

Geology of Colorado Nahcolite Deposits

Nahcolite is an evaporite mineral that forms as inland 

lakes evaporate and concentrate sodium and carbonate 

ions. In Colorado, nahcolite is contained in the lacustrine 

sediments of the Parachute Creek Member of the Eocene 

Green River Formation (Keller and Widman, 2002). The 

Green River Formation contains sandstone, claystone, 

shale, dolomitic marlstone, oil shale, and thin beds of 

volcanic tuff deposited in Eocene Lake Uinta. Lake Uinta 

occupied the Uinta Basin in Utah and the Piceance Basin 

in northwestern Colorado. During especially arid times, 

evaporation caused the lake to become so saline that a 

large quantity of sodium salts, primarily nahcolite and 

halite, were precipitated from lake waters into pore spaces 

in sediments (Dyni, 1996).

Mining and Production

In Colorado, nahcolite ore is recovered from Eocene 

evaporite beds that lie about 610 m (2,000 ft) below the 

surface. Hot water injected through deep wells dissolves 

the nahcolite; nahcolite brine is then pumped to the surface 

and transported to a processing plant (fig. 59). If market 

conditions warrant, beds of nahcolite may also be developed in the future as a byproduct of shale oil production 

(Kostick, 1994).

Soda ash, sodium bicarbonate, and caustic soda (NaOH, 

sodium hydroxide) are removed from evaporite beds by a 

variety of processes. In the case of soda ash, one process 

bubbles carbon dioxide gas into a saturated solution of 

sodium carbonate–bearing brines. The bicarbonate precipitates out and is then collected, filtered, and calcined to light 

soda ash (Kostick, 1994). Rotary bleaching units remove 

residual organic contaminants from the material; then the 

Figure 58. View northwest from Arkansas River, showing the main fault zone between hills of Tertiary rhyolite welded 

tuff (left) and Precambrian rocks (right) and the Colorado-American fluorspar mine, Chaffee County, Colo., about 1945. 

Photograph by R.E. Van Alstine. Courtesy of USGS Photographic Library.
76 Development of Industrial Minerals in Colorado

light soda ash is concentrated, screened, dewatered, washed, 

and dried to yield dense soda ash. Clean recycled water can 

be piped from the processing plant to the mine site, where 

it is used again to dissolve more nahcolite. Producers may 

dredge additional sodium carbonate decahydrate crystals (a 

naturally occurring form of soda ash, Na2CO3∙10H2O) from 

tailing ponds or directly inject the waste tailings underground 

(Kostick, 1994).

A possible adverse effect of extracting nahcolite is subsidence of the ground surface over mined areas.

In 2004, Colorado produced 79,400 tons of sodium bicarbonate from nahcolite in Rio Blanco County, less than in 2003 

(Cappa and others, 2004). Additional sodium bicarbonate is 

produced in Rio Blanco County from trona brought by rail from 

Green River, Wyo. Although Colorado produced 550,000 tons 

of soda ash during 2003, production of soda ash ceased after 

spring, 2004 (Cappa and others, 2003; Cappa and others, 2004).

Titanium

Titanium ore was first discovered in 1791 in Cornish 

beach sands by an English clergyman and named after the 

giants of Greek mythology, the Titans (Encyclopedia Britannica, 2004b). The principal source of titanium is still sand 

deposits containing high-density minerals (“heavy minerals”) 

such as zircon and the titanium minerals rutile (which is about 

95 percent TiO2) or ilmenite (FeTiO3).

Approximately 97 percent of titanium mineral concentrates 

are used as titanium dioxide (TiO2), a pigment that is white 

and nonmetallic, rather than in a metallic form (Ti) (Keller 

and Widmann, 2002; Gambogi, 2005). Non-pigment uses of 

titanium ores are mostly in the production of titanium metal and 

titanium compounds. Because of its high strength, light weight, 

and resistance to corrosion, titanium is used in parts for aircraft, 

spacecraft, and ships; in joint prostheses as a replacement for 

bone and cartilage; as heat exchangers in desalination plants; 

and in other industrial processes (Christie and Brathwaite, 

1998). On the basis of research on weathered ilmenite sands in 

the Murray Basin, Australia, ilmenite might be used to remove 

heavy metal and radioactive pollutants from mine drainage, 

industrial waste streams, and groundwater (Rive, 2004).

Geology of Colorado Titanium Deposits

Primary rutile is found in igneous and metamorphic 

rocks: alkalic igneous complexes (carbonatites), alkalic mafic 

complexes of norite or anorthosite, granitic to syenitic pegmatites, and high-grade, aluminum-rich metamorphic rocks. 

A third mineral, perovskite, is the primary titanium ore in an 

alkalic stock in the Powderhorn district, Gunnison County; 

ilmenite is present but less abundant. Primary ilmenite is 

associated with titaniferous iron ores of hematite or magnetite, 

often as magmatic segregations in alkalic and mafic intrusive 

rocks (Schwochow and Hornbaker, 1985). Sediments eroded 

from these rocks often contain large concentrations of heavy 

minerals, including rutile and ilmenite, which may form 

valuable secondary placer deposits.

The largest unmined titanium resource in the United States 

is the White Earth deposit in the Powderhorn district near Gunnison, Colo. (Colorado Mining Association, 2008). Titanium 

minerals (rutile and ilmenite), garnet, zircon, and some rare 

earth minerals are present within ancient beach placer deposits 

of minerals on the plains of eastern Colorado. These deposits 

occur in the Upper Cretaceous Fox Hills Sandstone and have 

been examined in recent years for their commercial potential.

Mining and Production

Ore from hard-rock deposits is crushed to a size that will 

liberate impurities, and then the titanium minerals are concentrated by magnetic separators or froth flotation (Christie and 

Brathwaite, 1998). Beneficiation is similar to that used for 

beach sands described below.

Heavy-mineral beach sands are extracted by suction 

dredges (DuPont, 2004). The sand slurry is discharged 

into a wet mill where it is screened and crushed, and the 

raw ore is roughly separated into valuable heavy mineral 

concentrates (including titanium minerals) and lighter 

minerals (such as quartz and feldspar) by gravity concentration methods (for example, gravity spirals or sluices). 

The tailings discharge is directed back into the pond as 

backfill. The heavy mineral concentrates often contain 

grains coated with organic material and clays; these impurities are removed through scrubbing with caustic soda 

(NaOH, sodium hydroxide). The concentrate is then dried 

and the titanium minerals are separated from other products by electrostatic separators. Next, the various titanium 

Figure 59. Nahcolite plant in Rio Blanco County, northwestern 

Colorado. Colorado is home to the only pure sodium bicarbonate 

deposits in the United States. Photograph by John Keller, Colorado 

Geological Survey.
Colorado Industrial Minerals—Occurrence, Use in Colorado, Mining, and Production 77

minerals are magnetically separated from each other. The 

magnetic fraction is collected and shipped as ilmenite; the 

nonmagnetic fraction is treated again to recover rutile and 

leucoxene (an alteration mineral of ilmenite). Zircon, a 

zirconium-bearing mineral, is a byproduct.

Titanium dioxide (TiO2) can be produced by sulfate or 

chloride processes (Christie and Brathwaite, 1998). In the 

sulfate process, ilmenite ore is digested with sulfuric acid 

to remove iron, generating large quantities of waste iron 

sulfate. Alkali or oxygen is added to precipitate hydrous 

titanium dioxide, and the precipitate is heated to drive off 

water. The chloride process calcines a mixture of a mineral 

rutile (or synthetic rutile—ilmenite that has been processed to remove the iron component), a source of carbon 

(for example, coke), and chlorine to form “tickle” (TiCl4, 

titanium tetrachloride). Tickle is condensed to a liquid from 

which impurities are removed as solids; it then is heated to 

a gas and mixed with oxygen, forming TiO2. Increasingly 

stringent environmental controls favor the chloride process 

because it creates fewer waste byproducts (Christie and 

Brathwaite, 1998, p. 8); the sulfate process generates large 

volumes of ferrous sulfate.

Mining beach sand for ilmenite generally presents few 

environmental hazards. However, some heavy-mineral sands 

have substantial quantities of the mineral monazite, which 

contains radioactive thorium (Australian Uranium Association, 

2009). Monazite’s radioactivity is low enough to not pose a 

health hazard unless the monazite itself is concentrated. Mitigating dust produced during processing of monazite sand reduces 

the potential hazard from inhaling thorium in dust form (Australian Uranium Association, 2009). However, disposal of wastes 

from pigment-producing processes that use ilmenite does cause 

concern (Garnar and Stanaway, 1994).

