Data of Geochemistry

* 

Chapter T. Nondetrital Siliceous Sediments

GEOLOGICAL SURVEY PROFESSIONAL PAPER 440-T
Data of Geochemistry

Michael Fleischer, Technical Editor

Chapter T. Nondetrital Siliceous Sediments

By EARLE R. CRESSMAN

GEOLOGICAL SURVEY PROFESSIONAL PAPER 440-T

Tabulation and discussion of chemical 

analyses of chert with respect to 

mineralogic composition, petrographic 

type, and geologic occurrence

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1962
UNITED STATES DEPARTMENT OF THE INTERIOR 

STEW ART L. UDALL, Secretary

GEOLOGICAL SURVEY 

Thomas B. Nolan, Director

For sale by the Superintendent of Documents, U.S. Government Printing Office

Washington 25, D.C.
DATA OP GEOCHEMISTRY, SIXTH EDITION

Michael Fleischer, Technical Editor

The first edition of the Data of Geochemistry, by F. W. Clarke, was published in 1908 as U.S. Geological 

Survey Bulletin 330. Later editions, also by Clarke, were published in 1911, 1916, 1920, and 1924 as Bulletins 491, 616, 695, and 770. This, the sixth edition, has been written by several scientists in the Geological 

Survey and in other institutions in the United States and abroad, each preparing a chapter on his special 

field. The current edition is being published in individual chapters, titles of which are listed below. 

Chapters already published are indicated by boldface type.

CHAPTER A. The chemical elements

B. Cosmochemistry

C. Internal structure and composition of the Earth

D. Composition of the earth's crust

E. Chemistry of the atmosphere

F. Chemical composition of subsurface waters, by Donald E. White, John D. Hem, and G. A. 

	Waring

G. Chemical composition of rivers and lakes, by Daniel A. Livingstone

H. Chemistry of the oceans

I. Geochemistry of the biosphere

J. Chemistry of rock-forming minerals

K. Volcanic emanations, by Donald E. White and G. A. Waring

L. Phase equilibrium relations of the common rock-forming oxides except water

M. Phase equilibrium relations of the common rock-forming oxides with water and (or) carbon 

	dioxide

N. Chemistry of igneous rocks

O. Chemistry of rock weathering and soils

P. Chemistry of bauxites and laterites

Q. Chemistry of nickel silicate deposits

R. Chemistry of manganese oxides

S. Chemical composition of sandstones excluding carbonate and volcanic sands, by F. J. Petti John

T. Nondetrital siliceous sediments, by Earle R. Cressman

U. Chemical composition of shales and related rocks

V. Chemistry of carbonate rocks

W. Chemistry of iron-rich rocks

X. Chemistry of phosphorites

Y. Marine evaporites, by Frederick H. Stewart

Z. Continental evaporites

AA. Chemistry of coal

BB. Chemistry of petroleum, natural gas, and miscellaneous carbonaceous substances

CC. Chemistry of metamorphic rocks

DD. Abundance and distribution of the chemical elements and their isotopes

EE. Geochemistry of ore deposits

FF. Physical chemistry of sufide systems

GG. The natural radioactive elements

HH. Geochronology

II. Temperatures of geologic processes

J J. Composition of fluid inclusions
CONTENTS

Abstract_______________________________

Definitions____________________________

Classification and occurrence______________.

Bedded nonfragmental siliceous deposits. 

Diatomaceous deposits ____________

Radiolarian deposits______________

Deposits of sponge spicules______.

Other bedded chert_______________

Nodular chert in carbonate rock. _______

Other siliceous deposits._______________

Mineralogic composition.__________________

Chemical composition.____________________

Major constituents _________________

age 

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5

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6

Chemical composition Continued

Iron ___ _________ __ _____ ____ 

Relation of iron to manganese. __ _ _

Owop pn

Solubility of silica. ____ ____ _____ _ _

Origin_________________ ___ ___ ___ _ ____

Index. __________ _ _____ _ __ ___ _

Page 

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ILLUSTRATIONS

FIGURE 1. Frequency diagrams of four types of nonfragmental siliceous sedimentary rocks_________ ___ ___ ________ T7

