Kaolin, Refractory Clay, Ball Clay, and

Halloysite in North America, Hawaii,

and the Caribbean Region
Kaolin, Refractory Clay, Ball Clay, and 

Halloysite in North America, Hawaii, 

and the Caribbean Region

By SAM H. PATTERSON and HAYDN H. MURRAY

GEOLOGICAL SURVEY PROFESSIONAL PAPER 1306

Geologic descriptions of kaolin 

deposits occurring at 46 localities

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON: 1984
UNITED STATES DEPARTMENT OF THE INTERIOR 

WILLIAM P. CLARK, Secretary

GEOLOGICAL SURVEY 

Dallas L. Peck, Director

Library of Congress Cataloging in Publication Data

Patterson, Sam H. (Sam Hunting), 1918-

Kaolin, refractory clay, ball clay, and halloysite in North America, Hawaii, and the Caribbean region.

(Geographical Survey professional paper ; 1306)

Bibliography: p.

1. Kaolin North America. 2. Kaolin Hawaii. 3. Kaolin Caribbean Area. 4. Clay North America. 5. Clay Hawaii. 6.

Clay North America. I. Murray, Haydn H. (Haydn Herbert), 1924- II. Title. III. Series. 

TN942.P34 1984 553.6T097 83-600272

For sale by the Distribution Branch, U.S. Geological Survey, 

604 South Pickett Street, Alexandria, VA 22304
CONTENTS

Abstract 

Introduction 

Definitions 

Types of deposits 

Hydrothermal 

Residual 

Sedimentary 

United States 

History and production 

Sedimentary deposits 

Atlantic and Gulf Coastal Plains -

South Carolina-Georgia-Alabama kaolin belt -

Location 

Occurrence and age 

Arkansas bauxite region 

Other districts in the Coastal Plains 

Districts in North Central and Western United States - 

Minnesota 

Latah County, Idaho 

Spokane County, Wash. 

lone, Calif. 

Mesa Alta, N.M. 

Underclays 

Clear-field, Pa. 

Olive Hill, Ky. -

Occurrence and characteristics 

Mineralogy 

Origin 

Other districts in Eastern United StatesMissouri 

Colorado 

King County, Wash. 

Cowlitz, Wash. 

Hobart Butte, Oreg. 

Alberhill, Calif. -

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35

United States Continued

Sedimentary deposits Continued 

Underclays Continued

Holocene underclay, Hawaii - 

Occurrence - 

Mineral composition 

Chemical composition 

Ball clays -

Western Kentucky-Tennessee regionTroup, Tex. -

Other ball-clay districts 

Residual kaolin deposits 

Spruce Pine, N.C. 

Other residual kaolin deposits 

Hydrothermal deposits 

Little Antelope Valley, Calif. 

Tintic, Utah - 

Terraced Hills, Nev.

Minor hydrothermal alteration of sedimentary claysOther hydrothermal kaolin deposits 

Problematical kaolins and deposits of uncertain origin 

Indiana halloysite 

Vermont kaolin 

Mount Holly Springs, Pa. 

Halloysite near Gore, Ga. 

Kaolin in sinkholes in the Appalachian region 

("JflTlfid.3. _____________________ ____________________________

Mexico 

Central America 

Guatemala 

Nicaragua 

Caribbean region 

Cuba - 

Jamaica 

Puerto Rico 

References cited 

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ILLUSTRATIONS

FIGURE 1. Kaolin sold or used by producers for specified uses, 1929-77, compiled from U.S. Bureau of Mines Minerals Yearbooks 

2. Map showing kaolin, ball-clay, halloysite, and refractory-clay deposits in the United States 

3. Locations of the six major districts in the South Carolina-Georgia-Alabama kaolin belt 

4. Generalized geologic section, Macon-Gordon kaolin district, Georgia 

5. Electron micrograph of kaolin of Eocene age from near Wrens, Ga., showing sponge spicule 

6. Particle-size distribution of Cretaceous and lower Tertiary kaolins 

7. Electron micrograph of kaolin of Cretaceous age from near Gordon, Ga., showing vermicular crystals 

8. Electron micrograph of kaolin of Eocene age from near Wrens, Ga., showing fine particle size 

9. Diagrammatic section of residual kaolin deposits in the Arkansas bauxite district 

10. Diagrammatic section of kaolin deposits in the Kemper-Pinedale area, Mississippi 

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in
w CONTENTS

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FIGURE 11. Generalized sections illustrating: A, the regional geology of the Minnesota kaolin deposits, and B, the kaolin and associated beds along the Minnesota River valley 18

12. Stigmaria from the "Olive Hill" clay bed of the Lee Formation in Kentucky, showing main rootstock, attached rootlets (at

right angles), and nodular root scars 21

13. Cross section of a petrified root of Stigmaria ficoides Brongniart from a Pennsylvanian coal bed, Leslie County, Ky., showing

delicate outer cortical tissue ________________________________________________________ 22

14. X-ray diffractometer traces (CuKct^ radiation) of flint, semiflint, and plastic clays from the "Olive Hill" clay bed of the Lee

Formation in Kentucky 26

15. Differential thermal analysis curves of clays from the "Olive Hill" clay bed of the Lee Formation in Kentucky 28

16. Geologic sections of the Cowlitz kaolinitic clay deposits, Washington 34

17. Geologic sections of the Hobart Butte kaolinitic clay deposits, Oregon 36

18. Diagrammatic section illustrating the occurrence and nature of plastic clay deposits, Hawaii 37

19. X-ray diffraction traces of samples of plastic clay from Alakai Swamp, Hawaii 38

20. Locations of kaolinitic clay districts in Canada 49

21. Locations of major kaolin mining areas in Mexico 50

22. Locations of kaolin districts in Central America and Caribbean region 51

TABLES

* Page

TABLE 1. Temperature end points of American pyrometric cones 3

2. Kaolin, refractory clay, ball clay, and halloysite found in the United States 8

3. Characteristics of the Cretaceous and Eocene kaolin deposits in the Macon-Gordon district, Georgia 12

4. Chemical comparison of unweathered Columbia River Basalt Group with saprolite derived from basalt 20

5. Types and alumina contents of clay in the "Mercer bed," Clearfield district, Pennsylvania 22

6. Chemical analyses of varieties of clay in the "Mercer" deposits 23

7. Mineral composition and chemical analyses of clays from the "Olive Hill" clay bed of the Lee Formation in Kentucky, arranged

in order of pyrometric cone equivalents 27

8. Chemical analyses of Missouri fire clays 31

9. Analyses of kaolinitic clays from Hobart Butte, Oreg. 35

10. Chemical analyses of plastic underclay on the Waimea Canyon Volcanics and clay, typical saprolite, and fresh basalt from the

Koloa Volcanics, Kauai, Hawaii 39

11. Description and X-ray mineralogic analyses of ball-clay samples from the Claiborne Formation (Group), Tenn. and Ky. 42

12. Bulk mineral compositions of saprolite in the Spruce Pine district, North Carolina 43

13. Partial chemical analyses of kaolin from the Little Antelope Valley district and of theoretical kaolinite 44

14. Semiquantitative spectrochemical analysis of clay material, Little Antelope mine 44

15. Partial chemical analyses of waters in the Little Antelope Valley district, California 45

16. Particle-size content, clay-mineral ratios, and content of SiO2 , A12O3 , and FezO3 in clay from the Philadelphia Clay Co.

17. Estimates of chemical composition of kaolin in Costa Rica 52
Kaolin, Refractory Clay, Ball Clay, and Halloysite 

in North America, Hawaii, and the Caribbean Region1

By SAM H. PATTERSON and HAYDN H. MURRAY2

ABSTRACT

The valuable types of kaolinitic clays occurring in North and Central America, Hawaii, and the Caribbean region are kaolin, halloysite, ball clay, and refractory clay. Most valuable deposits have formed 

by sedimentary processes, but a few are the result of hydrothermal 

activity, and some are residual accumulations of weathered rocks. 

The kaolinitic clays are widely distributed and occur in rocks of several different ages. Most refractory clay deposits are associated with 

coal beds; these deposits are called underclays. Most underclays are 

of Pennsylvanian age (Late Carboniferous of the European time 

scale), but a few are in Cretaceous and Tertiary rocks, and small 

deposits in Hawaii are of Holocene age. Most of the large kaolin and 

ball-clay deposits are in sedimentary rocks of Cretaceous age and 

younger. Hydrothermal kaolin deposits, which include most halloysite clays, are thought to have formed mainly in Cenozoic time, but 

the host rocks of some deposits are much older. Some residual deposits are related to the present land surface, and others are covered 

by younger rocks. They occur mainly on igneous and crystalline rocks.

INTRODUCTION

Valuable kaolin deposits occur at many places in 

North and Central America, a few have been found in 

the Caribbean region, and small deposits of scientific 

interest are located in Hawaii. White commercial kaolin occurs mainly in sedimentary deposits, but this 

type of clay also occurs in residual deposits formed by 

weathering and in hydrothermal deposits. Underclays, 

which form under coal or peaty material, are classified 

as sedimentary because virtually all are in sedimentary sequences. However, small underclay deposits in 

Hawaii formed by weathering of basalt in swamps, 

indicating that some underclays may have formed 

more by weathering and residual accumulation than 

by sedimentary processes. In this report, ball clay, a 

variety of kaolin, is included with the underclays 

because all but one minor occurrence of ball clay are 

closely associated with lignitic material. Commercial 

halloysite, another variety of kaolin, is found mainly 

in hydrothermal deposits, but this type of clay is also

Contribution to International Geological Correlation Programme, Project 23 

Genesis of Kaolins. 

"Geology Department, Indiana University, Bloomington, IN 47401.

recovered as a coproduct of kaolin from residual 

deposits.

Definitions

Kaolin. The term "kaolin" is now variously used to 

mean a clay-mineral group, a rock (consisting of more 

than one mineral), and an industrial mineral commodity and interchangeably with the term "china clay." 

The following definition of kaolin by Ross and Kerr 

(1931, p. 154) is probably the most widely accepted one:

"By kaolin is understood the rock mass which is composed essentially of a clay material that is low in iron and usually white or 

nearly white in color. The kaolin-forming clays are hydrous aluminum silicates of approximately the composition 2H2O«Al2O3 «2SiO2 , 

and it is believed that other bases if present represent impurities or 

adsorbed materials. Kaolinite is the mineral that characterizes most 

kaolins, but it and the other kaolin minerals may also occur to a 

greater or lesser extent in clays and other rocks that are too heterogeneous to be called kaolin. * * *"

Dickite and nacrite are two polymorphic forms of kaolinite that can be characterized in terms of two crystallattice structures, as Bailey (1963, p. 1196) described in 

his abstract as follows:

"1) direction and amount of interlayer shift, and 2) location of the 

vacant octahedral site in successive layers. Kaolinite and dickite 

have the same interlayer shift of -Yaa^ when referred to a standard 

layer orientation. The two structures differ only in regard to the distribution of the vacant cation site in successive octahedral sheets and 

the consequences of this distribution in terms of symmetry, layer distortion, and Z-axis periodicity. In well-crystallized kaolinite the 

vacant site is the same in each layer. The structure is triclinic and 

may be right-handed or left-handed, because either of two octahedral 

positions, related by a mirror plane in an undistorted monoclinic 

structure, may be vacant. In dickite the vacant site alternates 

between these two positions in successive layers, creating a twolayer monoclinic superstructure that is a regular alternation of 

right- and left-handed kaolinite layers. Comparison of the two structures is facilitated by changing the standard orientation of the dickite unit cell to correspond to that of kaolinite. The interlayer shift in 

nacrite is %b^ relative to the same axes as for kaolinite and dickite. 

The layer sequence is that of a 6R polytype, but the pattern of vacant 

sites reduces the symmetry to Cc and allows selection of a smaller
KAOLIN IN NORTH AMERICA, HAWAII, AND THE CARIBBEAN

two-layer unit cell. A modified system of polytype notation is suggested for describing the kaolins and other minerals in which the 

actual Z-axis periodicity or crystal system differs from that of the ideal 

trioctahedral polytype as a result of cation or vacancy ordering.* * *"

The term "anauxite" is repeated in a few places in 

this article as used in old publications. Anauxite is 

described by Grim (1968, p. 68) as one of the problematical kaolin minerals that has a considerably higher 

silica-to-alumina molecular ratio than kaolinite.

When applied as a term for an economic clay commodity, the foregoing definition must be modified to 

include some indication of use and to account for the 

fact that most kaolin now marketed is beneficiated to 

improve its purity and whiteness. The following definition will apply to further discussions of kaolin in this 

report. Kaolin is a clay consisting of substantially pure 

kaolinite, or related clay minerals, that is naturally or 

can be beneficiated to be white or nearly white, will 

fire white or nearly white, and is amenable to beneficiation by known methods to make it suitable for use in 

whiteware, paper, rubber, or paint, or for similar uses. 

Many very large kaolin deposits are essentially pure 

and require little concentration during preparation for 

market. Some deposits are very impure, and the kaolin 

is recovered by washing. Most are slightly off-color and 

require leaching. China clay is an ancient term originating from the use of clay, later found to be kaolinitic, 

in porcelain tableware and art objects in China.

Halloysite. Halloysite occurs in two forms: one has 

the composition (OH)3Si4Al4O10 »4H2O, and the other, 

(OH)3Si4Al4O10 . Halloysite (10A)3 is a porcelainlike 

hard clay that dehydrates at or slightly above surface 

temperatures to a white or light-colored porous, friable, or almost cottony-textured material. Halloysite 

(7A) is a similar to kaolinite in composition and mineral structure, but the hydrated form has a c-axis spacing greater than that of kaolinite. In older reports, the 

name "halloysite" is applied to the hydrated forms, 

and the dehydrated form is called "metahalloysite." 

However, some reports use the name "endellite" for 

the hydrated form and the name "halloysite" for the 

dehydrated form. Virtually all subsurface halloysite is 

halloysite (10A). Halloysite, like ball clay, is a variety 

of kaolin and is included with kaolin in most industrial 

classifications.

Ball clay. Ball clays are defined by the American 

Society for Testing and Materials (ASTM) (1971) as sec3In compliance with the recommendations of the AIPEA (Association Internationale Pour 1'Etude des Argiles) Nomenclature Committee (Bailey, 1980), 

"halloysite (10A)" will be used to refer to the hydrated form and "halloysite 

(7A)" will be used for the dehydrated form. No angstrom indication will be made 

where halloysite is used as a general term, where both forms may be present, or 

where the hydration state is unknown.

ondary clays commonly characterized by the presence 

of organic matter, high plasticity, high dry strength, 

long vitrification range, and a light color when fired. 

Kaolinite is the principal mineral constituent of ball 

clay, and it typically makes up more than 70 percent of 

this type of clay. The minor differences between the 

light fired color required by this definition and the 

white required for kaolin provide little practical basis 

for distinguishing these two types of clay. Therefore, 

ball clay is actually a variety of kaolin, but it is treated 

as a separate type of clay because of its wide application in marketing and as a use term in the ceramics 

industries.

Refractory clays. Refractory clays include several 

varieties of kaolinitic clays that are used in the manufacture of products requiring resistance to high temperatures. The quality and properties of refractory 

clays are expressed in terms of pyrometric cone equivalents, a method of designating fusion points (ASTM, 

1971, p. 198): "* * * Pyrometric Cone Equivalent is 

defined as the number of that standard cone whose tip 

would touch the supporting plaque simultaneously 

with that of a cone of the material being investigated, 

when tested in accordance with the Standard Method 

of Test for Pyrometric Cone Equivalent (PCE) of refractory materials (ASTM Designation C24) of the American Society of Testing Materials. * * *"

The fusion points of products made from refractory 

clays range from just above PCE 19, the lower cutoff 

according to accepted definitions (Norton, 1968), to as 

high as PCE 36 (table 1). The refractory properties of 

kaolinitic clays are ordinarily classified according to 

suitability for heat service as low duty (PCE 19-26), 

moderate duty (PCE 26-31%), high duty (PCE 

31V2-33), and super duty (PCE 33-34). A few essentially pure kaolinite clays have fusion points as high as 

PCE 35, and some refractory kaolins and fire clays containing diaspore, boehmite, or gibbsite have PCE's as 

high as PCE 37.

The principal types included in the refractory clays 

are fire clay, kaolin, and ball clay. Kaolin and ball clay 

used in refractory products are referred to as refractory 

kaolin and refractory ball clay. The definition of fire 

clay used in this paper is essentially that of Norton 

(1968), who assigned this term to all clays that are not 

white burning and that have a PCE above 19. The term 

"fire clay," therefore, excludes most kaolin and ball 

clay because they burn white, but it does include kaolin and ball clay that are colored when fired. This classification of "refractory clay" as a group name and the 

threefold subdivision is by no means universally applied. Other reports, including earlier ones by the authors themselves, have used the terms "refractory 

clay" and "fire clay" interchangeably.
INTRODUCTION

TABLE I. Temperature end points of American pyrometric cones

[Temperatures given are approximate and are applicable only when heated at

specified rates (Norton, 1968)]

End point

No. of cone

18

19

20

23

26

27

28

29

30

31

32

32%

33

34

35

36

37

38

2,714

2,768

2,786

2,876

2,903

2,921

2,939

2,984

3,002

3,056

3,092

3,137

3,173

3,200

3,245

3,290

3,308

3,335

1,490

1,520

1,530

1,580

1,595

1,605

1,615

1,640

1,650

1,680

1,700

1,725

1,745

1,760

1,785

1,810

1,820

1,835

Saprolite. Saprolite is decomposed weathered rock 

in which many if not all of the original minerals have 

been replaced by pseudomorphs consisting of other 

minerals. Textures and structures of the parent rock 

are preserved in saprolite, and little or no volume is 

lost as it forms. The term "saprolite" is now widely 

used in the literature on soil science and the geology of 

weathered rocks. It has essentially the same meaning 

as the term "lithomarge" used in India and the German term "Zersatz."

Under clay (seat earth). Underclay is a type of clay 

normally underlying a coal bed or peat bed. Underclay 

is generally nonbedded and slickensided, fractures 

irregularly, and contains imprints of plant roots and 

other physical characteristics indicating formation as 

a waterlogged soil. Underclay has the same meaning 

as "seat earth" as used in England and is very similar 

to the German term "Tonstein." In this report, the 

term "underclay" is used according to the above definition. However, the term has also been used in a more 

general way for clay of almost any type or soil occurring below a unit of another lithology.

Types of Deposits

Kaolin in North America occurs in hydrothermal, 

residual, and sedimentary deposits. In some districts

and regions, all the kaolin is a single type. For example, all kaolin produced in Mexico is the hydrothermal 

type, all in the Spruce Pine district in the United 

States is residual, and all in the Georgia Coastal Plain 

is sedimentary. Both residual and sedimentary kaolin 

deposits are present in other districts, but no large 

deposits containing both hydrothermal and sedimentary types have been found. A few of the sedimentary 

clays in the United States have been mildly altered by 

hydrothermal solutions.

HYDROTHERMAL

Hydrothermal kaolin deposits form elongate pods, 

pipelike bodies, and irregular masses. Deposits tend to 

be alined along joints, faults, pyroclastic beds, or other 

permeable zones that allowed movement of warm or 

hot solutions. Solubility of the host rock is a factor in 

determining the location of large replacement deposits, 

as dissolution is required to make space for the kaolin. 

An example is the halloysite body in the Dragon mine, 

Tintic district, Utah, that replaces limestone adjacent 

to a less soluble rhyolite intrusive rock. Many hydrothermal kaolin deposits are enclosed by halos of silicaenriched rock. Alunite, cristobalite, and other forms of 

silica including opaline material occur in many 

deposits, and metallic sulflde minerals are present in 

some. Pseudomorphs of the minerals forming the host 

rock are found in many deposits. The age of hydrothermal kaolin formation is not necessarily related to 

the age of the host rock. Most hydrothermal clay deposits are probably no older than Tertiary, though some 

are found in much older rocks.

RESIDUAL

Residual kaolin deposits in weathered rocks are generally at or very near the surface, except where formed 

during ancient weathering cycles and later buried by 

younger rocks. Most residual kaolin deposits have 

formed from granitic and gneissic and other types of 

crystalline metamorphic rocks. The age of kaolin formation is commonly controlled by the age of the present land surface rather than by the age of the parent 

rock. Residual kaolin deposits are generally irregularly shaped and grade downward into the parent rocks 

through partly altered, weathered saprolite zones. 

Residual boulders or blocks of parent rock enclosed by 

concentric layers of partly weathered rock are common 

in the least weathered parts of many deposits of this type.

All kaolin formed at the surface involves the removal 

of silica and other elements, and some downward 

movement of kaolinite undoubtedly took place in the 

formation of many of the sedimentary deposits. Therefore, such deposits as the underclays and ball clays 

that served as soils are in part residual.
KAOLIN IN NORTH AMERICA, HAWAII, AND THE CARIBBEAN

SEDIMENTARY

In this report, all kaolin deposits in sedimentary 

rocks are considered the sedimentary type. Most kaolin 

deposits in this group are thought to have been formed 

by the transportation and deposition of kaolinite formed 

elsewhere. Underclay (seat earth) and ball clay, of 

which most deposits are varieties of underclay, are 

included with this type because with very few exceptions they occur in sedimentary rock.

The underclay and some kaolin deposits may have 

formed mainly by weathering in place from aluminous 

minerals in sedimentary rocks. Therefore, some of the 

deposits in this group are interrelated with the residual type. Many clays in the sedimentary group have 

undergone diagenetic changes and, therefore, may be 

considered to have formed by a process other than sedimentation. However, it is rarely possible to distinguish 

the characteristics of clay resulting from sedimentation from those formed after deposition, and no attempt 

is made to classify any of the deposits as diagenetic type.

Sedimentary kaolin deposits typically are ameboid 

tabular lenses that vary considerably in size. Many 

such lenses tend to have nearly flat or gently undulating upper surfaces and to extend convexly downward 

in the thicker central parts. Channel-fill deposits are 

common in some districts. One large blanket-shaped 

deposit in Georgia extends for more than 18 km, and 

for most of this distance it is 10-25 m thick.

UNITED STATES 

History and Production

The sedimentary kaolins of the Coastal Plain of 

Georgia and South Carolina and the residual kaolins of 

North Carolina have been known since Colonial times. 

Smith (1929, p. 1) quoted from Sholes's chronological 

history of Savannah, "* * * 1741 Porcelain Clay was 

discovered in or near Savannah by Mr. Duchet, and 

china cups made. * * *" Probably even earlier, clays 

from New Jersey and Massachusetts had been used for 

lining pots and ladles used in making glass and iron 

(The Refractories Institute, 1979). In 1767, Josiah 

Wedgwood sent Thomas Griffiths to Macon County, 

N.C., to send a shipment of china clay to England (Goff, 

1959). Minton (1922) recorded that "* * * As early as 

1766 American clays from Georgia, Florida, and the 

Carolinas were being sent to England in considerable 

quantities. * * *" These clays were regularly imported 

and used by Wedgwood until 1768, when kaolin was 

discovered in Cornwall (Barton, 1966); this discovery 

ended the mining of the Georgia kaolins for more than 

a century. In 1876 (Smith, 1929, p. 1), the mining of the

sedimentary kaolins of Georgia was started again by 

Riverside Mills of Augusta in Richmond County. Mining of the Georgia kaolins has been continuous since 

that time. In addition to the original pottery in Savannah, a second pottery was established near Bath, Aiken 

County, S.C., at an early date. This plant was destroyed 

during Sherman's march to the sea in 1865 (Lang and 

others, 1940). However, kaolin mining was active 

again in Aiken County shortly after the Civil War and 

has continued with only minor interruptions until the 

present.

South Carolina has ranked as the second leading 

kaolin-producing State for several decades. Kaolin 

mining in North Carolina started in 1888 in Jackson 

County (Parker, 1946), and, in 1904, the earliest mines 

opened in the Spruce Pine district. The first kaolin 

operation in Vermont (Ogden, 1969) was in the early 

1800's.

For most areas, production figures for kaolin in the 

late 1800's and early 1900's are difficult to trace. It is 

estimated that about 3 million tons was produced in 

Georgia before 1932 (Kesler, 1956), after which much 

better statistics are available. In 1972, total production 

in Georgia alone was nearly 4 million tons, and South 

Carolina, ranking second, produced more than 680,000 

tons. Total kaolin produced in the United States in 

1977 was 6,488,558 short tons (5,885,800 metric tons) 

(Ampian, 1977, table 5). Approximately 77 percent of 

this total was produced in Georgia, and 11 percent in 

South Carolina. In 1977, 894,277 short tons (811,200 

metric tons) of ball clay was produced (Ampian, 1977, 

table 12), and more than one-half of this tonnage was 

produced in Tennessee. The 1977 output of fire clay, 

which was mainly kaolinite, was 2,965,607 short tons 

(2,690,100 metric tons) (Ampian, 1977, table 14). Missouri, Ohio, and Pennsylvania were the leading producing States.

Use

Kaolin has many industrial applications (Murray, 

1963a), and new uses are still being discovered. It is a 

unique industrial mineral because it is chemically 

inert over a relatively wide pH range, is white, has 

good covering or hiding power when used as a pigment 

or extender in coated films and filling applications, is 

soft and nonabrasive, has low electrical and thermal 

conductivity, and costs less than most competing materials. Some uses of kaolin require very rigid specifications including particle-size distribution, color and 

brightness, and viscosity, whereas other uses require 

practically no specifications; for example, in cement, 

the chemical composition is most important. The better 

grades of kaolin make up most of the tonnage sold and,
UNITED STATES-USE

of course, have the highest value. Many grades of kaolin are specially designed for specific uses, in particular for paper, paint, rubber, plastics, and ceramics.

The paper industry is by far the leading consumer of 

kaolin (fig. 1); approximately 50 percent of the total 

production is used in paper products. Much of the paper 

used in today's color picture magazines contains as 

much as 30 percent by weight of kaolin. Kaolin used in 

paper fills the interstices of the sheet and coats the surface, imparting smoothness, gloss, brightness, opacity, 

and printability (Bundy and others, 1965). Kaolin is 

less expensive than paper pulp and thereby effectively 

lowers paper-production costs, and it is cheaper or 

more efficient than other materials used in filling and 

coating. It is inert to the other ingredients in paper, is 

retained well between the paper fibers, and is available in large quantity, and the platy structure of kaolinite lends itself to the production of high-gloss 

papers. The low viscosity of kaolin at both high and low 

shear rates is a very important property, because at 

today's very high speed production rates the coating 

must be applied at high solids content and still impart 

the correct coating thickness and opacity to the paper. 

High-quality paper-coating kaolin flows readily when 

applied with very high speed coating equipment, giving the paper a smooth and even film.

The rubber industry uses large tonnages of kaolin as 

a filler or extender in both natural and synthetic rubber (fig. 1). Kaolin is incorporated in the latex mix to 

improve properties such as strength, abrasion resistance, and rigidity; furthermore, it lowers the cost. 