Titanium sponge (Ti), so called because of its appearance and high porosity, is the commercially pure, basic 

form of titanium metal. It is obtained by the Kroll process, 

in which rutile and rutile substitutes are treated with chlorine to form a volatile liquid (TiCl4

, titanium tetrachloride), 

and the liquid is reduced with liquid magnesium in an 

argon or helium atmosphere that yields the titanium sponge 

(Christie and Brathwaite, 1998). Nitric acid or hydrochloric 

acid is used to leach the sponge, whereas vacuum distillation separates the sponge. After drying, crushing, and 

screening, the sponge is processed into ingots or crushed to 

create titanium powder.

Titanium is not presently mined in Colorado (John Keller, 

Colorado Geological Survey, oral commun., 2006).

Zeolite

The word zeolite comes from the Greek zein, to boil, 

and lithos, stone, because the crystals bubble and froth when 

they are heated with a blowpipe (Holmes, 1994). Zeolites are 

associated with volcanic rocks and tuffaceous sedimentary 

rocks derived from volcanism. They are a group of natural or 

synthetic hydrated aluminosilicates of the alkaline and alkaline 

earth elements (Virta, 2003). Zeolites are sometimes called 

molecular sieves (fig. 60) because channels in their molecular 

structure allow them to absorb many cations or small molecules. 

Zeolites are used to remove harmful atmospheric and aqueous pollutants, as catalysts in many chemical processes (thus 

making reactions more energy efficient), in ion exchange (water 

softening and purification), and in reversible dehydration.

Zeolitic tuff has been used as a sculpturing stone and 

dimension stone for nearly 3,000 years (Christie and others, 

2002). More than 70 percent of domestic natural zeolite is used 

for pet litter, animal feed, water purification, and horticultural 

applications (Virta, 2003). Zeolites are also used as a substitute 

for dimension stone, in lightweight aggregates, pozzolanic 

cement, and soil conditioners. Synthetic zeolites, which can be 

manufactured to a specific size of molecular channel, are used 

as catalysts, detergents, and molecular sieves (Virta, 2003). 

Environmental applications include treatment of water and sewage, adsorption and removal of pollutants, such as heavy metals, 

and purification of air and gas (Christie and others, 2002).

Geology of Colorado Zeolite Deposits

In basaltic to andesitic rocks, zeolites commonly 

occur as euhedral crystals filling open spaces. These crystals are sought by mineral collectors but have limited value 

as commercial industrial minerals. Volcanic rocks capping North and South Table Mountain near Golden, Colo., 

are widely known for museum-quality zeolite specimens. 

Commercial volumes of zeolites occur in bedded tuffs. 

These zeolites form by the reaction of pore water with 

Figure 60. Euhedral crystals and intercrystal porosity in zeolite 

from a clinoptilolite-rich tuff, as seen in a scanning electron 

micrograph. Photograph courtesy of Richard Shepard. Euhedral 

is “said of a mineral grain that is completely bounded by its 

own rational faces, and whose growth during crystallization or 

recrystallization was not restrained or interfered with by adjacent 

grains” (Bates and Jackson, 1987, p. 224).
78 Development of Industrial Minerals in Colorado

volcanic glass, poorly crystalline clay minerals, plagioclase, and silica. The specific zeolite minerals that form 

depend on the composition of the tuffs and on their temperature, pressure, partial pressure of pore water, and pH. 

With age, the first-formed zeolites are commonly replaced 

by different zeolite minerals such that older zeolite deposits are much less mineralogically diverse than younger 

ones (Harben and Kuzvart, 1997).

In Colorado, zeolites have been described in the oil 

shale and tuffaceous facies of the Green River Formation (Eocene), in tuffaceous mudstone in the Brushy Basin 

Member of the Morrison Formation (Jurassic), in a tuff in the 

Windy Gulch Member of the Bachelor Mountain Rhyolite 

(Oligocene), and in tuffaceous rocks of the Bridger Formation (Eocene) and Creede Formation (Oligocene) (Olson, 

1983; Larsen and Crossey, 1995). Because a large volume of 

volcanic rocks erupted during the Tertiary in Colorado, other 

zeolite-bearing tuffs no doubt exist.

Mining and Production

Zeolite deposits are mined by conventional open pit 

mining methods and, if necessary, by blasting (fig. 61). 

Selective mining and blending may be used to produce 

high-value zeolites (Holmes, 1994). Excavated material 

is transported to a processing plant where it is crushed, 

screened, and milled for low-value products such as pet 

litter. The ore may be further processed by grinding and air 

separation to recover a particular particle size for industrial applications (Virta, 2003). In some cases, acid or salt 

washes are used to improve the quality of the zeolite.

Zeolite is not presently mined in Colorado (John Keller, 

Colorado Geological Survey, oral commun., 2006).

References Cited

Adams, G.C., 1993, Gypsum and anhydrite in Nova Scotia: 

Nova Scotia Department of Natural Resources Information Circular ME16. Accessed December 29, 2004, at URL 

http://www.gov.ns.ca/natr/meb/pdf/ic16.asp

Agricola, Georgius, 1556, De re metallica: Accessed December 21, 2009 at URL http://www.mining-heritage.com

Alpers, C.N., Blowes., D.W., Nordstrom, D.K., and Jambor, J.L., 1994, Secondary minerals and acid mine-water 

chemistry, in Jambor, J.L., and Blowes, D.W., eds., Short 

course handbook on environmental geochemistry of sulfide 

mine-wastes: Waterloo, Ontario, Mineralogical Association 

of Canada, v. 22, p. 247–270.

Anderson, Bob, Berry, David, and Shields, Deborah, 2002, 

Sustainable development and its influence on mining operations on Federal lands—A conversation in plain language: 

Washington, D.C., U.S. Government Printing Office, 

Bureau of Land Management Information pamphlet BLM–

WO–GI–02–008+3000, 4 p.

Anglin, M.K., 2002, Women, power, and dissent in the hills of 

Carolina: Chicago, University of Illinois Press, 216 p.

Arbogast, Belinda, 2002, An overview of reclamation law 

dealing with mineral resource development in the USA, in 

Scott, P.W., and Bristow, C.M., eds., Industrial minerals and 

extractive industry geology: Geological Society [London], 

p. 283–293.

Arbogast, B.F., Knepper, D.H., Jr., and Langer, W.H., 2000, 

The human factor in mining reclamation: U.S. Geological 

Survey Circular 1191, 28 p.

Arkansas Geological Survey, 2009, Industrial minerals. 

Accessed December 21, 2009, at URL http://www.geology.

ar.gov/minerals/industrial.htm

Armbrustmacher, T.J., 1988, Geology and resources of thorium and associated elements in the Wet Mountain area, 

Fremont and Custer Counties, Colorado: U.S. Geological 

Survey Professional Paper 1049–F, 34 p.

Arthur, L.M., Daniel, T.C., and Boster, R.S., 1977, Scenic assessment—An overview: Landscape Planning, v. 4, p. 109–129.

Austin, Gordon, 1995, An overview of production of specific 

U.S. gemstones: U.S. Bureau of Mines Special Publication 

14–95, Washington, D.C., U.S. Government Printing Office, 

41 p. Accessed June 22, 2005, at URL http://minerals.

er.usgs.gov/minerals/pubs/commodity/gemstones/sp14-95/

Australian Uranium Association, 2009, Radiation control in 

the mining and mineral processing industry: Australian 

Uranium Association Radiation Workers’ Handbook, 50 p. 

Accessed September 28, 2010, at URL http://www.aua.org.

au/DisplayFile.Aspx?FileID=46

Figure 61. Small zeolite production pit in the Sucker Creek

Formation, near Sheaville, Oregon, date unknown. Photograph 

by Richard Shepard.
References Cited 79

Baldwin, Jonathan, Fisher, Peter, Wood, Joseph, and Langford, 

Mitchell, 1996, Modeling environmental cognition of the 

view with GIS, in International Conference and Workshop 

on Integrating GIS and Environmental Modeling, 3d, Santa 

Fe, New Mexico, National Center for Geographic Information and Analysis, CD-ROM.

Bancroft, Peter, 2000, UCSB geology—The Bancroft collection: 

Santa Barbara, University of California, Santa Barbara. Accessed 

September 3, 2010, at URL http://bancroft.geol.ucsb.edu/

Banks, K.M., 1999, Indians, reclamation, and historic preservation [abs.]: Plains Anthropologist, v. 44, no. 170, p. 5–12.

Barker, J.M., and Austin, G.S., 1994, Construction materials—

Decorative stone, in Carr, D.D., ed., Industrial minerals and 

rocks (6th ed.): Littleton, Colorado, Society for Mining, 

Metallurgy, and Exploration, p. 367–378.

