Contributions to Industrial-Minerals Research

U.S. Department of the Interior

U.S. Geological Survey

Bulletin 2209–D

With or Without Salt—a Comparison of Marine 

and Continental-Lacustrine Diatomite Deposits

Chapter D of
Contributions to Industrial-Minerals Research

James D. Bliss, Phillip R. Moyle, and Keith R. Long, Editors

Bulletin 2209–D

U.S. Department of the Interior

U.S. Geological Survey 

With or Without Salt—a Comparison of Marine 

and Continental-Lacustrine Diatomite Deposits

By Phillip R. Moyle and Thomas P. Dolley 

Chapter D of
U.S. Department of the Interior

Gale A. Norton, Secretary

U.S. Geological Survey

Charles G. Groat, Director

Version 1.0, 2003

This publication is available only online at:

http://pubs.usgs.gov/bul/b2209-d/

Text edited by George A. Havach

Layout by Stephen L. Scott

Manuscript approved for publication, July 24, 2003

Any use of trade, product, or firm names in this publication

is for descriptive purposes only and does not imply 

endorsement by the U.S. Government 
CONTENTS

Abstract 1

Introduction 1

Marine and Continental-Lacustrine Diatomite Deposits 2

Diatoms 2

 Habitat and Environments of Deposition 2

 Postdepositional Processes 4

 Temporal Distribution 4

 Chemistry and Contaminants 4

 Physical Properties 5

 Mining, Processing, and Other Economic Factors 5

Summary and Recommendations 7

Acknowledgments 7

References Cited 7

Tables

1. Summary comparison of diatoms, their habitats, and factors affecting the 

 formation of marine and continental-lacustrine diatomite deposits 3

2. Summary comparison of chemical and bulk physical characteristics of marine 

 and continental-lacustrine diatomite deposits 5

3. Summary comparison of economic factors of marine and continental-lacustrine 

 diatomite deposits 6

III
1

Abstract

Diatoms in sedimentary deposits of marine and continental, especially lacustrine, origin have similar nutrient (for 

example, phosphate, nitrate, and silica) and light requirements; however, their geologic ranges and physiographic 

environments vary. Marine diatoms range in age from Early 

Cretaceous to Holocene, and continental diatoms range in 

age from Eocene to Holocene; however, most commercial 

diatomites, both marine and lacustrine, were deposited during 

the Miocene. Marine deposits of commercial value generally accumulated along continental margins with submerged 

coastal basins and shelves where wind-driven boundary 

currents provided the nutrient-rich upwelling conditions 

capable of supporting a productive diatom habitat. Commercial freshwater diatomite deposits occur in volcanic terrains 

associated with events that formed sediment-starved drainage 

basins, such as the Basin and Range Province, particularly 

in Nevada. Marine habitats generally are characterized by 

stable conditions of temperature, salinity, pH, nutrients, and 

water currents, in contrast to lacustrine habitats, which are 

characterized by wide variations in these conditions. Marine 

deposits generally are of higher quality and contain larger 

resources, owing to their greater areal extent and thickness, whereas most of the world’s known diatomites are of 

lacustrine origin. Both types of deposit are commonly mined 

by open-pit methods and subjected to processing designed 

to remove organic matter, CO2, pore water, and inorganic 

contaminants in order to produce purified products. The highest quality diatomites, predominantly from marine sources, 

are used in filtration, although both types of deposit produce 

filter grades, and additional end uses include fillers, additives, 

absorbents, and abrasives.

Introduction

Diatomite, an earthy, very fine grained siliceous sedimentary rock, commonly light in color, is composed primarily of 

opaline frustules (walls or skeletons formed of secreted silica) 

from single-celled aquatic plants called diatoms. Also known 

as diatomaceous earth or diatomaceous silica, deposits of diatomaceous rock occur globally and may be of either marine 

or continental origin. Continental deposits are primarily of 

lacustrine origin, although fluvial, paludal, or estuarine deposits are also known. Large deposits with commercial grades, 