Through the years, two terms, "hard kaolins" and 

"soft kaolins" (Klinefelter and others, 1943), have 

become commonplace in describing types of kaolin 

used by the rubber industry. The hard kaolin, though 

distinctly softer than flint kaolin or flint clay, is a very 

fine particle-size kaolin that tends to improve the tensile strength of rubber and its resistance to tearing and 

abrasion. The principal uses of hard kaolin in rubber 

are in the production of footwear and cable covers. Soft 

kaolin lacks the reinforcing properties of the hard kaolins and is used to lower elasticity and improve abrasion resistance, particularly in such products as floor 

tile and soft rubber goods.

Kaolin is used as an extender in paints because it is 

chemically inert, has a high covering power, gives 

desirable flow properties, is low in cost, is white, and 

reduces the amount of expensive pigment required. In 

addition, it has very excellent suspension properties 

and is available in a wide range of particle sizes that 

can be used in many types of paints. For example, 

coarse-particle kaolins are used in paints where a dull 

or flat finish is required, and fine-particle kaolins are 

used in high-gloss paints. Large quantities of calcined

kaolin and water-beneficiated kaolin are used in interior flat wall paints and in metal primers. Waterbeneficiated grades of kaolin disperse easily in water 

and are, therefore, particularly suited to latex paints. 

Some kaolin is chemically treated to make it organophilic or hydrophobic and thereby suitable for use in 

exterior oil-based paints. Calcined kaolin, because of 

its resistance to abrasion and its dry covering properties, is being used in increasing quantities by paint 

manufacturers. Calcined kaolin is an excellent extender 

for TiO2 , the leading paint pigment, particularly in 

latex paint, and its use reduces costs and simplifies the 

formulation of the paint.

Kaolin is used extensively as a filler in plastics. The 

use of kaolin in plastics results in smoother surfaces, 

more attractive finish, dimensional stability, and resistance to chemical attack. Manufacturers of polyvinyl 

chloride (PVC) use kaolin as a reinforcing agent, and it 

makes the plastic more durable. Calcined and partially 

calcined kaolins are used as a filler in PVC wire insulation to improve electrical resistivity. In the manufacture of glass-reinforced polyesters, kaolin has helped 

eliminate flow problems that hindered production of 

large products, such as automobile body parts and boat 

hulls. The kaolin actually results in a stronger, more 

uniform part or body. Plastics are a major area of 

future growth for kaolin products. They are used extensively in vinyl floor coverings, and surface-modified 

kaolin gives improved dispersibility in certain plastic 

systems, which will greatly increase their usage.

Historically, kaolin was first used in ceramics, and 

this is perhaps still the best known application, even 

though the total tonnage sold for this use is small compared with that marketed for paper, paint, and rubber 

manufacturing (fig. 1). It is used in the manufacture of 

whitewares, wall tile, insulators, refractories, and in 

some face brick when a white color is desired. Specially 

designed grades having high green and dry strengths 

are available for use by whiteware manufacturers. The 

most important properties for this use are plasticity, 

strength, and fired color. Kaolin is used in insulators 

because of its properties of low conductivity, high dielectric constant, low power loss, plasticity, and fired 

strength. It is used in casting because of its excellent 

flowability, suspension properties, color, and waterrelease characteristics. It also is used in porcelain, 

again because of its excellent suspension characteristics and good color.

Kaolin has many other important applications, but 

the tonnages required are rather small in comparison 

with the aforementioned uses. Although the following 

list is not complete, it shows the extremely wide variety of products containing kaolin as a suspending agent, 

filler, extending agent, or a main constituent:
KAOLIN IN NORTH AMERICA, HAWAII, AND THE CARIBBEAN

7000

6500 -

6000 -

5500 -

5000 

4500 -

4000 -

Other uses

Refractories

Pottery, stoneware, tile

Rubber

Paper filling and coating

V:*:?:?:?:*:?:?:?:-*:'*:*:-*:?:-*:*^^

3500 

3000 -

2500 -

2000 -

1500 

1000 

1930 1940 1950 1960 1970

FIGURE 1. Kaolin sold or used by producers for specified uses, 1929-77. [Compiled from U.S. Bureau of Mines Mineral Yearbooks.

Short tons can be converted to metric tons by dividing by 1.1024]
ATLANTIC AND GULF COASTAL PLAINS

ink

adhesives

insecticides

medicines

food additives

catalyst preparations

bleaches

adsorbents

cement

fertilizers

plaster

filter aids

cosmetics

chemicals

crayons

pencils

detergents

porcelain enamels

paste

roofing granules

sizing

foundries

linoleum

floor tiles

textiles

Sedimentary Deposits

Sedimentary kaolinitic clays are far more abundant 

and widely distributed in the United States than are 

the other deposit types (fig. 2, table 2). Kaolin, underday, and ball clay occur mainly in sedimentary deposits.

ATLANTIC AND GULF COASTAL PLAINS

Many kaolin deposits are in sedimentary beds underlying the Atlantic and Gulf Coastal Plains. The largest

deposits are in the South Carolina-Georgia-Alabama 

belt, but other deposits are in districts in Florida, 

northwestern Alabama, Mississippi, southern Illinois, 

southeastern Missouri, Arkansas, and Texas. The ball 

clays that are grouped with the underclays in this 

report also occur in the Coastal Plains.

SOUTH CAROLINA-GEORGIA-ALABAMA KAOLIN BELT 

Location

The South Carolina-Georgia-Alabama kaolin belt 

extends for a distance of nearly 400 km from the Aiken, 

S.C.-Augusta, Ga., district on the northeast to the 

Eufaula, Ala., district on the southwest (fig. 3). This 

belt contains estimated kaolin resources of 7 billion-10 

billion tons and is the world's leading producer of sedimentary kaolin. More than 100 million tons have been 

mined in the six major districts shown in figure 3. The 

four districts located northeast of the Ocmulgee River 

(fig. 3) are the principal source of white clay having the 

properties required for the American usage of the term 

"kaolin" as an industrial mineral commodity. The 

Andersonville district, Georgia, is a center of production of light-gray to white refractory kaolin and kaolin

r'~

i - 

_____ --3s

' /

6* \ /

22. ) / «

1 " 1,26 l^ 35 « >

f /FT»*1

South CarolinaGeorgia-Alabama 

kaolin belt

Kaolin 

A Halloysite

 Ball clay

 Fireclay

FIGURE 2. Map showing kaolin, ball-clay, halloysite, and refractory-clay deposits in the United States. (Numbers refer to table 2.)
KAOLIN IN NORTH AMERICA, HAWAII, AND THE CARIBBEAN

TABLE 2. Kaolin, refractory clay, ball clay, and halloysite found in the United States

[Sed., sedimentary or transported; Res., residual; Hyd., hydrothermal; K, kaolin; H, halloysite; B, ball clay; Rk, refractory kaolin; Rf, fire clay, chiefly underclay.

Numbers refer to figure 2]

Number

1 

2 

3 

4 

5

6

7 

8 

9

10

11 

12 

13

14 

15

16

17

18 

19 

20

21 

22 

23

24 

25

26 

27 

28 

29 

30

31 

32

33

34 

35

36

37 

38

39 

40

District

Hart

Alberhill 

Latah County 

Rnllinn

Stoker

Terraced Hills - 

Tintic

A^AOQ Ali'l

Trnnn

East Central 

Glen Alien

Shoals

Oak Hill

Olive Hill

Rr^avr^Y* A^allr^v

Snmfirspt. P.niintv

State

rln

rln

California 

do

do

Idaho 

do

_____ <j0 ________ 

Utah

rln

rln

T^AVflC!

do

do

do

do

do

(Thin

rln

rln

rln

rln

rln

rln

Type of clay

QArl "Rf

QArl "Rf

Sed.,K,Rk 

Qprl T?f

Sed.,K,Rk 

Wvrl PC JTLjTU., JY 

Wvrl R

Sed., Res., Rf 

Sed., Res., K, Rk 

Hyd., H 

Wvrl TC

Hyd., H _ _

Wvrl nyu., Wn

Sed., Rf 

CUJ "Rf

Sed., K

TT,T J If

Sed., K

Sed., B 

Sed., K 

CUJ T>pq ~K

Sed Rf

QArl "Rf

CUrl K" kJCU-.j XV

Cl^rl T?AQ TC T?k

Glprl TC

GAfl T3

^rl R

Clprl K"

? JJ

CUrl 1C

Sed., Rf

Qprl f>f

Sed., Rf 

Sed., Rf ______ 

Sed., Rf

Qprl T?f

Sed., Rf

Res., Hyd.(?), K

So/l Pf

Age

do

middle Eocene 

rln

Paleocene - 

Miocene -

TVrHarvf?')

Miocene and Pliocene 

rln

Jurassic and Cretaceous

rln

rln

Pennsylvanian 

frnppri pC?')

TTr>f»ono/'?1l

early to middle EocenePaleocene and EoceneMiddle PennsylvanianEarly and Middle 

Pennsylvanian.

rln

Middle Pennsylvanianrln

Early and Middle 

Pennsylvanian.

TVrtiarvf?1

ATirlrllf> Pf>nnevlvanian

Reference

Nichols, 1946 

Popoff, 1955 

Hosterman, 1969a 

Alien and others, 1951 

Pask and Turner, 1952

Cleveland, 1962 

Kelley, 1966 

Cleveland, 1957 

Ponder and Keller, 

1960. 

Olson, 1964

f)n

Papke, 1971 

Kildale and Thomas, 

1957. 

Waage, 1961 

Waage, 1953

Reeves, 1963 

Patterson and Holmes, 

1965. 

Fisher, 1965 

Stenzel, 1950 

Pence, 1954

Parham, 1970 

McQueen, 1943 

Keller, 1952 

Tennissen, 1960 

Tracey, 1944

Grim, 1934 

Olive and Finch, 1969 

Bicker, 1970 

Conant, 1965 

Callaghan, 1948

Clarke, 1966 

Hosterman and others, 

1968.

Tin U\J.

Stout and others, 1923 

Patterson and Hosterman, 1962.

Hosterman and others, 

1968.

T\r\

Foose, 1944 

Hosterman, 1969b

WnstArman 1979

41 Frostburg - Maryland Sed.,Rf do Waage, 1950
ATLANTIC AND GULF COASTAL PLAINS

TABLE 2. Kaolin, refractory clay, ball clay, and halloysite found in the United States Continued

Number District State Type of clay Age Reference

42

43

44

North East do Sed., B

Spruce Pine North Carolina - 

Gore Georgia -

 Res., K -

 Sed.(?), H -

 Cretaceous 

 Tertiary(?) 

 in Devonian rocks 

Knechtel and others,

1961.

Parker, 1946 

Broadhurst and Teague,

1954.

46 Hyd.(?), K

cene. 

? Ogden, 1969

Lower Tertiary 

', E?^ Cretaceous

v. AUGUSTA, GA.- 

\ AIKEN, S. C.

FIGURE 3. Locations of the six major districts in the South CarolinaGeorgia-Alabama kaolin belt.

used for making alum-type chemicals and bauxite. 

Similar refractory kaolin and bauxite are mined in the 

Eufaula district, Alabama. Kaolin and small bauxite 

deposits occur in the belt between the Andersonville 

and Eufaula districts (Zapp and Clark, 1965; Clark, 

1965), but there has been no mining in this area for 

several decades. Kaolin is also known to occur between 

the Macon-Gordon and Andersonville districts, and 

deposits in this part of the belt may be very large; however, little information about these deposits is available, 

because the results of company drilling are privileged.

Occurrence and Age

All of the kaolin deposits in the South CarolinaGeorgia-Alabama belt are in sedimentary beds, and,

except for a small outlier at Warm Springs (fig. 3), all 

underlie the Coastal Plains. The greatest inland overlap of Cretaceous and lower Tertiary sediments onto 

crystalline rocks is in the Wrens district (fig. 3). The 

kaolin deposits in the Wrens and other districts northwest of the Ocmulgee River are alined along the landward edge of the overlap. The Andersonville district, 

Georgia, and the Eufaula district, Alabama, are 60-75 

km south of the edge of the overlap. The small kaolin 

deposits in a downfaulted outlier of Coastal Plain sedimentary beds in the inactive Warm Springs district, 

Georgia, are about 35 km north of the edge of the overlap.

The kaolin deposits of Late Cretaceous age are in the 

Aiken-Augusta, the western part of the Sandersville, 

and the Macon-Gordon districts (fig. 3). The kaolin 

deposits of this age are in a wedge-shaped Cretaceous 

sand unit that is truncated updip by erosion and is 

known to be more than 335 m thick where penetrated 

by a well downdip. This unit rests unconformably on 

pre-Cretaceous crystalline rocks, and it is overlain by 

overlapping Tertiary formations. The Cretaceous beds 

consist chiefly of white to buff, crossbedded, irregular 

and channel-fill deposits of medium to very coarse, subrounded to angular quartz sand. Interstitial kaolinitic 

clay, kaolin balls, and white mica flakes are common 

in the sand. The only fossils known to be present in the 

unit are plant remains. The Cretaceous unit is dated 

by regional correlations and age of pollen. A pollen 

sample collected stratigraphically above a kaolin deposit in the Macon-Gordon district was found to be of 

Maestrichtian Age, and another from 70 m below the 

top of the unit was of definite Cretaceous age (Tschudy 

and Patterson, 1975). The kaolin deposits in the Cretaceous unit are generally lenticular or saucer-shaped 

bodies ranging greatly in thickness and extent. Some 

are as much as 12 m thick and more than 2 km long. 

Most deposits mined are in the upper part of the Cretaceous unit because of the cost of removing thick overburden.

Kaolin deposits of early Tertiary age occur in all
10 KAOLIN IN NORTH AMERICA, HAWAII, AND THE CARIBBEAN

three districts northeast of the Ocmulgee River that 

contain Cretaceous kaolin and in the Wrens district. 

The Tertiary strata containing the kaolin are similar 

to the Cretaceous beds on which they rest unconformably. The lower Tertiary beds overlap the Cretaceous 

unit and extend onto crystalline rock at several localities. The lower Tertiary kaolin deposits tend to be 

larger than the Cretaceous deposits. One deposit in the 

eastern part of the belt, where thicknesses are 10-25 m, 

is 18 km long (Murray, 1976, p. 117).

The lower Tertiary strata in the Macon-Gordon district have been named the Huber Formation, which as 

defined by Buie (1978) includes all the strata between

the Cretaceous or older rock, upon which it unconformably rests (fig. 4), and the base of strata of Jacksonian 

Age (late Eocene). Lithologically, the Huber is typical 

of a tidal-flat environment of deposition. Channel-fill 

deposits are abundant, and most of the formation is 

intricately crossbedded. Ilmenite and other dark heavy 

minerals are abundant and are concentrated along 

bedding planes. Lignitic clays, which contain pollen, 

occur at many places, usually as single beds or as restricted lenses. Rounded boulders of pisolitic kaolin 

and gibbsitic kaolin, ranging in diameter from a few 

centimeters to more than 2 m, are present in the upper 

part of the formation at many places. Many of these

Era

y

o

1 c tj

u

io

U)

S

U

o

gw 

<oPerod

&

t

3

^

gj

O

I

Epoch and 

age

1

1

^3'e

-a

"i>

u

~ ? j~

i?OH

1

c 

^ f

E

2

3

i

1

^

J

i

 a

s

Formation and members

|

1

1

co

Irwinton Sand 

Member

Twiggs Clay Member

Tivola Limestone

Clmchfield Sand

Huber Formation

Cretaceous beds, undivided

Paleozoic (?)

crystalline rocks

Lithology

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i^^^jILLL '"^^f^^vix

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Thickness

0-150 ft

(0-46 m)

0-1 5 ft

(0-4. 5 ml

0-15 ft

(0-4.5 m)

0-94 ft

(0-28.6 m)

0-1 100 ft

(0-335 m)

Description

Clay, pale-green to gray, laminae of fine-grained sand abundant, upper part commonly fissile.

contains lithographic limestone as much as 1 ft (0.3 m) thick, Bryozoa common in lowest 

part, locally lenticular, contains lenses of Irwinton Sand Member.

Limestone, mostly light-gray, sandy, has distinctive knobby appearance, diverse marine

fauna, Bryozoa very abundant in upper part at several places, echinoids common.

Sand, white to yellow where fresh, fine- to medium-grained, massive, crossbedded.

well-sorted, heavy minerals moderately abundant, locally calcite-cemented, poorly

preserved echinoid remains rare. Lower part locally is fine- to coarse-grained, poorly sorted. 

I locally contains white nodules of sandy limestone, bioturbated; contains small pectin.

\pelecypod, oyster, and gastropod fossils.

Sand, white, mostly medium grained to very coarse grained, abundant channel fill deposits

and crossbedding, fine-grained heavy minerals abundant along bedding planes; contains

scattered small lignitic and carbonaceous clay deposits bearing middle Eocene pollen.

dwarfed marine fauna present locally; kaolin balls and rounded masses of pisolitic clay and

bauxite occur locally; contains abundant large commercial white kaolin deposits. Formation is

mainly of Claibornian Age, but lignitic clays containing Paleocene pollen and brown kaolin

lenses rich in organic material are present locally m lower part.

Sand, white, medium grained to very coarse grained, dark heavy minerals rare to moderately

abundant, contains balls and thin layers of white kaolin as well as large commercial deposits;

lignitic clay at one locality contains pollen of Late Cretaceous age.

Sericite schist, granite gneiss, and intrusive granitic rocks.

EXPLANATION LU Ka°lm [^"J Lignitic clay deposit

FIGURE 4. Generalized geologic section, Macon-Gordon kaolin district, Georgia.
ATLANTIC AND GULF COASTAL PLAINS 11

boulders are enclosed in sand, and they clearly indicate 

a high-energy environment of deposition. The upper 

parts of kaolin deposits in the Wrens district contain 

sponge spicules (fig. 5), and Scrudato and Bond (1972) 

reported that spicules are also present in deposits farther to the northeast.

The age of some of the kaolin in the Huber Formation 

is now known to be Claibornian (middle Eocene part), 

and some may be somewhat older Tertiary. The Claibornian Age is assigned on the basis of the discovery of 

pollen of this age below a clay deposit that is overlain 

by fossiliferous marine beds of Jacksonian Age (late 

Eocene) (Tschudy and Patterson, 1975). Diverse suites 

of small marine mollusks of early or middle Eocene age 

also occur in a stratigraphic position below commercial 

kaolin deposits at several localities (Buie and others, 

1979). The possibility that some of the Tertiary kaolin 

may be older than middle Eocene is based on the identification of pollen from lignitic material in impure 

clays and kaolinitic sands (Tschudy and Patterson, 

1975). A sample of drill core from a locality east of the

FIGURE 5. Electron micrograph of kaolin of Eocene age from near 

Wrens, Ga., showing sponge spicule. (Micrograph by W. D. Keller, 

University of Missouri.)

Macon-Gordon district contained probable Wilcoxian 

(early Eocene) pollen. Definite Paleocene pollen were 

found in samples from three localities in one mine area 

in the district. This pollen is associated with dinoflagellates that are probably marine. The recognition of 

the older strata and the occurrence of Paleocene kaolin 

in the Andersonville district to the southwest make it 

seem likely that some of the valuable kaolin in the 

Macon-Gordon district and other districts to the northeast is older than middle Eocene.

At one locality, lignitic clay of Paleocene age located 

stratigraphically between kaolin deposits contains 

marine dinoflagellates. These fossils and the megascopic marine fauna of Claibornian Age indicate at 

least two intervals of marine or brackish-water deposition. Other intervals of marine deposition may have 

occurred during the approximately 20 million years 

when the Huber Formation was being deposited. However, during much of this time, this region was undergoing erosion, and neither marine nor continental sediments were being deposited.

Three types of tubular features or borings of animals 

are found in the Huber Formation. One type, found 

only in the kaolin deposits, is a peculiar spaghettilike 

form; some of these tubes are branching and resemble 

Bryozoa, whereas others appear to be filled borings. 

Most are about 2.5 mm in diameter, and some are as 

much as 3 cm long. A second type of tubular feature is 

present in sand and clayey sand beds in the upper part 

of the formation. This type is commonly as much as 10 

cm long. Most of these features are vertical, but they 

are oriented in various directions. Most are preserved 

only as clayey or slightly cemented sand fillings in 

unconsolidated sand. The third type consists of boring 

fillings called Halymenites in older reports (Eargle, 

1955). This type is as much as 5 cm in diameter and is 

known to extend downward nearly 2 m.

Kaolin deposits of Paleocene age occur in the Andersonville and Warm Springs, Ga., and the Eufaula, Ala., 

districts (fig. 3). The ages assigned to the deposits in 

the two districts in Georgia are based on recent pollen 

studies (N. O. Frederiksen, oral commun., 1979). The 

deposits in the Eufaula district, like those at Andersonville, are in the Nanafalia Formation and therefore are 

the same age. The Warm Springs deposits have been 

exhausted, and little is known about them other than 

that they are associated with small gibbsitic bauxite 

deposits in a downfaulted block of sediments surrounded by crystalline rocks in the Piedmont region. 

They are of interest mainly because their geographic 

location strongly suggests that kaolin deposits were far 

more extensive in the region north of Andersonville 

before the extensive erosion of Paleocene and Upper 

Cretaceous beds.
12 KAOLIN IN NORTH AMERICA, HAWAII, AND THE CARIBBEAN

The kaolin and bauxite deposits in the Andersonville 

district are in the Nanafalia Formation, which consists 

mainly of medium to coarse kaolinitic and micaceous 

sand (H. E. Gofer and J. P. Manker, written commun., 

1979). The kaolin is in tabular lenticular bodies ranging from less than 1 m to about 15 m in thickness; some 

deposits extend over areas of several hectares. The 

bauxite is also in lenticular bodies, which typically are 

enclosed by bauxite kaolin that grades into kaolin. 

Most bauxite bodies are 1-3 m thick, and the maximum thickness of bauxite and bauxitic clay units is 

about 18 m.

The kaolin and bauxite in the Eufaula, Ala., district 

described by Clarke (1972) and Burst (1974) are 

remarkably similar to the deposits in the Andersonville, Ga., district. One difference in the geology of the 

two districts is that there is more evidence that sinkholelike depressions were, as postulated by Clark 

(1972, p. 83-88), the sites of bauxite formation in the 

Eufaula district than in the Andersonville district. The 

Clayton Formation, which underlies the Nanafalia 

Formation, is thicker, contains much more limestone, 

and shows more evidence of solution in the Eufaula district than in the Andersonville district.

Mineralogy

The kaolin deposits of Cretaceous and early Tertiary 

age in the districts northeast of the Ocmulgee River 

are quite similar in gross mineralogy. Kaolinite is by 

far the dominant mineral in these deposits and constitutes 90-95 percent of most clay mined. Trace amounts 

of smectite occur in many deposits, and this mineral 

makes up 30-40 percent of the kaolin at a few localities. Quartz is the most abundant nonclay mineral 

impurity in the kaolin, and amounts present range 

broadly. Most deposits mined are less than 5 percent 

quartz, but greater amounts are present in subeconomic kaolin, and very sandy kaolinitic beds contain 

more than 75 percent of this mineral. Ilmenite is the 

second most abundant nonclay mineral, and this mineral and very fine grained anatase contain the TiO2 in 

the kaolin. Other minerals commonly present as accessories in kaolin are muscovite, biotite, magnetite, tourmaline, zircon, kyanite, monazite, goethite, leucoxene, 

graphite, and occasionally other heavy minerals.

The Cretaceous and lower Tertiary kaolin deposits 

northeast of the Ocmulgee River are similar in many 

ways, but they differ in several characteristics, including particle size, abundance of vermicular crystals, 

crystal perfection, and specific gravity (table 3). Although Cretaceous and lower Tertiary kaolins are similar in particle-size range (fig. 6), the older deposits seldom are more than 65 percent < 2/tm particles, whereas 

the younger deposits generally are more than 90 percent <2/un particles. The Cretaceous kaolin contains 

appreciable quantities of vermicular crystals (fig. 7) 

that are as much as 30 /on long. These relatively large 

crystals are in a fine matrix of kaolinite books and

TABLE 3. Characteristics of the Cretaceous and Eocene kaolin deposits 

in the Macon-Gordon district, Georgia

General 

characteristics Cretaceous Eocene

Color White to cream or buff; 

natural brightness 

high.

Mainly white to cream, 

buff, or gray; commonly 

has a slight greenish 

tinge that changes to a 

faint pinkish tint upon 

exposure; some deposits 

are very light gray; natural brightness moderate to low.

Fracture or Smooth; when dry, breaks Mostly breaks into irregparting. easily into friable 

blocks having sharp 

angles and smooth flat 

or subconchoidal faces; 

commonly called "soft 

kaolin."

ular chunks with rough 

or hackly fracture; commonly called "hard 

kaolin."

Tubular 

structures 

resembling 

borings or 

Bryozoa.

Pisolitic 

texture.

Particle sizeCrystal 

perfection.

Absent Common

Rare

Generally 65 percent < 2 

IJLTa; vermicular crystals and "books" cornCommon in upper parts 

of deposits.

Generally more than 90 

percent <2 ^m; vermicular crystals scarce.

Generally good Generally poor

TiO2 content- About 1 percent About 2 percent

Mineral impurities 

other than 

quartz 

sand.

Mainly mica, miscellaneous heavy minerals; 

fine-grained dark minerals are rare or unobservable in hand specimens.

Very fine grained dark 

heavy minerals moderately abundant and observable in most hand 

specimens.
ATLANTIC AND GULF COASTAL PLAINS 13

I ' ' ' ' I ' ' ' 

Lower Tertiary kaolin

100 50 10 5 15 

EQUIVALENT SPHERICAL DIAMETER IN MICROMETERS

FIGURE 6. Particle-size distribution of Cretaceous and lower Tertiary

kaolins.

FIGURE 7. Electron micrograph of kaolin of Cretaceous age from 

near Gordon, Ga., showing vermicular crystals. (Micrograph by 

W. D. Keller, University of Missouri.)

plates. Vermicular crystals are rare in Tertiary kaolin, 

which consists chiefly of thin plates with few thick 

books (fig. 8). In addition to the crystal characteristics 

shown in the electron micrographs, X-ray diffraction 

patterns of Tertiary kaolin show broad, diffuse prism 

reflections, indicating a poorly ordered crystal strucFIGURE 8. Electron micrograph of kaolin of Eocene age from near 

Wrens, Ga., showing fine particle size. (Micrograph by W. D. Keller, 

University of Missouri).

ture (Murray and Lyons, 1956), whereas the Cretaceous kaolinite shows sharp, distinct prism reflections, 

indicating a well-ordered structure. Klinefelter and 

others (1943) determined that the bulk specific gravity 

of the Cretaceous kaolin (soft) ranged from 1.32 to 1.55, 

whereas the bulk specific gravity of the Tertiary kaolin 

(hard) ranged from 1.61 to 1.79.