2. Relation between SiO2 and the ratio SiO2/Al 2Os in chert and related rocks._________ ___ _ ___ - 9

3. Relation of Fe 2Os to AJ2Os in 46 radiolarian cherts_____ _________________________________ __ ______ 11

4. Relation of iron to manganese in chert and related rocks-____-_---_-------_-_ __ 13

5. Relation of TiO2 to A12O3 in chert and related rocks__________ _____ 14

TABLES

Page 

TABLE 1. Analyses of three nearly pure cherts________________ ____________ ____________ __________ __ T6

2. Spectrochemical analyses of igneous and hydrothermal quartz____________________ _____

3. Analyses of diatomaceous rocks____________________ ______ 

4. Analyses of radiolarian rocks__________________________________ ___ _______ ______

5. Analyses of spicular cherts_________________________________ ___________ ______

6. Analyses of bedded cherts containing few or no siliceous skeletal remains. __________ _________

7. Analyses of chert nodules, lenses, and layers in carbonate rock_________________ ___ ____.

8. Analyses of silcrete and other siliceous materials_______________________ _____ _____.

9. Relation of iron and manganese to depth of water in sediments of the equatorial Atlantic Ocean10. Trace-element content of chert________________________ _________________________ ___ 

11. Relative abundance of Si isotopes in nonfragmental siliceous sedimentary rocks.

8

8

10

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15

16

12. Relative abundance of oxygen isotopes in nonfragmental siliceous sedimentary rocks - - - 16
DATA OF GEOCHEMISTRY 

NONDETRITAL SILICEOUS SEDIMENTS

By EARLE R. CHESSMAN

ABSTRACT

Chemical analyses of nondetrital siliceous sediments and sedimentary rocks chert, siliceous earth, siliceous ooze, siliceous 

shale culled from the literature have been grouped according 

to the following classification: 

Bedded:

Diatomaceous deposits 

Radiolarian deposits 

Sponge-spicule deposits 

Bedded chert containing few or no siliceous skeletal

fragments. 

Nodular

Mineralogically, the rocks consist of biogenic and chemogenic 

opal, chalcedony, and quartz, singly or as mixtures, admixed 

with the same clastic and authigenic minerals that are in the 

associated nonsiliceous sedimentary rocks. Opaline tests consist originally of truly amorphous silica, but much sedimentary 

opal has been shown by many authors to give an X-ray pattern 

of crlstobalite or tridymite.

Small amounts of Al, Fe, and alkali and alkali-earth elements 

may occur within the lattice of the silica minerals; however, 

most of these elements are apparently in the admixed clastic 

and authigenic minerals, and the chemical composition of the 

rocks can, for the most part, be interpreted as the result of the 

mixture of mudstone or sandstone with pure SiO2 or by the 

replacement of calcite or dolomite in carbonate rocks by pure 

SiO2. Compositional differences between the rock types reflect 

(1) the association of diatomaceous rocks with pyroclastics, (2) 

the association of radiolarian rocks with argillaceous and volcanic rocks of bathyal and possibly abyssal origin, (3) the association of spicular rocks with sublittoral sandstone and limestone, and (4) the common occurrence of nodular chert in 

limestone of sublittoral origin.

Recent work suggests that chert cannot form by direct inorganic precipitation of silica from sea water except locally in 

areas of volcanism and supports the hypothesis that much bedded 

chert has resulted from the accumulation of siliceous skeletal 

remains and that most nodular chert has resulted from the 

replacement of carbonate rock. Many authors report abundant 

evidence that silica deposited as skeletal remains or in volcanic 

ash dissolves, migrates, and reprecipitates during diagenesis.

DEFINITIONS

Chert, by most modern American usage, is a dense 

cryptocrystalline rock composed dominantly of quartz, 

chalcedony, or opal, either singly or as mixtures, and 

having a tough splintery to conchoidal fracture (Tarr, 

1938). As used in this report, chert is a general term 

that includes flint, a translucent variety with a conchoidal fracture; jasper, an opaque, red, yellow, brown, 

or green variety; and novaculite, a pure, dense, eventextured, light-colored variety with a porcelaneous texture. Diatomaceous, radiolarian, and spicular chert are 

varieties that contain conspicious skeletal remains of 

the type specified. Two varieties of radiolarian chert 

frequently described in the literature are lydite (lydian 

stone or culm-type), a black radiolarian chert, and 

radiolarian jasper.