generally referred to as diatomite, are uncommon. Just as 

societal end uses of this important commodity are a function 

of its physical and chemical properties, so these properties are 

a consequence of various conditions and processes, ranging 

from the original nature of the organisms and their habitats, 

their depositional environment and diagenetic processes, 

modern tectonic settings, and weathering environments. This 

chapter examines specific aspects of diatomite—from the original life forms and their habitats, depositional environments, 

and chemical and physical properties, to mining and societal 

end uses—noting the similarities or differences between 

marine and nonmarine types of deposit. Mitchell’s (2002) 

demonstration of a few simple, low-cost tests for selected 

physical and chemical index properties to identify high-quality 

diatomite in Thailand points out the importance of understanding the characteristics of both marine and lacustrine deposits. Here, we emphasize diatomite of lacustrine origin, as in 

Shenk’s (1991) descriptive deposit model 31s.

Diatomite is white if pure, commonly buff to gray in 

place, and rarely black. It can be further described as chalklike, soft, friable, very finely porous, or very low in density (floating on water until saturated), and the frustules 

essentially are chemically inert in most liquids and gases. 

Diatomite also has a low thermal conductivity, owing to its 

high pore volume, and a high fusion point. Combinations 

of physical and chemical properties of high-grade diatomite 

make it suitable for many specialized applications, especially 

for filtration, its principal use. The Greeks used diatomite 

2,000 years ago as a lightweight building material and in 

ceramic pottery (Breese, 1994). Much later, it was used as 

an absorbent to stabilize nitroglycerine in the manufacture 

of dynamite, beginning in 1867 (Harben and Kuzvart, 1996; 

Harwood, 1999). Society has discovered many additional 

uses for diatomite, such as a filler in such products as paints 

and dry chemicals, as an absorbent for industrial spills and 

in pet litter, as an insulator in sawn and molded shapes, as a 

mild abrasive in polishes, and as a silica additive in cement 

and other products. Some diatomite deposits, such as those 

hosted by the Middle to Upper Miocene Monterey Formation 

and the Upper Miocene to Lower Pliocene Sisquoc Formation 

in the California Coastal Ranges, may also contain significant petroleum sources or reservoirs (Harben and Kuzvart, 

1996; Krebs, 1999). The broad geographic and temporal 

(Cretaceous or older to Holocene) ranges of diatoms also 

make them important tools as biostratigraphic markers for 

With or Without Salt—a Comparison of Marine 

and Continental-Lacustrine Diatomite Deposits

By Phillip R. Moyle and Thomas P. Dolley

Introduction
2 Contributions to Industrial-Minerals Research 

chronologic dating and lithologic correlation in oil and gas 

exploration (Krebs, 1999), as well as indicators of marine and 

continental paleoenvironments (Stoermer and Smol, 1999; 

Wallace, 2003).

Marine and Continental-Lacustrine 

Diatomite Deposits

Diatoms

Diatoms are single-celled golden-brown algae, assigned 

to the class Bacillariophyceae (Barron, 1987, p. 166). They 

occur as two morphologic types based on their symmetry, 

either centric (also called radial or circular) or pennate (also 

called axial or elongate). The frustules are characterized by 

ornate, highly sculptured walls of silica with species-specific 

intricate patterns and symmetries (Wetherbee, 2002) that are 

used for taxonomic classification. Diatoms have adapted to 

various marine and continental aquatic conditions, particularly to planktonic or benthic environments. Some of the 

similarities and differences between lacustrine and marine 

diatoms and their habitats and environments of deposition, 

discussed in this and the following sections, are summarized 

in table 1. Marine environments favor planktonic diatoms 

because diatoms flourish in the widespread photic zone—less 

than 100 to 200 m deep (Barron, 1987; Boardman and others, 

1987). Most planktonic diatoms are centric and are the primary nutrient producers in the photic zone. Depending on 

nutrient supply, turbulence, and illumination in the photic 

zone, diatoms can occupy various benthic habitats (Bradbury 

and Krebs, 1995) in shallow ocean margins, but they are rare 

in deep-sea sediment. Barron (1987) noted that lakes support 

both planktonic and benthic diatoms but that benthic diatoms 

dominate in streams and soils. He further described a group 

of marine tychopelagic diatoms that are intermediate between 

planktonic and benthic forms.