Except for the much greater abundance of gibbsitic 

bauxite bodies and the darker color, the kaolin deposits 

in the Andersonville district are similar to those northeast of the Ocmulgee River. Although most of the kaolinite in the Andersonville deposits is in the <l-/*m 

particle-size range, it also has a broad range of larger 

particles (H. E. Gofer and J. P. Manker, written commun., 1979). The books of coarse-grained kaolinite tend 

to be more perfectly ordered than the fine-grained clay 

matrix, and the coarser clay is generally most abundant in the bauxite and bauxitic clay.

Clay-mineral impurities in the Andersonville deposits include smectite, illite, and glauconite (H. E. 

Gofer and J. P. Manker, written commun., 1979). The 

iron content of kaolinite is thought to be the principal
14 KAOLIN IN NORTH AMERICA, HAWAII, AND THE CARIBBEAN

cause of this kaolin being darker than kaolin in deposits to the northeast. Smectite is present in varying 

amounts throughout most of the Andersonville kaolin 

but tends to be most abundant in the upper parts of 

deposits that are overlain by marine beds. At places, 

nearly 50 percent of the upper few centimeters of clay 

is smectite. The glauconite in the Andersonville deposits was found in the sand fraction of a lens of darkgray, lignitic clay, nearly 2 m thick, within a much 

thicker kaolin deposit. The glauconite occurs as abraded, 

lobate, and fragmented grains.

Nonclay minerals other than quartz in the Andersonville kaolin that were apparently deposited with the 

clay include muscovite, tourmaline, staurolite, kyanite, biotite, and zircon. Pyrite and siderite are common 

in parts of the kaolin. Both of these minerals formed 

diagenetically, as is indicated by their occurrence as 

euhedral crystals, fracture fillings, and concretionlike 

nodules.

Origin

Though geologists who have worked on the kaolin 

deposits in the South Carolina-Georgia-Alabama belt 

have some differing opinions, most agree that the clay 

was transported from weathered rocks located to the 

north and west. The principal source is commonly 

thought to have been weathered crystalline rocks in 

the Piedmont. However, there is some uncertainty as 

to whether or not the source of much of the kaolin may 

have been farther inland. Reasons for the uncertainty 

include lack of knowledge about how far the sedimentary overlap extended. The overlapping sediments may 

have extended much farther before erosion formed the 

present land surface, for the following reasons: (1) the 

existence of Coastal Plain sediments and kaolin in the 

Warm Springs outlier (fig. 3); (2) the occurrence of commercial kaolin near the edge of the overlap in the 

Wrens district, which is the maximum landward extent of conterminous Coastal Plain sediments; (3) the 

occurrence of boulders and cobbles of kaolin, some of 

which are pisolitic, at several places along the edge of 

the overlap; and (4) the dendritic drainage developed 

on the crystalline rocks in the Piedmont. Staheli (1976) 

pointed out that structurally controlled trellis drainage patterns would have developed on the folded and 

faulted crystalline rocks, if they had been at the surface when the drainage systems developed. He therefore concludes that present patterns have been superimposed on Coastal Plain sediments. Considering the 

four points in the foregoing outline, we conclude that 

the source of the kaolin can be, at best, little more than 

an opinion.

Sedimentary features in the kaolin and associated

beds make it clear that the Tertiary kaolin was deposited in a tidal-flat environment. Cretaceous deposits 

probably accumulated in a similar environment, but 

the evidence is less clear. The sedimentary features 

strongly suggest that, during early Tertiary time, the 

kaolin belt was a lowland much like the present Atlantic coast of Georgia. This coastal area is characterized by 

lengthy offshore bars, back bays, lagoons, salt marshes, 

and sluggish meandering streams having abundant 

oxbow lakes and intricately meandering distributaries. Advances and withdrawals of the seas took 

place in the kaolin belt in at least two, and probably 

several, intervals during early Tertiary time. Evidence 

for advances includes Paleocene glauconite in the 

Andersonville district, dinoflagellates in the MaconGordon district, and middle Eocene mollusks in the 

Macon-Gordon district. The sponge spicules in the kaolin in the Wrens and Aiken-Augusta district certainly 

indicate deposition in an aqueous environment, but it 

is not certain whether the sponges are marine or freshwater forms. Many of the tubular features in Tertiary 

kaolin are probably borings of littoral animals, but the 

identification is far too uncertain to provide acceptable 

evidence of depositional environments. Periodic emergences are indicated by the abundant plant remains, 

channel deposits, erosional contacts, and boulders and 

cobbles of kaolin in the Macon-Gordon district and the 

plant roots in kaolin in the Andersonville district. The 

bauxite also is evidence of emergence, if the conclusion 

that it formed by subaerial weathering is correct. The 

sporomorphs in the plant remains throughout the belt 

strongly suggest that the climate throughout the early 

Tertiary was subtropical.

We believe that the vermicular kaolinite crystals are 

authigenic and are the result of recrystallization influenced by moving subsurface water. We favor this origin over Hinckley's theory (1961) explaining vermicular growths as forming from mica and euhedral plates 

from feldspar. The following reasons are in opposition 

to the mica-parent idea for the vermicular forms: (1) The 

idea does not account for the abundance of vermicular 

crystals in the Cretaceous clay and their absence in 

Tertiary kaolin, as the kaolins of both ages are likely 

to have had the same source areas; (2) the Cretaceous 

kaolin, being older, has had considerably more time for 

recrystallization to take place; (3) the large vermicular 

crystals could not have withstood transportation even 

in an aqueous medium; and (4) the vermicular crystals 

in the Paleocene clay deposits in the Andersonville district occur almost exclusively in the bauxite and not in 

the associated fine-grained kaolin masses. It seems certain that the gibbsitic bauxite has undergone considerably more alteration and recrystallization than has the 

fine-grained kaolin.
ATLANTIC AND GULF COASTAL PLAINS 15

The mineralogy and sedimentary characteristics of 

the kaolin and bauxite in the Andersonville district 

indicate that the deposits accumulated in a shallow 

estuarine environment and were altered during periods of emergence and submergence (H. E. Gofer, Jr., 

and J. P. Manker, written commun., 1979). The deposits 

accumulated as fine-grained kaolinitic sediments of 

widely varying purity that were transported by 

streams. The principal source was weathered crystalline rock to the north. Upper Cretaceous sedimentary 

formations also may have contributed kaolin, but this 

is uncertain because the presence of kaolin of Paleocene age in the Warm Springs district 60 km north of 

Andersonville suggests that Cretaceous beds may not 

have been exposed at the time of its deposition. Local 

basins of deposition were areas of shallow water between deeper distributaries in deltas of streams flowing into the estuary. Zones of root remains and carbonaceous material containing sporomorphs of land plants 

in kaolin deposits indicate emergences above sea level 

once during the period of kaolin deposition and again 

at the close of the interval. The gibbsitic bauxite is 

believed to have formed by weathering and leaching of 

kaolin during periods of emergence. Bauxitic clay 

enclosing the bauxite apparently formed in two ways. 

The clay on the sides of and below the bauxite represents incomplete stages of bauxite formation during 

weathering. The bauxitic clay above bauxite formed by 

resilication of gibbsite in silica-bearing water after 

submergence. The location of the larger kaolin deposits 

in the northern (landward) part of the district and the 

presence of glauconite interbedded with kaolin in the 

southern part of the district suggest that the principal 

centers of kaolin deposition were parts of the estuary 

having fresh or low-salinity water. At places in the 

southern part of the district and farther south, impure 

smectite associated with gypsum occurs at the stratigraphic position of the kaolin deposits; these minerals 

suggest deposition in saline water.

FLORIDA

Irregularly shaped, sandy kaolin deposits containing 

some quartz gravel are scattered throughout a narrow 

belt more than 200 km long in peninsular Florida 

(fig. 2, location 45). The deposits are near the surface in 

a problematical unit of clayey sand and gravel that is 

thought by some geologists to be part of the Citronelle 

Formation of Pliocene age and by others to be weathered Miocene beds. One raw sample of the kaolin for 

which composition data have been published (Pirkle, 

1960, table 2) was 75-85 percent kaolin, 6-8 percent 

quartz, 5-8 percent hydrous mica, 2-3 percent ironoxide minerals, and <1 percent smectite. However,

many of the deposits are known to contain considerably more than 8 percent quartz.

The origin of the Florida deposits is difficult to explain because of the absence of an obvious source of 

kaolinite and the abundance of coarse sand and gravel 

in the clay. Several theories have been advanced, 

including deposition in a deltaic environment and 

alteration of feldspar sand (Pirkle, 1960). We favor the 

idea that the deposits formed mainly by in-place 

weathering of older argillaceous sediments. Little can 

be mustered in support of this opinion except that Miocene beds of peninsular Florida are known to be rich in 

smectite, which Altschuler, Dwornik, and Kramer 

(1963) have shown conclusively weathers to kaolinite 

in the Florida phosphate region.

Kaolin has been produced intermittently in Florida 

(fig. 2, location 45) by hydraulic methods for more than 

75 years. The total output is estimated to be nearly 

2 million tons.

ARKANSAS BAUXITE REGION

In the Arkansas region (fig. 2, location 25), kaolin is 

abundant in residual and sedimentary deposits associated with the bauxite with which the kaolin intergrades, so that there are all degrees of mixture from 

fairly pure gibbsite rock to almost pure kaolin (Gordon 

and others, 1958, p. 87-88, 255). Kaolinite, where present in bauxite, occurs as white to gray masses of fine 

micaceous crystals in veins and veinlets cutting the 

gibbsitic masses and as cavity fillings. It also forms 

vermicular crystals or long accordionlike books, which 

in thin sections of bauxite have been observed to range 

in width from 0.005 to 0.7 mm. They frequently are 

contorted and have a characteristic wavy optical 

extinction. In pisolitic bauxite, kaolinite usually fills 

veinlets and cavities in the matrix; less commonly, it 

forms tiny veinlets that cut pisolites, or it fills their 

interiors. The kaolin deposits are scattered through 

the bauxite region, which is 40 km long and more than 

10 km wide, and the total kaolin present is estimated 

to be more than 0.5 billion tons.

The residual kaolin deposits are in saprolite developed on nepheline syenite masses that are the principal parent rock of both the kaolin and the bauxite. The 

residual kaolin represents an intermediate stage of 

weathering between the syenite and bauxite. This kaolin and some of the bauxite show preserved textures of 

the syenite, and for this reason a few of the bauxite 

deposits are referred to as the granitic-textured type 

(fig. 9).

Electron micrographs (Gordon and others, 1958, 

fig. 28) of the clay in what is apparently the least 

weathered syenite show that the dominant mineral
16 KAOLIN IN NORTH AMERICA, HAWAII, AND THE CARIBBEAN

FIGURE 9. Diagrammatic section of residual kaolin deposits in the 

Arkansas bauxite district. (From Gordon and others, 1958, fig. 36.)

developed in pseudomorphic replacement of nepheline 

and microcline is tubular halloysite. Hexagonal kaolinite crystals are present in pseudomorphs after feldspar 

that are probably intermediate stages of weathering 

between halloysite and gibbsite formation.

The largest kaolin deposits in the region are of the 

sedimentary type that commonly surround and grade 

into transported bauxite bodies through zones of bauxitic kaolin. The bauxite-kaolin deposits form lenticular 

bodies that have a maximum thickness of about 25 m, 

but in most places they are no more than 20 m thick. 

The bauxite-kaolin zone constitutes a facies along the 

upslope edge of the Berger Formation. Downdip the 

bauxite-kaolinite zone interfingers and grades into 

greenish and bluish sandy clay containing lignite. The 

Berger Formation is of early Eocene age, which dates 

the transported kaolin. The nepheline syenite and 

other rocks in the source areas are believed to have 

weathered to form kaolinite in both Paleocene and 

early Eocene time.

According to Tracey (1944), the typical sedimentary 

kaolin contains more than 35 percent alumina, less 

than 45 percent silica, and less than 5 percent iron 

oxide. In the transition through bauxitic clay to bauxite, the alumina increases and the silica decreases. In 

the bauxite, the alumina content is normally 45-60 

percent and the silica < 1-20 percent. The titanium 

oxide content of the clays is 1-4 percent, usually 2-3 

percent. Crystalline siderite is the most abundant 

impurity. Siderite fills cavities in the bauxite and also 

forms disseminated pellets and granular aggregates. 

Siderite is most abundant, on the whole, in the lower 

bauxitic clays but also is abundant in other parts of 

some deposits, and a few deposits contain abundant 

siderite throughout. Aggregates and heavy concentrations of siderite are commonly of small extent. Limonite is present, probably as an oxidation and hydration 

product of the siderite. Biotite occurs rather sparsely in

the lower white clay. Tiny grains of a titaniferous iron 

mineral, probably ilmenite, are disseminated in the 

clays.

OTHER DISTRICTS IN THE COASTAL PLAINS

Very large deposits of sandy kaolin and kaolinitic 

sand of early Eocene age extend across Limestone and 

neighboring counties in Texas (Fisher, 1965). Lightcolored kaolin and silica sand are recovered as coproducts by washing material from these deposits at Kosse, 

Tex. (fig. 2, location 20). This beneficiated kaolin is sold 

for use in special ceramic products, but it is not white 

enough to meet specifications for paper filler and coater 

clay. Sandy kaolin from near Kosse has also been used 

in making white portland cement, brick and tile, and 

pottery.

Kaolinitic clay deposits occur at several places in 

Rusk County, Tex. (fig. 2, location 18). These clays are 

in the upper beds of the Wilcox Group of early Eocene 

age. They are reported to have high plasticity and are 

mined at several localities to supply brick plants at 

Henderson (Fisher, 1965). Fisher also considered the clay 

in Rusk County to be a potential source of aluminum.

Appreciable tonnages of kaolin were mined in the 

Anna, 111., district (fig. 2, location 26) when clay for crucibles and glass pots was produced in 10 mines during 

World War I (Lamar, 1948, p. 23), but there has been 

very little mining in the district in recent years. The 

kaolin in the Anna district was illustrated by Grim 

(1934, fig. 1) as occurring with sand in sinkhole depressions in Mississippian (Lower Carboniferous of the 

European system) limestone. The deposits are as much 

as 30 m thick and some are nearly 100 m in diameter. 

Minor amounts of lignite are in both the sand and the 

basal parts of clay deposits. The clay is overlain by red 

and white sand containing some clay pockets. Dr. Grim's 

petrographic studies and chemical analyses show that 

the kaolin is essentially pure. On the basis of X-ray 

analysis, Professor P. F. Kerr identified it as a member 

of the kaolinite-anauxite group (Grim, 1934, p. 663- 

664). The age of the kaolin at Anna is somewhat uncertain. Grim concluded, on the basis of its heavy-mineral 

content, that it is of either Late Cretaceous or early 

Tertiary age, and Lamar (1948) used Cretaceous(?) to 

indicate his uncertainty. In table 1 of this report, we 

use Eocene(?) for the age of this clay; this suggestion is 

based on the likelihood that the Anna kaolin is the 

same age as the Kentucky-Tennessee ball clay farther 

south.

Kaolin deposits that were mined in the early 1900's 

are near Glen Alien, Bollinger County, Mo. (fig. 2, location 24), and in nearby areas. This kaolin is thought to 

occur in sinkholes or other solution depressions in car-
DISTRICTS IN NORTH CENTRAL AND WESTERN UNITED STATES 17

bonate rock. Tennissen (1960) described some deposits 

as bedded and others as residual accumulations with 

chert and sand. He considered the deposits to be of Cretaceous age.

Kaolin deposits, many of which are associated with 

small high-silica gibbsitic bauxite deposits, are scattered through northeastern Mississippi. Deposits in 

several areas have been investigated, and typical ones 

in the Kemper-Pinedale area (fig. 2, location 29) will be 

discussed here. Conant (1965) found that the kaolin 

occurs in the uppermost part of Porters Creek Clay of 

Paleocene age and the lower part of the overlying Wilcox Formation of Eocene age. The two formations are 

separated by an unconformity representing an interval 

of weathering and erosion. The kaolin in Paleocene 

beds is residual, being preserved in weathered parts of 

the Porters Creek Clay (fig. 10) that were not eroded 

prior to the deposition of Eocene beds. The kaolin in 

the Eocene part of the Wilcox is mainly in channel-fill 

deposits. The lower strata in the fills commonly consist 

of kaolin conglomerate that was eroded and transported from the Porters Creek Clay. Presumably, massive kaolin in the channel-fill deposits also was transported from the Porters Creek Clay.

White kaolin occurs at a site known as Chalk Bluff 

several kilometers south of Hackelburg, Ala. (fig. 2, 

location 31). The deposit is in the upper beds of Late 

Cretaceous age assigned to the Tuscaloosa Group. This

kaolin is therefore approximately the same age as the 

Cretaceous kaolin in central Georgia located several 

hundred kilometers to the east. The Chalk Bluff deposit rests unconformably on weathered shale, part of 

the Pottsville Formation, which is of Westphalian Age 

of the European time classification. The upper parts of 

the deposit were eroded prior to the deposition of overlying beds, causing considerable variation in thickness. It is about 3 m thick at one mine and more than 

8 m thick at another nearby mine (Clarke, 1966, p. 26). 

The < 2-/*m fraction of a sample of this kaolin was 90 

percent kaolinite, 5 percent chlorite, and 5 percent 

illite. It contained only a trace of quartz. Kaolin from 

this deposit is air floated and sold for use in pottery, 

glasses, carriers for insecticides, and pharmaceutical 

preparations.

DISTRICTS IN NORTH CENTRAL AND WESTERN UNITED STATES

MINNESOTA

The principal kaolin deposits in Minnesota (fig. 2, 

location 21) are in weathered rocks that are exposed in 

the Minnesota River valley between Granite Falls and 

Fort Ridgley State Park, a distance of 75 km (Parham, 

1970). The deposits formed by humid tropical weathering during the latter part of the Mesozoic Era, probably 

early Late Cretaceous time. This weathering produced 

a kaolinitic residuum (fig. 11, unit 1), as much as 30 m

METERS 2 

135-1

EXPLANAT ION

TERTIARY

A

Eocene

A

Wilcox Formation

A

Paleocene

\ r 

Midway Group

A

Porters Creek Clay

A

Fearn Springs Sand Member

Gray sandy Crossbedded Brown,silty, 

clay sand and

lignitic clay

Kaolin Lignite Kaolin Kaolin grading White, sandy, Black, sandy, Wilcoxconglomerate downward into and and Midway

next unit micaceous clay micaceous clay contact

FIGURE 10. Diagrammatic section of kaolin deposits in the Kemper-Pinedale area, Mississippi. (Modified from Conant, 1965, fig. 2.)
18 KAOLIN IN NORTH AMERICA, HAWAII, AND THE CARIBBEAN

200 KILOMETERSHEDWOOD 

FALLS

(Minnesota River

Unit 3 

Unit 2 

Unit ^

St. Cloud

F LEIST1 0 CErsTE

Terrace gravel

Till

Cross-bedded sand

Gas-bearing 

organic-rich clay and silt

Pisolitic kaolinite

Kaolinitic residuum

Igneous and metamorphic rocks

FIGURE 11. Generalized sections illustrating: A, the regional geology of the Minnesota 

kaolin deposits and, B, the kaolin and associated beds along the Minnesota River valley. 

(From Parham, 1970, p. 8.)

thick, over much of Minnesota, mainly from Precambrian metamorphic and igneous rocks. The weathered 

zone is now covered by younger Cretaceous sedimentary rocks and Pleistocene glacial deposits except locally along the Minnesota River valley in southwestern 

Minnesota and between St. Cloud and Little Falls in 

the central part of the State. The sedimentary beds and 

glacial deposits overlying the residuum are 12 m or

more in thickness. The Cretaceous beds contain sedimentary kaolin deposits that have been reworked from 

the residuum.

The clay minerals of the residuum (fig. 11, unit 1) 

that were formed from weathering of felsic rock types 

are composed primarily of kaolinite. In the least 

weathered parts of the profile, the kaolinite has an 

irregular platy form. Tubular halloysite is present in
DISTRICTS IN NORTH CENTRAL AND WESTERN UNITED STATES 19

minor amounts, especially in the lower part of the 

weathering profile. Mafic rock types weathered first to 

montmorillonite and under progressively more intense 

weathering to kaolinite.

Two Upper Cretaceous units of kaolinitic sedimentary rocks (fig. 11, units 2 and 3) overlie the residuum. 

The lowermost of these (unit 2), which was derived 

from erosion of the weathered residuum and which also 

underwent tropical weathering, has a maximum observed thickness of about 15 m. It is composed of varying proportions of kaolinite and quartz, with trace 

amounts of halloysite. An iron-rich, kaolinitic, pisolitic 

clay 1-2.5 m thick that contains small amounts of gibbsite and boehmite occurs at the top of unit 2 in several 

places. Sedimentary rocks of unit 3 disconformably 

overlie unit 2 and consist of gray to black, organic-rich 

clays and shales, thick beds of lignite, and at least one 

thin bed of bentonite. Kaolinite is abundant in the 

basal part of unit 3 but grades upward into montmorillonite and illite, suggesting that the humid tropical climate under which units 1 and 2 had formed had been 

replaced by a more temperate climate by the time unit 

3 formed.

LATAH COUNTY, IDAHO

The Latah County, Idaho, district (fig. 2, location 9) is 

located at the eastern edge of the Columbia Plateau 

physiographic province.

Three types of clay occur in the Latah district: residual clay derived from the Columbia River Basalt Group 

of Miocene age; residual clay derived from the granodiorite and related intrusive rocks of the Idaho batholith of Late Jurassic or Cretaceous age; and transported 

clay, an erosional product of the granodiorite and related intrusive rocks, deposited as part of the Latah 

Formation of middle or late Miocene age (Ponder and 

Keller, 1960; Hosterman and others, 1960). The two 

types of residual clay were formed during an interval 

of weathering called the "Excelsior weathering 

period" that occurred between flows of the Columbia 

River Basalt Group, when the land surface had a low to 

moderate relief and the climate was warm and humid 

with good oxidation conditions.

X-ray and differential thermal determinations on 

these clays show that kaolinite and halloysite (10A) 

are the principal clay minerals. The residual clay derived from basalt is composed of white halloysite commonly colored blue, gray, or black by ilmenite and 

occasionally stained brown by limonite or green nontronite. The residual clay derived from granodiorite 

and related intrusive rocks contains both halloysite 

(10A) and kaolinite, whereas the transported clay is 

predominantly kaolinitic. The latter two types of clay

are very similar in physical appearance both are 

white and both contain abundant quartz grains and 

mica flakes but the residual clay retains a relict granitic texture and is not bedded.

SPOKANE COUNTY, WASH.

The types of kaolin in Spokane County, Wash. (fig. 2, 

location 3), according to Hosterman (1969a) include 

(1) transported and a minor amount of residual clay in 

the Latah Formation of Miocene age, (2) bluish-gray 

residual saprolite formed on the Columbia River Basalt Group, and (3) white residual clay formed on preTertiary igneous and metamorphic rocks. Transported 

kaolin and other clays and silts forming the shale and 

the sand that make up the Latah Formation were deposited in lakes believed to have formed by basalt flows 

damming rivers. The evidence for lacustrian deposition is the presence of diatoms and sponge spicules and 

many species of plant fossils found in Latah beds. The 

residual clay in the Latah Formation consists of kaolin 

formed by weathering of shale; this clay is overlain by 

transported kaolin. The age of the residual and transported kaolin and the saprolite on basalt is Miocene, 

because the Latah Formation, as well as the Columbia 

River Basalt Group with which this formation is interbedded, is of this age. Hosterman (1969a, p. 25) reports 

that, at the time weathering took place, the climate 

was temperate and the annual rainfall was 75-120 cm. 

This conclusion is based on the prolific fossil representation, which includes a large number of plant species 

that today live mainly where these climatic conditions 

exist. The age of the weathering that formed the kaolinite in the pre-Tertiary rocks is less clear, as weathering could have taken place well before emplacement of 

the Miocene Columbia River Basalt Group.

Five clay minerals have been identified by X-ray diffraction in samples from these deposits. Kaolinite is 

found in all types of clay, except residual clay derived 

from basalt. Halloysite (10A) is found primarily in the 

residual clay derived from basalt, and traces are found 

in the residual clay derived from pre-Tertiary rocks. 

Smectite and illite do not occur in residual clay derived 

from basalt but do occur in varying amounts in all 

other types of clay. Nontronite is found only in the 

residual clay derived from basalt.

The clays formed under similar physical, chemical, 

and bacterial conditions during Tertiary time. It is 

likely, therefore, that the mineralogic composition of 

the unweathered parent rock controlled the type of 

clay mineral produced during katamorphic alteration. 

The augite in basalt altered to nontronite, and the plagioclase (labradorite) to halloysite. The pre-Tertiary 

rocks contained feldspars and muscovite altered to kaolinite and ferromagnesian minerals altered to smectite.
20 KAOLIN IN NORTH AMERICA, HAWAII, AND THE CARIBBEAN

The chemical composition of 220 samples determined 

by the X-ray fluorescence method indicates that the 

residual clay derived from basalt has an average AlaO3 

content of 22 percent and individual samples as high as 

39 percent; the Latah Formation clays, 20 percent and 

a high of 37 percent; and the residual clay derived from 

pre-Tertiary rocks, 20 percent and a high of 29 percent.

Analyses of fresh and partly weathered basalt and 

saprolite (table 4) show that the chemical changes taking place during the weathering are the leaching of Si, 

Fe, Ca, K, Mg, and Na. Al and Ti are the major elements 

concentrated, and HaO is added.

TABLE 4. Chemical comparison of unweathered Columbia River 

Basalt Group with saprolite derived from basalt

[From Hosterman, 1969a, table 2; data in weight percent. , no data. 

1, Average of 13 samples of Columbia River Basalt Group (Waters, 1955, 

p. 705); 2, one sample of Columbia River Basalt Group from sec. 3, T. 27 N., R. 

44 E., Spokane County, Wash, (analysis by rapid-rock method; Paul Elmore, 

Samuel Botts, and Gillison Chloe, analysts, U.S. Geological Survey); 3, one 

sample of Columbia River Basalt Group from an outcrop on the road at Mica 

Creek, sec. 4, T. 23 N., R. 45 E., Spokane County, Wash, (analysis by X-ray 

fluorescence); 4, one sample of partly decomposed Columbia River Basalt 

Group from sec. 3, T. 23 N., R. 45 E., Spokane County, Wash, (same analysts 

as for 2); 5, average of six samples of residual clay derived from Columbia 

River Basalt Group from sec. 23, T. 24 N., R. 44 E., and sec. 3, T. 23 N., R. 45 

E. (same analysts as for 2) ]

Unweathered

Partly 

decomposed Saprolite

Si02 

A120S 

r e2Us 

FeO 

MnO

TiO2 

CaO 

K2O 

PA 

MgO 

Na2O 

H2O+ 

H2O 

52.31

14.38

2.47

9.95

,4 91J.