Bastian, C.T., McLeod, D.M., Germino, M.J., Reiners, W.A., 

and Blasko, B.J., 2002, Environmental amenities and agricultural land values—A hedonic model using geographic 

information systems data: Ecological Economics, v. 40, 

no. 3, p. 337–349.

Bates, R.L., 1969, Geology of the industrial rocks and minerals: New York, Dover Publications, 459 p.

Bates, R.L., and Jackson, J.A., 1987, Glossary of geology (3d ed.): 

Alexandria, Virginia, American Geological Institute, 788 p.

Belnap, Jayne, 2003, The world at your feet—Desert biological soil crusts: Frontiers in Ecology and the Environment,

v. 1, no. 5, p. 181–189.

Bennett, J.W., 1993, Human ecology as human behavior: New 

Brunswick, New Jersey, Transaction Publishers, 357 p.

Berlin, George, 1964, Limestone for sugar refining, in Mineral 

and water resources of Colorado. Report of the United 

States Geological Survey in collaboration with the Colorado 

Mining Industrial Development Board: Washington, D.C., 

U.S. Government Printing Office, p. 202–203.

Bingham, Nancy, 2000, Mining’s image—What does the public 

really think?: Mining Engineering, v. 46, no. 3, p. 200–203.

Bolen, W.P., 2004a, Sand and gravel (construction), in U.S. Geological Survey mineral commodity summaries 2004: Washington, D.C., U.S. Government Printing Office, p. 140–141.

Bolen, W.P., 2004b, Perlite, U.S. Geological Survey mineral 

commodity summaries 2004: Washington, D.C., U.S. Government Printing Office, p. 120–121.

Boulder County Land Use Department, 2008, 2d ed., Boulder 

County comprehensive plan “Goals, Policies, and Maps element”: Land Use Department Publication, 137 p.

Breese, R.O.Y., and Barker, J.M., 1994, Perlite, in Carr, 

D.D., ed., Industrial minerals and rocks (6th ed.): Littleton, Colo., Society for Mining, Metallurgy, and Exploration, p. 735–749.

Brobst, D.A., 1994, Barium minerals, in Carr, D.D., ed., Industrial minerals and rocks (6th ed.): Littleton, Colo., Society 

for Mining, Metallurgy, and Exploration, Inc., p. 125–134.

Brown, W.H., 1989, When worlds collide—The gravel 

pit evaporation conflict: The Colorado Lawyer, Feb., 

p. 237–239.

Buchanan, B.J., ed., 2006, Gunpowder, explosives, and the 

state—A technological history: Burlington, Vermont, Ashgate Publishing Co., 425 p.

Bugosh, Nicholas, 2002, Slope and channel reclamation 

using fluvial geomorphic principles at San Juan Coal Company mines in New Mexico, [abs.], in Approaching bond 

release—Post-mining land use in the arid and semi-arid 

West: Bismarck, North Dakota, Office of Surface Mining, 

North Dakota State University, and North Dakota Public 

Service Commission, August 25–30, 2002, not paginated.

Bush, A.L., 1976, Vermiculite in the United States, in Proceedings of the Eleventh Forum on the Geology of Industrial Minerals, June 18–20, 1975, Kalispell, Montana: Montana Bureau 

of Mines and Geology Special Publication 74, p. 145–155.

Buttleman, C.G., 1992, A handbook for reclaiming sand and 

gravel pits in Minnesota: St. Paul, Minnesota Department of 

Natural Resources Division of Minerals, 65 p.

Buyhoff, G.J., Miller, P.A., Roach, J.W., Zhou, D., and Fuller, 

L.G., 1994, An A1 methodology for landscape visual assessment: A1 Applications, v. 8, no. 1, p. 1–13.

Cappa, J.A., Widmann, Beth, Carroll, C.J., Keller, J.S., and 

Young, Genevieve, 2003, Colorado mineral and mineral 

fuel activity 2003: Colorado Geological Survey Information 

Series 69, 56 p. Accessed September 8, 2010, at URL http://

www.geosurvey.state.co.us/pubs/mr/MMF-IS-69.pdf

Cappa, J.A., Young, Genevieve, Keller, J.W., Carroll, C.J., and 

Widmann, Beth, 2004, Colorado mineral and mineral fuel 

activity: Colorado Geological Survey Information Series 

70, 45 p. Accessed September 8, 2010, at URL http://www.

geosurvey.state.co.us/portals/0/MMF_2004_small.pdf

Carlson, Allen, 2001, On aesthetically appreciating human environments: Philosophy and Geography, v. 4, no. 1, p. 9–24.

Carr, D.D., Rooney, L.F., and Freas, R.C., 1994, Limestone 

and dolomite, in Carr, D.D., ed., Industrial minerals and 

rocks (6th ed.): Littleton, Colorado, Society for Mining, 

Metallurgy, and Exploration, p. 605–629.

Carter, D.A., 1964, Metallurgical limestone, in Mineral and 

water resources of Colorado—Report of the United States 

Geological Survey in collaboration with the Colorado Mining Industrial Development Board: Washington, D.C., U.S. 

Government Printing Office, p. 203–205.
80 Development of Industrial Minerals in Colorado

Carter, W.D., 1964, Sand and gravel, in Mineral and water 

resources of Colorado―Report of the United States Geological Survey in collaboration with the Colorado Mining 

Industrial Development Board: Washington, D.C., U.S. 

Government Printing Office, p. 205–211.

Chadwick, John, 2004, Supplying sustainability: Mining Environmental Manager, November, p. 2.

Christie, Tony, and Brathwaite, Bob, 1998, Mineral commodity report 16—Titanium: New Zealand Mining, 

v. 23, 11 p. Accessed August 11, 2010, at URL http://

www.crownminerals.govt.nz/cms/pdf-library/minerals/

minerals-overview-pdfs-1/report16_titanium.pdf/view

Christie, Tony, Brathwaite, Bob, and Thompson, Bruce, 2002, 

Mineral commodity report 23—Zeolites: New Zealand 

Mining, v. 31, p. 16–24. Accessed August 11, 2010, at URL 

http://www.crownminerals.govt.nz/cms/pdf-library/minerals/

minerals-overview-pdfs-1/report23-zeolite.pdf/view

Christie, Tony, Thompson, Bruce, and Brathwaite, Bob, 

2001a, Mineral commodity report 22—Aggregate: New 

Zealand Mining, p. 6–26. Accessed August 11, 2010, at 

URL http://www.crownminerals.govt.nz/cms/pdf-library/

minerals/minerals-overview-pdfs-1/report22_aggregate.pdf

Christie, Tony, Thompson, Bruce, and Brathwaite, Bob, 

2001b, Mineral commodity report 20—Clays: Ministry of Economic Development, 18 p. Accessed August 

11, 2010, at URL http://www.crownminerals.govt.nz/

cms/pdf-library/minerals/minerals-overview-pdfs-1/

report20_clays.pdf/view

Colorado Department of Local Affairs Division of Local Government, 2010, Preliminary population forecasts by region, 

2000–2035: State Demography Office. Accessed September 10, 2010, at URL http://dola.colorado.gov/dlg/demog/

pop_colo_forecasts.html

Colorado Department of Natural Resources Division of Minerals and Geology, 1998, In-stream aggregate extraction and 

reclamation guidance document: 46 p. and 6 appendixes.

Colorado Department of Natural Resources Division of 

Wildlife, 2003, Species conservation. Accessed September 

10, 2010, at URL http://wildlife.state.co.us/WildlifeSpecies/

SpeciesOfConcern

Colorado Geological Survey, 1999, Colorado diamonds: Colorado Geological Survey RockTalk, v. 2, no. 3, 12 p.

Colorado Geological Survey, 2004a, Definitions and characteristics—Subsidence. Accessed September 10, 2010, at URL 

http://geosurvey.state.co.us/Default.aspx?tabid=358

Colorado Geological Survey, 2004b, Home page. Accessed 

September 10, 2010, at URL http://geosurvey.state.co.us

Colorado Historical Society Office of Archaeology and 

Historic Preservation, 2001, Colorado preservation 2005—

Enriching our future by preserving our past. Statewide 

historic preservation plan: Denver, Colorado Historical 

Society, 61 p. Accessed September 10, 2010, at URL http://

coloradohistroy-oahp.org/publications/pubs/1508.pdf

Colorado Historical Society Office of Archaeology and 

Historic Preservation, 2003, Directory of mining-related 

properties in the Colorado State register of historic properties (2d ed.): Denver, Colorado Historical Society, 28 p.