As many as 20,000 marine and continental diatom taxa 

may exist worldwide, according to Bradbury and Krebs 

(1995), who also noted that in North America and Europe are 

more than 1,000 common freshwater diatom species, with 

species endemic to specific ancient lakes typically ranging in 

abundance from 10 to 30 percent of the taxa.

The silica (opaline) in the cell walls of diatoms allows 

them to be well preserved in the fossil record relative to 

microorganisms that lack silica. Barron (1987) reported that 

more than 90 percent of photic-zone-produced diatom frustules dissolve in the silica-undersaturated marine environment 

before they reach the sea-floor-bottom sediment, whereas 

diatom frustules coated in organic matter or encapsulated in 

fecal pellets are protected from dissolution. Bradbury and 

Krebs (1995) noted that unaltered diatoms are not likely to 

be recovered from below a burial depth of 1,524 m; however, 

Krebs (1999) stated that the formation of calcareous concretions early in the burial or diagenetic process can preserve 

frustules.

Habitat and Environments of Deposition

Diatoms, both marine and nonmarine, require three conditions to sustain life: an aqueous environment, light, and a 

continuous supply of nutrients and minerals. Although these 

conditions are far from unique, satisfaction of all three conditions controls sustained diatom viability and production and, 

thus, the distribution and size of deposits. Such nutrients as 

phosphates and nitrates return to the water column when the 

organism dies and decays on the sea floor or lake bottom. In 

contrast, silica incorporated into the diatom frustules is permanently removed from the water if it is not dissolved while 

passing through the water column (Harben and Kuzvart, 

1996). Therefore, a continuous supply of silica is needed to 

refresh the diatom-productivity zone for both marine and 

continental environments. Although marine environments 

range from the deep oceans to the continental shelf and nearshore conditions, the requirement for light and nutrients 

restricts viable environments to the uppermost 100 to 200 m 

(Barron, 1987; Boardman and others, 1987). Furthermore, 

most marine forms are stenosaline—that is, they tolerate only 

a narrow range of salinity (Sverdrup and others, 1970). Thus, 

favorable conditions are limited to environments with stable 

salinity—from areas along continental margins that support 

upwelling of deeper, generally colder, nutrient-rich water, to a 

near-surface photic environment where wind-driven currents 

disperse and recirculate nutrient-depleted surface waters to 

the open ocean. Western continental margins with submerged 

coastal basins and shelves (Harben and Kuzvart, 1996) and 

wind-driven boundary currents, such as selected sections 

of the California, South American, and Southwest African 

coasts (Barron, 1987), are examples of areas that provide 

the nutrient-rich upwelling conditions capable of supporting 

diatom habitat. In addition to continental margins, Sverdrup 

and others (1970) noted that an accumulation of more than 

50 volume percent diatom frustules in a 1,500-km-wide band 

of ooze is present along the 60th Parallel in the South Pacific 

Ocean (table 1), where conditions in the photic zone favor 

diatom productivity.

Nonmarine diatoms have the same nutrient (phosphate, 

nitrate, and silica) and light requirements as marine organisms, but they have inhabited a wide variety of freshwater 

aquatic environments, including lakes, ponds, rivers, streams, 

and springs (Barron, 1987; Bradbury and Krebs, 1995) since 

the Eocene. Commercial freshwater diatomite is most commonly associated with lakes, where thick deposits of significant areal extent can accumulate. These deposits generally 

are associated with volcanic terranes and events that formed 

sediment-starved drainage basins, such as basin-and-range 

extension. In Nevada, these basins subsequently filled with 

freshwater, thus promoting the growth of diatoms (Bradbury 

and Krebs, 1995). Volcanic processes, such as hot springs, 

provide a supply of silica needed for skeletal development 

(Breese, 1994). Continental diatoms can be of the planktonic, 

benthic, or epiphytic (attached) type; however, planktonic 

varieties dominate lacustrine environments, and pennate 

benthic species prevail in fluvial systems (Barron, 1987; 
3

Bradbury and Krebs, 1995). Barron noted that temperature, 

salinity, pH, nutrients, and water currents vary much more 

widely in nonmarine than in marine environments. For example, nonmarine diatoms are euryhaline—that is, they tolerate 

a wide range of salinities (Sverdrup and others, 1970) relative 

to the stenosaline marine diatoms described above; however, 

lacustrine diatoms do not thrive in alkaline water (Barron, 

1987).