Diatomite, radiolarite, and spiculite are rocks that 

consist largely of diatom f rustules, radiolarian tests, or 

sponge spicules, but do not exhibit the characteristic 

physical properties of chert; as used in this report, 

these terms include the diatomaceous, radiolarian, and 

spicular earths. Their equivalents on present sea and 

lake bottoms are diatom, radiolarian, and spicule ooze.

Siliceous shales are rocks that consist mainly of finegrained detrital minerals but contain noteworthy 

amounts of nonfragmental silica. Varieties are diatomaceous, radiolarian, and spicular shale and their 

equivalent muds in present sea and lake bottoms. 

Logically, the siliceous mudstones should not be treated 

in this section, but the distinction between siliceous mudstone and rocks composed dominantly of nonfragmental 

silica is not always made; much of the sediment called 

diatom, or radiolarian ooze in the literature actually 

consists largely of detrital minerals, and the terms 

lydite and radiolarian jasper have been applied both to 

rocks composed almost entirely of nonfragmental silica 

and to siliceous mudstones.

Silcrete is a term applied to silicified layers in unconsolidated surficial material. The name was coined by 

Lamplugh (1907), who applied it to silicified surface 

layers in southern Africa. The term is used widely by 

South African geologists.

Stratigraphic nomenclature used is that of the published sources and is not necessarily that of the U.S. 

Geological Survey.

CLASSIFICATION AND OCCURRENCE

The analyses of the nonfragmental siliceous rocks 

have been organized in accordance with a classification 

modified from that of Hatch, Kastall, and Black (1938, 

p. 198) that is based on gross morphology (bedded or 

nodular), the relative amounts of organic and inorganic 

silica, and the type of siliceous organisms present. A 

mineralogic classification proved impractical because of 

the paucity of detailed petrographic descriptions acTl
T2 DATA OF GEOCHEMISTRY

companying the analyses in the literature. For the 

same reason, the class boundaries in the adopted classification cannot be quantitatively defined and a general 

class must be reserved for analyses accompanied by 

only the most meager rock descriptions.

The classification, together with a brief description 

of the occurrence and association of each type 1 is as 

follows.

BEDDED 3STONFRAGMENTAL SILICEOUS DEPOSITS 

DIATOMACEOUS DEPOSITS

[Table 3]

Diatom ooze. Diatom ooze occurs on the sea floor 

in a belt around Antarctica and in an arc from the 

Gulf of Alaska to east of Japan (Sverdrup and others, 

1942, p. 976). Deposits are found in shallower water 

in regions of coastal upwelling; diatomaceous mud 

floors part of the Gulf of California (Kevelle, 1950) 

and exists at depths of as little as 50 meters on the continental shelf off the coast of Angola and Southwest 

Africa (Currie, 1953, p. 499). Diatom frustules are 

not the dominant constituent by weight in much 

oceanic diatom ooze, and the sediments might more 

properly be termed diatomaceous mud.

Diatom ooze is also found in some fresh-water glacial 

lakes where its presence depends on a relatively high 

silica content of the inflowing streams and the absence 

of diluting carbonates and detritus (Conger, 1942).

Diatomite. These fossil diatom oozes may also be 

divided into marine and lacustrine types. A remarkable deposit of marine diatomite is in the Monterey 

Formation (Miocene) of California where as much as 

1,000 feet of diatomite is present in the upper part of 

the formation. The Monterey also contains feldspathic 

sandstone, rhyolitic tuff, mudstone (some of which is 

black), and small amounts of phosphatic mudstone and 

basalt (Bramlette, 1946). Diatomite is also present in 

rocks of Miocene age in Algeria where it totals about 

one-third of a sequence that is 200 meters thick (Anderson, 1933). It is interbedded with andesitic pyroclastics, marl, and clay shale; the sequence contains some 

gypsum lenses and is overlain by gypsum-bearing beds. 

Similar deposits occur in rocks of the same age in Sicily 

and Italy and in the Caucasus (Anderson, 1933, p. 693).