2.10

8.37

1.26

.36

4.46

2.94

.74

.39

48.5

13.0

8.8

7.3

on .fia

3.3

8.4

1.0

.82

2.6

2.6

2.4

1.2

52

15

*19

 

3.7

8.8

1.7

 

 

 

 

 

46.6

20.6

4.8

3.5

.07

5.8

6.7

.44

1.2

.28

3.5

3.4

1.8

38.2

30.4

2.8

3.3

c\a .Ub

8.7

.83

.09

.66

.25

.18

11.7

2.4

Total- 99.9 100.2 100.5 98.7 99.6

'Total Fe is expressed as Pe-jO,.

The following mineralogical changes taking place as 

the basalt weathers are described by Hosterman (1969a, 

p. 17-18):

"* * * The katamorphic alteration of the Columbia River Basalt 

appears to have been controlled largely by ground-water movement. 

Most of the flows are vesicular and are cut by numerous vertical 

joints. It seems likely that surface water entered these joints but 

could not move freely until the basalt began to alter. Under the conditions of poor ground-water movement and poor drainage, the 

oxidation-reduction reactions probably proceeded at a slow rate, and 

the alkalies were not removed. The basaltic glass first altered to 

palagonite; subsequently, the palagonite and augite altered to nontronite which formed in vesicles and cracks. The formation of nontronite increases the permeability by removing some of the SiO2 , 

A12OS) and Fe20s from the basalt surrounding the vesicles and 

cracks. Under these new conditions, ground water moved freely, oxidation took place, alkalies were removed easily, and plagioclase 

(labradorite) altered to halloysite. As more of the basalt became 

exposed to the oxidation process the early formed nontronite was 

replaced by halloysite. * * *"

The alteration of nontronite to halloysite was observed in vesicles partly filled with clay; more massive 

accumulations along cracks remained unaltered. In 

the vesicles, greenish-yellow nontronite was replaced 

by white halloysite. Ilmenite is the principal resistant 

mineral in the parent basalt remaining in the saprolite. Disseminated fine grains of this mineral cause the 

gray color of the saprolite.

IONE, CALIF.

The principal deposits of high-alumina clay in California are in the lone Formation of Eocene age, which 

crops out in a discontinuous belt bordering the western 

foothills of the Sierra Nevada Range (fig. 1, location 5). 

Most of the lone clay that has been mined is near lone, 

Amador County, but appreciable tonnages have been 

mined near Lincoln, Placer County. In recent years, 

deposits have been mined at Valley Springs, Calaveras 

County; Knights Ferry, Stanislaus County; Michigan 

Bar and Folsom, Sacramento County; and near Cooperstown, Tuolumne County (Cleveland, 1957, p. 136). These 

mines are scattered through a belt more than 190 km 

long. Most of the beds have an average thickness of 

about 5 m, but in places they are much thicker, as near 

Lincoln where the thickness is about 30 m. The lone 

clay formed by the deposition of materials, including 

sand, transported from weathered rock higher in the 

Sierra Nevada Mountains to the east (Bates, 1945). 

The depositional environment is believed to have been 

lagoonal or deltaic. Because sand contents range from 

20 to more than 50 percent, washing is required for the 

recovery of high-quality clays.

According to Bates (1945), the clay consists mainly of 

kaolinite, but an earlier report (Alien, 1929, p. 377- 

378) indicates that anauxite is present. On the basis of 

thorough differential-thermal-analysis (DTA) investigations, Pask and Turner (1952) concluded that some of 

the lone kaolin is highly crystalline and some has a 

tendency toward halloysite, which presumably means 

it is disordered. These same authors report that PCE of 

the fire clay recovered from these clays ranges from 31 

to 34.

MESA ALTA, N.M.

The Mesa Alta kaolin deposits (fig. 2, location 16) 

occur along the unconformity between Jurassic and 

Cretaceous sedimentary formations (Reeves, 1963).
UNITED STATES-UNDERCLAYS 21

The deposits are in an irregular bed < 1-6 m thick. The 

clay ranges from pure white kaolin to very impure, 

commonly bluish, sandy material. An electron micrograph of the white type (Davis and others, 1950, pi. 5) 

shows that the kaolin occurs in subhedral and anhedral crystals. Though the origin of the Mesa Alta kaolin deposits is not adequately understood, it is likely 

that the clay has been transported from kaolinite formed 

by weathering of igneous rocks during the hiatus between the deposition of Jurassic and Cretaceous formations. The principal evidence for the igneous parent 

rocks is feldspar partly altered to kaolinite in granite 

pebbles in the sand overlying the kaolin. The clay probably was transported to local basins occupied by lakes 

or swamps. Some of the kaolin has been reworked, as is 

indicated by the presence of rounded clay pebbles at a 

few localities.

UNDERCLAYS

Underclays are more widely distributed and have a 

greater range in geologic age than all the other kaolinitic clays in the United States. They are most abundant 

in formations of Pennsylvanian age (Late Carboniferous 

of the European time scale) in the Appalachian Basin 

and in strata of this age in Missouri. The underclay 

deposits in Colorado are of Early Cretaceous age (Aptian), and those in Washington, Oregon, and California 

are of Paleocene and Eocene age. The small plastic-clay 

deposits in Hawaii of Holocene age also are underclays 

in the sense that they occur under peat.

Underclays also vary much more widely in mineral 

composition than do the other types of kaolin. Those 

discussed in this report consist mainly of kaolinite, but 

other large underclay deposits consist principally of 

mixtures of illite, chlorite, mixed-layer clays, minor 

amounts of kaolinite, and abundant nonclay impurities. The kaolinite ranges in crystallinity from very 

well ordered crystals to the extremely poorly ordered 

forms of the so-called fire-clay mineral. The underclay 

deposits in Hawaii are principally halloysite and 

apparently contain considerable quantities of noncrystalline matter. Diaspore and boehmite occur in some of 

the older underclay deposits. Gibbsite has been found 

in some deposits of Pennsylvanian age, as well as in 

Eocene deposits in Washington and the Holocene deposits in Hawaii.

A general relationship between mineral composition 

of the clays and thickness of the overlying coals exists 

in the United States. The purest kaolinitic underclays, 

including those containing diaspore, are restricted, 

with very few exceptions, to places where the overlying 

coal is no more than a few centimeters or at the most a 

fraction of a meter in thickness. On the other hand, the

thick coal beds that have been mined extensively tend 

to be underlain by impure underclays.

Another characteristic of underclays is that many of 

them contain fossil roots that prove they once served as 

soils. The most common root in deposits of Pennsylvanian age can be identified as that of the genus Stigmaria, S. ficoides Brongniart. The best preserved fossils 

consist of a stout rootstock, usually now compressed to 

form a thin, coaly sheet, on which the points of attachment of roots, or scars at the points of former attachment, are spirally arranged. Rootstocks (fig. 12) are not 

as abundant as rootlets. The rootlets are commonly 

compressed into very thin, filmy ribbons that cut the 

rock at all angles. Occasionally the coaly film has been 

lost and only more obscure impressions remain. The 

rootstock of Stigmaria was a spongy plant structure 

(fig. 13), and considerable volume must have been lost 

as the roots were reduced to coaly imprints.

In the following sections, several of the underclay 

districts of the United States will be discussed, and 

some of the others will be mentioned in an effort to 

show the wide occurrence of these deposits. The small

FIGURE 12. Stigmaria from the "Olive Hill" clay bed of the Lee 

Formation in Kentucky, showing main rootstock, attached rootlets 

(at right angles), and nodular root scars. Pocket knife is 7 cm long.
22 KAOLIN IN NORTH AMERICA, HAWAII, AND THE CARIBBEAN

10 mm

FIGURE 13. Cross section of a petrified root of Stigmaria 

ficoides Brongniart from a Pennsylvanian coal bed, Leslie County, Ky., showing delicate outer cortical tissue. 

The inner and middle cortex have broken down, leaving a 

large open cavity and a thin strand of conductive tissue. 

Shown about five times natural size. (Identified and 

drawn by J. M. Schopf, U.S. Geological Survey.)

deposits in Hawaii are included because of their youth 

and because they show that clay minerals form, iron is 

removed, and titanium concentrated in a swarnpy environment similar to that thought to prevail in a typical 

swamp in which plant material accumulated during 

Pennsylvanian time and later converted to coal.

CLEARFIELD, PA.

The principal fire-clay deposits in the Clearfield district, Pennsylvania (fig. 2, location 38), are in the 

"Mercer bed," which underlies the lowermost Mercer 

coal bed of Pottsville age (Foose, 1944). The deposits 

are lenticular and 0-7 m thick; major lateral variations commonly take place within distances of a few 

tens of meters. The varieties of clay and the alumina 

contents of the "Mercer" deposits also range broadly 

(table 5).

Plastic clay, containing <35 percent A12O3, is the 

most abundant type of clay in the "Mercer bed." The 

most abundant type of the much higher grade refractory material is flint clay, which breaks with a subconchoidal fracture and weathers into jagged fragments. 

Block clay is similar to flint clay in alumina content 

but lacks flinty characteristics and is much less resistant to weathering. Nodules 1-5 mm long occur in both 

flint clay and block clay.

The relationships of the types of clay in the "Mercer 

bed" vary considerably. At most places, the flint and 

nodule clays are in the middle part of the bed and are 

overlain by plastic clay. Locally the entire bed is plastic clay. Nodule clay, where present, is typically near

Table 5. Types and alumina contents of clay in the "Mercer bed" 

[From Foose (1944, table 2)]

Percent of 

alumina

"Burnt" nodule clay 70-75 

Rusty-brown, porous, cindery appearance.

Fine-grained (or blue) nodule clay 60-65 

Homogeneous appearance; all small nodules, finer 

grained and harder than green nodule clay.

Gree n nodule clay 55 (approx.) 

Coarsely nodular, rough fracture, usually greenish cast.

Nodule-block clay 40-50 

Gradation between green nodule and flint or block 

clay, nodules and nodular areas less than half of 

mass, scattered through block clay, greenish, fracture more blocky though still rough.

Spotted flint 40-42 

Few scattered small nodules in flint clay, fracture 

smooth conchoidal.

Flint clay 38 

Very hard, fracture smooth conchoidal with sharp 

edges and points, ringing flinty noise under hammer blow, weathers by breaking into smaller 

jagged fragments; never slacks down.

Block clay 38 

Softer than flint clay, fracture semiconchoidal to 

irregular blocky, no ringing sound when struck, 

weathers by crumbling into rounder granules 

than flint.

Semiflint clay ______________________ 35 37 

Gradational from flint to soft plastic clay, present 

in minor amounts, hardness about same as block, 

fracture rough and irregular, not very conchoidal.

Associated nonrefractory clays include: 

Slabby soft clay 30 (approx.)

Fracture slabby and irregular, slickensides very 

common. 

Soft (plastic) clay 25-30

Soft, fracture very irregular, chips and crumbles 

under little pressure. Slickensides common. 

Shaly clay or clay shale 20-30 

Bedding evident, fracture shaly, siliceous.

the middle of flint-clay units, and the contacts are gradational. Two beds of nodule clay separated by block 

clay have been found. Lateral gradations between 

types of clay are very common. At most places, the 

uppermost part of the clay is very carbonaceous, and 

coal layers 7-20 cm thick are locally present between 

different types of clay.

Kaolinite is by far the most abundant mineral in the 

"Mercer" deposits. According to Bolger and Weitz 

(1952), it forms the ground mass of the clay, and minor 

amounts are in large vermicular crystals in replacements of diaspore, scattered nodules of fine to coarse 

angular crystals, and veinlets of fine to medium crys-
UNITED STATES-UNDERCLAYS 23

tals. The kaolinite in vermicular crystals and in flint 

and nodular clays is very well crystallized, and that in 

the plastic clays tends to be very poorly ordered (Erickson, 1963).

Diaspore is the second most abundant mineral in 

underclay. It is mainly in aggregates of crystals forming nodules, but minor amounts are scattered through 

parts of the kaolin matrix and in the so-called secondgeneration vein deposits. Some of the nodular clay is 

more than 75 percent A12O3 and more than 75 percent 

diaspore. Some of the diaspore is in the form of pisolitelike pellets having concentric spheroidal layering. 

Commonly, some of the internal layers of these structures are selectively replaced by kaolinite, and concentric layers are cut by veinlets of kaolinite.

Boehmite is the third most abundant mineral in the 

"Mercer" clay (Bolger and Weitz, 1952, p. 87). It forms 

crystals of < 0.03 mm making up nodules in the clay 

and intermixed with diaspore in other nodules.

Impurities in the "Mercer" clay include minor amounts 

of quartz and flaky sericite, which tend to be most 

abundant in the lower parts of deposits (Foose, 1944, 

p. 567). The sericite was identified as 2M muscovite by 

Erickson (1963, p. 164-165), who described it as present in small aggregates and clear, sharply defined 

flakes as much as 2 mm long. Erickson found the sericite to be most common in plastic clay but absent in 

well-crystallized flint clay. Foose (1944, fig. 8) showed 

illite as being a primary mineral in the clay but did not 

discuss its distribution. Bolger and Weitz (1952, p. 89) 

stated "* * * Illite is an uncommon accessory mineral. 

It may have been the latest mineral formed, for it can 

be seen replacing the latest crystalline kaolinite along 

cleavage planes. * * *" Pyrite occurs as small grains in 

some of the clay and, in other parts, as nodules as much 

as 2.5 cm in diameter and as thin veins. Siderite occurs 

as rounded masses and lenticular bodies as much as 

5 mm in diameter in the kaolin ground mass and as

replacements of kaolinite and diaspore in nodules. 

Most of the siderite is partly altered to iron oxide. Subhedral grains of tourmaline and anhedral grains of zircon are scattered through much of the clay. Iron oxide, 

mainly in the form of goethite, is present in minor 

quantities in the plastic, flint, and block clay and in 

much greater amounts in the burnt nodule clay, in 

which it causes the rusty appearance. Amounts of iron 

oxide in some of the nodules are several times the 2.17 

percent listed for the analyzed sample (table 6), which 

was selected for its purity.

On the basis of a study of textural and structural features, Foose (1944, p. 575) identified paragenetic relationships of the minerals in the "Mercer bed." He considered that kaolinite was the first and chief mineral 

deposited and that minor detrital impurities, including 

quartz, tourmaline, and zircon, were deposited with it. 

A second generation of kaolinite is indicated by the 

vein deposits cutting the earlier bodies. A first generation of diaspore may have formed at the time of the second generation of kaolinite, but this relationship is 

uncertain. A second generation of diaspore is evidenced by veins cutting nodules formed earlier. Siderite formed contemporaneously with and later than the 

second-stage diaspore. Pyrite veinlets and iron oxides 

formed after the last diaspore stage. Bolger and Weitz 

(1952, p. 87), who recognized the presence of boehmite, 

believed that this mineral, as well as kaolinite, diaspore, and iron oxides, formed early from colloidal gels 

and that there were two additional stages of kaolinite 

and diaspore formation. Bolger and Weitz (1952, p. 93) 

summarized their more lengthy discussions of the origin of the "Mercer" clay as follows:

"* * * Study of petrography and field relationships has led to the 

conclusion that the source material of the Mercer was a colloidal 

mixture of hydrous aluminum silicates and aluminum hydroxides. 

These colloidal gels were transported into swamps by sluggish streams. 

The gels were then concentrated and crystallized to form kaolinite,

TABLE 6. Chemical analyses of varieties of clay in the "Mercer" deposits 

[From Foose (1944, table 3). , no data]

Ignition

Type of clay ALA SiO2 Fe2O3 K2O + TiO2 CaO MgO Total

Flint

Block

Slabby soft 

Plastic (soft) _________________________

14.40

1 Q QQ

13.50

1 Q 1 a

13.40

11.17

8.76 

8.09

7C 79

61.52

54 50

4Q Q4

QQ Q7

t\rj CC

OK 1 O

30.99 

27.40

4.0

Ofl IK.

43.74

43.40

A a 17 c.

52.62 

56.84

917

on

1 9Q

1

f\a

1 59

1.63 

1.82

n QQ

QE

1.51

2

f*f\

3.21 

2.99

2

rjrr

O f)f*

1 79

1.77

1 57

1.28 

1.28

0.10

1 ft

.04

1 Q

1 ft

.30 

.30

n 95

on

90

A O

7Q

.75 

.91

QQ 77

QQ 95

99.56

QQ 95

QQ fifi

99.54 

99.63
24 KAOLIN IN NORTH AMERICA, HAWAII, AND THE CARIBBEAN

diaspore, and boehmite. After lithification, shrinkage cracks appeared, into which a silica-rich kaolinitic material was introduced, 

resulting in the replacement of diaspore by kaolinite. The silication 

of diaspore released free alumina, which recrystallized in voids as a 

later stage of diaspore. The process of cracking and crack filling continued over a long period until the mass was completely solid. Hardening took place before the deposition of post-fireclay sediments. * * *"

Erickson's ideas (1963, p. 167) on the origin of the 

"Mercer" clay are more or less in agreement with 

those of Bolger and Weitz. According to his explanation, kaolinite and high alumina precipitates and gels 

accumulated in a coastal swamp environment under 

conditions of acid pH and negative Eh. Both mineralogical and chemical differences are explainable by differences in the nature and amount of sediment originally 

deposited rather than as responses to epigenetic leaching.

OLIVE HILL, KY. 

Occurrence and Characteristics

The underclay deposits in the Olive Hill district, 

Kentucky (fig. 2, location 35), occur in the Olive Hill 

clay bed in the lower part of the Lee Formation, which 

is of early Westphalian Age as used in the European 

time scale. The coal that overlies the clay ranges from 

0 to 25 cm in thickness, but in most outcrops it is only 

7.5-15 cm thick. The coal extends over more than threequarters of the area of the clay, and, in most places 

where it is absent, its stratigraphic position is marked 

by nearly black discoloration in the uppermost part of 

the clay or by a thin zone of carbon-rich black shale 

above the clay.

The "Olive Hill' clay bed consists of irregular lenses 

that rest on an undulating surface. Neither the lenses 

nor the areas in which the clay is missing show any 

regional alinement or preferred orientation. The maximum thickness of most lenses is less than 3 m, but in 

one old mine, now inaccessible, the bed is reported to 

be 7.5 m thick. The undulating surface on which the 

clay bed rests has a local relief of as much as 12 m. 

Although some of these undulations appear to reflect 

unevenness of the surface on which the clay was deposited, most of them probably formed after deposition of 

the clay, by differential compaction or other processes 

that caused slight warping of the rocks above and below the clay.

The "Olive Hill" clay bed is composed of three types 

of clay in irregular lenses of variable thickness and 

shape. About one-third of the bed is flint clay and the 

other two-thirds is chiefly semiflint clay and subordinate amounts of plastic clay, but all variations in hardness from flint to semiflint and from semiflint to plastic 

clay are present in different parts of the bed. Boundaries between one type of clay and another are ordinarily sharp. Except for the superposition of one type of 

clay above another, the clay is essentially nonbedded. 

Typically, the flint clay overlies semiflint clay, but at 

many places the reverse is true, and at a few places the 

flint and semiflint clay are irregularly interlayered. 

Where plastic clay is present, it is ordinarily in the 

uppermost part of the bed, but there are many exceptions to this generalization.

Colors, nonclay minerals, soluble salts, organic materials, and fossils are similar in all three types of clays; 

the types of clay differ, however, in the type and crystallinity of the clay minerals and in certain physical 

properties such as resistance to high temperature, 

hardness, plasticity, resistance to erosion, and spacing 

of slickensides. Most of the clay is medium gray to 

brownish gray, but colors range from very light gray to 

almost black. Rusty iron stains are common along 

joints and in weathered outcrops. The content of nonclay minerals ranges from trace amounts to more than 

50 percent in very sandy parts of the bed; lateral gradations from sand-free clay to very sandy clay within a 

few yards are common. Gypsum, the principal saline 

mineral present, occurs as crusts along joints. The 

plant-root fossil Stigmaria is preserved as carbonaceous films in all three types of clay. Locally the main 

rootstock with rootlets attached (fig. 12) is preserved in 

flint clay, but commonly only the detached rootlets 

remain. The carbonaceous films seldom make up as 

much as 2 percent of the clay.

The flint clay in the "Olive Hill" clay bed is a hard, 

resistant, nonplastic refractory clay. It possesses flintlike characteristics of homogeneity and conchoidal 

fracture, but it is distinctly softer than true flint (SiO2). 

Most high-grade flint clay has a Mohs-scale hardness 

slightly greater than 3; the clay intermediate between 

flint and semiflint clay is slightly softer. Flint clay will 

not slake in water and has no plasticity unless very 

finely ground, and then plasticity is developed to approximately the same degree as similarly prepared 

quartz. Flint clay is sufficiently resistant to erosion to 

form small benches in stream beds. It weathers to angular blocks which, in turn, break down into shardlike 

fragments having sharply curved knife edges and 

pointed corners. Slickensides are extremely rare in 

flint clay. Oolites are abundant in some of the flint clay 

but are not present in all deposits. The PCE's of highgrade flint clay range from 34 to 36.

Semiflint clay is intermediate between flint and plastic clay in physical characteristics and clay-mineral 

composition. It has a Mohs-scale hardness between 2 

and 3, and it possesses very little natural plasticity 

except when finely ground. Nearly all semiflint clays 

contain abundant diversely oriented slickensides. 

Parting occurs mostly along the slickensides; and com-
UNITED STATES-UNDERCLAYS 25

monly, when fresh semiflint clay is subjected to a single rainfall, it breaks down into a rubble of irregular 

polyhedra having a slickenside on each face. Semiflint 

clays are seldom seen in natural outcrops except where 

they are protected by overlying flint clays or other 

resistant beds. However, some of the harder semiflint 

clays, which grade into the flint clays, are remarkably 

resistant to weathering. A good example is the semiflint clay that for many years has supported the footing 

of the bridge on a highway west of Elliotville, Olive 

Hill district. The semiflint clays consist chiefly of mixtures of kaolinite, illite, and mixed-layer minerals, and 

the kaolinite generally ranges from 60 to 80 percent or 

a little more. The PCE's of semiflint clays are mostly 

31-33, and these clays are distinctly lower in heatresisting properties than is good-quality flint clay. In a 

few places, semiflint clays are very refractory, and 

PCE's are as high as 34+ (table 7). The refractory properties of most semiflint clays are lower than those of 

flint clays chiefly because of higher contents of alkalibearing clays such as illite and mixed-layer minerals. 

Plastic clays consist of mixtures of kaolinite, illite, 

and mixed-layer minerals. Weathered plastic clay 

readily develops considerable plasticity when wet, but 

some grinding is required to develop maximum plasticity in the fresh clay. Abundant slickensides are present 

in the fresh plastic clay, but as weathering progresses 

the slickensides are sealed and the clay becomes a 

homogeneous mass. Natural exposures of plastic clay 

are exceedingly rare because it is soft and lacks resistance to weathering. Only a small amount of plastic 

clay is present in the "Olive Hill" clay bed. The few 

samples examined were very similar in mineralogical 

composition to the poorer quality semiflint clays. The 

content of illite and mixed-layer clay minerals was 

high; accordingly, the alkali content should be high 

and refractory properties should be relatively low.

Mineralogy

Kaolinite is by far the dominant clay mineral in the 

"Olive Hill" clay bed, and in places it makes up as 

much as 95 percent of the bed. The kaolinite in the flint 

clay is predominantly well crystallized. In the plastic 

clay and in some semiflint clay, the kaolinite has a 

poor degree of crystallinity similar to the "fireclay" 

kaolinite mineral of Brindley and Robinson (1947). 

Intermediate stages of crystallinity are present in most 

semiflint clays. Recognition of well-crystallized kaolinite is based on the narrow basal (001) X-ray diffraction 

peak at 7.1 A and the sharp peaks from the pyramidal 

and prismatic planes (fig. 14). Poorly crystallized kaolinite gives a broad (001) peak at slightly greater than 

7.1 A, and the peaks from the pyramidal and prismatic

planes are diffuse. The degree of crystallinity of the 

kaolinite varies with the proportions of other clay minerals present in the clay. The well-crystallized kaolinite occurs only in clays that contain small amounts of 

other clay minerals, and therefore it is restricted to the 

flint clays. Poorly crystalline fire-clay kaolinite occurs 

only where appreciable amounts of illite and mixedlayer clays are also present. Kaolinite having intermediate crystallinity occurs in both the flint and semiflint 

clays that contain small amounts of illite and mixedlayer minerals. The conclusions regarding the crystallinity of the kaolinite are based on the criteria outlined 

by Brindley (1951, p. 46, 50-52). Our conclusions closely 

parallel those of Keller and others (1954, p. 19) and 

McConnell and others (1956, p. 279), who studied similar 

clays. The proportion of nonclay mineral bears no relation to the crystallinity of the clay, and well-crystallized 

kaolinite occurs in parts of the bed that contain as 

much as 50 percent quartz.

DTA curves of samples from the "Olive Hill" clay 

bed (fig. 15) appear to support the conclusion that kaolinite is the dominant clay mineral present and that 

the kaolinite in flint clay is more perfectly crystallized 

than that in plastic clay. The prominent endothermic 

peak resulting from the loss of hydroxyls is at approximately 600 °C for flint clay (fig. 15, sample 25) and at 

only 580 °C for plastic clay (fig. 15, sample 24). Also, 

the exothermic reaction for flint clays at about 975 °C 

is intense and is completed within a temperature range 

of 25 °C, whereas this reaction for plastic clays is much 

less intense and takes place over a temperature range 

of approximately 75 °C. The DTA curves for semiflint 

clay (not illustrated in this report) are intermediate 

between those for plastic and flint clay. The higher 

energy required to drive the hydroxyl ion of the claymineral structure from the flint clay suggests that the 

hydroxyl ion is more tightly bound in flint clay than in 

plastic clay.

Illite is the second most common clay mineral in the 

"Olive Hill" clay bed. The amount ranges from a trace 

in the flint clay to about 40 percent in the plastic and 

the softer semiflint clays. Illite is recognized in X-ray 

diffraction traces by its basal (001) spacing at approximately 10A (fig. 14). Weak second-order (002) peaks at 

5A and third-order (003) peaks at 3.3A are also present 

in diffractometer traces of some samples. Only material that does not expand when treated with ethylene 

glycol is considered to be illite; if there is some expansion, the material is considered to be mixed-layer clay. 

In DTA curves, the presence of small amounts of illite 

is suggested by broad weak endothermic reactions 

between 100 ° and 200 °C (fig. 15, samples 9 and 24) and 

by small endothermic reactions beginning between 

450° and 500 °C.
26 KAOLIN IN NORTH AMERICA, HAWAII, AND THE CARIBBEAN

FLINT CLAY, loc. 6. sample 13, Holdemon quadrangle FLINT CLAY, loc. 20, sample 33, Wrigley quadrangle SEMIFLINT CLAY, loc. 16, sample 27, Wrigley quadrangle

EXPLANATION

Whole sample unoriented

Heoled to 300°C

Ethylene glycol treated

K, koolmile 

/, illite 

Oil, quartz

SEMIFLINT CLAY, loc. 16, sample 28, Wrigley quadrangle PLASTIC CLAY, loc. 3, sample 6, Holdemon quadrangle

FIGURE 14. X-ray diffractometer traces (CuKc^ radiation) of flint, semiflint, and plastic clays from the "Olive Hill" clay bed of the 

Lee Formation in the Wrigley and Haldeman quadrangles, Kentucky. Sample descriptions and locations in Patterson and Hosterman (1962).