Dilution also plays an important role in the formation of 

diatomite deposits. A common, but serious, disadvantage of 

near-shore marine environments is that they may be subject 

to rapid and voluminous input of terrigenous sediment from 

adjacent continental margins, thus diluting the concentration 

of diatoms on the seabed. In addition, Boardman and others 

(1987) noted that some biota, such as radiolarians, are commonly associated with diatoms; thus, biogenic dilution factors 

may also be present. Therefore, the formation of commercial 

quantities and grades of diatomite in marine environments 

is favored by a low influx of both terrigenous and biogenic 

sediment. The favorable physical conditions and nutrient 

supply described above must also be sufficiently continuous 

and persistent to accumulate thick, widespread deposits of 

commercial value. Marine diatomites deposited along stable, 

long-lived marine shorelines and in tidal areas with good 

water quality (low clastic input, adequate nutrients and silica, 

and stable salinity) and clarity generally form in a few large, 

Table 1. Summary comparison of diatoms, their habitats, and factors affecting the formation of marine and continental-lacustrine diatomite deposits.

[Where information spans both marine and continental-lacustrine deposits, we were unable to determine different characteristics for the specific factor]

Marine and Continental-Lacustrine Diatomite Deposits

Factor Marine deposits Continental-lacustrine deposits

Diatoms and habitat----------------- Primarily planktonic forms, with lesser benthic and tychopelagic forms; benthic forms

rare in deep-sea sediment.

Planktonic and benthic forms in lakes, but

planktonic dominant. Benthic forms dominant in streams and soil.

As many as 20,000 total combined marine and continental taxa worldwide. Estimated 1,000

common freshwater species; 10 to 30 percent lacustrine species endemic.

Primarily continental margins with cycle

of upwelling, nutrient-rich currents and

surface currents that disperse nutrientdepleted water in upper 100–200 m; also

deep-sea plankton.

Primarily small lacustrine systems associated

with volcanism that dams fluvial systems

to form lakes; require continuous supply of

nutrient-rich/silica-rich freshwater in lowalkaline lakes. Also occur in slow fluvial

systems, ponds, swamps, and soil.

Stenosaline---------------------------------- Euryhaline; not excessively alkaline.

Stable temperature, salinity, pH, nutrients,

and water currents.

Widely varying temperature, salinity, pH,

nutrients, and water currents.

Depositional environment--------- High diatom productivity; long duration;

minimal clastic and biogenic dilution;

water column allows diatoms to reach

bottom.

High diatom productivity; long duration but

shorter than marine; minimal clastic and

biogenic dilution; periodic volcanism.

Dilution-------------------------------- Dilution by terrigenous sediment near continental margins or by such biogenic forms

as radiolarians during deposition.

Dilution by introduction of excess clastic sediment and volcanic ash into basins.

Diagenesis and preservation------- Limited marine sediment cover compacts

and removes water, and leaching removes

excess organic matter thus increasing

quality. Excess compaction may crush

frustules, and deeper burial (�600 m,

�50�C) may recrystallize silica.

Limited clastic sediment or volcanic cover

compacts and removes water, and leaching removes excess organic matter, thus

increasing quality. Excess compaction may

crush frustules, and deeper burial (�600 m,

�50�C) may recrystallize silica.

Preservation primarily due to silica in

frustules. Also, cover by younger marine

sediment protects diatomite deposit when

uplifted and exposed to weathering and

erosion.

Preservation primarily due to silica in frustules. Also, cover by terrigenous sediment

or volcanic flows protect diatomite deposit

from weathering and erosion.

Geologic timespan------------------- Early Cretaceous to Holocene------------- Eocene to Holocene.

Optimum period of deposition---- Miocene------------------------------------------ Miocene, especially middle Miocene.

Distribution in western North

America.

California Coast Range but primarily at

Lompoc in San Bernardino County, Calif.