Colorado Mining Association, 2008, Mining—Colorado’s 

first industry: Accessed September 10, 2010, at URL 

http://www.coloradomining.org/Content/Body_Pdf/CMA_

Brochure_6-09_small.pdf

Colton, R.B., and Fitch, H.R., 1974, Map showing potential sources of gravel and crushed-rock aggregate in the 

Boulder–Fort Collins–Greeley area, Front Range urban 

corridor, Colorado: U.S. Geological Survey Miscellaneous 

Investigations Map I–855–D, scale 1:100,000.

Coopersmith, H.G., and Schulze, D.J., 1996, Development and 

geology of the Kelsey Lake diamond mine, Colorado, in

Thompson, T.B., ed., Diamonds to gold: Society of Economic Geologists Guidebook 26, p. 5–19.

Courtney, Ann, 2001, Accelerated recovery—Bioremediation 

of the visual impact of limestone quarry scarps: Quarry 

Management, v. 28, no. 12, p. 47–48.

Daly, H.E., and Farley, Joshua, 2004, Ecological economics: 

Washington, D.C., Island Press, 454 p.

Daniel, T.C., and Vining, J., 1983, Methodological issues 

in the assessment of landscape quality, in Altman, I., and 

Wohwill, J., eds., Behavior and the natural environment: 

New York, Plenum Press, chap. 2, p. 39–83.

Daniels, Tom, 1999, When city and county collide—Managing 

growth in the metropolitan fringe: Washington, D.C., Island 

Press, 363 p.

Darmer, Gerhard, 1990, Landscape and surface mining— Ecological guidelines for reclamation. v. 1, Dietrich, N.L., 

ed., Berlin, Patzer Verlaz Gmblt U. Co., variously paged. 

[translated into English]

Denver Mineral Engineers, Inc., The basic processes of 

gold recovery: Sterling, Colo., Denver Mineral Engineers. Accessed September 10, 2010, at URL http://www.

denvermineral.com/basicp~1.html

Dolley, T.P., 2004, Stone (dimension), in U.S. Geological 

Survey mineral commodity summaries 2004: Washington, 

D.C., U.S. Government Printing Office, p. 158–159.

Dorr, Ann, and Paty, A.H., 2002, Minerals—Foundations of 

society (3d ed.): Alexandria, Virginia, American Geological 

Institute, 96 p.
References Cited 81

Dumont, Michel, 2004, Clays: Natural Resources Canada 

Mineral and Metal Commodity Reviews, Ottawa, Ontario, 

Natural Resources Canada, 13 p. Accessed September 11, 

2010, at URL http://www.nrcan.gc.ca/mms-smm/busi-indu/

cmy-amc/content/2004/clays.pdf

DuPont, 2004, DuPont titanium technologies. Accessed September 10, 2010, at URL http://www.titanium.dupont.com/

NASApp/TTPORTAL/Meidator?action=261&reference

Dyni, J.R., 1996, Sodium carbonate resources of the Green 

River Formation: U.S. Geological Survey Open-File Report 

OFR 96–729, 39 p.

Eckel, E.B., 1961, Minerals of Colorado—A 100-year record: 

U.S. Geological Survey Bulletin 1114, 399 p.

Eckel, E.B., 1997, Minerals of Colorado (4th ed.): Golden, 

Colorado, Fulcrum Publishing, 665 p.

Elzea, Jessica, and Murray, H.H., 1994, Bentonite, in Carr, 

D.D., ed., Industrial minerals and rocks (6th ed.): Littleton, 

Colorado, Society for Mining, Metallurgy, and Exploration, 

p. 233–246.

Encyclopedia Britannica, 2004a, Fluorspar, in Encyclopedia 

Britannica Premium Service. Accessed September 10, 2010, 

at URL http://www.britannica.com

Encyclopedia Britannica, 2004b, Titanium, Encyclopedia 

Britannica Premium Service. Accessed September 10, 2010, 

at URL http://www.britannica.com

English Nature, Quarry Products Association, and Silica and 

Moulding Sands Association, 1999, Biodiversity and minerals—Extracting the benefits for wildlife: Newcastle upon 

Tyne, United Kingdom, Entec UK Ltd., 13 p.

Environment Australia, 2002, Overview of best practice environmental management in mining. Accessed September 13, 

2010, at URL http://www.ret.gov.au/resources/Documents/

LPSDP/BPEMOverview.pdf

Environmental Mining Council of British Columbia, 2004, A 

mineral-efficient future. Accessed September 13, 2010, at 

URL http://www.miningwatch.ca/en/mineral-efficient-future

Foley, Nora, 1999, Environmental characteristics of clays and 

clay mineral deposits. Accessed September 13, 2010, at 

URL http://pubs.usgs.gov/info/clays/

Fong, Tillie, 2005, Aurora OKs water-storage deal: Rocky 

Mountain News, March 22, p. 6A

Fulton, R.B., and Montgomery, Gill, 1994, Fluorspar, in Carr, D.D., 

Industrial minerals and rocks (6th ed.): Littleton, Colorado, Society for Mining, Metallurgy, and Exploration, p. 509–522.

Gambogi, Joseph, 2005, Titanium and titanium dioxide, p. 

178–179. Accessed September 13, 2010, at URL http://

minerals.usgs.gov/minerals/pubs/commodity/titanium/

tidiomcs05.pdf

Garnar, T.E., and Stanaway, K.J., 1994, Titanium minerals, 

in Carr, D.D., ed., Industrial minerals and rocks (6th ed.): 

Littleton, Colorado, Society for Mining, Metallurgy, and 

Exploration, p. 1071–1089.

Goldman, H.B., 1994, Sand and gravel, in Carr, D.D., ed., Industrial minerals and rocks (6th ed.): Littleton, Colorado, Society 

for Mining, Metallurgy, and Exploration, Inc., p. 869–877.

Gratzfeld, Joachim, ed., 2003, Extractive industries in arid and 

semi-arid zones: Gland, Switzerland, The World Conservation Union, 111 p.

Hammarstrom, J.M., and Smith, K.S., 2002, Geochemical and 

mineralogic characterization of solids and their effects on 

waters in metal-mining environments, in Seal II, R.R., and 

Foley, N.K., eds., Progress on geoenviromental models for 

selected mineral deposits types: U.S. Geological Survey 

Open-File Report 02–195, Online version 1.0, Chapter B, 

47 p. Accessed January 19, 2005, at URL http://pubs.usgs.

gov/of/2002/of02-195

Harben, P.W., and Kuzvart, Milos, 1997, Zeolite, in Industrial 

minerals—A global geology: Worcester Park, Surrey, U.K., 

Industrial Minerals Information, Ltd., p. 445–450.

Hedrick, J.B., 2004, Mica, in U.S. Geological Survey mineral 

commodity summaries 2004: Washington, D.C., U.S. Government Printing Office, p. 108–111.

Herrick, D.H., 1994, Stone, crushed, in Carr, D.D. Industrial 

minerals and rocks (6th ed.): Littleton, Colorado, Society 

for Mining, Metallurgy, and Exploration, p. 975–986.

Hindman, J.R., 1994, Vermiculite, in Carr, D.D., Industrial 

minerals and rocks (6th ed.): Littleton, Colorado, Society 

for Mining, Metallurgy, and Exploration, p. 1103–1111.

Holmes, D.A., 1994, Zeolites, in Carr, D.D., Industrial minerals and rocks (6th ed.): Littleton, Colorado, Society for 

Mining, Metallurgy, and Exploration, p. 1129–1158.

Hosterman, J.W., and Orris, G.J., 1998a, Preliminary descriptive model of hydrothermal bentonite, in Orris, G.J., ed., 

Additional descriptive models of industrial mineral deposits: 

U.S. Geological Survey Open-File Report 98–505, p. 18–20.

Hosterman, J.W., and Orris, G.J., 1998b, Preliminary descriptive model of hydrothermal kaolin, in Orris, G.J., ed., Additional descriptive models of industrial mineral deposits: U.S. 

Geological Survey Open-File Report 98–505, p. 21–23.

Industrial Minerals Association North America, 2004, About 

industrial minerals. Accessed October 26, 2004, at URL 

http://www.ima-na.org/

Jefferson County, Colorado Planning and Zoning, 1977, Mineral extraction policy plan, 44 p. Accessed September 13, 

2010, at URL http://www.co.jefferson.co.us/jeffco/planning_

uploads/plans/mineral_extraction_policy.pdf
82 Development of Industrial Minerals in Colorado

Jellicoe, Geoffrey, and Jellicoe, Susan, 1987, The landscape of man—Shaping the environment from prehistory 

to the present day: London, Thames and Hudson Ltd., 

400 p.