Lacustrine diatomite is found in many parts of the 

world, and other than in a few desiccated Pleistocene

1 In the notes on occurrence and association, references have been 

made whenever possible to summary articles, the most helpful of which 

have been those of Davis (1918) and Kobayashi and Kimura (1944) 

on the occurrence of radiolarian rocks, that of Taliaferro (1933) on the 

occurrence of diatomaceous rocks, and the indispensable work of Caveux 

(1929) on the petrography of the siliceous rocks of France. Excellent recent summaries of the petrography, occurrence, and origin of 

the nonfragmental siliceous sediments are found in Pettijohn (1957, 

p. 432-448), Dunbar and Rodgers (1957, p. 245-255), and CarozzI 

(1960, p, 291-343). The literature on chert and related siliceous 

rocks is too vast to allow citation of more than a few examples and 

a few references for each type.

lakes, is nearly invariably associated with volcanics 

(Taliaferro, 1933, p. 36).

Diatomaceous chert. Many diatomite deposits, both 

marine and lacustrine, contain beds, lenses, and nodules 

of chert (Taliaferro, 1933, p. 23, 26; Bramlette, 1946, 

p. 46), but the most striking occurrence is in the Monterey Formation in which the cherty beds comprise as 

much as several thousand feet of strata (Bramlette, 

1946). Many of the opaline chert layers in the Menelitic Shale of the lower Tertiary Flysch of the eastern 

Carpathians are diatomaceous (Gawel, 1950, p. 186). 

The noncherty beds of the Menelitic Shale consist mostly 

of bituminous shale and marl that is rich in fish remains 

and is at least in part tuffaceous (Athanasiu and others, 

1927, p. 332-337; Ksiazkiewicz, 1956, p. 406). Sediments which now comprise the Monterey accumulated 

at depths of not more than a few hundred meters 

(Bramlette, 1946, p. 9, 11), and the Menelitic Shale 

has been interpreted as a lagoonal deposit (Athanasiu 

and others, 1927, p. 337), although its occurrence in 

a section of turbidites suggests deeper water.

RADIOLARIAN DEPOSITS

[Table 4]

Radiolarian ooze. Radiolarian ooze occurs today in 

a belt crossing the north equatorial Pacific, where it 

has accumulated at depths of several thousand meters. 

Most sediments termed radiolarian ooze are actually 

dominantly clay (Kuenen, 1950, p. 358).

Radiolarite. Radiolarite is present in the lower Tertiary throughout much of the Lesser Antilles, and those 

on Barbados have been studied in detail by JukesBrown and Harrison (1892), who give excellent petrographic descriptions but only partial chemical analyses. 

These radiolarites are associaed with foraminiferal 

limestone and tuffaceous argillaceous beds and are 

thought by Senn (1940) to be deep-sea deposits. However, Beckmann (1953) concluded from studies of benthonic f oraminif era that they were deposited at depths 

of 1,000 to 1,500 meters, so they are probably not analogous to the radiolarian ooze of modern abyssal depths. 

Radiolarites have been described from beds of Eocene 

age in central California by Clark and Campbell 

(1945), who believe them to be of shallow-water origin; 

f acies relations strongly indicate that they could not 

have formed in either the abyssal or lower bathyal 

environments.

Radiolarian chert. The common European practice 

is to divide radiolarian chert into two varieties red 

or green radiolarian jasper and lydite. Lydite is particularly abundant in the lower Carboniferous of 

Europe.
NONDETRITAL SILICEOUS SEDIMENTS T3

Radiolarian chert is commonly associated with mafic 

flows or tuffs or both. Many of the associated flows 

are spilitized. Among those radiolarian cherts not 

closely associated with volcanic rocks are cherts of 

Ordovician age in eastern New York (Ruedemann and 

Wilson, 1936) and cherts of Triassic to Jurassic age in 

western Japan (Kobayashi and Kimura, 1944, p. 158). 

The radiolarian cherts, particularly the jaspers, are 

commonly intercalated in sequences of laminated shale 

and graywacke (Sujkowski, 1957, p. 547; Kobayashi 

and Kimura, 1944, p. 100), but a few are accompanied 

by limestone (Sujkowski, 1932; Sinclair and Berkey, 

1923, p. 90) in an assemblage similar to that in the 

Barbados deposits. The lydites are generally associated with carbonaceous shale; particularly noteworthy 

is the association with highly organic alum shale in the 

Silurian of Saxony and Thuringia (Leutwein, 1951; 

Davis, 1918, p. 326). Bedded chert with sparse radiolaria in eugeosynclinal rocks of Paleozoic age in central 

and western Navada is estimated by R. J. Roberts (oral 

communication 1959) to aggregate more than 5,000 feet 

thick.