All the Western United States, but largest

deposits in Nevada; additional major deposits also in Idaho, Oregon, and Washington.
4 Contributions to Industrial-Minerals Research 

high-grade deposits suitable for multiple uses at all market 

levels, including filtration (Breese, 1994). For example, the 

Miocene Monterey Formation, a marine diatomaceous unit, 

as much as 2,000 m thick, composed of biogenic silica, carbonate, detrital sediment, and volcanic ash, is exposed extensively for nearly 800 km along the California Coast Ranges 

(Barron, 1987). The formation hosts one of the largest commercial diatomite deposits in the world near Lompoc, Calif., 

where diatomite is mined from a section as much as 300 m 

thick (Cressman, 1962).

Postdepositional Processes

Once deposited, siliceous diatoms are more resistant to 

dissolution than other types of biogenic matter; however, 

the deposits are subject to diagenesis, burial, and exposure, 

all of which can have significant effects. Diagenesis may 

preserve a deposit, enhance its quality, or completely destroy 

it, depending on the type and severity of the process. A sediment cover can preserve the deposit by protecting it from 

erosional processes; in addition, a sediment cover can compact the diatomite and remove excessive water from the diatomaceous materials. Leaching may remove organic matter 

and other biogenic materials from the diatoms and enhance 

the deposit quality (table 1). Barron (1987), however, 

observed that deeper burial and related increasing temperature can cause recrystallization of frustules and destruction 

of some of their useful physical properties. He described a 

progression of rock-property changes, associated with burial 

depths ranging from 600 to 1,500 m, that transition from 

biogenic silica to opal-CT at 50°C and then to quartz at about 

80°C. The lithified final products of this diagenetic process, 

porcellanite and chert, have significantly lower porosity and 

higher density than those associated with commercial diatomite.

Uplift of both lacustrine and marine deposits exposes 

them to weathering and erosional processes. Marine deposits are best preserved by postdeposition cover by younger 

marine sediment. Volcanic flows covered and protected many 

continental lacustrine deposits (table 1), particularly in the 

Great Basin, Columbia River Basin, and Snake River Plain 

in the Western United States.

Temporal Distribution

Marine diatomites have been associated with upwelling and other favorable environments since at least 66 Ma, 

when diatomaceous silica became a significant component 

in Cretaceous marine sediment (Heath, 1974; Barron; 1987). 

Boardman and others (1987) also mentioned a fossil record 

of diatoms that extends from the Cretaceous to the Holocene; however, Bradbury and Krebs (1995) cited evidence 

of marine diatoms in sediment as old as Early Cretaceous or 

even Jurassic. Clearly, our level of knowledge on this subject 

is evolving. The oldest (middle Eocene) continental diatoms 

apparently evolved from marine ancestors during the early 

Tertiary or Late Cretaceous (Bradbury and Krebs, 1995). 

Bradbury and Krebs (1995) also noted that the Miocene was 

a time of both marine and continental diatom productivity, 

rapid evolution, and environments favorable for preservation 

(table 1).

Chemistry and Contaminants

The chemistry of commercial diatomite deposits is dominated by the siliceous composition of the diatom frustules, 

which are formed by biologic secretion, or precipitation, of 

amorphous silica (Cummins, 1960; Durham, 1973) (see subsection above entitled “Diatoms”). Frustules in living diatoms 

or of Holocene age resemble amorphous soluble silica gel, 

whereas fossil frustules resemble opaline silica and have a 

lower solubility than younger ones (Kamatani, 1971). Chemical analyses of bulk diatomite samples typically range in SiO2

content from 70 to 90 weight percent and reportedly as high 

as 97 weight percent in marine deposits (Cummins, 1960; 

Durham, 1973; Breese, 1994). The chemical and bulk physical characteristics of marine and continental diatomite deposits are summarized in table 2.

Combined H2O content in the frustule opaline structure 

ranges from 1.9 weight percent in some marine species to 

9.6 weight percent in some lacustrine species (Breese, 1994). 

Diatomite contains abundant free water, ranging from 10 to 

60 weight percent H2O. Additional major components from 

several world-class deposits include 2 to 10 weight percent 

Al2O3 and small, but varying, amounts of Fe, Ti, P, Ca, Mg, 

Na, and K oxides (Cummins, 1960; Durham, 1973). In the 

same samples, CO2 and organic-matter contents range from 

less than 1 to more than 17 weight percent (table 2; Cummins, 

1960, LOI, table 1).