Complex mixed-layer minerals are closely associated 

with the illite. Some of these minerals resemble smectite in that X-ray diffraction traces show a slight increase in intensity of the 14A peak when samples are 

treated with ethylene glycol. Smectite layers are most 

common in plastic clays and softer semiflint clays (fig. 

14). Other mixed-layer clays consist of heterogeneous 

mixtures of minerals resembling chlorite, smectite, 

and probably vermiculite. X-ray traces of these clays 

have broad irregular bulges near 10A, and peaks are 

little changed by heat or ethylene glycol treatments. 

Efforts to improve the mineral structure of mixed-layer 

minerals by treatment with potassium ions were not 

successful. The structure of these minerals appears to 

be far more complex than that of some mixed-layer 

clays that are mostly potassium-deficient illites. Heterogeneous mixed-layer assemblages occur only in small 

amounts. They are probably present in all types of clay 

in the Olive Hill area, but they are most abundant, or 

at least most easily recognized, in the softer flint and 

harder semiflint clays.

The "Olive Hill" clay bed contains a very small 

amount of a clay mineral that is probably chlorite. In 

X-ray diffraction traces, this mineral has a fundamental basal spacing of 14A, and it does not swell 

when treated with ethylene glycol or collapse when 

heated to 300 °C. Some doubt regarding the correct 

identification of this mineral remains, however, because it was neither destroyed nor enhanced by heat 

treatment at 650 °C, and it was not destroyed by 3N 

hydrochloric acid treatment as are most chloritic clay 

minerals. Possibly the clay mineral here reported to be 

chlorite is a highly aluminous variety. Chlorite is most 

abundant in the softer flint clays and harder semiflint 

clays (fig. 14, samples 33, 27), but in none of the clay 

did the estimated amounts exceed 5 percent (table 7). 

The materials other than clay minerals in the "Olive 

Hill" clay bed include allogenic minerals that were 

introduced during deposition of the clay, authigenic 

minerals that formed after deposition of the clay, and 

organic matter in the form of thin carbonaceous films. 

The allogenic minerals are quartz, zircon, tourmaline, 

garnet (which in the "Olive Hill" clay bed is probably 

almandite), ilmenite, and magnetite. The amount of 

quartz ranges from traces to approximately 50 percent. 

The other allogenic minerals are present only in trace 

amounts. The most abundant authigenic mineral is 

siderite, in amounts as great as 10 percent. Other
UNITED STATES-UNDERCLAYS 27

TABLE 7. Mineral composition and chemical analyses of clays from the "Olive Hill" clay bed of the Lee Formation in Kentucky, arranged

in order ofpyrometric cone equivalents

[Samples located and described in Patterson and Hosterman (1962). Clay-mineral and non-clay-mineral compositions given in parts of 10. E, excellent; VG, very 

good; VP, very poor; Tr, trace; , no data. Chemical analyses in weight percent. Sample 1 analyzed by E. L. Prew, Alfred University, Alfred, N.Y., using standard methods; samples 13,33, and 6 analyzed by P. L. D. Elmore, S. D. Botts, M. D. Mack, and J. H. Goode under supervision of W. W. Brannock, using methods 

like those of Shapiro and Brannock (1956). Summations rounded to nearest whole number. Samples for which TiO2 only is given analyzed by Patterson and 

Hosterman using methods of Shapiro and Brannock (1953). * indicates sample contains organic matter that may cause FeO percentage to be in error]

Sample no. 25 13 33 27 1 24 28

Type of clay Flint Flint Flint Flint Semi- Flint Plastic 

	flint. 

Pyrometric cone equivalent 36 34+ 34- 33+ 33+ 32% 32-

	Clay minerals

Kaolinite 9-9% 9-9% 9 8 7-8 7%-8 7

Illite Tr V4-% %-l Tr Tr l%-2

Chlorite % Tr 

Mixed-layer clay minerals Tr Vi %-% % 1-1% 1-2 %-l

Crystallinityofkaolinite VG E VG VG VP VG VP

	Nonclay minerals

Quartz %-l Tr Tr Tr

Anatase Tr Tr Tr Tr Tr Tr Tr

Pyrite ____________________ __ __ __ Tr __ Tr __

Organic material Tr Tr+ Tr

pH index 6.0 4.9 5.5 4.3 5.5 4.1 4.4

	Chemical analyses

SiO2 45.0 45.5 39.0 45.4

A12O3 38.2 36.0 34.2 34.0

Fe2O3 .46 .8 3.4 1.4

FeO ___________________ __ 19 38* __ __ __ 41

MgO .13 .36 .55 .69

CaO .06 .08 .32 .11

Na.,0 .06 .10 .44 .24

K2O .30 1.0 2.57 3.1

TiO2 0.9 1.9 2.0 2.0 1.5 2.17 1.4

P2O5 .01 .05 .24 .02

MnO .00 .00 .00

H2O 13.8 13.0 11.6

CO2 .05 .12 3.54 .26

SO2 .20 .72

S (total) .29

Ignition loss 17.39 

Sum 100. 99. 99.

Plastic Semiflint. 

29- 29-

5%-6 

2

1 

VP

5% 

Tr 

VP

Tr

4.8

2-3 

Tr

6.5

1.0 0.5

authigenic minerals, present in minor amounts in samples studied in the laboratory, are pyrite, iron oxide 

minerals such as limonite, goethite, lepidocrocite, and 

hematite, and the soluble salts gypsum and iron sulfate. Traces of galena and sphalerite have also been 

reported in the clay bed; they are probably authigenic. 

Anatase is present in small amounts throughout the 

"Olive Hill" clay bed, but whether it was introduced at 

the time of deposition or formed after deposition is not 

known. 

The allogenic minerals vary considerably in grain

size, roundness, and amount of alteration. Quartz forms 

both rounded and angular grains; most of the rounded 

grains are frosted and most of the angular ones are 

clear. Locally quartz grains are coated with an iron 

oxide mineral that is probably limonite. Grain size of 

the quartz ranges from very fine silt to medium sand. 

The quartz in plastic and semiflint clay is essentially 

unaltered, but many of the grains in flint clay are serrated and etched and partially replaced by clay minerals. 

Most of the allogenic minerals other than quartz 

form rounded grains. Garnet and zircon grains are
28 KAOLIN IN NORTH AMERICA, HAWAII, AND THE CARIBBEAN

100 200 300 400 500 600 700 800

TEMPERATURE, IN DEGREES CENTIGRADE

900 1000

FIGURE 15. Differential thermal analysis curves of clays from the 

"Olive Hill" clay bed of the Lee Formation in Kentucky. Sample 

descriptions and locations in Patterson and Hosterman (1962).

essentially unaltered. Most of the magnetite, however, 

is partly altered to limonite or hematite, and most of 

the ilmenite is coated with leucoxene.

The authigenic minerals, which apparently were 

formed at two different times, have a variety of crystal 

forms. Pyrite and siderite are scattered throughout the 

clay, and hematite, limonite, gypsum, and soluble salts 

are closely associated with joints in the clay. Probably

the pyrite and siderite formed long before the other 

minerals, which may be still forming by precipitation 

from ground water. Siderite occurs commonly as oolites, 

spherulites, and euhedral crystals, and, at the locality 

where it makes up 10 percent of the bed, it is in the 

form of nodular concretions as much as 3 mm in diameter and 1 cm in length. Many of the siderite concretions 

contain irregular inclusions of white kaolinite. Some of 

the pyrite occurs locally as small euhedral crystals disseminated throughout the clay, but most of it is in the 

form of small irregular nodular concretions. Most of 

these pyrite concretions are closely associated with carbonaceous films of Stigmaria, suggesting that the pyrite was concentrated in the space originally occupied 

by a plant rootlet. Pyrite, in very fine particles, gives 

an exothermic reaction between 400° and 500 °C in 

DTA (fig. 15, sample 9). Limonite and hematite occur 

as films along joints in the clay and as finely disseminated particles causing red, brown, and yellow discoloration of the clay adjacent to joints. The gypsum and 

soluble iron sulfate salts are chiefly in the form of films 

along joints. Iron oxides, gypsum, and soluble iron sulfate salts are present only in small amounts in most of 

the "Olive Hill" clay bed. The DTA curves give no indication that these minerals were present in any of the 

samples investigated, and the percentages of iron, calcium, and sulfur are low in the chemical analyses of 

most samples of these clays (table 7).

Anatase occurs in all samples of the "Olive Hill" clay 

bed examined in the laboratory (table 7) and appears to 

be present in essentially all parts of the bed; it probably contains nearly all the titanium present in the 

clay. Anatase was identified by the strongest X-ray diffraction peak at 3.51 A. Inasmuch as this peak is masked 

by the second-order basal (002) peak of kaolinite, it was 

necessary to heat the clay to 550 °C for half an hour to 

destroy the kaolinite structure in order to recognize 

the presence of anatase. The strongest diffraction peak 

of anatase was weak for all samples, but the proportion 

of anatase indicated on the X-ray diffraction traces was 

probably sufficient to account for nearly all of the titanium, which ranges from 0.9 to 2.7 percent shown in 

the chemical analyses (table 7).

Anatase appears to be in very fine particles uniformly 

distributed throughout large bodies of the clay. The 

<2-/tm fractions contained the same proportions of 

anatase as did the whole clay in samples investigated 

by X-ray methods. This observation and the absence of 

recognizable anatase in thin sections indicate that the 

mineral is present in very fine particles. The distribution of titania in the clay was investigated by chemical 

analyses of the type outlined by Shapiro and Brannock 

(1953). Samples were taken from opposite sides of 

blocks of flint clay and semiflint clay approximately
UNITED STATES-UNDERCLAYS 29

0.5 m in diameter. Samples from the same block contained essentially identical amounts of titania for each 

type of clay, though blocks from different localities differed within the range indicated in table 7.

The "Olive Hill" clay bed in one mine near Olive 

Hill, Ky., is reported by Greaves-Walker (1907, p. 470) 

to contain nodules and oolites of uncommonly high alumina content. He referred to the material as "aluminite"; it was later identified as gibbsite, A12O8 «3H2O, by 

Galpin (1912, p. 324-329). Greaves-Walker reported as 

much as 48.5 percent alumina and a small amount of 

alkali and iron. Accordingly, the so-called aluminite 

was more valuable for refractory purposes than were 

parts of the bed that contain only kaolinite. During the 

present investigation a special effort was made to locate samples of gibbsite-bearing clay in the Haldeman 

and Wrigley quadrangles, but without success. The 

effort included X-ray examination of concentrated 

oolites from several localities within the clay bed. In 

all samples, the oolite concentrates contained only kaolinite of essentially the same composition as the enclosing nonoolitic clay.

Coaly organic matter appears to be abundant in the 

"Olive Hill" clay bed because black films and specks 

are conspicuous in hand specimens, but the total content of organic matter in the clay is low. Most of the 

carbonaceous films and specks are remains of detached 

rootlets of Stigmaria, but locally nearly complete root 

systems are preserved by such films (fig. 12). The presence of organic matter is also indicated in some DTA 

curves by a sharp exothermic reaction between 650° 

and 720 °C (fig. 15, sample 1). Of all samples investigated, sample 1 contained the most organic matter, 

and the exothermic peak shown by the curve of that 

sample is of the same order of magnitude as peaks 

obtained from a 2-percent mixture of coal from the bed 

overlying the "Olive Hill" clay bed in clay that contains essentially no organic matter. No organic matter 

was indicated in the DTA curves of most of the clays 

investigated, and organic matter probably makes up 

considerably less than 1 percent of most parts of the 

"Olive Hill" clay bed.

Origin

According to Patterson and Hosterman (1962, p. 79- 

81), stratigraphic, paleontological, mineralogical, and 

chemical evidence all support the conclusion that the 

clay deposits in the "Olive Hill" clay bed were formed 

by the alteration of ordinary fine-grained Pennsylvanian sediment in acid swamps. Some of the facts and 

observations pertaining to the origin of the clay are as 

follows:

1. The clay is a true underclay, as indicated by (a) the 

thin overlying coal bed, (b) abundant fossil plant 

roots, Stigmaria, in the clay, (c) absence of bedding in 

the clay, (d) abundant slickensides in semiflint and 

plastic clays.

2. Root fossils indicate that the clay supported plant 

growth and, therefore, served as a subaqueous soil; 

however, evidence for a soil profile in the clay is absent.

3. The clay bed is discontinuous and consists of irregular lenses having no preferred orientation.

4. The kaolinite, illite, and mixed-layer clay minerals 

in plastic clays are similar to clay-mineral assemblages in Pennsylvanian shale enclosing the clay bed.

5. Proportions of kaolinite increase gradually from 

plastic to flint clay, and this increase is accompanied 

by a corresponding decrease in the amounts of illite 

and mixed-layer clay minerals.

6. Recrystallization of the kaolinite in flint clay is 

indicated by interlocking grains and by comparatively light-colored, large kaolinite grains in a darkcolored, very fine grained matrix. Semiflint and plastic clays show little evidence of recrystallization.

7. Some of the quartz grains in sandy flint clay are 

fresh, but others show evidence of solution and replacement by clay.

8. The clay bed contains no feldspar.

9. The titania content of most flint clay is about 2.0 

percent; of semiflint, about 1.5 percent; and of plastic 

clay, 1.0-1.5 percent. Titania is one of the most stable of all chemical components, and, if it has not 

migrated, the increase in percentage from plastic to 

flint clay indicates a residual enrichment.

The shapes of the irregular lenses of clay, the relation of lithologic units within the bed, the presence of 

fossil roots, the absence of a soil profile, the lack of bedding, the overlying coal, and the marine or brackishwater fossils in the dark shale above the clay all point 

toward an origin of the clay in coastal swamps. Clearly 

the irregularly shaped lenses of clay lack the orientation, continuity, and bedding that would be expected if 

they (1) formed by dissection of a blanket of sediment,

(2) accumulated in channels, as did certain kaolin deposits of Tertiary age in Mississippi (Conant, 1965) or

(3) formed in cutoff stream meanders as Kesler (1956, 

p. 553) has suggested for the kaolin deposits in Georgia. The irregular shapes and lack of orientation of the 

clay lenses, however, would be expected if the deposits 

accumulated in swamps in which bodies of water were 

irregular in shape and depth. Further evidence that 

the clay deposits formed in swamps lies in the root fossils in the clay and the overlying coal; this relation is 

remarkably in accord with the invasion of modern 

swamps by plants and with the accumulation of peat in
30 KAOLIN IN NORTH AMERICA, HAWAII, AND THE CARIBBEAN

modern swamps, as described by Twenhofel (1950, 

p. 81-84). The best explanation for the absence of a soil 

profile seems to be that none developed because the 

clay was waterlogged at the time it served as a soil. 

The absence of bedding in the clay is probably due to 

the churning action of roots and to plastic flowage. The 

later gradation from pure clay to very sandy clay appears to be similar to the decrease in grain size away 

from shore in sediments in modern swamps diagramed 

by Twenhofel (1950). A sparse marine fauna, chiefly 

small Lingula, in the shale a short distance above the 

clay and the conformable relation of the shale and clay 

suggest that only slight subsidence was required to 

lower the clay below sea level. This, in turn, suggests 

that the swamps were located along coastal lowlands, a 

possibility that seems in accord with the evidence for 

deltaic deposition in the sandstone facies of the Lee 

Formation.

The clay appears to have formed by the leaching and 

alteration of ordinary fine-grained Pennsylvanian sediment in acid swamps, a theory similar in some respects 

to those proposed by Keller and others (1954) and by 

McMillan (1956). Inasmuch as the clay minerals in 

plastic clay do not differ greatly from those in the Pennsylvanian shale enclosing the clay bed, there is no reason to assume that special sedimentary sorting processes were involved. The three types of clay plastic, 

semiflint, and flint clay can be explained as representing progressive stages of leaching. According to 

this theory, kaolinite formed concurrently with the 

removal of alkalies and silica from illite and mixedlayer clays and certain nonclay minerals. Leaching of 

the clay is indicated by both direct and indirect evidence, but unfortunately little evidence supports the 

idea that kaolinite formed from other clay minerals, 

and nothing reveals what happened to the dissolved 

materials. The etched quartz grains and their replacement by clay minerals are convincing evidence that 

leaching took place. Also the absence of feldspars, 

which are present in many plastic underclay beds, is 

suggestive of leaching. The 50-percent increase in 

titania from plastic clay to flint clay seems to represent 

an expected increase in resistates with leaching. The 

root fossils provide another line of indirect evidence, 

for they clearly indicate that the clay supported plants, 

and alkalies and perhaps silica would be removed from 

any material that served as a soil. Perhaps most of the 

leaching took place while the rotted roots of many generations of plant growth provided channels for the acid 

waters to circulate through the sediments lying on the 

floors of the swamps. The materials removed by the 

leaching process and by upward diffusion into the overlying body of water were flushed away by sluggish 

movement of water through the swamps. The acidity of

the swamps is indicated by the present acid characteristics of the clay, by the overlying coal, and by organic 

material scattered throughout the clay. A suggestion 

that kaolinite formed from other clay minerals lies in 

the relation of the crystallinity of the kaolinite and its 

proportions to other clay minerals in the three types of 

clay. The kaolinite in plastic clay is a poorly crystallized fire-clay variety, and its proportion to other clay 

minerals is low. The flint clay is essentially pure, wellcrystallized kaolinite. In the semiflint clay, the perfection of the kaolinite structure as well as the proportions present are intermediate between plastic and 

flint clays. This progressive increase in the perfection 

of the kaolinite structure as the amount of other clay 

minerals decreases seems more than a coincidence; it 

may represent a tendency for the crystal structure of 

kaolinite to become more perfect as the alkalies and 

silica are leached.

OTHER DISTRICTS IN EASTERN UNITED STATES

Underclay beds occur in Pennsylvanian coal-bearing 

strata at many places in the Appalachian region in the 

Eastern United States. All of these deposits are kaolinitic; however, many of them are not as pure as those in 

the Olive Hill and Clearfield districts previously described. Some of the deposits in the upper strata of the 

Pottsville Group or Formation (lower Westphalian, 

according to European general classification) include 

those in the following districts and beds: (1) Tuscarawas Valley, Ohio (fig. 2, location 33), "Brookville" bed 

(Hosterman and others, 1968, p. 180-181); (2) Oak Hill 

district, Ohio (fig. 2, location 34), "Sciotoville" bed 

(Stout and others, 1923). A few of the deposits in the 

Allegheny Group or Formation of Middle Pennsylvanian age (upper Westphalian of the general European 

classification) include the "Clarion," the widespread 

"Lower Kittanning," and younger beds. The "Clarion" 

bed is present in the East Liverpool district, Ohio (fig. 

2, location 32), and nearby areas (Hosterman and others, 

1968, p. 180) and in Somerset County (fig. 2, location 40) 

and nearby areas in Pennsylvania and Maryland (Hosterman, 1972). The "Lower Kittaning" bed occurs in 

the East Liverpool, Tuscarawas Valley, and Oak Hill 

districts, Ohio, and in the Beaver Valley district (fig. 2, 

location 36) (Hosterman and others, 1968, p. 180) and 

Somerset County, Pennsylvania. The younger underclays include the "Upper Kittanning" and "Bolivar" 

beds in Somerset County, Pa., and the nearby Frostburg district, Maryland (fig. 2, location 41) (Waage' 

1950).

MISSOURI

The fire-clay deposits in Missouri occur mainly in a 

large district in the east-central part of the State north
UNITED STATES-UNDERCLAYS 31

of the Missouri River (fig. 2, location 22) and in the 

Ozark region south of the river (fig. 2, location 23). All 

these clays are in sedimentary beds of Pennsylvanian 

(Late Carboniferous of the European time scale) age. 

Because of the presence of minor quantities of coal 

associated with some of the deposits, these clays are 

classed with the underclays in this report. However, 

the Missouri fire clays are not as clearly associated 

with overlying coal beds as are underclays elsewhere. 

The most abundant clay mineral in the Missouri 

fire clay is kaolinite (85 percent or more in high-grade 

clay). Some very high grade fire clay contains appreciable amounts of diaspore, a mineral that is 85 percent 

A12O3 . The fire clays are commonly classed as plastic, 

semiplastic, semiflint, flint, and superrefractory clays 

(burley and diaspore clays). McQueen (1943, p. 5-6) 

described the different clay types as:

"* * * (1) Plastic to semiplastic or semiflint fire clay, varies from soft 

to fairly hard, varies also in color and texture; grades imperceptibly 

into (2) flint fire clay, a hard, compact nonplastic fire clay. Flint fire 

clay is characterized by a conchoidal fracture and sharp splintery 

edges, and grades into (3) burley clay, so called because of the presence of 'burls' or shot-like particles (oolites) or small nodules (pisolites), which usually are highly aluminous in character. As the number and aluminous content of particles increase, this clay grades into 

(4) diaspore clay, which is usually a rough textured, compact clay of 

varying color and hardness, distinguished by a high alumina content. Diaspore clay is the designation used in Missouri for clay containing a minimum of 70 percent alumina (A12O3). More recently, the 

grades of clay have been designated in Missouri as flint, less than 

55 percent alumina, and diaspore, above 65 percent alumina. * * *"

East-central district Fire-clay deposits in the eastcentral district are scattered throughout an area of several hundred square kilometers. The fire clay occurs in 

the "Cheltenham Formation" of the Des Moinesian 

Provincial Series (Middle Pennsylvanian of the U.S. 

classification and Westphalian C and D of the European system).

The deposits in the "Cheltenham Formation" consist 

chiefly of plastic clays. The lower part of the "Cheltenham Formation" in the district is irregular in extent 

and thickness, and clay in this part of the formation 

chiefly forms sinklike structures. The middle part of 

the "Cheltenham" is a nearly continuous blanketlike 

deposit present over wide areas in Audrian, Callaway, 

and Montgomery Counties. In these counties, the bed 

has an average thickness of about 5 m. It yields the 

largest tonnage of plastic clays now produced in the 

district. The upper part of the "Cheltenham" is discontinuous and contains the least refractory clays of the 

district.

Flint and semiflint clays also occur in the east-central 

district but are less abundant there than in the southern district. Although deposits of these clays are scattered over much of the district, most deposits are outliers separated from the main mass of Pennsylvanian 

rocks in Callaway, Montgomery, and Warren Counties. The deposits occur in restricted circular or oval 

sinkhole structures in older rocks, many of which are 

steepsided or even have one or more vertical walls.

Ozark district. The Ozark district (fig. 2, location 23) 

is a large area south of the Missouri River and west of 

St. Louis County. It covers parts of Osage, Gasconade, 

Franklin, Maries, Pulaski, Miller, Crawford, and 

Phelps Counties. The clay is above conglomerate and 

sandstone at the base of the Pennsylvanian, which by 

their outcrops indicate the general area in which the 

clay deposits occur. Many of the scattered deposits are 

filled-sink structures (Keller, 1952; Keller and others, 

1954). Most deposits are small, the typical ones containing about 15,000 tons. A few of the larger deposits 

are as much as 240 m long and 150 m wide and have a 

maximum thickness of about 8 m. Some smaller deposits are known to extend to depths of as much as 

30 m. Flint and semiflint clays are the principal types 

found in these deposits; bedded plastic clay is not found 

in the district. Super heat-duty refractory burley and 

diaspore clays are associated with many deposits, and 

these high-grade clays have been mined extensively. 

The typical deposit containing diaspore consists of 

about 8,000 tons of flint clay, 250 tons of abrasivegrade diaspore, 750 tons of no. 1 grade diaspore, and 

6,000 tons of no. 2 and no. 3 grades diaspore. A12O3 contents of the diaspore clays are as much as 76.2 percent 

(table 8). As noted by Keller (1979), the diaspore deposits are depleted and the prospects for the discovery 

of more deposits are very poor.

TABLE 8. Chemical analyses of Missouri fire clays, in percent 

[From Keller and others (1954). 1, Diaspore clay, NE^4SE%, sec. 29, T. 41 N., R. 

7 W., Maries County, Mo. (McQueen, 1943, p. 163); 2, Flint fire clay, SE%, sec. 

19, T. 51 N., R. 1 W., Lincoln County, Mo. (McQueen, 1943, p. 47); 3, Semiflint 

fire clay, NWV4 , sec. 29, T. 47 N., R. 3 W., Warren County, Mo. (McQueen, 

1943, p. 50); 4, Semiplastic fire clay, A. P. Green Fire Brick Co., Pit No. 4, 

Audrian County, Mo. (McQueen, 1943, p. 58); 5, Plastic "foundry" clay, A. P. 

Green Fire Brick Co., Pit No. 4, Audrian County, Mo. (McQueen, 1943, p. 64)]

Sample no. 12345

SiQ2

A12U3 

Fe2 03

TiO2

CaO

MgO

3.89 44.42 45.92 48.90 56.10

K2O

76.21

.98

3.52

.08

.06

.79

.24

14.56

38.63

.55

2.12

.04

.10

.30

.12

13.90

35.79

.75

2.28

.06

.36

.44

.41

13.06

33.20

1.47

1.58

.56

.34

.10

1.53

11.55

24.47

3.64

1.58

.61

1.11

.17

2.89

8.39

Total 100.33 100.18 99.07 99.23 98.96
32 KAOLIN IN NORTH AMERICA, HAWAII, AND THE CARIBBEAN

COLORADO

The principal kaolinitic clay deposits in Colorado are 

in the south-central (fig. 2, location 15) and Front 

Range (fig. 2, location 14) districts. Most of these clays 

are overlain by coal seams a few centimeters thick, and 

many of them contain carbonaceous imprints of plant 

roots resembling Stigmaria. They, therefore, are classified as the underclay type.

South-central Colorado district The largest and 

most important clay deposits in Colorado are in Fremont, Pueblo, Custer, Huerfano, and Las Animas Counties in the south-central part of the State. These deposits 

are in the Glencairn Shale Member of the Purgatoire 

Formation and in the Dakota Sandstone, both of Early 

Cretaceous (Albian) age. The two formations are exposed in hogbacks at the south end of the Colorado 

Front Range and the east side of the Wet Mountains, 

and they also crop out in broad irregular belts farther 

east. The outcrops east of the mountains are particularly extensive in south-central Pueblo County, where 

nearly horizontal clay-bearing strata are cut by tributaries of the Arkansas River. The clay in the Glencairn 

Shale Member forms tabular lenses near the top of the 

member. At most places where this clay is mined, its 

thickness is 1.5-6 m. In the Dakota Sandstone, the clay 

is in a discontinuous unit of sandy clay, fire clay, and 

evenbedded sandstone in the middle part of the formation. These clay bodies are of various sizes, and they 

may be remains of a continuous bed that was dissected 

by erosion prior to the deposition of the overlying sandstone. Most of the Dakota Sandstone clay bodies that 

are mined are 1-2.5 m thick.