Bedded manganese deposits accompany many radiolarian jaspers; many such occurrences are described in 

the Symposium on Manganese Deposits of the 20th 

International Geological Congress, particularly in the 

volume on Asia and Oceania. The manganese may 

occur either as the carbonate or as oxides. Bedded deposits of manganiferous hematite and magnetite are 

associated with radiolarian jasper in Japan (Tababatake, 1956).

Much controversy has existed about the depth of 

water in which radiolarian cherts have accumulated. 

Some radiolarian cherts could not have been deposited 

at depths of more than a few hundred meters. For 

example, radiolarian chert of the Leonard Formation 

of Texas grades into conglomerate in one direction, 

into limestone containing a shallow-water fauna in another, and is interbedded with limestone that contains 

chert pebbles and wave-worn shells (King, 1930); and 

radiolarian chert (Carboniferous) of Gower, England, 

occurs in a sequence containing coal and oolitic and 

crinoidal limestone (Dixon and Vaughan, 1911). 

However, inasmuch as coarse littoral debris can be 

transported to deeper waters by turbidity currents, 

much of the evidence cited to support shallow-water 

origin must be re-evaluated (Pettijohn, 1957, p. 443), 

and the lithologic association of most radiolarian cherts, 

particularly those within eugeosynclinal tracts, indicates that they accumulated in the bathyal environment 

or deeper.

DEPOSITS OP SPONGE SPICUUBS

[Table 5]

Spicule ooze. The only reported occurrences of spicule ooze are in the Antarctic Ocean, where some spicular sediments have been found at depths of 100 to 400 

meters (Lisitzin, 1960), and in Lake Baikal (Votinsev, 

1948).

Spiculite. A sediment as much as 200 feet thick that 

consists mostly of uncemented and loosly cemented 

sponge spicules occurs in the Plantagenet Series of 

early Tertiary age in Western Australia (David, 1950, 

p. 539; Hinde, 1910). Similar but thinner beds have 

been reported from the Marble Falls Formation (Pennsylvanian) of Texas where the spiculite has resulted 

from the removal of calcite from a spicule-bearing 

limestone (Damon, 1946).

Spicular chert. Cayeux (1929, p. 298) has described 

fresh-water spicular chert associated with coal in the 

Stephanian of France, but nearly all other spicular 

cherts are marine in origin.

The lithologic association is varied. Spicular chert 

of the Phosphoria Formation (Permian) of Montana 

occupies a f acies position between glauconitic sandstone 

and black shale and is underlain by phosphorite and 

overlain by dolomite and calcareous shale (Cressman, 

1955); spicular chert of the Lgota Beds (Lower Cretaceous) of the Carpathians is underlain by black shale 

and sandstone and overlain by light-colored sandstone 

(Ksiazkiewicz, 1956, p. 373, 374; Sujkowski, 1933a); 

Spicular chert of Cretaceous age in the Paris basin 

((raises d Spicules and Spongolithes of Cayeux, 1929, 

p. 253) occur in a sandy, marly sequence; and spicular 

chert in the Lias of the Tatra Mountains is intercalated 

in a complex of argillaceous limestone, some of which is 

red (Sujkowski, 1933a). None of these cherts is closely 

associated with volcanic rocks. Spicular chert of the 

Pumpernickel Formation (Pennsylvanian?) in western 

Nevada is associated with argillite and thin sandy beds; 

ripple marks and invertebrate tracts suggest deposition 

at depths of 100 meters or less (R. J. Roberts, oral communication 1959).

Siliceous sponges of the class Hyalospongia generally 

occur at depths of greater than 1,000 meters. Sponges 

of the class Demospongia are found throughout a considerable depth range, but they generally thrive only 

in the photic zone that is, at depth of less than 300 

meters and generally less than 50 meters (de Laubenfels, 1957, p. 771, and oral communication, 1957). 

Chert in the Lias of the Tatras contains mostly Hyalospongia remains and is probably a bathyal deposit 

(Sujkowski, 1933a), but the other spicular cherts mentioned above consist mostly of spicules from Demo-
T4 DATA OF GEOCHEMISTRY

spongia and probably accumulated in sublittoral 

regions.