A wide range of contaminants are associated with diatomaceous sediment. Chert, manganese nodules, phosphates 

(for example, vivianite), radiolarians, silicoflagellates, sponge 

spicules, ostracods, and bivalves, as well as volcanic rocks, 

are more likely associated with marine deposits (Shenk, 1991; 

Breese, 1994). Marine deposits may also contain silanol (SiOH bonded) and siloxane (Si-O-Si bonded) on the surface 

of the siliceous materials (Kadey, 1967). Lacustrine-fluvial 

deposits more likely contain varying common terrigenous 

components, such as volcanic ash, quartz, mica, and feldspars, as well as such biogenic materials as fossil leaves, 

fish and reptile bones, peat, marl, and tufa (Breese, 1994). 

Contaminants common to both types of deposit include clays, 

gypsum, calcite, and, less commonly, salt, pyrite, and sulfur 

(table 2; Shenk, 1991; Breese, 1994).

Physical Properties

Marine diatomite deposits are generally thicker and of 

greater areal extent than lacustrine deposits (Bradbury and 

Krebs, 1995). Additional distinct differences in physical properties between marine or lacustrine deposits are not identified; 
5

however, we provide a general overview because the industrial uses of diatomite are a direct function of these properties 

(table 2).

Diatomite frustules are microscopic in size, ranging in 

diameter from 0.75 to 1,000 μm (1 mm), mostly from 10 to 

150 μm (Breese, 1994). The opaline silica that composes frustules ranges in specific gravity from 1.9 to 2.35, about twice 

that of water (Cummins, 1960); however, the best known 

characteristics of diatomite, imparted by the complex-shaped 

frustules with 10 to 30 volume percent voids, are its low 

bulk density and high porosity. The bulk density of diatomite 

ranges from 0.320 to 0.640 g/cm3 (Cummins, 1960), about 

half that of water. Diatomite can absorb 1.5 to 3 times its 

weight of water (Durham, 1973). The apparent density of dry 

diatomite powder (or diatomite product) ranges from 0.080 to 

0.256 g/cm3 and of wet diatomite powder from 0.160 to 0.480 

g/cm3 (table 2; Cummins, 1960; Durham, 1973).

Diatomite’s low thermal conductivity is due to its abundant pore volume and its melting point, which ranges from 

1,400 to 1,750°C (Durham, 1973). These properties probably 

led the Greeks to use it as a lightweight building stone and 

in ceramic pottery 2,000 years ago (Breese, 1994). The hardness of massive diatomite is only about 1.5 Mohs, owing to 

its friability, and so it is easy to quarry. Diatomite frustules 

themselves range in hardness from 4.5 to 6.0 Mohs (table 2; 

Cummins, 1960).

Table 2. Summary comparison of chemical and bulk physical characteristics of marine and continental-lacustrine diatomite deposits.

[Where information spans both marine and continental-lacustrine deposits, we were unable to determine different characteristics for the specific factor]

Marine and Continental-Lacustrine Diatomite Deposits

Factor Marine deposits Continental-lacustrine deposits

SiO2 content of diatomite (wt pct)----- 70–97 70–90

H2O content of frustules (wt pct)------- Relatively lower; as low as 1.9 in specific

marine species.

Relatively higher; as high as 9.6 in some

lacustrine species.

H2O content of diatomite (wt pct)------ 10–60

Chert, manganese nodules, phosphates

(e.g. vivianite), radiolaria, silicoflagellates, sponge spicules, ostracods,

bivalves, clay, gypsum, calcite, salt,

pyrite, sulfur, and fish bones.

Quartz, mica, feldspars, and marl, and

biogenic materials such as peat, vegetal

material, reptile and fish bones, clay,

gypsum, calcite, salt, pyrite, and sulfur.

Contaminants (codeposited and diagenetic).

Many others, such as clay, gypsum, calcite, salt, pyrite, sulfur, and fossil fish bones,

may be common to both.

Areal extent of deposits----------------- More extensive------------------------------- Less extensive.

Thickness of deposits-------------------- Thicker----------------------------------------- Thinner.