The fire clay in the Glencairn Shale Member is bluish gray to light bluish gray and plastic, and it parts 

with a blocky fracture. It is fairly uniform in chemical 

composition, has a silica-alumina ratio of about 3:1, 

and has fusible impurities of approximately 5 percent 

(Waage' 1953). This clay is low grade to semirefractory 

but is commonly mixed with higher grade clays to 

obtain a more refractory product. Clay in the Glencairn 

Shale Member has been mined extensively in the 

Canon City district, in the hogback between Oil and 

Sixmile Creeks northeast of Canon City, and at Capers 

Spur in south-central Pueblo County.

Clay deposits in the Dakota Sandstone consist of an 

upper zone of plastic and semiplastic clay and a lower 

zone of flint clay. The plastic clay is light gray to blue 

gray and has a blocky to massive structure. It is compact and tough and parts with a splintery to roughblocky fracture. The semiplastic clay is black and moderately hard and has a splintery to poorly developed 

conchoidal fracture. Semiplastic clay is the least common of the three types, and it occurs only locally between the plastic and flint clay. The flint clay is hard, 

light gray to light blue gray, and massive and has a 

well-developed conchoidal fracture. All three types of 

clay in the Dakota Sandstone are composed principally 

of kaolinite (Waage' 1953, p. 38). The kaolinite in flint 

clay is fine grained, but plates, books, and vermicular 

crystals as much as 0.2 mm long occur in the plastic 

clay. Quartz sand is the principal impurity in the flint 

clay, and small lenses and pockets of sand are present 

in the clay at a few places. Scattered muscovite grains 

as much as 0.05 mm long and minor amounts of nontronite and organic matter also are present in some of 

the clay. The plastic and semiplastic clays in the Dakota Sandstone are of better grade than the clays in 

the Glencairn Shale Member, being white-burning 

semirefractory to refractory clay. Nonsandy plastic 

clay contains less than 5 percent of fusible impurities 

(Waage, 1953) and has an average A12O3 content of 29 

or 30 percent. Most of this clay fuses at about PCE 29, 

and samples fusing up to PCE 31 are not uncommon. 

The flint clay is a white-burning highly refractory clay 

that fuses between PCE 31 and 36. It is fairly uniform 

in composition, and the only major impurity variation 

is in silica content, which is related to the amount of 

quartz sand present. The A12O3 content of nonsandy 

flint clay is approximately 35 percent, and the fusible 

impurities are low.

Colorado Front Range district Refractory clay and 

clay shale deposits in the northern Front Range occur 

in the Lower Cretaceous South Platte and Lytle Formations of the Dakota Group, which is approximately 

equivalent to the Dakota Sandstone. These deposits 

extend south in a narrow belt from near Boulder, Boulder County, to the northwestern part of Douglas County. 

The largest and most abundant deposits are in the Van 

Bibber Shale Member of the South Platte Formation. 

Other deposits occur in the sandstone units overlying 

the Van Bibber, and a few scattered deposits are present near the top of the Lytle Formation (Waage', 1961, 

p. 1). The best grade clays in the Van Bibber Shale 

Member are almost pure kaolinite (Waage' 1961, p. 26), 

and probably this mineral is abundant in the other 

clays. Deposits of refractory clay and shale in the Golden area have been mined intensively since the 1860's, 

and many of the best grade and most cheaply mined 

deposits are exhausted.

KING COUNTY, WASH.

Six underclay deposits in King County, Wash. (fig. 2, 

location 1), about 30 km southeast of Seattle and 50 km 

northeast of Tacoma (Nichols, 1946), are in the Puget 

Group, which consists of formations of Eocene age 

(Vine, 1969). The underclay deposits range in thick-
UNITED STATES-UNDERCLAYS 33

ness from about 1 m to more than 10 m. The clay is 

mostly gray to black, but some of it is bleached to nearly 

white, and part of it is brown where weathered siderite 

is abundant. Most of the deposits consist of slickensided semiplastic clay, but parts of deposits are flinty 

material that has a subconchoidal parting. Small clay 

pellets and grains that are mostly about 10 mm in 

longest dimension and rounded, subrounded, or angular in form are scattered through the clay. Near the top 

of the clay, thin layers of carbonaceous clay containing 

small coal seams are less than 5 mm wide and several 

centimeters long. Other coal beds are found in the 

strata above and below the clay, and some of them are 

thick enough to be mined.

According to Nichols (1946), the clay is mainly kaolinite, as determined by DTA, X-ray, and petrographic 

methods. Boehmite is the second most abundant aluminous mineral, and minor amounts of dickite, diaspore, 

and gibbsite were thought to be present. Siderite, in 

the form of spherical, cylindrical, or dumbbell-shaped 

concretions that are about 1 mm in size, is locally the 

most abundant impurity. Small spherical concretions 

of pyrite occur sparsely.

According to Nichols (1946), one large sample of clay 

from one pit was estimated to be 51 percent kaolinite, 

34 percent boehmite, and 14 percent limonite. It was 

48.6 percent A12O3 , 10.05 percent Fe2O3 , 24.0 percent 

SiO2 , 0.5 percent MgO, 0.1 percent CaO, 0.12 percent 

Na2 O, 0.13 percent K2 O, 0.054 percent P, 0.02 percent 

S, 1.1 percent free H2O, and 15.65 percent combined 

H2 O. This sample was exceptionally high in alumina; 

the average boehmite content of the clay is less than 10 

percent.

Hydrothermal solutions have invaded the clay at one 

locality, as is indicated by the minor amount of realgar 

and chalcopyrite. Hydrothermal alunite is present in 

other parts of the Puget Group.

Nichols (1946) thought that the clay was deposited in 

a lacustrine environment and was transported from 

weathered rocks to the east. His opinion is supported 

by the following: (1) the presence of minute lamination 

and pellets of kaolinite in clay; (2) the fine-grained texture that suggests deposition as a clay; (3) the lack of 

quartz and mica that would be expected if the clay 

were a residual deposit formed by weathering of the 

Puget Group; (4) the sharp contact between the clay 

and the underlying strata. One of the clay deposits is 

underlain by a weathered zone, and Nichols implied 

that some of the kaolin in the lower part of this deposit 

is residual.

The origin of the boehmite is uncertain, as reported 

by Nichols (1946) as follows:

"* * * Several theories for the origin of the boehmite have been considered. They are: (1) the boehmite was deposited with the kaolinite;

(2) it was formed from the kaolinite in an Eocene weathering profile;

(3) it was formed from the kaolinite in a profile developed on the present topography; (4) the boehmite was derived from the kaolinite by 

the action of ground water; (5) substances derived from the coal were 

responsible for the alteration of some of the kaolinite to boehmite; (6) 

two or more of the above processes were effective in the formation of 

the boehmite.

"There are several valid arguments which prove that the boehmite 

was not formed from kaolinite in a profile developed on the present 

topography. It suffices to say, however, that the boehmite is as plentiful in the high-alumina clay which is 200 feet below the surface as 

it is in clay which crops out at the surface. No definitive statement 

with regard to the origin of the boehmite can be made. * * *"

COWLITZ, WASH.

The clay deposits in the Cowlitz district, Washington 

(fig. 2, location 2), are in two beds separated by strata as 

much as 30 m thick that consist of argillaceous silt 

layers interbedded with sand and carbonaceous materials (fig. 16). Both clay beds are tabular units varying 

considerably in thickness and composition. The lower 

bed, called the principal bed (Popoff, 1955; Nichols, 

1945) is more than 15 m thick at most places, and the 

thickness of the upper bed is commonly somewhat less. 

The lower bed is underlain by waterlaid volcanic breccia; bedded sand capped by basalt is present above the 

upper bed.

The clay having the highest alumina content is in 

the basal 4-6 m of the principal bed. It is composed 

mainly of bluish-gray and gray, dense semiflint clay 

(Popoff, 1955, p. 18). White clay pellets are abundant in 

some seams in this clay, and siderite oolites and concretions are abundant in other parts. Only a minor 

amount of lignitic material is present. The upper part 

of the principal bed contains less alumina; it is gray or 

nearly black clay because it contains abundant minute 

particles of carbonaceous matter. This bed also contains lignite units, some of which are a meter or more 

thick.

According to Popoff (1955, p. 15), the Cowlitz clay 

deposits contain kaolinite, halloysite, gibbsite, smectite similar to beidellite, and nontronite, which were 

identified by DTA and optical methods. The gibbsite, 

which occurs in the white pellets in the lower bed, was 

found to be as much as 50 percent in selected specimens. One gibbsite-rich sample of the clay contained 

49.3 percent A12 O3 , but representative samples contained 32-34 percent. Gibbsite was assumed to have 

formed by the leaching of silica by ground water carrying organic acids.

The upper clay bed in the Cowlitz district consists 

mainly of reddish-brown and greenish-blue semiplastic 

clay. It contains little more than trace amounts of lignite and lignitic clay. The average A12 O3 content of the 

upper bed is 31.6 percent.
-90

500 METERS 

I

&g£g-4 Quatern

I"*" 1*! clay 

|,%*J Middle 

1 ' basal

Lower 

beds

ir^rir:! Clay, v

1 ' with 

Lignite 

clay 

Hii;iilj||!jij| Clays 

^^^^^^^ volc

Volcan

FIGURE 16. Geologic sections of the Cowlitz kaolinitic clay deposits, Washington. (Modified from Popoff, 1955, fig. 4.)
UNITED STATES-UNDERCLA YS 35

HOBART BUTTE, OREG.

The Hobart Butte (fig. 2, location 4) is located about 

25 km south of Cottage Grove, Lane County, Oreg. The 

kaolinitic deposits in this district are erosional remnants of more extensive deposits that are preserved in 

the higher parts of the butte. They are in the sedimentary Calapooya Formation of late Eocene and Oligocene age. The deposits are irregularly shaped and as 

much as 60 m thick (fig. 17). They consist of zones of 

massive clay or of mixed clay, sand, and pebbles (Alien 

and others, 1951). The sedimentary origin of the clays 

is indicated by zonation of flattened and reworked clay 

pellets, organic coating on pellets, and the presence of 

lignitic material, diatoms, and silicified wood. The kaolinite and associated sediments in the Calapooya Formation were probably transported from weathered 

rock at higher elevation to the east.

Kaolinite is the dominant mineral of the kaolin 

group in the Hobart Butte deposits (Alien and others, 

1951), but minor amounts of dickite are present. The 

dickite apparently was altered from kaolinite or deposited along with additional kaolinite by hydrothermal 

solutions that invaded the deposits in late Miocene 

time. Minor amounts of sulfide minerals were introduced by the hydrothermal solutions. The clays are 

remarkably low in iron oxide (table 9). The analyses 

also show that no Mg, Ca, Na, or K is present; however, 

the analytical methods used may not have been sufficiently sensitive to recognize trace amounts.

TABLE 9. Analyses of kaolinitic clays from Hobart Butte, Oreg., 

in percent

[From Alien and others, 1951, table 2; W. W. Brannock, analyst. 16G, Waterlaid breccia in which the long axes of white fragments are alined in one direction, and surrounded by dark-gray clay containing organic matter and appreciable iron. 16W, Bleached zone, 5 cm wide, in contact with clay represented 

by sample 16G, and retaining the same arrangement of fragments as 16Gbut 

in a white clay matrix. Some organic matter and ferric oxide have been 

removed by hydrothermal solutions]

Sample no. 16G 16W

giO _____ _ 

Al r*12Ov-'3

Fe2 03 

Mo-O

CaO

Na O

K n

H2O (-110 °C) _ 

H O (+110°C)

TiO

Total 

50.80 

33.45

81

.61

1911

1 Q9

qi

100.01

50.91

oo an

en

.61

11 Q7

1 QQ

t a

QQ 81

ALBERHILL, CALIF.

The Alberhill district and nearby areas in the northern 

Santa Ana Mountains (fig. 2, location 8) have been the 

major source of kaolinitic refractory clays in southern 

California (Cleveland, 1957, p. 136-138). In these areas, 

both sedimentary and residual clays occur in a single 

zone that apparently formed during Paleocene time. 

The complex sedimentary clays include (1) underclaytype fire clay underlying lignite, (2) hard pisolitic clay, 

and (3) sandy clay from which high-grade white or 

nearly white kaolin has been recovered by hydraulic 

methods. The commercial underclay ranges in thickness from about 1 m to more than 2 m. The best grades 

are flint clay having PCE's of 33 and 34. The lower 

grades contain disseminated quartz, lenses of sand, 

and some chlorite. Contacts between various grades 

are gradational; the quality of clays commonly changes 

considerably within short distances along the strike of 

beds. Most of the pisolitic material is in the upper parts 

of flint-clay units, and it tends to grade into light-colored 

hard clay.

The residual clays, which are as much as 34 m thick, 

are described by Cleveland (1957, p. 137) as grading 

"downward and laterally into weathered metasedimentary rocks of the Triassic Bedford Canyon formation and andesitic rocks of the Jurassic(?) Santiago 

Peak volcanics. Slaty cleavage, outlines of feldspar 

phenocrysts and of angular rock fragments, and hexagonal quartz grains are remnant structures that indicate 

that the residual clay was derived from slate, volcanic 

breccia, and hypabyssal igneous rocks respectively. * * *"

HOLOCENE UNDERCLAY, HAWAII 

Occurrence

Plastic clay deposits occur in swamp areas at several 

localities on Kauai, Hawaii, and deposits in five areas 

were investigated (Patterson, 1971). The deposits are of 

the underclay type and occur below peat layers and 

muds rich in organic matter. The swamps containing 

the clay are at altitudes of 120-1200 m and in belts 

that receive 250-500 cm of rainfall a year. The clay in 

Alakai Swamp is on rocks of the Waimea Canyon Volcanics, and the deposits at the other four localities are 

on the Koloa Volcanics. Alakai Swamp and one of those 

on the Koloa Volcanics are of the upland type that 

have been called summit swamps (Wentworth and 

others, 1940, p. 8); they are on narrow ridges surrounded 

by deep steep-walled valleys. The swamps in the other 

three areas are in gently sloping areas adjacent to 

highlands. Rainfall is the only water now reaching the 

swamps on the ridges. The preservation of swamps
36 KAOLIN IN NORTH AMERICA, HAWAII, AND THE CARIBBEAN

150 METERS

Top of cloy pellet 

conglomerate

-640

610

METERS 

730

-700

-670

-640

-610

580

EXPLANATION

Clay-pellet conglomerate

Clay-pellet sandstone

Clay-pel]et shale 

(Symbols mixed where appropriate)

30 20 

AI 2 03

Diagram showing percent A 

m analyzed drill core

I

0 10 

Fe 2 03

Diagram showing percent Fe2 0 3 

in analyzed drill core

Limit of ore body

FIGURE 17. Geologic sections of the Hobart Butte kaolinitic clay deposits, Oregon. (From Alien and others, 1951, pi. 2.)
UNITED STATES-UNDERCLAYS 37

under such conditions is partly due to the slow rate of 

evaporation caused by extended periods of rainfall and 

dense fog. Ground-water seepage probably contributes 

to the swamps in flat areas adjacent to highlands. 

Some of the swamps support only low-growing vegetation that consists, in part, of dwarfed forms of species 

that grow as large trees in the surrounding dense forest.

The clay deposits are young and are almost certainly 

still being formed. The oldest part of the Koloa Volcanics has been dated by the magnetic-reversal and 

potassium-argon methods as late Pliocene, but most of 

the basalt flows in it are Pleistocene. Therefore, some 

of the clay formed on Pleistocene rocks. The restriction 

of the clays to peat and organic-rich layers makes it 

certain that clay and the organic material are genetically related. Peat formation in Hawaii began at the 

close of the last glacial period, as determined by pollen 

analysis (Selling, 1948, p. 118), and that it is still in 

progress in areas having such heavy precipitation is a 

valid assumption. We may, therefore, conclude that 

much of the clay formed in Holocene time.

The plastic clays are light-colored, nonbedded, irregular lenticular deposits covered by a layer of peat or 

organic-rich mud. The clays and overlying organic 

layers are thickest in the central parts of the swamps 

and thin sharply toward the edges (fig. 18). Both commonly wedge out in the zone where the stunted swamp 

vegetation changes to normal forest growth. Several 

holes augered by hand in the central parts of swamps 

failed to penetrate the base of the clay at depths of 7 m. 

One power-auger hole penetrated 8 m of clay. Deeper 

holes were not successful because of poor sample recovery, but a few cuttings from greater depths indicate 

that maximum thicknesses are more than 9 m. All of 

the clay in the swamps is very plastic, and some waterlogged deposits are almost fluid, as shown by the fact 

that a hand auger weighing about 14 kg sank under its 

own weight at several localities.

Most of the clay is light gray, but some is darker 

shades of gray, and parts of deposits in contact with the 

overlying peaty layers are ordinarily so rich in organic 

matter that they are almost black. Lower margins of 

deposits are commonly tan or brown and are richer in 

iron than middle and upper parts. Relict masses of

A Soil horizon

-B Soil horizon partly consisting of

\ saprolite

Saprolite, soft,with basaltic 

structures and textures preserved, 

residual boulders of hard 

/ basalt in lower part and ghosts 

of boulders throughout

Basalt, hard, jointed

FIGURE 18. Diagrammatic section illustrating the occurrence and nature of plastic clay deposits, Hawaii.
38 KAOLIN IN NORTH AMERICA, HAWAII, AND THE CARIBBEAN

brown and gray saprolite are common near the base of 

deposits, and large residual boulders of nepheline basalt 

are scattered through parts of the clay in one swamp. 

The cores of these boulders are dark and hard rock, but 

their outer rims, 2-3 cm thick, are lighter colored and 

softer than the cores. Much of the iron has been leached 

from the boulder rims, and nepheline has been altered 

to clay minerals.

The clay in all the swamps investigated grades downward through saprolite from which much of the iron 

has been leached into iron-rich saprolite, which is the 

parent material of most of the clay. This saprolite is 

similar to the saprolite at depth in well-drained areas, 

except that it contains much more goethite in the form 

of veins and vesicle and vug fillings.

The pH of water in peat and clay, and of open-swamp 

water, was measured in the field; all are acid. One sample of swamp water had a pH of 3.5. Water from peat at 

five localities ranged in pH from 3.5 to 4.5; however, 

pH's as low as 3.2 have been recorded for water in this 

peat, and the water has been described as "extremely 

acid" (Cline and others, 1955, p. 573).

Mineral Composition

The plastic clay consists chiefly of halloysite (10A), 

gibbsite, illite, quartz, and anatase, and it contains 

traces of ilmenite and magnetite. Much of the clay 

probably also contains appreciable quantities of amorphous inorganic matter. The estimated ranges in abundance of these minerals and amorphous matter, expressed as parts of ten or trace, are as follows:

Halloysite (10A) 5-8

Quartz 0-2 

Gibbsite 0-3 

Goethite Trace 

Magnetite Trace 

Ilmenite Trace to 1 

Anatase Trace to 2 

Amorphous matter 0-4(?)

Halloysite (10A) is the most abundant mineral in the 

plastic clay, and in some samples it is the only one 

identifiable by X-ray methods (fig. 19). It is identified 

by its prominent 10A reflection from the 001 planes, 

while the natural moisture is still present (fig. 19A), 

and the collapse of this spacing to about 7A after the 

mineral converts to the less hydrous form (fig. 19B). 

Electron micrographs of the plastic clay (Patterson, 

1971, fig. 12) show the presence of tubular structures 

characteristic of halloysite (7A), the halloysite (10A) 

having dehydrated during sample preparation or exposure required to obtain the micrograph.

i i

EXPLANATION 

A

Anatase

G 

Gibbsite

H 

Halloysite

Illite

llm 

Ilmenite

Q 

Quartz

A Clay, gray (7.5YR N5) 

from hole 5; depth 

interval 5.2-6 m

B Sample a, dried at 105 C

C Clay, gray (10YR 5/1) 

from hole 9; depth 

interval 1.2-2.8 m, 

air-dried

D Sample c, heated 550 C

E Clay, gray (10YR 5/1); 

from hole 10; depth 

interval 2.4-4.6 m, 

air-dried

F Sample e, heated 550 C

FIGURE 19. X-ray diffraction traces of samples of plastic clay from 

Alakai Swamp, Hawaii, CuKa filtered radiation. Holes are located 

on map by Patterson (1971, pi. 5).
UNITED STATES-UNDERCLAYS 39

Illite is generally not abundant in the plastic clay, 

but it makes up as much as 20 percent of parts of some 

deposits. It is uncommonly abundant in a layer 2 m 

thick below the thickest peat penetrated in augering in 

Alakai Swamp and in a thin bed interlayered with peat 

and mixed peat and clay in another swamp. Illite was 

identified by its 10A peak in samples that had been 

dried to collapse the 10A peak of halloysite (fig. 19D-FK 

Illite probably contains nearly all the K2O in the plastic clay, inasmuch as the sample richest in this oxide 

(table 10, sample 2; fig. 19£) also contains considerable 

illite and no other K2O-bearing minerals were identifiable in this clay.

Quartz is present in sufficient quantities in much of 

the plastic clay to produce prominent X-ray reflections 

(fig. 19F). Most is extremely fine grained, similar to 

that found in the clay of the Koolau Volcanics on Oahu 

by Wentworth and others (1940, p. 25).

Gibbsite occurs as irregularly rounded grains and 

impure nodules, ranging from silt size (< 0.0625 mm 

diameter) to more than 15 cm in longest dimension, 

scattered throughout most of the clay. However, in 

some zones gibbsite is absent, and in other zones small 

nodules are so abundant that the clay has a granular 

texture and is difficult to auger by hand.

TABLE W. Chemical analyses of plastic underclay on the Waimea 

Canyon Volcanics and clay, typical saprolite, and fresh basalt from 

the Koloa Volcanics, Kauai, Hawaii, in percent

[LOI, loss on ignition; , no data. From Patterson (1971)]

Waimea 

Canyon 

Volcanics

Plastic clay

Sample no.

Si02 

Al O

Fe2 03 

FeO

MgO 

PaO

Na O

K2O 

Hc\ 2 (J _______

H2 r\ U+ i - 

TiO

P O

MnO

pn

LOI

Total -

1

34.0 

34.8 

2.2 

.67 

.06 

.00 

.08 

.21 

6.8 

13.5 

7.5 

.41 

.08 

<.05

100

2

33.1 

26.7 

2.2 

1.5 

.54 

.00 

.22 

1.7 

6.1 

9.3 

17.5 

.31 

.16 

<.05

99

Koloa Volcanics

Plastic clay

3

29.5 

34.6 

1.8 

.68 

.10 

.00 

.08 

.28 

10.8 

12.6 

8.9 

.31 

.08 

<.05

100

4

29.7 

32.7 

.72 

.44 

.00 

.00 

.07 

.09 

15.0 > 

11.9 f 

7.6 

.98 

.08 

<.05

99

Typical 

Saprolite 1

5

4.2 

29.6 

35.6 

.71 

.10

.05 

.10

21.7

5.4 

.31 

.06 

<.05

OQ G.

98

Fresh 

basalt2

6

42.27 

10.90 

4.32 

8.66 

12.77 

11.67 

2.85 

.83

{ 1.31 

2.69 

.69 

.13

99

'Sample from 1.3 to about 3 m below land surface. 

2Average of 13 samples.

Anatase is the principal titanium mineral in the 

plastic clay, and it is most abundant in the < 2/nm fraction, but some is also present in the largest gibbsite 

nodules. The purest anatase found was sand-sized 

grayish-blue nodules that were concentrated in the 

heavy-mineral fraction separated by heavy liquid from 

a clay sample. These nodules were found to contain 

approximately 47 percent TiO2 and to consist chiefly of 

anatase, though trace amounts of ilmenite may be 

present.

Ilmenite is rare in most of the plastic clay, but a few 

zones contain as much as 10 percent. Most ilmenite 

grains are of fine-silt size, but a few grains are as large 

as fine sand.

Traces of goethite and magnetite were found in the 

silt and sand fractions separated from the clay. Neither 

mineral was sufficiently abundant in whole samples to 

be identified by X-ray methods.

Amorphous inorganic material is probably present in 

some of the clay because intensities of X-ray reflections 

from minerals in many samples are low, and estimated 

amounts of identifiable minerals are inadequate to 

account for the composition of whole samples. Also, the 

electron micrograph of the clay shows much finely dispersed material that is probably amorphous.

Chemical Composition

The plastic clays consist chiefly of A12O3, SiO2, TiO2 , 

and H2O (table 10); they are uncommonly low in Fe2O3 

but rich in alkalies and several minor elements. The 

abundance of SiO2 in surficial plastic clay deposits, 

which ranges from 29.5 to 34.0 percent in the samples 

analyzed (table 10, samples 1-4), contrasts sharply 

with the very low SiO2 contents of saprolite near the 

surface in well-drained areas. Iron oxide, in very small 

quantities in the clay, is the most abundant component 

of most saprolite in well-drained areas. Titania is more 

abundant in plastic clay than in the saprolite; TiO2 

forms as much as 17.5 percent of the plastic clay (table 

10, sample 2).

The alkali and alkaline-earth elements in the plastic 

clays vary considerably, but they tend to be more abundant in the clay than in saprolite. A comparison of the 

semiquantitative spectrographic analyses of plastic 

clays and saprolite from depths of less than 6 m shows 

that Mg, Na, and K all tend to be significantly more 

abundant in plastic clays in swamps than in saprolite 

in well-drained areas. The local concentration of K2O is 

as great as 1.7 percent (table 10, sample 2) in clay formed 

on the Waimea Canyon Volcanics. This percentage of 

K2O, though small, represents a considerable concentration, inasmuch as the nine rocks in the Waimea 

Canyon Volcanics that have been analyzed (Macdon-
40 KAOLIN IN NORTH AMERICA, HAWAII, AND THE CARIBBEAN

aid, 1960) range from 0.22 to 0.47 percent K2O, arid the 

average is only 0.32 percent.

Two samples of plastic clay on the Koloa Volcanics 

and two on the Waimea Canyon Volcanics were analyzed for minor elements by semiquantitative spectrographic methods. The analyses suggest some differences in the behavior of minor elements during weathering in a swamp environment from that in typical 

well-drained areas. The minor elements concentrated 

in the clay are Sc, Ga, Nb, and V. Ce was found in all 

samples, and Ge was found in one sample of clay on the 

Waimea Canyon Volcanics. As neither element was 

found in any hard or weathered rock in well-drained 

areas, both may be concentrated by weathering under 

swamp conditions. Minor elements that are leached, 

but at a much slower rate than in well-drained areas, 

are Na, Mg, Ca, Co, Ni, Cu, Sr, Y, Zr, Ba, La, and Pb.

Origin

The plastic-clay deposits and associated saprolite 

both formed chiefly from parent rocks of similar composition and age. The plastic-clay deposits are restricted 

to swamps having peat or organic-rich layers, indicating that their origin is related to poor drainage conditions and decaying organic matter. Saprolite, which 

formed in well-drained areas, has a mineral content 

and a texture very different from those of the clay. Halloysite (10A), illite, quartz, and anatase are much more 

abundant and gibbsite, goethite, hematite, and magnetite are less abundant in the clay than in the saprolite. Textures of the parent rocks have been destroyed 

in the clay but are well preserved in the saprolite.