Kasprzak, Rick, 2000, Artificial reef program: Louisiana 

Department of Wildlife and Fisheries. Accessed September 

16, 2010, at URL http://www.wlf.louisiana.gov/fishing/

programs/habitat/artificialreef.cfm

Keller, J.W., and Widmann, B.L., 2002, Industrial minerals—

What are they, where are they, and what good are they?: 

Colorado Geological Survey RockTalk, v. 5, no. 3, 12 p. 

Accessed September 16, 2010, at URL http://geosurvey.

state.co.us/pubs/rocktalk/rtv5n3.pdf

Kellert, S.R., and Wilson, E.O., eds., 1993, The biophilia 

hypothesis: Washington, D.C., Island Press, 484 p.

Ketner, K.B., 1973, Silica sand, in Brobst, D.A., and Pratt, 

W.P., eds., United States mineral resources: U.S. Geological 

Survey Professional Paper 820, p. 577–580.

King, T.V.V., ed., 1995, Environmental considerations of 

active and abandoned mine lands—Lessons learned from 

Summitville, Colorado: U.S. Geological Survey Bulletin 

2220, 38 p.

Knepper, D.H., Jr., ed., 2002, Planning for the conservation and development of infrastructure resources in urban 

areas—Colorado Front Range urban corridor: U.S. Geological Survey Circular 1219, 27 p.

Kostick, D.S., 1994, Soda ash, in Carr, D.D., ed., Industrial 

minerals and rocks (6th ed.): Littleton, Colorado, Society 

for Mining, Metallurgy, and Exploration, p. 929–958.

Kostick, D.S., 2004, Soda ash, in Mineral commodity summaries 2004: Washington, D.C., U.S. Government Printing 

Office, U.S. Geological Survey, p. 152. Accessed September 

16, 2010, at URL http://minerals.usgs.gov/minerals/pubs/

commodity/soda_ash/

Krönert, Rudolf, Volk, Martin, and Steinhardt, Uta, 2001, 

Introduction—Landscape balance and landscape assessment, in Krönert, Rudolf, Steinhardt, Uta, and Volk, Martin, 

eds., Landscape balance and landscape assessment: Berlin, 

Springer, p. 1–22.

Kuzvart, Milos, 2003, Industrial minerals support economic 

geology in a globalized world: Society for Geology 

Applied to Mineral Deposits, 13 p. Accessed September 

16, 2010, at URL http://www.e-sga.org/fileadmin/sga/

newsletter/news12/art1.html

Landscape Institute and Institute of Environmental Management 

and Assessment, 2002, Guidelines for landscape and visual 

impact assessment (2d ed.): London, Spon Press, 166 p.

Lafarge North America, 2005, Reclaiming land and 

ancestry. Accessed November 18, 2010, at URL http://

www.lafargenorthamerica.com/wps/portal/!ut/p/

kcxml/04_Sj9SPykssy0xPLMnMz0vM0Y_QjzKLN4

r3MgXJgFjGQBayiEG8I1zA1yM_N1U_SN9bP0C_

IDc0otzRUREAM6pfXA!!/delta/base64xml/L3d

JdyEvd0ZNQUFzQUMvNElVRS82XzJfU0M!?

WCM_GLOBAL_CONTEXT=/wps/wcm/connect/LNA/

Library/Case+Studies/Environment/Case_Study_

Lafarge+Land+Donation

Langer, W.H., and Glanzman, V.M., 1993, Natural aggregate—Building America's future: U.S. Geological Survey 

Circular 1110, 39 p.

Larsen, Daniel, and Crossey, L.J., 1995, Depositional environments and authigenic mineral distributions in the Oligocene 

Creede Formation, Colorado, USA, in Bethke, P.M., ed., 

Preliminary scientific results of the Creede caldera continental scientific drilling program: U.S. Geological Survey 

Open-File Report 94–260E, 76p.

Lin, Hui, Gong, Jianhua, Tsou, Jinyeu, Zhao, Yibin, Zhang, 

Zongyu, and Zhan, F.B., 2002, VGE—A new communication platform for general public, in International 

Conference on Web Information Systems Engineering, 

3d, Singapore. Accessed September 16, 2010, at URL 

http://www.computer.org/portal/web/csdl/doi/10.1109/

WISEW.2002.1177846

Lindsey, D.A., Langer, W.H., and Knepper, D.H., Jr., 2005, 

Stratigraphy, lithology, and sedimentary features of Quaternary alluvial deposits of the South Platte River and some 

of its tributaries east of the Front Range: U.S. Geological 

Survey Professional Paper 1705, 70 p.

Lindvall, R.M., 1964, Stone, in Mineral and water resources of 

Colorado: Report of the United States Geological Survey in 

collaboration with the Colorado Mining Industrial Development Board: Washington, D.C., U.S. Government Printing 

Office, p. 211–215.

Lovering, T.S., and Goddard, E.N., 1950, Geology and ore 

deposits of the Front Range, Colorado: U.S. Geological 

Survey Professional Paper 223, 319 p.

Lovering, T.S., and Mallory, W.W., 1962, The Eagle Valley Evaporite and its relation to the Minturn and Maroon 

Formations, northwest Colorado: U.S. Geological Survey 

Professional Paper 450–D, p. D45–D48.

Macaulay Land Use Research Institute, 2005, Review of 

existing methods of landscape assessment and evaluation. Accessed September 16, 2010, at URL http://www.

macaulay.ac.uk/ccw/task-two/evaluate.html

Magill, A.W., 1992, Managed and natural landscape—What 

do people like?: Albany, Calif., Pacific Southwest Research 

Station, 28 p.
References Cited 83

Makhzoumi, J.M., 2002, Landscape in the Middle East—An 

inquiry: Landscape Research, v. 27, no. 3, p. 213–228.

Mallory, W.W., 1971, The Eagle Valley Evaporite, northwest 

Colorado—A regional synthesis: U.S. Geological Survey 

Bulletin 1311–E, 37 p.

McCarl, H.N., 1994, Aggregates—Markets and uses, in Carr, 

D.D., ed., Industrial minerals and rocks (6th ed.): Littleton, 

Colorado, Society for Mining, Metallurgy, and Exploration, 

Inc., p. 286–294.

Meitner, M.J., and Daniel, T.C., 1997, Vista scenic beauty 

estimation modeling—A GIS approach, in ESRI International User Conference, San Diego, July 1997, Proceedings. Accessed September 17, 2010, at URL http://training.

esri.com/campus/library/Bibliography/RecordDetail.

cfm?ID=4631

Meredith, T.C., 2004, Community participation in environmental information management—Exploring tools for developing an impact assessment preparedness program: Canadian 

Environmental Assessment Agency Research and Development Monograph Series 2000, Catalog no. En105–3/81–

2004E. Accessed September 17, 2010, at URL http://www.

ceaa-acee.gc.ca/default.asp?lang=En&n=5EC2AF64-1

Merriam-Webster, 2009, Merriam-Webster OnLine. Accessed 

September 17, 2010, at URL http://www.merriam-webster.

com/dictionary

Miller, M.M., 2001, Fluorspar, 11 p. Accessed September 

17, 2010, at URL http://minerals.usgs.gov/minerals/pubs/

commodity/fluorspar/280401.pdf

Miller, M.M., 2004a, Lime, in U.S. Geological Survey mineral 

commodity summaries 2004: Washington, D.C., U.S. Government Printing Office, p. 96–97.

Miller, M.M., 2004b, Fluorspar, in U.S. Geological Survey 

Mineral commodity summaries 2004: Washington, D.C., 

U.S. Government Printing Office, p. 62–63.

Mineral Information Institute, 2004, Everything we have 

and everything we use comes from our natural resources. 

Accessed September 17, 2010, at URL http://www.mii.org

Moss, Elaine, ed., 1977, Land use control in the United 

States—A handbook on the legal rights of citizens (National 

Resources Defense Council): New York, Dial Press, 362 p.

Murphy, J.A., 1995, Geology tour of Denver’s buildings and 

monuments: Denver, Historic Denver, Inc., 96 p.

Murphy, J.A., and Modreski, P.J., 2002, A tour of Colorado gemstone localities: Rocks & Minerals, v. 77, no. 4, p. 218–238.

National Academy of Sciences, 1974, Rehabilitation potential 

of western coal lands: Cambridge, Mass., Ballinger Publishing Co., 198 p.

National Academy of Sciences, 1999, Hardrock mining on 

Federal lands: Washington, D.C., National Academy Press, 

260 p. Accessed September 17, 2010, at URL http://www.

nap.edu/catalog.php?record_id=9682

National Industrial Sand Association, 1997, Crystalline silica 

respiratory health effects. Accessed September 17, 2010, at 

URL http://www.riccisand.com/pages/health1.html

National Stone Association, 1995, Environmental management guide: Washington, D.C., National Stone Association, 

variously paged.