Size: 0.75–�1,000 �m, mostly 10–150 �m.

Voids, 10–30 volume percent.

Specific gravity, 1.9–2.35.

Frustule physical properties------------

Hardness, 4.5–6.0 Mohs.

Bulk density (in place) (g/cm3)-------- .320–0.640

Bulk density (dry powder) (g/cm3)---- .080–0.256

Bulk density (wet powder) (g/cm3)---- .160–0.480

Bulk hardness (Mohs)------------------- �1.5, owing to friability

Thermal properties----------------------- Low conductivity; melting point, 1,400–1,750�C
6 Contributions to Industrial-Minerals Research 

Mining, Processing, and Other Economic 

Factors

Although diatomaceous silica is a relatively common 

sedimentary rock, large economically minable deposits with 

commercial grades, referred to as diatomite, are uncommon to 

rare (Harben and Kuzvart, 1996). Factors that determine the 

economic viability of high-grade diatomite deposits, whether 

marine or lacustrine, include the areal extent, thickness, and 

continuity of the deposit; the number and uniformity of beds; 

the dominant diatom species; and the degree of selective 

mining required. Marine and continental-lacustrine diatomite 

deposits have much in common with respect to deposit quality and mining, beneficiation, and end uses; however, they 

also exhibit some key differences. Kadey (1975) noted that 

most of the world’s known diatomites are of lacustrine origin 

but that marine deposits are generally larger. For example, the 

marine deposit at Lompoc, Calif., is the largest single producer of diatomite in the United States, although the cumulative production from the several smaller lacustrine deposits 

in the Western United States is considerably greater (Dolley 

and Moyle, 2003). Furthermore, Harben and Kuzvart (1996) 

observed that marine deposits are considered to be of superior 

quality, owing to their higher diversity in the size and shape 

of diatoms. No additional significant differences in mining 

or processing of marine or lacustrine deposits are noted; the 

economic factors of marine and continental deposits are summarized in table 3.

Diatomite’s physical properties—its low bulk hardness, 

low bulk density, and friability—make surface or near-surface 

high-grade marine and continental-lacustrine deposits amenable to open-pit mining. Depending on the geologic configuration of a deposit, this low-cost, bulk-tonnage mining method 

generally consists of selectively grading large volumes of 

ore from exposures of high-grade rock, lifting the select 

high-grade material with scraper-loaders or loading it onto 

truck haulers, and transporting to a processing plant (Breese, 

1994; Harben and Kuzvart, 1996). At some deposits where 

basalt, chert, or other contaminants are interbedded with the 

diatomite, coarse contaminants must be selectively mined 

or screened out at the minesite before shipment to the plant. 

Although open-pit mining is the dominant method, Harben 

and Kuzvart (1996) noted that a few foreign operations utilize 

underground methods to mine diatomite, for example, the Sig 

deposit in Algeria, as well as underwater dredging, such as at 

Lake Myvatn in Iceland.

Crushing and grinding of crude diatomite are accomplished in a series of careful steps designed to preserve the 

diatom skeletal (frustule) structure, an important attribute of 

most products. Dolley and Moyle (2003) present a generalized diagram of a typical diatomite-processing plant, and 

Harben and Kuzvart (1996) briefly described the processes. 

Where possible, heated air is used to dry and transport diatoms through the beneficiation process, including separation 

of diatoms from denser and coarser contaminants and classification of diatoms into different sizes. Selected grades of 

natural diatomite may be calcined in a kiln at 870–1,093°C, 

volatilizing such contaminants as organic matter, CO2, and 

pore water to produce a pink granular material. CO2 and 

organic-matter contents range from less than 1 to more than 

17 weight percent (Cummins, 1960, LOI table 1) in some 

deposits. Calcining also recrystallizes 40 to 60 weight percent 

Table 3. Summary comparison of economic factors of marine and continental-lacustrine diatomite deposits.

[Where information spans both marine and continental-lacustrine deposits, we were unable to determine different characteristics for the specific factor]

Factor Marine deposits Continental-lacustrine deposits

Number of deposits--------------- Fewer--------------------------------------------- Greater

Size of deposit-------------------- Larger--------------------------------------------- Smaller.