Plastic clay has formed from both saprolite and hard 

basalt. Clay formation from saprolite is indicated by 

the downward and lateral gradation of clay into saprolite and by residual lumps of saprolite in the lower 

parts of clay deposits. In one swamp, the residual nepheline basalt boulders have outer rims in intermediate 

stages of alteration to clay, indicting that the clay does 

form from the aluminous minerals in the parent rock. 

Weathering of basalt probably began shortly after the 

lavas cooled, as has been suggested for the rocks in 

well-drained areas. Probably some swamps in which 

the clay formed have always been areas of poor drainage, resulting from flow damming at the time the parent rocks accumulated. The thickness of the peat indicates that the swamps have existed for a long time, and 

the absence of evidence for any significant change in 

the swamp environment leads to the conclusion that 

both clay and peat are still forming today. The earliest 

date that can now be established for the beginning of 

clay formation is the close of the last glacial stage. This 

date is based on analysis of pollen (Selling, 1948, p. 118)

from near the base of the thickest peat that overlies 

clay on the Waimea Canyon Volcanics.

Part of the halloysite (10A) in the plastic clay probably formed in the swamps, and part has been preserved 

from a saprolite already rich in this mineral. Some of 

this clay formed in place and is probably still forming, 

as indicated by the several stages of replacement of 

nepheline by halloysite in the altered rims of residual 

boulders. Formation of part of the clay by preservation 

of the halloysite (10A) already present in the parent 

saprolite is indicated by the isolated masses in the 

lower parts of clay bodies and by the gradation of clay 

downward into saprolite. The preservation of the clay 

is due to the influence of the low-pH swamp environment; under these conditions, silica removal is impeded, 

but iron is leached efficiently.

Recent investigations by Jackson and others (1968) 

and Rex and others (1969) have established that the 

quartz in the plastic clay was introduced from a distant 

source by atmospheric transport.

The origin of the potassium-bearing illite in the plastic clay deposits is difficult to explain, because the 

traces of biotite in the volcanic rock on Kauai are inadequate to supply sufficient micaceous parent material, and the saprolite on which some of the clay formed 

must have already been leached of potassium. The 

problem is further complicated by the fact that one concentration of illite is under the thickest peat, whereas 

clay in the same stratigraphic position under thin peat 

in this swamp contains little or no illite. The relationship between abundance of illite and thickness of peat 

suggests that illite may form in a swamp environment. 

Such an origin of illite under surface conditions would 

be similar to the one suggested for mica in several 

Hawaiian soils by Swindale and Uehara (1966) and 

Juang and Uehara (1968). Another concentration of 

illite is in a thin bed interlayered with peat and mixed 

clay and peat in one swamp where the source of potassium may have been partly from decaying plant material. However, clays at both locations where illite is 

concentrated also contain angular quartz and a few 

euhedral microscopic grains of other minerals. The 

occurrences of these minerals suggest that an ash fall 

might have been the original rock of the bedded clay; 

therefore, an air-transported volcanic material, anomalously rich in mica and from an unknown source, 

might have been the parent of the illite.

BALL CLAYS

WESTERN KENTUCKY-TENNESSEE REGION

An extensive belt of deposits in the western parts of 

Kentucky and Tennessee (fig. 2, location 27) is the 

major domestic source of ball clay. The deposits, which
UNITED STATES-BALL CLAYS 41

are found in lower, middle, and upper Eocene beds 

(Olive and Finch, 1969), are in sedimentary beds in the 

Mississippi embayment, a northern extension of the 

Gulf Coastal Plain. Deposits mined at one locality are 

of early Eocene age, but the clay in many other deposits 

is in the middle Eocene part of the Claiborne Formation or Group. The following discussions will be concerned only with the younger deposits.

The Kentucky-Tennessee ball clays occur in lenticular units, in which clay is interstratified with sand, 

silt, and lignite. Clay units range from less than 1 m to 

more than 5 m and are thinly laminated to thick bedded 

and massive. The aggregate thickness of clay in a single mine is as much as 10 m. The physical and ceramic 

properties of the clay in any given deposit commonly 

vary considerably, due to differences in mineral composition. Therefore the clays are selectively mined to 

meet product specifications. Minable bodies of clay 

range from about 100 m in longest dimension to deposits that are 800 m long and 300 m wide. Much of the 

clay is gray, and some of it is dark gray due to finely 

divided carbonaceous particles. Black carbonized imprints of fossil leaves, twigs, and other plant debris are 

common. Lignite and lignitic clay in discontinuous 

beds and lenticular units ranging from a few centimeters to nearly 3 m thick locally overlie the ball clay 

and are interbedded with it in a few places (Whitlatch, 

1940).

The Kentucky-Tennessee ball clays of Claibornian 

Age are a mixture of clay minerals and nonclay impurities, and compositions vary greatly. Kaolinite is the 

dominant mineral present. Mixed-layer clays were 

found to make up 5-25 percent of the clay fraction of 11 

samples studied (table 11). Illite is the second most 

abundant clay mineral, and smectite and chlorite are 

present in minor amounts in parts of deposits. Quartz 

is the major nonclay mineral and is found in amounts 

ranging from 4 to 43 percent in the 11 samples. Minor 

quantities of plagioclase, calcite, dolomite, and possibly potassium feldspar also are present.

Olive and Finch (1969, p. 14-15) offer the following 

explanation for the depositional environment of the 

ball clay:

"* * * Seeking evidence concerning environments of deposition, 

R. H. Tschudy (written commun., 1968) examined pollen assemblages obtained from the Claiborne Formation at localities shown in 

figure 1. Many assemblages contain taxa, such as freshwater algae 

and water fern, that indicate deposition in lakes and fresh-water 

ponds. Others contain large spores that are not likely to have survived long-distance transport. A clay sample from locality C-15 

(fig. 1) yielded abundant hystrichospheres, a few dinoflagellates, and 

abundant plant tissue, which point to a marine or near-shore marine 

depositional environment. A sample from locality C-7 (fig. 1) contained much trash and a few hystrichospheres, which suggest a 

marine or brackish-water environment. The shapes and distribution

of the clay bodies and the ecologic information provided from a study 

of pollen assemblages suggest that the climate during Claiborne 

time was warm and humid with heavy seasonal rainfall; the terrain 

was a rather flat plain traversed by south- to east-flowing, meandering, low-gradient, aggrading streams that occupied broad flat shallow valleys. Flooding following seasonal rains caused shifts in the 

major channels and abandonment of channel segments, which became locales for accumulations of clay deposits and associated 

sediments. * * *"4

The foregoing comments on the depositional environment of the ball clay are plausible, but they provide no 

explanation of the origin of the kaolinite in the source 

area. Very little evidence can be mustered to support 

any proposed origin of the kaolin, because of the lack of 

knowledge of geography, geomorphology, and soils in 

the region in Eocene time.

TROUP, TEX.

The principal ball-clay deposits in Texas are in the 

Troup district (fig. 2, location 19). This clay is in the 

lower Eocene part of the Wilcox Group (Stenzel, 1950), 

which is separated from the overlying formation by a 

prominent undulating unconformity. The deposits are 

restricted to the higher parts of the Wilcox Group below this unconformity, which were once hills on the 

erosional surface existing prior to the deposition of the 

overlying formation.

The ball clay is described by Stenzel (1950) as being a 

tough clay, most of which has a subconchoidal parting 

and a uniform color of light bluish gray where fresh. 

This clay bleaches to nearly white with prolonged 

exposure to the sun. The deposits contain abundant 

carbonaceous tubes filled with ball clay that are fossil 

roots, proving that the clay once was a soil. The clay is 

cut by numerous inclined slippage planes having wavy 

slickensides. Displacement along such planes is not 

greater than 2 mm. The deposits typically grade downward into sandy lignitic clay and are overlain locally 

by thin zones of impure lignite.

According to Pence (1950), the clay near Troup is 

remarkably similar to the Tennessee ball clay. Kaolinite having imperfect crystallinity is the dominant clay 

mineral, and the deposits contain about 20 percent 

quartz. One incomplete analysis shows that the clay is 

32.69 percent A12 03 and 53.73 percent Si02, and the 

PCE is 32.

OTHER BALL-CLAY DISTRICTS

Ball clay, which is mined by one company, occurs in 

the Panola, Miss., district (fig. 2, location 28). This clay 

is in the Zilpa Clay (Bicker, 1970), which is of middle

4Sample locations and figure 1 refer to Olive and Finch's report (1969).
42 KAOLIN IN NORTH AMERICA, HAWAII, AND THE CARIBBEAN

TABLE 11. Description and X-ray mineralogic analyses of ball-clay samples from the Claiborne Formation, Tennessee and Kentucky 

[Modified from Olive and Finch (1969, table 3) to conform with the recommendations of the AIPEA Clay Mineral Nomenclature Committee. Whole-rock analyses, 

in percent, calculated from X-ray diffraction data. Clay-mineral fraction, in percent, estimated from X-ray analyses, using methods described by Schultz (1964), 

except that total clay is reported as the difference between the sum of the nonclay minerals and 100 percent. Precision of determinations generally within 10 

percent, , no data]

Sample no.

12 

1 ^

14

1^1

1fi

17

18

19 _______ 

90

91

Location

Paschall No. 5 clay pit, 4.1 mi northeast of Cottage 

Grove, Henry County, Tenn. 

Etheridge mine, 4.3 mi east-northeast of Cottage 

Grove, Henry County, Tenn. 

Scott mine, 2.35 mi southwest of junction of U.S. 

Route 641 and Tennessee Route 140 in Puryear, 

Henry County, Tenn. 

Clay pit, 0.4 mi southeast of Bell City, Galloway 

County, Ky. 

Lamkin clay pit, 2 mi west-northwest of West 

Viola, Graves County, Ky. 

Middle of Powell pit, 1 mi southeast of Hickory, 

Graves County, Ky.

Outcrop, 0.4 mi east of Wickliffe City limit, north 

side Kentucky Route 440, Ballard County, Ky. 

Outcrop, 3.8 mi east of Lovelaceville in Illinois 

Central Railroad cut, McCracken County, Ky. 

Outcrop, 0.75 mi south of Camelia, McCracken 

County, Ky. 

Outcrop, 0.9 mi north-northeast of Camelia, 

McCracken County, Ky.

Lithologic description

Brownish-gray ball clayrln

do

Dark-gray carbonaceous, 

slightly silty clay.

Whole-rock analyses

O11

4 

23 

34

34 

20 

20

18 

43

31 

26 

23

Plagioclase

? 

?

1

? 

? 

2

feldspar Potassium 

?

-

?

<u

J3 

cB O

-

1 

1

-

? 

? 

2

Dolomite

-

1

? 

? 

?

Total clay

96

77 

65

63 

80 

80

82

57

69 

70

77

Clay -mineral fraction

Kaolinite

70 

83 

79

67 

70 

90

77 

61

68 

76 

72

1

5 

6

14

9 

22 

5

13

8

9 

9

18

Smectite

-

-

16 

3

Mixed-layer cla

25

11

7

24

8 

5

8 

15

20 

15 

10

Chlorite

-

2

-

Proportions of (M) andsmectite 

illite (I) mixed-layer cla in 

I>M 

I>M 

I>M

I>M

M>I 

I>M 

I>M

'Includes clay-sized mica, chiefly muscovite.

Eocene age, the same age as most of the deposits in the 

large Kentucky-Tennessee ball-clay district farther 

north. The "Panola" ball clay is remarkably similar in 

geologic occurrence and mineral content to the clay in 

the Kentucky-Tennessee district.

Deposits of white kaolin at Hart, Calif, (fig. 2, location 7), are classified by the California Division of Mines 

and Geology as ball clay (Kelley, 1966; Dietrich, 1928, 

p. 193-194). Though this kaolin is plastic and has some 

of the other physical properties of ball clay, it is of 

hydrothermal origin and, therefore, differs from the 

other ball-clay deposits in the United States, which are 

of sedimentary origin. It formed by the alteration of 

eruptive rocks that were high in alumina and low in 

alkali contents.

A ball-clay district at North East, Md. (fig. 2, location 42), was active for many years. However, mining 

has ceased in this district, because much of the better 

grade clay is exhausted and most of the remaining clay 

is on land that is unavailable for strip mining. The ball 

clay in the North East district, which is in nonmarine 

beds of Cretaceous age (Knechtel and others, 1961), 

varies considerably in composition, and some deposits 

have little value because they contain too much quartz 

sand for industrial use. The clay fraction of most deposits is 60-80 percent kaolinite, and the rest is illite 

and mixed-layer clay.

Residual Kaolin Deposits

Residual kaolin deposits occur at many places in the 

Eastern United States and at several places in the
UNITED STATES-RESIDUAL KAOLIN DEPOSITS 43

western part of the Nation. The residual kaolin in the 

Eastern States is mainly in weathered pegmatites and 

granitic igneous rock masses that are scattered through 

the Appalachian and Piedmont regions from Vermont 

and New Hampshire in the north to Alabama in the 

south. Many of these deposits were mined on a small 

scale in the last century. All are now (1980) inactive 

except the Spruce Pine district, North Carolina, and 

only this district will be discussed in this section of the 

report. Several of the districts in the other regions containing residual kaolin deposits have been discussed 

previously and will only be listed by name and parent 

rock type in this section.

SPRUCE PINE, N.C.

Numerous scattered deposits of residual kaolin occur 

in the Spruce Pine district, North Carolina (fig. 2, location 43). The deposits have formed by weathering of 

feldspathic rocks and contain high percentages of quartz 

and other resistant minerals (Parker, 1946, p. 42). 

High-quality kaolin containing 37 percent or more 

A12O3 and less than 1 percent Fe2O3 is recovered by 

washing.

Sand (1956, p. 33), in reporting on the genesis of residual kaolins that included 12 samples from Gusher 

Knob, the principal mining area (table 12), and others 

from seven more locations in the Spruce Pine district, 

described the following alteration:

"* * * Hydrated halloysite predominated over kaolinite in all of 

these deposits. In individual samples the hydrated halloysite to kaolinite ratio varied from 30:1 to 1:1 with an average for the region of 

about 10:1. The feldspars, whether sodic plagioclase or microcline, 

weather to hydrated halloysite with plagioclase the first to decompose. This can be observed in the hand specimen of a partially altered 

perthite where the potash feldspar stands out in relief. Large, only 

slightly altered, microcline crystals were found next to completely 

altered plagioclase. However, in this region it was found that all feldspars alter to hydrated halloysite even though the rate of weathering 

differs. In only one sample, from the Woody Deposit, was the potash 

feldspar observed altered in small part to secondary mica. The primary mica was altered to vermicular kaolinite in all samples 

studied. * * *"

OTHER RESIDUAL KAOLIN DEPOSITS

Residual kaolin deposits discussed previously in this 

report, because they occur in districts where the principal deposits are sedimentary, include those that have 

weathered from the following rocks: (1) basalt in Spokane County, Wash., (2) nepheline syenite in the Bauxite district, Arkansas, (3) andesite, slate, and volcanic 

breccia in the Alberhill district, California, and (4) gneiss 

in the Minnesota kaolin district.

Weathering, the process that forms residual kaolin 

deposits, no doubt was active on many sedimentary 

kaolin deposits either before burial by younger rocks or 

near the present land surface much later. Therefore, 

many of the other kaolins, ball clays, and underclays 

are in part residual.

TABLE 12. Bulk mineral compositions ofsaprolite in the Spruce Pine district, North Carolina, in percent 

[Modified from Sand (1956, table 5). S.F., analysis of size fraction; T.S., point count of thin section; Tr, trace]

Deposit

Gusher Knob1 

School Hill 

Fluken Ridge

Tin

Do

Do

Do

1 7- Acre Prospect 

Tin

Do

Do

Do

Carter Ridge 

Do

Do

Analysis

S.F. 

S.F. 

T S

T S

G T?

G I?

SF

S.F. 

S.F. 

T S

SF

T 9

T S

T.S. 

SF

G I?

G TT

Parent rock

Granite 

____ do ____

do

PprtViitp

do

Pegmatite 

______________ (JO ____________

do

do

Hn

Hn

 do 

do

do

Quartz

24.1 

58.2 

99 4

.4

.7

Tr

5.5 

8.8

q rj

3.4

1

0

None 

4.4

9Q Q

c 7

Mica

16.4 

1.9

i °.

7.0

9 1

16.8 

18.2 

17.1

Q q

Q Q

a Q

2.9

14.8

on 7

1Q 4

Feldspar

0.5 

None

Q

4.7

on 7

rrc c

None 

None

None

.7

O1 R

Hydrated 

halloysite

46.6 

35.3

70 7

QA Q

74.4

CO O

1 C Q

64.5 

61.8

CC Q

7C c

QC C

QA Q

84.3

70 n

OK 1

43. 1

Kaolinite

12.4 

4.9 

9 a

7 9

101

1.7

1.4

13.2 

11.1

101

ion

Q Q

Q Q

12.8 

9 7

4.7

109

"Average of 12 samples.
44 KAOLIN IN NORTH AMERICA, HAWAII, AND THE CARIBBEAN

Hydrothermal Deposits

Hydrothermal kaolin deposits occur at several places 

in the Western United States, but only a few of these 

have been mined. The deposits in the Little Antelope 

Valley district, California, are the only ones consisting 

mainly of kaolinite that have been mined recently. 

Hydrothermal halloysite has been produced in the Tintic district, Utah, and at Terraced Hills, Nev.

LITTLE ANTELOPE VALLEY, CALIF.

The Little Antelope Valley clay deposits (fig. 2, location 6) are in an area of considerable geothermal activity in a range of low hills on the east side of the Sierra 

Nevada Range. The range of hills consists mainly of 

rhyolite flows, and the valley in which the clay is located was occupied by a freshwater lake in which tuff 

was deposited during Pleistocene time. Thermal springs, 

fumaroles, mud pots, and patches of warm ground are 

found at three localities in the district. Numerous vents 

along two northwest-trending faults about 1 km apart 

emit hot water and steam.

The deposits were described by Cleveland (1962); at 

the time his report was written, the largest of the Little Antelope clay deposits was exposed in an open-cut 

mine 210 m long. The cut extended into the hillside 

100 m, and the working face was about 8 m high. The 

deposit was exposed along the principal fault for 600 m 

northward from the mine. The clay produced has been 

used as fillers in paint, plastics, rubber, and paper; as a 

whitener in paint and Portland cement; and in stucco 

mixes. It had PCE's in the 30-34 range.

The kaolin varies considerably in mineral composition and other characteristics. Most of the kaolinite, 

the principal mineral, is well ordered, but some formed 

by alteration of tuff is described as "poorly crystalline" 

(Cleveland, 1962, table 4). Quartz, in amounts of as 

much as 20 percent, is the principal impurity. Cristobalite is present locally, and veins of opal and trace 

amounts of alunite occur at places. Noncrystalline 

matter that is presumably aluminous is abundant 

locally. Most of the clay is pale yellowish orange, but 

some is light gray to white. It ranges from hard to soft 

friable material (Mohs scale 1-4), contains megascopic 

and microscopic cavities, and has an earthy luster and 

specific gravity of about 2.5.

Chemical analyses (table 13) of the Little Antelope 

Valley kaolin indicate that it contains appreciably 

more silica and less alumina than theoretical kaolinite. Trace elements in this clay include Zr, Li, Ba, Mg, 

Ga, Pb, V, and Mn (table 14). Some of the trace elements, particularly Pb, V, and Mn, may have been 

introduced by thermal solutions.

TABLE 13. Partial chemical analyses of kaolin from the Little Antelope 

Valley district and of theoretical kaolinite, in percent

[Modified from Cleveland (1962, table 3). 1, Sample from Little Antelope Mine. 

Analysis by Smith-Emory Company, Los Angeles, Calif. 2, Sample from Casa 

Diablo kaolin deposit. Analysis by Smith-Emory Company, Los Angeles, 

Calif. 3, Theoretical kaolinite. , no data]

SiOa - 

AlaO, -

Fe,0, _ 

MgOCaO - 

K2O - 

NasO - 

TiOa 

59.88

28.67

.01

.01

.01

.01

.01

0

53.01

31.13

.48

1.37

.11

.06

.59

.20

.57

46.54

39.50

H20 13.96

Total- 88.60 87.52 100.00

TABLE l4. Semiquantitative spectrochemical analysis of clay material,

Little Antelope Mine

[From Cleveland (1962, table 4), G. A. Ulman, analyst. Elements given in order 

of decreasing concentration]

Element Concentration

Si -

Al -

 Major constituent

 Major constituent

Fe 1 percent (approx.)

Ti Between 0.2 and 0.002 percent

Ba 

Mg

Do. 

Do.

Do.

Do

The kaolin in the Little Antelope Valley district 

clearly formed by hydrothermal solutions. Cleveland 

(1962, p. 20-21) stated that most of the alteration was 

by sulfuric acid, and he believed that the water in earlier intervals contained even more sulfur than it does 

now (table 15). Most of the altered host rocks are rhyolites, and the clay formed from older rhyolite is purer 

and of higher commercial value than the deposits from 

younger rhyolite and lacustrine tuff and tuff breccia. 

The typical alteration zone consists of a core of clay 

that grades outward into country rock or partly altered 

rock brightly tinted with iron oxide. Deposition of silica by the thermal solutions has caused local contamination of clay, and silicified zones several tens of meters 

in longest dimension are bypassed in mining.
UNITED STATES-HYDROTHERMAL DEPOSITS 45

TABLE 15. Partial chemical analyses of waters in the Little Antelope 

Valley district, California, in parts per million

[From Cleveland (1962, table 2). 1, Hot Creek at Fish Hatchery; 2, Boiling Pot 

in Hot Creek Gorge; 3, Hot Creek at County Road (NEV4 sec. 19, T. 3 S., R. 29 

E.); 4, Hot Springs on Little Hot Creek; 5, Casa Diablo Hot Springs. , no data]

Si _____ .

re 

Ca 

Mg ____ _ 

Na 

so _____________

Cl_ _________

B _________ 

As

Total ___ 

- 

11.

12.

23.

8. 

11.

.45

65.45

_______

11.

6.

119.

31. 

65.

2.96

234.96

 56. -

 .04 -

13. -

4.8 -

69.0 -

£ Q

21.0 - 

37.0 7.25

1.84 11.9 

.10

A. 1 

210.78 19.15

-

15.60

15.60

TINTIC, UTAH

Most of the catalytic-grade halloysite that has been 

mined in the United States came from the Dragon 

mine, Tintic district, Utah (fig. 2, location 13). The 

total production during the period 1931-62 was nearly 

750,000 metric tons. The recorded output since 1962 is 

unavailable. However, the deposit is known to be exhausted, and another deposit in this district was being 

worked in the 1970's. The Dragon mine was originally 

operated for iron ore.

The halloysite bodies at the Dragon mine are located 

along conspicuous fissures at the northeast end of a 

monzonite porphyry stock (Kildale and Thomas, 1957). 

They are hydrothermal replacements of lower Paleozoic limestone near the contact with the porphyry and 

were known to extend from the surface to a depth of 

about 120 m. Layers of chert nodules that formed beds 

in the limestone before replacement are present in 

parts of the deposit. Outer edges of the deposit grade 

into limestone and masses of iron oxide containing 

very little clay.

The typical fresh clay is nearly pure halloysite containing very fine grained disseminated pyrite that is 

rarely sufficiently large to be observed in hand specimen. The purest halloysite is white and has a lustrous 

porcelainlike appearance, and this form grades into a 

duller white variety. Both 10A and 7A forms of halloysite are reported to be present, but virtually all the 

freshly mined clay was the hydrated type. Iron oxides 

were present in sufficient quantities to stain the clay 

near the surface and along fissures well below the surface. Manganese stains occur along fractures. An 

American Petroleum Institute reference sample from

the Dragon mine examined by Kerr and others (1950, 

p. 49) was 93.9 percent pure halloysite.

TERRACED HILLS, NEV.

Large deposits of hydrothermal halloysite in the Terraced Hills district, Nevada (fig. 2, location 12), have 

been mined intermittently for use in portland cement. 

The deposits range in thickness from about 3 m to more 

than 18 m (Papke, 1971). Most of the clay is grayish 

orange to light brown, but some is light gray. It has 

altered from andesitic tuff of Miocene to Pliocene age. 

The unaltered tuff commonly contains fragments of 

pumice and other volcanic rocks* including irregular 

beds of arkose or conglomerate arkose. Outlines or 

ghosts of the pyroclastic fragments are preserved in 

the clay. The clay is underlain by vesicular, locally porphyritic andesite and basalt flows and is unconformably overlain by thick basalt flows that are mostly finegrained and dense.

The mineralogy of the deposits is described by Papke 

(1971, p. 72) as follows:

"* * * The clay bodies are composed of compact, brittle material with 

a dull to slightly waxy luster that slakes rapidly in water to form 

granules or small curved chips. Study of numerous samples by X-ray 

diffraction, differential thermal analysis and the optical microscope 

showed that the clay is composed principally of halloysite, hydrated 

iron oxides, and variable amounts of residual feldspar and residual 

or introduced quartz. About 1 percent magnetite is present in small 

disseminated grains. Montmorillonite was detected in a few samples. 

"Most of the samples were cut from within 1 ft of an exposed face. 

The samples were stored in air-tight containers, except while being 

pulverized in a mortar and pestle, to prevent any change of hydration state. X-ray diffraction studies showed that all samples were 

mixtures of the fully-hydrated and dehydrated forms of halloysite. 

Portions of some samples were dried in air for 48 hr and examined 

again by X-ray. These contained a much higher percentage of the 

dehydrated form than did the original material. It is probable that 

the fully-hydrated form is the only type present in deeper, unexposed portions of the deposits. * * *"

The hydrothermal solutions that formed the clay rose 

along the high-angle faults occurring in the district 

and spread out in permeable and chemically favorable 

beds. The open-textured tuffs between less permeable 

flows formed a natural channelway for the hot solutions. The evidence that the solutions rose along faults 

is that near faults all the tuff is altered to clay, whereas 

farther away only the upper, more permeable part of 

the tuff has been altered to halloysite.

The hydrothermal process was selective, and finegrained glass fragments are much more thoroughly 

altered than are fragments of crystalline rock. During 

the alteration of the andesitic tuff to halloysite, silicon, 

calcium, magnesium, sodium, potassium, and probably 

iron were removed and water was added. No silicaenriched halo was found above or surrounding the
46 KAOLIN IN NORTH AMERICA, HAWAII, AND THE CARIBBEAN

deposits, as associated with hydrothermal halloysite 

elsewhere (Keller and Hanson, 1969). Therefore, the 

fate of the elements removed by the hydrothermal 

activity is unknown.

MINOR HYDROTHERMAL ALTERATION OF SEDIMENTARY CLAYS

Though only minor alteration of the clay by invading 

solutions took place, rare occurrences of hydrothermal 

activity in sedimentary clays have been found at Hobart Butte, Oreg. (fig. 2, location 4), by Alien, Loofbourow, and Nichols (1951) and in one deposit in King 

County, Wash. (fig. 2, location 1), by Nichols (1945). 