Nichols, J.C., 1999, Minerals and geology: U.S. Department 

of Agriculture Forest Service. Accessed September 17, 

2010, at URL http://www.fs.fed.us/r8/ouachita/naturalresources/minerals/index.shtml

Noel, T.J., Mahoney, P.F., and Stevens, R.E., 1994, Historical 

atlas of Colorado: Norman, University of Oklahoma Press, 

variously paged.

Norman, D.K., and Lingley, W.S., Jr., 1992, Reclamation of sand 

and gravel pits: Washington Geology, v. 20, no. 3, p. 20–31.

Norman, D.K., Wampler, P.J., Throop, A.H., Schnitzer, E.F., 

and Roloff, J.M., 1997, Best management practices for 

reclaiming surface mines in Washington and Oregon: 

Washington Department of Natural Resources Division of 

Geology and Earth Sciences Open File Report 96–2, 128 p.

Northrop, H.R., and Whitney, Gene, 1987, Clays and associated minerals in the Alum Mountain fossil geothermal 

system near Gila Hot Springs, Grant County, New Mexico, 

in Mumpton, F.A., ed., Zeo-Trip ’87—An excursion to 

selected zeolite and clay deposits in southwestern New 

Mexico and eastern Arizona: Brockport, New York, International Committee on Natural Zeolites, p. 1–12.

Ober, J.A., 2002, Materials flow of sulfur: U.S. Geological Survey Open-File Report 02–298, version 1.0, 56 p. 

Accessed September 20, 2010, at URL http://pubs.usgs.gov/

of/2002/of02-298/of02-298.pdf

Ober, J.A., 2004, Sulfur, in U.S. Geological Survey mineral 

commodity summaries 2004: Washington, D.C., U.S. Government Printing Office, p. 162–163.

Olsen, J.C., Marvin, R.F., Parker, R.L., and Mehnert, H.H., 

1977, Age and tectonic setting of lower Paleozoic alkalic and mafic rocks, carbonatites, and thorium veins in 

south-central Colorado: U.S. Geological Survey Journal of 

Research, v. 5, no. 6, p. 673–687.

Olson, D.W., 2004a, Gypsum, in U.S. Geological Survey mineral commodity summaries 2004: Washington, D.C., U.S. 

Government Printing Office, p. 76–77.

Olson, D.W., 2004b, Diamond (industrial), in U.S. Geological 

Survey mineral commodity summaries 2004: Washington, 

D.C., U.S. Government Printing Office, p. 56–57.
84 Development of Industrial Minerals in Colorado

Olson, R.H., 1983, Zeolites, in Lefond, S.J., ed., Industrial 

minerals and rocks (5th ed.): New York, Society of Mining 

Engineers, v. 2, p. 1391–1399.

Organization for Economic Co-operation and Development, 2001, 

Significant environmental achievements in the 1990s, says 

OECD: Science of the Total Environment, v. 278, p. 265–266.

Panagapko, Doug, 2003, Stone, in Canadian minerals yearbook: 

Ottowa, Ontario, Natural Resources Canada, 17 p. Accessed 

September 20, 2010, at URL http://www.nrcan-rncan.gc.ca/

mms-smm/busi-indu/cmy-amc/content/2003/56.pdf

Patterson, S.H., 1964, Clays, in Mineral and water resources 

of Colorado—Report of the United States Geological 

Survey in collaboration with the Colorado Mining Industrial 

Development Board: Washington, D.C., U.S. Government 

Printing Office, p. 183–190.

Pavement Interactive, 2008, Superpave mix design: Accessed 

September 10, 2010, at URL http://pavementinteractive.org/

index/php?tot;e=Superpave_Mix_Design

Pearl, R.M., 1972, Colorado gem trails and mineral guide (3d 

ed.): Athens, Ohio, Ohio University Press and Swallow 

Press, 222 p.

Perry, Edward, 2004, EMS for integrated business risk management: Mining Engineering Management, November, 

p. 17–19.

Peters, W.C., 1978, Exploration and mining geology (2d ed.): 

New York, John Wiley, 685 p.

Petts, G.E., and Amoros, C., eds., 1996, Fluvial hydrosystems: 

London, Chapman and Hall, 322 p.

Pickering, S.M., Jr., and Murray, H.H., 1994, Kaolin, in Carr, 

D.D., ed., Industrial minerals and rocks (6th ed.): Littleton, 

Colorado, Society for Mining, Metallurgy, and Exploration, 

p. 255–278.

Porteous, J.D., 1996, Environmental aesthetics—Ideas, politics and planning: London, Routledge, 290 p.

Potter, M.J., 2005, Feldspar, in U.S. Geological Survey mineral commodity summaries 2005: Washington, D.C., U.S. 

Government Printing Office, p. 60–61.

Power, W.R., 1994, Stone, dimension, in Carr, D.D., ed., 

Industrial minerals and rocks (6th ed.): Littleton, Colorado, Society for Mining, Metallurgy, and Exploration, 

p. 987–1001.

Prasciunas, M.M., 2003, Archeological testing at the Black 

Dumps site, Chaffee County, Colorado: University of 

Wyoming George C. Frison Institute of Archaeology and 

Anthropology Bulletin, p. 6. Accessed September 20, 

2010, at URL http://www.uwyo.edu/frisoninstsupport/docs/

bulletins/BLTN%2010.pdf

Pring, G.W., 2003, International law and mineral resources, in 

Mining, environment and development—A series of papers prepared for the United Nations Conference on Trade and Development (UNCTAD): New York, UNCTAD, 55 p. Accessed 

September 20, 2010, at URL http://www.adbi.org/3rdpartycd

rom/2003/12/01/772.mining.environment.and.development/

Raabe, Steve, 2002, Trapper mine reclamation attracts wildlife, wins praise: Colorado Mining Association, November 

12, 2002. Accessed September 8, 2010, at URL http://www.

coloradomining.org/releasedetail.php?R_ID=102

Reckling, K., Hoy, R.B., Lefond, S.J., Fullerton, D.G., and 

Rowell, U.H., 1994, Diamonds, industrial, in Carr, D.D., 

ed., Industrial minerals and rocks (6th ed.): Littleton, 

Colorado, Society for Mining, Metallurgy, and Exploration, 

p. 379–395.

Rive, Meg, 2004, Ilmenite sieves could capture toxic wastes: 

Process Magazine. Accessed September 20, 2010, at URL 

http://www.csiro.au/resources/ProcessJune04.html

Robertson, Andy, and Shaw, Shannon, 2004, Use of the 

multiple accounts analysis process for sustainability 

optimization, in Society for Mining and Engineering 

Annual Meeting, February 23–25, 2004, Denver, Proceedings, 8 p. Accessed September 20, 2010, at URL http://

www.robertsongeoconsultants.com/publications/MAA_

SME_2004.pdf

Schumann, Walter, 2007, 3d ed., Gemstones of the world: 

New York, Sterling Publishing Co., Inc., 324 p.

Schwochow, S.D., and Hornbaker, A.L., 1985, Geology and 

resource potential of strategic minerals in Colorado: Denver, 

Colorado Geological Survey, Information Series 17, 70 p.

Scott, Alister, 2002, Assessing public perception of landscape―The LANDMAP experience: Landscape Research, 

v. 27, no. 3, p. 271–295.

Scott, G.R., 1964, Gem stones, in Mineral and water resources 

of Colorado: U.S. Geological Survey and Colorado Minerals Industrial Development Board, 90th Congress, 2d session, p. 165–168.

Searls, J.P., 2003, Barite, in U.S. Geological Survey minerals 

yearbook—2003: U.S. Geological Survey, 11 p. Accessed 

September 20, 2910, at URL http://minerals.usgs.gov/

minerals/pubs/commodity/barite/080303.pdf

Searls, J.P., 2004, Barite, in U.S. Geological Survey mineral 

commodity summaries 2004: Washington, D.C., U.S. Government Printing Office, p. 28–29.

Shaw, S.C., Roberts, A. MacG., Maehl, W.C., Kuipers, J., and 

Haigt, S., 2001, Review of the multiple accounts analysis 

alternatives evaluation process completed for the reclamation of the Zortman and Landusky mine sites, in National 

Association of Abandoned Mine Lands Annual Conference, 

August 19–22, 2001, Athens, Ohio, Proceedings, 17 p.
References Cited 85

Simmons, W.B., Jr., and Heinrich, E.W., 1980, Rare-earth 

pegmatites of the South Platte district, Colorado: Colorado 

Geological Survey Resource Series 11, 131 p.