Production------------------------- Large---------------------------------------------- Medium to small.

Mining method------------------- Open pit.

Milling and processing---------- Careful crushing and grinding to preserve frustules; hot-air transport and classification;

natural, calcined, and flux-calcined varieties.

Reduced H2O, CO2, and organic-matter contents; calcined variety is pink because of Fe

oxide; flux-calcined variety changes color to white

Increased hardness, from 4.5 to 6.0 Mohs.

Postprocessing properties------

Increased specific gravity, from 1.95 to 2.3

Primarily filtration; also fillers, additives,

absorbents, and abrasives

Primarily fillers, additives, absorbents,

abrasives; also filtration.
7

of the silica in the frustules to cristobalite for such specific 

end uses as special filter grades. Diatomite may also be fluxcalcined by the addition of soda ash or salt flux to the kiln at 

1,148°C to produce a white grade wherein the Fe oxides are 

converted to a clear glassy phase. Calcining and flux calcining increase the hardness from 4.5–5.0 to 5.5–6.0 Mohs and 

the specific gravity from 1.95 to 2.3 (Harben, 1999). Natural, 

calcined, and flux-calcined diatomites can be sorted by size 

and other properties to yield a wide range of products.

In general, processing costs are lower if H2O and 

organic-matter contents, as measured by loss on ignition, are 

lower because less energy is required to remove these contaminants (Benton, 1983). The cost to process some mediumgrade lacustrine diatomites, suitable for such lower-end uses 

as absorbents and fertilizer, can be prohibitive at a loss on 

ignition as high as 20 weight percent (Breese, 1994) because 

of the high energy required to volatilize the water and organic 

matter. At a loss on ignition of more than 5 weight percent, 

marine diatomite becomes too expensive to heat-treat for such 

high-grade uses as filtration. For example, an accounting at 

the Lompoc, Calif., marine diatomite mine shows that mining 

accounts for 10 percent, processing for 60 percent, and packaging and shipping for 30 percent of the total costs (Benton, 

1983). Any increase in processing cost due to excess H2O 

content could make parts of a deposit uneconomic.

Filtration-grade diatomite is produced from both marine 

and some lacustrine deposits; however, lower grades of 

lacustrine deposits generally limit end uses to abrasives, 

fillers, fertilizer and pesticide, polish, catalyst material, 

insulating brick, and absorbents (Breese, 1994). The greatest demand for high-grade ore of marine origin is as a filter 

product, used in processing beer, wine, and liquor, sugars, and 

pharmaceuticals; however, low-purity marine or lacustrine 

diatomite with increased contaminant contents may be processed for such lower-end uses (Breese, 1994) as fillers or 

additives.

Summary and Recommendations

Although we have discussed many of the characteristics 

of diatomite deposits and identified important differences 

between those of marine or lacustrine origin, we did not 

obtain detailed data that distinguish between marine and 

lacustrine deposits for some important factors (tables 1–3). 

On the basis of descriptions of depositional environments, 

several differences between marine and continental-lacustrine 

diatomite deposits are apparent. Marine deposits form over 

broad areas on the ocean floor, whereas lacustrine deposits 

form under areally limited, specialized environmental conditions. Furthermore, marine deposits are generally thicker 

and represent longer periods of geologic time than lacustrine 

deposits. In addition, the physical, chemical, and environmental conditions of marine diatomaceous systems clearly vary 

less widely than those of lacustrine systems.

We lack detailed data that distinguish between specific 

numbers and varieties of taxa, as well as the physical properties and some chemical properties of marine and nonmarine 

diatomite deposits; additional research is warranted on these 

topics. We also lack data that differentiate specific deposit 

parameters, such as diatom size and shape and frustule density and trace-element chemistry, which may affect milling 

and processing methods, as well as products and end uses. 

Many of these factors are important from an economic perspective with regard to the national diatomite resource base.

Acknowledgments

James Newton and Christina Tuggle, both students at 

Eastern Washington University, assisted with the background 

literature search and provided preliminary reviews of this 

manuscript. We appreciate the helpful technical reviews by 

Alan Wallace, Jim Evans, and Dave Boleneus.

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