The clays at Hobart Butte were deposited in late Eocene 

and Oligocene time, and the hydrothermal activity was 

related to volcanism in the Miocene. The solutions 

deposited minor amounts of stibnite (Sb2S3), realgar 

(AsS), pyrite (FeS2), scorodite (FeAsO4 »2H2O), cinnabar 

(HgS), calomel (HgCl), and other minerals. They also 

either altered some of the kaolinite to nacrite or deposited this kaolin mineral. Realgar and stibnite occur as 

coatings of slickensides, fillings and replacements of 

porous material, coatings of pellets, and disseminated 

minute crystals. Well-formed pyritohedrons of pyrite 

are associated with the realgar. Scorodite occurs as 

green crusts and spherulites along crevices and replacements of the clay. The King County clay contains minor 

quantities of realgar and flakes of chalcopyrite.

OTHER HYDROTHERMAL KAOLIN DEPOSITS

Kaolin and halloysite of hydrothermal origin occur 

in varying quantities in many mining districts of the 

Western United States. Many of these occurrences ar^ 

associated with metallic minerals in mines that have 

long been inactive, and none of them have been adequately investigated. The Stoker deposit (fig. 2, location 11) and the Bullion district (fig. 2, location 10), 

both in Nevada, have been described by Olson (1964, 

p. 186).

"* * * The Stoker kaolin deposit, Pershing County, probably is the 

largest known kaolin deposit in Nevada. It may be traced for at least 

one-half mile along the base of the western flank of the Stillwater 

Range immediately north of New York Canyon. The body probably is 

on the order of a few hundred feet across. Bulldozed trenches have 

shown that it is as much as 25 feet [7.5 m] deep. The kaolin is thought 

to have been formed by hydrothermal alteration of a Mesozoic(?) 

phyllite. * * * A large deposit of halloysite occurs in the Bullion 

(Railroad) mining district, * * * Elko County, which originally was 

developed for silver, lead, copper, and gold in 1869. At the intersection of two large dikes of quartz porphyry on the north face of Bunker 

Hill, the porphyry has been almost entirely converted by hydrothermal processes to halloysite and other clays. The exact extent of 

the clay is unknown, but one adit which cuts the dike at an approximate angle of 45 ° is in clay for 350 feet [105 m]. This halloysite is 

reported to have potential value as a catalytic agent. * * *"

Large deposits consisting of a mixture of highly crystalline kaolinite and cristobalite occur in hydrothermally altered tuffs and other volcanic rocks along the 

Continental Divide about 22 km west of Winston, Sierra 

County (fig. 1, location 17), N.M. Parts of this deposit 

consist of rather uniform light-colored clay, but much 

of it contains appreciable vein quartz or other forms of 

silica and only partially altered volcanic rock. A few 

tons of clay from this deposit was used experimentally 

in making ceramic tile; the deposits have been explored 

in some detail and evaluations for use as paper coater 

are being made by private interests.

Problematical Kaolins and Deposits of Uncertain Origin

INDIANA HALLOYSITE

Halloysite (10A) was discovered at Shoals, Ind. (fig. 2, 

location 30), in 1874 (Callaghan, 1948), and small deposits have been found in several other places in the 

State. The best known deposits are in the Gardner 

Ridge mine area several kilometers northeast of Shoals. 

These deposits were mined intermittently on a small 

scale for use in floor tile and alum-type chemicals between 1880 and about 1930. They are of interest mainly 

because they are a problematical and uncommon occurrence of halloysite (10A).

The Gardner Ridge deposits are in irregularly shaped 

discontinuous bodies scattered along the unconformable contact between Mississippian limestone and 

Pennsylvanian sandstone (between Lower and Upper 

Carboniferous of the European classification). Isolated 

veins of halloysite (10A) and other veins extending 

from clay bodies occur in the overlying sandstone. In 

places the clay is disseminated and forms a matrix in 

the sandstone. The clay bodies range from about 1 m to 

a little more than 2 m in thickness. The larger bodies of 

clay mined are estimated to have contained only about 

20,000 tons. The forms of clay present include glassy, 

banded, massive, and nodular, and some of it is plastic. 

It is described as white, grayish, some of it bluish and 

greenish, and parts of it are stained with manganese 

and iron oxide. The uppermost parts of the clay bodies 

are brown or mahogany. Though most of the clay is 

halloysite (10A), it is intermixed with allophane and 

contains minor quantities of alunite and gibbsite.

Callaghan (1948) reviewed the many theories offered 

to explain the origin of the Gardner Ridge halloysite 

deposits, pointing out that the most widely accepted 

theories are (1) the halloysite was introduced by solutions and (2) the deposits are ancient laterites consisting of residual material on limestone that have undergone considerable postburial changes. Among the
UNITED STATES-PROBLEMATICAL KAOLINS AND DEPOSITS OF UNCERTAIN ORIGIN 47

difficulties in explaining the origin of this uncommon 

type of deposit are the uncertainty of the source of the 

sulfur to form the alunite and the formation of gibbsite. It has been suggested that the gibbsite formed by 

the leaching of clay minerals by sulfuric acid that 

formed by alteration of pyrite in ground water. However, this theory is supported only by the negative evidence of the absence of pyrite in the overlying sandstone near the clay deposits and its presence elsewhere.

VERMONT KAOLIN

The largest known deposits in Vermont are located 

at East Monkton (fig. 2, location 46) in the west-central 

part of the State. Several attempts have been made to 

produce kaolin in this district since the late 1700's. 

Small tonnages were processed and used in refractory 

and other ceramic products, as a filler for soft rubber, 

and as a binder for animal feed, but the kaolin is too 

coarse grained to be used in paper making. The district 

has been inactive since the late 1960's, and the last 

processing plant, built in 1959, has been dismantled.

The kaolin occurs in the Cheshire Quartzite of Early 

Cambrian age as thin beds of quartz-rich clay and kaolinitic quartzite. Parts of the kaolin-bearing beds are 

cut by milky quartz veins as much as 10 cm thick.

The origin of the Vermont kaolin is not well understood because of uncertainty about the source of alumina. Early ideas included the weathering of graphic 

granite and feldspathic quartzite. Neither idea seems 

sound because no graphic granite occurs in the vicinity, and the Cheshire Quartzite contains very little 

feldspar. A graphic granite source rock also is improbable because most of the quartz grains associated with 

the kaolin are rounded (Ogden, 1969). Ogden favored 

the theory that the deposits formed by hydrothermal 

replacement by solutions from a deepseated intrusion. 

Whether or not this explanation is correct is difficult to 

prove.

MOUNT HOLLY SPRINGS, PA.

The kaolin deposits in the Mount Holly Springs district, Pennsylvania (fig. 2, location 39), consist of sandy 

and silty clay (table 16) that formed on phyllite of Early 

Cambrian age (Hosterman, 1969b). They are mined for 

use in light-colored brick and white portland cement. 

Some clay is washed for filler applications. The whitest 

and best quality clay is in the upper parts of the deposits, and this clay grades downward into grayishgreen and light-gray phyllite through a zone of yellow, 

pink, red, and brown variegated silty clay. The deposits 

have long been thought to be residual and to have formed 

by weathering. However, Hosterman (1969b) found 

that the deposits contain alunite, and he suggested 

that they were formed by hydrothermal alteration and 

later modified by weathering.

HALLOYSITE NEAR GORE, GA.

Halloysite of uncertain origin occurs near Gore, Ga. 

(fig. 2, location 44). According to Broadhurst and Teague 

(1954), the halloysite is in a bed less than 1 m thick 

within a chert formation of Devonian age. One sample 

from this bed was 37.30 percent A12O3 , 42.20 percent 

SiO2 , and 19.95 percent H2O. This sample also contains 

trace amounts of iron, manganese, cobalt, titanium, 

and calcium. Several hundred tons of halloysite was 

mined in the Gore district in the early 1900's.

KAOLIN IN SINKHOLES IN THE APPALACHIAN REGION

Kaolin deposits in sinkholes, many of which also contain small bauxite bodies, are widespread in the Valley 

and Ridge province in the Appalachian region. The 

deposits are scattered from northwestern Georgia and 

northeastern Alabama to central Virginia, a distance 

of about 800 km. Gibbsitic bauxite was mined from 

many of these sinkhole deposits until the mid-1900's,

TABLE 16. Particle-size content (in weight percent), clay-mineral ratios, and content of SiO^ AL^O^ and Fe2O3 (in weight percent) in clay

from the Philadelphia Clay Co. deposit, Mount Holly Springs, Pa. 

[From Hosterman (1969b, table 1). , no data]

Clay-mineral ratios

No. of samples Sand Silt Clay Kaolinite Illite Smectite SiO2 A12O3 Fe2O3

Variegated silty clay - 

Weathered phyllite 

Ofi

3 

5

5

7

34 

33

70

61 

60

q

8 

1

1

2

7

Trace 

2

71

66 

56

10

19 

18

0.4

2.2 

6.3
48 KAOLIN IN NORTH AMERICA, HAWAII, AND THE CARIBBEAN

and kaolin used in ceramics and aluminous chemicals 

also was mined on a small scale until the 1970's.

Most of the kaolin and bauxite in the sinkhole deposits occurs as subconical fillings of depressions in 

Paleozoic carbonate rock. The deposits are commonly 

elliptical or subcircular and are less than 100 m in 

maximum horizontal dimension; the greatest depth 

from the surface to the bottom of deposits is a little less 

than 60 m. A few deposits are elongate, and they probably are in solution chambers along joints. The higher 

grades of bauxite are ordinarily enclosed by concentric 

envelopes of clayey bauxite, bauxitic kaolin, and kaolin. The outer kaolin envelope is commonly separated 

from the carbonate wallrock by an envelope of cherty 

red clay. Collapse structures in some deposits apparently were formed by the slumping of bauxite as the 

carbonate rock was dissolved. The outer red clay zone 

in some deposits has been referred to as terra rossa 

(Knechtel, 1963) and is similar in composition to the 

typical residuum on limestone and dolomite in the 

region.

Problems of explaining the origin of kaolin and bauxite in the sinkhole deposits are much the same as those 

relating to the karst bauxites of Europe, Jamaica, and 

elsewhere. Although a great deal of work has been 

done and a voluminous geologic literature exists on the 

origin of karst bauxites, much remains to be learned 

about their origin. Though American geologists generally agree that most of the bauxite in the Valley and 

Ridge province formed in sinkholes, opinions differ as 

to the parent rock and explanations for the enveloping 

kaolin and cherty materials. Bridge (1950, p. 193, fig. 7) 

postulated that the kaolin and bauxite were derived 

from crystalline rock debris transported from igneous 

and metamorphic rocks in the Blue Ridge and Piedmont provinces east of the Valley and Ridge. Knechtel 

(1963) pointed out similarities between terra rossa 

associated with the sinkhole deposits and the cherty 

residuum on carbonate rock and suggested that the 

bauxite formed as acid water leached accumulations of 

residuum in sinkholes. Collapse of deposits after the 

bauxite formed may account for the present concentric 

envelopment of deposits and their low iron contents. 

The acidity of the water is suggested by scattered 

organic-rich layers in the upper parts of some deposits 

and by the fact that typical sinkholes on the present 

surface are swampy and rich in decaying organic matter. Knechtel (1963) suggested that the bauxite in the 

Valley and Ridge formed at many different times since 

the close of the Paleozoic Era. However, pollen of early 

Tertiary age has been found in one sinkhole deposit, 

and it seems likely that most of these deposits formed 

at approximately the same time as the kaolin in the 

Coastal Plains.

CANADA

Canada has large resources of low- to moderate-quality 

kaolinite clays, but large high-grade deposits, such as 

would be suitable for paper coater use, have not been 

found. The larger deposits are of the sedimentary type, 

but hydrothermal kaolinitic clays have also been found.

Probably the largest resources of kaolinitic clays in 

Canada are in the Whitemud Formation of Late Cretaceous age that extends across most of southern Saskatchewan and southeastern Alberta (fig. 20, location 

3). The Whitemud clay is used in refractories and facebrick, and minor tonnages have been sold as ball clay 

(Brady, 1962). Brady found that the Whitemud clay is 

chiefly kaolinite and quartz, feldspar and mica are generally present, and smectite and chlorite are rare. Most 

of the clay is plastic, and PCE's of much of the clay are 

in the 20-32 range.

Small kaolin deposits occur at several places in Quebec and northern Ontario (Douglas, 1970, p. 222). The 

district that has produced the most kaolin is SaintRemi, Quebec (fig. 20, location 6). About 25,000 tons of 

kaolin was mined in this district in 1942. Some was 

mined later, but apparently no mining has been done 

since 1946. The kaolin in Saint-Remi is of hydrothermal 

origin. It occurs in veinlike masses ranging from about 

1 m to nearly 30 m across. The host rock is Precambrian quartzite.

Extensive deposits of kaolinitic clays occur in a Cretaceous sedimentary formation in the James Bay lowland, Ontario (fig. 20, location 5). This Cretaceous formation is a deltaic wedge-shaped unit of continental 

sediments that also contains lignite and silica sand 

(Vos, 1979). Significant tonnages of moderate-quality 

refractory kaolin are present.

Other clay deposits in Canada that are chiefly kaolinite include the fire clays at Giscome Rapids (fig. 20, 

location 1) and Sumas Mountain (fig. 20, location 2), 

B.C. (Brady and Dean, 1964), and a deposit at an unnamed location in Manitoba (P. Partridge, oral commun., 1977). Both deposits in British Columbia are in 

nonmarine sedimentary beds of Tertiary age. The Giscome Rapids clay has a PCE of 29, and the PCE of the 

Sumas Mountain clay is 31Vz. The clay in Manitoba 

(fig. 20, location 4) is a sand kaolin of pre-Pleistocene 

age and occurs as fillings of channels cut in Ordovician 

limestone.

MEXICO

Kaolin occurs in virtually every state in Mexico (Pasquera and others, 1969), mining is active in at least 9 

districts (fig. 21), and the clay is used in several prod-
MEXICO 49

7. Giscome Rapids, British Columbia

2. Sumas Mountain, British Columbia

3. Approximate extent of Whitemud Formation, 

Saskatchewan and Alberta

4. Unnamed location, Manitoba

5. James Bay Lowland, Ontario

6. St. Remi, Quebec

FIGURE 20. Location of kaolinitic clay districts in Canada.

ucts. Most of the mining is by open-pit methods, but 

several mines are underground. The kaolin is processed at grinding plants equipped with hammer mills 

and air classifiers, but there are no kaolin washing 

plants in Mexico. Domestic kaolin is used as fillers in 

paper, rubber, and plastics; as extenders in paint; and 

in ceramic and refractory products. The production of 

kaolin in Mexico is greater than 100,000 tons per year, 

and approximately 25,000 tons of fine-particle-sized 

paper coating kaolin is imported annually.

Kaolin formed by hydrothermal alteration, by weathering, and by sedimentary processes occurs in Mexico. 

All the deposits mined are the hydrothermal type. 

Those formed by weathering tend to contain too much 

iron to be of value, and most of the sedimentary clays 

are impure. Most of the hydrothermal clays are related 

to upper Cenozoic volcanic rocks, but some formed from 

schists, and others are in volcanic pipes in limestone. A

few of the occurrences will be discussed in following 

sections.

The hydrothermal kaolin deposits near Ciudad 

Hidalgo, Michoacan, described by Kesler (1970), are in 

a region having numerous hot springs, fumaroles, and 

a few small geysers. The hot springs and other vents 

have white kaolin aureoles in which alteration and 

leaching has been so thorough that walking over them 

is unsafe. Orifices through which water and vapor 

emerge gradually shift due to slumping of ground as 

leaching proceeds. Accumulations of clastic kaolin that 

has been transported short distances overly some of the 

deposits.

The volcanic rock being altered to white clay near 

Ciudad Hidalgo consists of obsidian and rhyolitic breccia of the San Andres rocks, which are rich in silica and 

aluminum. The associated rocks of intermediate composition alter to dark clays having a high shrinkage
50 KAOLIN IN NORTH AMERICA, HAWAII, AND THE CARIBBEAN

United States

i

Mexico

(1) Apulco, Hidalgo

(2) Ciudad Hidalgo, Michoacan

(3) Queretaro

(4) Guadalajara

(5) San Luis Potosf

(6) Com on fort, Guanajuato

(7) Iquala, Guerrero

(8) Jalisco

(9) Zacatecas

_v C

Zacatecas0 

San Luis Potosf0 ~

......... SxSSiJ «J

Guadalajara 0«. 8 6 oQueretaro

500 MILES

H

800 KILOMETERS f:*i

FIGURE 21. Location of major kaolin mining areas in Mexico.

characteristic of smectite. The white alteration product 

is a variable mixture of kaolinite, cristobalite, and 

alunite containing trace amounts of mercury. The kaolin ranges from soft plastic clay to material that is 

moderately hard. The harder kaolin is sufficiently 

indurated to withstand water transportation, as shown 

by clastic kaolin in sedimentary beds overlying the 

San Andres volcanic rocks.

The kaolin clay at the General Zaragosa mine, located about 50 km northwest of San Luis Potosi, was 

formed by hydrothermal argillation of part of a fault 

block of rhyolite flow breccia and probably welded tuff 

(Keller and Hanson, 1968). Like most of the hydrothermal kaolin deposits in Mexico, the surficial rocks 

above the kaolin in this mine consist of a silica halo. 

The progressive stages in the formation of this clay 

were recognized by Keller and Hanson (1968, p. 223), 

as follows:

«* * * (a) Bleaching of the breccia matrix accompanied by mobilization of much of the iron, which was concentrated locally as spots of 

reddish oxide in the least altered areas, (b) Mobilization, and removal of considerable alkali and alkaline earth metals, in excess of 

that required to form montmorillonite; mobilization of silica, which 

was redeposited as fine anhedral quartz crystals disseminated within 

the montmorillonite and associated kaolinite-halloysite, or developed tripolitic, argillized rock peripheral to the clay ore body, (c) Further desilication of the silica and clay yielding relatively pure, but 

poorly ordered, kaolinite-halloysite as the most intense end product

of argillation. Much silica removed during intense argillation was 

reprecipitated as tripolitic clay, as minor cristobalite in microscopic 

globules and massive aggregates characteristic of colloform opal, 

and in vastly larger amounts as opal and chalcedony replacing the 

rock overlying the clay (forming a silica gossan), (d) Minor amounts 

of alunite are present at two places in the deposit, which are interpreted tentatively as being the most probable loci of rising solutions."

A refractory kaolin deposit near Guanajuato, which 

formed from hornblende chlorite schist, is described by 

Hanson and Keller (1966) as occurring in hydrothermally altered zones along nearly vertical fractures and 

faults. The most refractory clay is chiefly kaolinite 

with variable amounts of finely crystalline quartz. The 

surficial rocks above the deposit consist of a halo of silica. The sequence of alteration that took place was as 

follows: (1) bleaching of the hornblende and chlorite 

accompanied by the oxidation of part of the iron, (2) leaching of alkali and alkaline earths accompanied by (3) partial desilication of the parent silicate minerals yielding 

kaolinite in flakes that tend to be oriented parallel to 

the chlorite in the schist, mobile silica, and finely divided quartz intermixed with kaolinite, and (4) final 

kaolinization and removal of silica and some iron.

Clay formed by hydrothermal alteration of volcanic 

pipes in limestone, described by Keller and Hanson 

(1969), occurs in the mining districts at Jasso Calera, 

which is near Apulco, Hidalgo (fig. 21), Zacatecas (fig. 

21), and near Iquala, Guerrero (fig. 21). Typical pipes
CENTRAL AMERICA 51

cut bluish-gray Cretaceous limestone that has been 

faulted and tilted as much as 90°. The pipes are circular to oval in horizontal section, as much as 100 m in 

diameter, and one was found by drilling to be kaolinized to a depth of more than 100 m. Most of the parent 

material of the clay was volcanic pyroclastic and brecciated rock. The central part of a typical deposit consists of moderately well ordered kaolinite. Outer parts 

of deposits commonly contain halloysite (10A). The 

outer parts of most deposits also contain excessive 

amounts of iron and are bypassed in mining. A deposit 

in the Zacatecas district has a green powdery sand zone 

15 cm thick at the contact of the clay and limestone. 

The material forming this zone was found to be a mixture of grossular and quartz. The grossular indicates 

that a high-temperature metamorphic reaction took 

place in the limestone near the margin of the volcanic 

pipe.

The total proven, probable, and possible reserves of 

kaolin in Mexico are estimated to be more than 500 

million tons (Pasquera and others, 1969). These authors list the following five districts as containing 

more than 20 million tons of kaolin each: Jimenez, Chihuahua; Peron Blanco, Durango; Juventino Rosas,

Guanajuato; Guayacocotla, Veracruz; and Ahualulco, 

San Luis Potosi. Eight other districts are listed as containing from 5 million to 20 million tons of kaolin each, 

and 45 more districts or occurrences are listed by name.

CENTRAL AMERICA

Kaolin deposits occur in most Central American 

countries (fig. 22); however, very few deposits have 

been investigated. The following incomplete information was found by the authors during the preparation 

of this report.

Costa Rica

White kaolin deposits occur at several places in Costa 

Rica (Castillo, 1965). Deposits are found along the Panamerican Highway between San Ramon and Esparta 

and between Robledal and Cartago. Deposits are reported to occur elsewhere, but little is known about 

them. Most of the kaolin mining in Costa Rica has been 

in the vicinity of Esparta (fig. 22, location 4). If estimates of the composition of kaolin in this vicinity

RITISH HONDURAS"^

Central America 

Guatemala

1. San Antonio la Pas 

Nicaragua

2. Somoto

3. Esteli 

Costa Rica

4. Esparta

Caribbean region 

Cuba

5. Isle of Pines 

Jamaica

6. Black River

7. Above Rocks 

Puerto Rico

8. Carolina

FIGURE 22. Location of kaolin districts in Central America and the Caribbean region.
52 KAOLIN IN NORTH AMERICA, HAWAII, AND THE CARIBBEAN

(table 17) are correct, it may be fairly high grade. According to Castillo (1965, p. 43), most of the kaolin 

deposits in Costa Rica formed by hydrothermal alteration, but many deposits have been further altered by 

weathering.

Guatemala

As stated by Miller (1965, p. 32), "several deposits of 

clay are known to have been worked in Guatemala, but 

information on the size of deposits, composition and 

quality of the clays, production, and utilization is practically nonexistent. * * *" However, Miller noted that 

one clay deposit at San Antonio la Paz in El Progreso 

Province (fig. 22, location 1) was reported to be white 

clay of ceramic grade, and some of it was sold to manufacturers of paper, paint, rubber, and soap. It seems 

certain that the clay at San Antonio la Paz is kaolin.

Nicaragua

Several kaolin occurrences are noted and a few are 

located on maps in a summary report on minerals in 

Nicaragua (Zoppis de Sena, 1956). The principal occurrences are in the northwestern part of the country. 

Occurrences near Somoto (fig. 22, location 2) include 

white kaolin in weathered acid volcanic rocks in the 

Boqueron zone and alluvial kaolin at Asserradero Los 

Pinos. Kaolin has been found in the Achuapa area 

about 25 km west of Esteli (fig. 22, location 3). At this 

locality, white kaolin has formed from feldspar in 

weathered granite. Kaolin is also reported to occur 

near Dario.

CARIBBEAN REGION

Cuba

The largest and most productive kaolin deposits in 

Cuba are on the Isle of Pines (fig. 22, location 5), and 

three small deposits are shown to be present on the

metallogenic map of the main island of Cuba (Judoley 

and others, 1963). The deposit on Isle of Pines is called 

Rio del Cayejon, and the three small ones on the main 

island are McKinley, Kilometer 13, and Ponte Suelo 

Canaquay (Fen'ko and others, 1973). The kaolin occurs 

in weathered schist and gneiss. The small kaolin deposits in the Dumanekos district on the main island 

are in sedimentary beds of Cretaceous age.

Jamaica

The small kaolin deposits in Jamaica, summarized 

by Versey (1969), occur in alluvium along the Black 

River (fig. 22, location 6), in residual deposits in the 

vicinity of the village of Above Rocks (fig. 22, location 

7), and in hydrothermal deposits at Jobs Hill. The alluvium along the Black River, which is in the southwestern part of Jamaica, has been transported from weathered Cretaceous tuffs. Some of the clay in this alluvium 

is in terrace deposits, but most of it underlies the flood 

plain. According to Versey (1969, p. 102), about 1 million tons of clay having the physical properties of ball 

clay could be recovered by washing this alluvium. The 

deposits in the vicinity of Above Rocks, which is in the 

east-central part of Jamaica, have formed by weathering of adamellitic rocks (quartz monzonite). The clay 

content of this rock is 20-25 percent. The deposits extend over an area of about 1 million m2 and they probably have an average thickness of about 5 m. The 

white kaolin clay at Jobs Hill, which is near Above 

Rocks, is dickite formed by hydrothermal alteration or 

replacement of a series of red sands and conglomerates. 

Only a few thousand tons is known to be present.

Puerto Rico

The Carolina clay deposits (fig. 22, location 8), located 

in coastal lowlands about 12 km east of San Juan, contain the best quality kaolin in Puerto Rico (Cadilla, 

1958). The clay is as much as 70 percent kaolinite, and 

the rest is mainly very fine grained quartz. The upper 

parts of the deposit are white, light bluish, and grayish 

white. Clay having these colors grades downward into

TABLE 17. Estimates of chemical composition of kaolin in Costa Rica, in percent 

[From Castillo (1965, table 3), based on spectrographic analyses by Octavio Durando]

Sample location SiO. A12 03 Fe2 03 MgO Na2O MnO CaO Ti02

Esparta 30-40 30-35 1-2 0.5-0.6 <0.1 0.01 <0.1 0.1-0.2 

Between San Ramon and Esparta 70-80 30-35 1-1.5 .5-1.0 .05-.! .01-.3 .1 1-2
REFERENCES CITED 53

brownish iron-stained clay at depth. The clay body 

extends over an area of about 1.3 km2 and has an average thickness of about 4.5 m. Clay resources present 

are estimated to be about 12 million tons. Because of 

its high plasticity, the clay has been used in extruded 

heavy clay products and in ceramic art objects. Six 

samples tested by the Ceramic Department of the University of California had PCE's in the range 27-34.

The Carolina clay is sedimentary, having been transported from weathered rocks at higher elevations farther inland. According to Cadilla (1958, p. 8-10), the 

Carolina clay was deposited on a flood plain or delta by 

a stream draining upland areas of weathered tuff and 

volcanic rocks. The deposition of the clay probably took 

place in Pleistocene time. The clay is thought to have 

been all red when deposited, and weathering has leached 

the iron oxides from upper parts of deposits to form the 

white, light-blue, and light-gray clay. The reason for 

believing the clay was all originally red is that virtually 

all weathered rocks at nearby higher elevations are red.

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54 KAOLIN IN NORTH AMERICA, HAWAII, AND THE CARIBBEAN

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