Sinkankas, John, 1988, Field collecting gemstones and minerals 

(formerly titled Gemstones and minerals—How and where to 

find them): Prescott, Arizona, Geoscience Press, 397 p.

Society for Ecological Restoration, 2004, The SER international primer on ecological restoration. Accessed September 

20, 2010, at URL http://www.ser.org/content/ecological_

restoration_primer.asp

Steinhardt, Uta, and Volk, Martin, 2001, Scales and spatial-temporal dimensions in landscape research, in Krönert, Rudolf, 

Steinhardt, Uta, and Volk, Martin, eds., Landscape balance 

and landscape assessment: Berlin, Springer, p. 137–162.

Stellman, J.M., 1998, Minerals (adapted from 3d ed.), in 

Bruusgaard, A., Cash, Jr., L.L., Donatello, G., D’Onofrio, 

V., Faraone, G., Kleinfeld, M., Landwehr, M., Meiklejohn, 

A., Pendergrass, J.A., Roach, S.A., Roscina, T.A., 

Sadkovskaja, N.I., and Stahl, R., Encyclopedia of occupation health and safety (4th ed.): International Labour Office 

Canadian Centre for Occupational Health and Safety. 

Accessed September 23, 2010, at URL http://www.ilo.org/

safework_bookshelf/english?content&nd=857170713

Stone, Tammy, 1999, The prehistory of Colorado and adjacent 

areas: Salt Lake City, University of Utah Press, 214 p.

Streufert, R.K., Kirkham, R.M., Widmann, B.L., and 

Schroeder, T.J., II, 1997, Geologic map of the Cottonwood 

Pass quadrangle, Eagle and Garfield Counties, Colorado: 

Colorado Geological Survey Open-file Report 97–5. 

Accessed September 23, 2010, at URL http://geosurvey.

state.co.us/Default.aspx?mid=904

Tapsell, S.M., 1995, River restoration—What are we restoring to?―A case study of the Ravensbourne River, London: 

Landscape Research, v. 20, no. 3, p. 98–111.

Tepordei, V.V., 1999, Natural aggregates—Foundation of 

America’s future: U.S. Geological Survey Fact Sheet FS 

144–97, 4 p. Accessed September 23. 2010, at URL http://

minerals.usgs.gov/minerals/pubs/commodity/aggregates/

fs14497.pdf

Tepordei, V.V., 2004, Stone, crushed, in U.S. Geological Survey 2004 minerals yearbook. Accessed September 29, 2010, 

at URL http://minerals.usgs.gov/minerals/pubs/commodity/

stone_crushed/cstonmyb04.pdf

Thompson, T.B., 1996, State Line kimberlite field trip—Kelsey 

Lake mine, in Thompson, T.B., ed., Diamonds to gold: Society of Economic Geologists Guidebook 26, p. 1–4.

Toy, T.J., and Hadley, R.E., 1987, Geomorphology and reclamation of disturbed lands: Orlando, Florida, Academic 

Press, 480 p.

Trimble, K.D., 1997, Scientific soundness and socio-economic 

realities in reclamation for habitat, in Brandt, J.E. and others, eds., Annual National Meeting of American Society 

for Surface Mining and Reclamation, 14th, Austin, Texas, 

Proceedings: p. 317–324.

Tweto, Ogden, 1987, Rock units of the Precambrian basement 

in Colorado: U.S. Geological Survey Professional Paper 

1321–A, 54 p.

Ulrich, R.S., 1977, Visual landscape preference—A model 

and application: Man–Environment Systems, v. 7, no. 5, 

p. 279–293.

United Nations, 1992, Statement of forest principles, in 

Report of the United Nations Conference on Environment 

and Development, Rio de Janeiro, 3–14 June, 1992, A/

CONF.151/26, v. III. Accessed September 29, 2010, at URL 

http://www.un.org/documents/ga/conf151/aconf15126-

3annex3.htm

United Nations, 2003a, Mining, environment and development—Documents of mining and sustainable development 

from United Nations and other organizations. Accessed September 23, 2010, at URL http://www.adbi.org/3rdpartycd

rom/2003/12/01/772.mining.environment.and.development/

United Nations, 2003b, Agenda 21, Chap. 4. Changing consumption patterns: New York, U.N. Department of Economic and Social Affairs Division for Sustainable Development. Accessed September 23, 2010, at URL http://www.

un.org/esa/dsd/agenda21/res_agenda21_04.shtml

U.S. Bureau of Land Management, 1964, Regulations pertaining to mining claims under the General Mining Laws of 

1872, multiple use, and special disposal provisions: U.S. 

Department of the Interior Circular 2149, 45 p.

U.S. Bureau of Land Management, 1984, Visual resource 

management—BLM manual handbook H–8400, Rel. 

8–24: Washington, D.C., U.S. Government Printing Office, 

approx. 24 p.

U.S. Bureau of Land Management, 1986a, Visual resource 

inventory—BLM manual handbook 8410–1: Washington, 

D.C., U.S. Government Printing Office, variously paged.

U.S. Bureau of Land Management, 1986b, Visual resource contrast rating—BLM Manual Handbook 8431–1: Washington, 

D.C., U.S. Government Printing Office, variously paged.

U.S. Bureau of Land Management, 1994, Data element dictionary: Denver, U.S. Bureau of Land Management, p. 204–233.

U.S. Bureau of Land Management, 1996, Mining claims and 

sites on Federal lands: Information pamphlet BLM–WO–

GI–91–002–4130, Washington, D.C., U.S. Government 

Printing Office, 27 p.
86 Development of Industrial Minerals in Colorado

U.S. Bureau of Land Management, 1997, Public lands 

statistics 1997. Part 1. Land resources and information: v. 

182, BLM/BC/ST–98/001+1165, March 1998. Accessed 

September 27, 2010, at URL http://www.blm.gov/natacq/

pls97/index.html

U.S. Bureau of Land Management, 2001, Integrating GIS 

technologies with the visual resource management inventory process―National Business Office Technical Note 

407: Denver, Colorado, Printed Materials Distribution 

Series, 27 p.

U.S. Bureau of Land Management, 2004, Minerals program—

Colorado. Accessed September 27, 2010, at URL http://

www.co.blm.gov/mines/minerals.htm

U.S. Bureau of Land Management, 2009, Rockhounding and 

fossil collecting: Bureau of Land Management brochure 

BLM/CO/GI-09-007. Accessed September 24, 2010, at 

URL http://www.blm.gov/pgdata/etc/medialib/blm/co/

programs/minerals.Par.44677.File.dat/Rockhounding%20

Brochure.pdf

U.S. Bureau of Mines Branch of Industrial Minerals, 1992, 

Crystalline silica primer: U.S. Bureau of Mines Special 

Publication 92–16938, 29 p. Accessed September 27, 2010, 

at URL http://minerals,usgs.gov/minerals/pubs/commodity/

silica/780292.pdf

U.S. Census Bureau, 2004, Colorado. Accessed September 27, 2010, at URL http://www.census.gov/population/

cencounts/co190090.txt and http://quickfacts.census.gov/

qfd/states/08000.html

U.S. Department of Agriculture Forest Service, 1995, Landscape aesthetics—A handbook for scenery management: 

Washington, D.C., U.S. Forest Service, Agricultural Handbook AH–701, 264 p.

U.S. Department of Agriculture Forest Service, 2001, The 

built environment image guide for the national forests 

and grasslands: Washington, D.C., U.S. Forest Service, 

FS–710, 275 p.

U.S. Department of Agriculture Forest Service, 2005, Forest Service—Caring for the land and serving people, 23 p. 

Accessed September 27, 2010, at URL http://www.usda.

gov/news/pubs/factbook/010a.pdf

U.S. Department of Agriculture Forest Service, 2010a, 

Minerals and geology: USDA Forest Service Rocky 

Mountain Region. Accessed September 27, 2010, at 

URL http://www.fs.fed.us/r2/resources/mgr/minerals/

index.shtml

U.S. Department of Agriculture Forest Service, 2010b, Minerals and geology program—Laws and regulations. Accessed 

September 27, 2010, at URL http://www.fs.fed.us/r2/

resources/mgr/laws/index.shtml

U.S. Department of the Interior National Atlas of the United 

States, 2005, The public land survey system (PLSS). 

Accessed September 27, 2010, at URL http://www.

nationalatlas.gov/articles/boundaries/a_plss.html

U.S. Department of the Interior National Park Service, 2001, 

Natural resource management reference manual 77: Washington, D.C.

U.S. Department of the Interior National Park Service, 2004, 

National Register of Historic Places. Accessed September 

27, 2010, at URL http://www.historicdistricts.com

U.S. Department of Labor, 2002, Crystalline silica exposure: 

U.S. Department of Labor, Occupational Safety and Health 

Administration Publication 3176. Accessed September 27, 

2010, at URL http://www.osha.gov/Publications/3176-2002-

English.html

U.S. Energy Information Administration, 1998, Natural gas 

and the environment. Accessed November 18, 2010, at 

URL http://www.eia.doe.gov/pub/oil_gas/natural_gas/

analysis_publications/natural_gas_1998_issues_trends/

pdf/chapter2.pdf

U.S. Environmental Protection Agency, 1995a, Profile of the 

non-fuel, non-metal mining industry: Washington, D.C., 

U.S. Government Printing Office, publication EPA/310-

R-95-011, 95 p. Accessed September 27, 2010, at URL 

http://www.epa.gov/compliance/resources/publications/

assistance/sectors/notebooks/nomtmisn.pdf

U.S. Environmental Protection Agency Office of Solid Waste, 

1995b, Lightweight aggregate production and air pollution control wastes, 15 p. Accessed September 27, 2010, at 

URL http://www.epa.gov/wastes/nonhaz/industrial/special/

mining/minedock/light/lwa.pdf

U.S. Environmental Protection Agency, 1995c, AP–42 (5th

ed.), v. 1, chapter 11, Mineral products industry. Accessed 

September 27, 2010, at URL http://www.epa.gov/ttnchie1/

ap42/ch11/final/c11s00.pdf

U.S. Environmental Protection Agency, 2002, Sulfur, 10 p. 

Accessed October 4, 2008 at URL http://www.epa.gov/

wastes/nonhaz/industrial/special/mining/minedock/id/id4-

sulf.pdf

U.S. Environmental Protection Agency, 2010, Vermiculite. 

Accessed September 27, 2010, at URL http://www.epa.gov/

opptintr/asbestos/pubs/verm.html

U.S. Geological Survey, 2000, Photo glossary of volcano 

terms. Accessed September 27, 2010, at URL http://

volcanoes.usgs.gov/images/pglossary/index.php

U.S. Geological Survey, 2003a, The mineral industry of Colorado, in U.S. Geological Survey minerals yearbook 2003, 11 

p. Accessed January 26, 2005, at URL http://minerals.usgs.

gov/minerals/pubs/state/2003/costmyb03.pdf
References Cited 87

U.S. Geological Survey, 2003b, Igneous rocks. Accessed 

September 27, 2010, at URL http://vulcan.wr.usgs.gov/

LivingWith/VolcanicPast/Notes/igneous_rocks.html

U.S. Geological Survey, 2004, Mineral commodity summaries 

2004: Washington, D.C., U.S. Government Printing Office, 

197 p.

U.S. Geological Survey, 2006, Stone, dimension, in U.S. Geological Survey 2006 minerals yearbook, 14 p. Accessed September 30, 2010, at URL http://minerals.usgs.gov/minerals/

pubs/commodity/stone_dimension/myb1-2006-stond.pdf

U.S. Senate, 2003, The Bankhead-Jones Farm Tenant Act. 

Accessed September 27, 2010, at URL http://agriculture.

senate.gov/Legislation/Compilations/Forests/bankhead.pdf

Van Alstine, R.E., 1969, Geology and mineral deposits of the 

Poncha Springs NE quadrangle, Chaffee County, Colorado: 

U.S. Geological Survey Professional Paper 626, 52 p.

Van Gosen, B.S., and Bush, A.L., 2001, Colorado vermiculite 

deposits—Mines, prospects, and occurrences: U.S. Geological Survey Open-File Report OF–01–475, 11p.

Van Gosen, B.S., Lowers, H.A., Bush, A.L., Meeker, G.P., 

Plumlee, G.S., Brownfield, I.K., and Sutley, S.J., 2002, 

Reconnaissance study of the geology of U.S. vermiculite 

deposits—Are asbestos minerals common constituents?: 

U.S. Geological Survey Bulletin 2192, 8 p.

Vanderwilt, J.W., 1947, Metals, nonmetals, and fuels, Pt. 1, in

Vanderwilt, J.W., ed., Mineral resources of Colorado: Denver, State of Colorado Mineral Resources Board, 290 p.

Virta, R.L., 2003, Zeolites, 4 p. Accessed October 28, 2004, 

at URL http://minerals.usgs.gov/minerals/pubs/commodity/

zeolites/zeolimyb03.pdf

Virta, R.L., 2004, Clays, in U.S. Geological Survey mineral 

commodity summaries 2004: Washington, D.C., U.S. Government Printing Office, p. 48–49.

Waage, K.M., 1953, Refractory clay deposits of south-central 

Colorado: U.S. Geological Survey Bulletin 993, 104 p.

WBB Minerals, 2005, Education Centre—Ball clay or china 

clay? Accessed September 27, 2010, at URL http://www.

wbbminerals.net/education_centre/ball_china.html

Wentworth, C.K., 1922, A scale of grade and class terms for 

clastic sediments: Journal of Geology, v. 30, p. 377–392.

Werth, J.T., 1993, Sand and gravel resources—Protection, regulation, and reclamation: Washington D.C., American Planning 

Association Planning Advisory Service Report 347, 33 p.

Western Governors’ Association, 2010, WGA Policy Resolution 10–16—National minerals policy, 3 p. Accessed 

September 28, 2010, at URL http://www.westgov.

org/index.php?option=com_joomdoc&task=doc_

details&gid=1275&Itemid=85

Wherrett, J.R., 2000, Creating landscape preference models 

using Internet survey techniques: Landscape Research, v. 25, 

no. 1, p. 79–96.

Wilburn, David, Goonan, Thomas, and Bleiwas, Donald, 

2001, Technological advancement—A factor in increasing 

resource use: U.S. Geological Survey Open-File Report 

01–197. Accessed January 19, 2005, at URL http://pubs.

usgs.gov/of/of01-197/html

Winterhalder, Keith, Clewell, A.F., and Aronson, James, 

2004, Values and science in ecological restoration—A 

response to Davis and Slobodkin: Restoration Ecology, 

v. 12, no. 1, p. 4–7.

Withington, C.F., 1964, Gypsum and anhydrite, in Mineral and 

water resources of Colorado―Report of the United States 

Geological Survey in collaboration with the Colorado Mining Industrial Development Board: Washington, D.C., U.S. 

Government Printing Office, p. 190–197.

Wohl, E.E., 2001, Virtual rivers—Lessons from the mountain 

rivers of the Colorado Front Range: New Haven, Yale University Press, 210 p.

Wolfe, J.A., 1964, Cement rock, in Mineral and water resources 

of Colorado—Report of the United States Geological Survey 

in collaboration with the Colorado Mining Industrial Development Board: Washington, D.C., U.S. Government Printing 

Office, p. 181–183.

Workman, W.E., 1964, Barite from the White River Formation of northeastern Colorado: Charlottesville, University of 

Virginia, Bachelor of Arts thesis.

Wright, M.A. and White, Susan, eds., 2004, The practical 

guide to reclamation in Utah: Utah Department of Natural 

Resources Division of Oil, Gas, and Mining, 163 p. Accessed 

on September 28, 2010, at URL http://fs.ogm.utah.gov/pub/

MINES/Coal_Related/RecMan/Reclamation_Manual.pdf

Xu, Feng, Mittelhammer, R.L., and Barkley, P.W., 1993, Measuring the contributions of site characteristics to the value of 

agricultural land: Land Economics, v. 69, no. 4, p. 356–369.

Zdunczyk, M.J., and Linkous, M.A., 1994, Industrial sand and 

sandstone, in Carr, D.D., ed., Industrial minerals and rocks 

(6th ed.): Littleton, Colorado, Society for Mining, Metallurgy, and Exploration, p. 879–891.

Zongyu, Zhang, Hui, Lin, Jinyeu, Tsou, and Hall, T.W., 2002, 

Dichotomy between the information inventory and public: 

Guangzhou, China, Guangzhou Urban Planning Bureau, 

21 p. Accessed on September 28, 2010, at URL http://www.

epa.com.tw/landscape/landscape%20assessment.pdf

Zube, E.H., Brush, R.O., and Fabos, J.G., 1975, Landscape 

assessment—Values, perceptions, and resources: Stroudsburg, Pa., Dowden, Hutchinson & Ross, 367 p.
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For more information concerning this publication, contact:

Center Director, USGS Central Mineral and Environmental 

Resources Science Center

Box 25046, Mail Stop 973

Denver, CO 80225

(303) 236-1562

Or visit the Central Mineral and Environmental Resources 

Science Center Web site at: http://minerals.cr.usgs.gov/
Arbogast and others—Development of Industrial Minerals in Colorado—Circular 1368