Chert in the Lgota beds occurrs within the Cretaceous 

Flysch (Ksiazkiewicz, 1956, p. 373) and is a eugeosynclinal deposit, but other spicular cherts were formed 

either on cratons in intracratonic basins, or in miogeosynclines and the bordering unstable shelf.

OTHER BEDI>EI> CHERT

[Table 6]

Included in this group are those bedded cherts in 

which siliceous organic remains are either absent, very 

sparse, or not reported. Examples are the chert of Carboniferous age at North Flintshire, England, which is as 

much as 400 feet thick and is underlain by limestone 

and overlain by black shale and sandstone (Sargent, 

1923), the Fort Payne Chert of Mississippian age in 

Georgia and adjacent states which overlies black shale 

and underlies limestone and calcareous shale (Hurst, 

1953), and the Kanawha black flint in the Pennsylvanian of West Virginia which is up to 10 feet thick 

and occurs in carbonaceous shale that overlies the 

Stockton coal (Price, 1921). In both megascopic character and lithologic association, these cherts resemble 

others that abound in siliceous skeletal material, particularly the spicular cherts. In the Permian of British 

Columbia, light-gray to black chert is interbedded with 

carbonaceous argillite and andesitic flows; the chert 

closely resembles radiolarian chert of other eugeosynclinal areas, but it contains no visibile radiolaria 

(Cairnes, 1937, p. 11).

The Arkansas Novaculite (Devonian and Mississippian) of Arkansas and Oklahoma and its correlative in 

Texas, the Caballos Novaculite, are placed in this group 

because, although both spicular and radiolarian cherts 

have been reported, especially in the dark chert members (King, 1937, p. 52; Goldstein and Hendricks, 1953, 

p. 428-430), most descriptions emphasize the absence of 

siliceous organisms.2 Ripple marks have been observed 

in the novaculite in both Arkansas (Miser, 191Y, p. 

66) and Texas (King, 1937, p. 49), indicating a sublittoral origin for at least the light-colored rocks, but 

shale, some of which is black, is intimately interbedded 

with the dark chert. The Arkansas Novaculite contains some silicified volcanic ash near the base, and the 

upper member in parts of Oklahoma contain manganiferous carbonate (Honess, 1923, p. 137). Deposits of 

manganese oxides are associated with the novaculite in 

Arkansas (Miser, 1917, p. 73-75).

Cherts of the iron formations of Precambrian age 

are included here although they are unique in their

« Goldstein and Hendricks (1953, p. 430) believe that the paucity of 

siliceous organisms in the areas described by Miser (1917) and Honess 

(1923) is a result of dynamic metamorphism.

close association and intimate interlayering with sedimentary iron deposits. Most chemical analyses in the 

more readily accessible literature are for the banded 

rock (jaspilite) rather than for the chert layers only, so 

they are treated very cursorily in this paper. According to James (1954, p. 279), the iron-formation of the 

Lake Superior region was deposited in marine waters 

in a basin marginal to the ocean during the initial 

stages of eugeosynclinal subsidence. Hough (1958) 

has stated the case for lacustrine deposition.

NODTTLAB CHEBT IN CABBONATE BOCK

[Table 7]

In addition to nodules, chert lenses and layers in carbonate rock are included in this group.

Much nodular chert is concentrated in the shallowwater phases of carbonate sequences where it may replace oolite (Young, 1934, p. 165; Choquette, 1955) or 

bioclastic carbonate rock (Hull, 1880, p. 74, 75). Chert 

in the Osage Group of the Mississippi Valley region is 

most common in a facies intermediate between sandstone and limestone (Robertson, 1952). In contrast, 

Lowenstam (1942a) reports the Niagaran chert of 

Illinois to be confined to shaly limestone and dolomite 

of the interbioherm facies, and chert bands and nodules 

occur in dense black limestone in the Bone Spring Limestone of west Texas that probably accumulated at depths 

of about 150 meters (Newell and others, 1953, p. 162 

and 190).

An interesting association is reported by Stout and 

Schoenlaub (1945, p. 9) who describe nodular and lenticular chert in marine limestone overlying coal beds in 

Pennsylvanian cyclothems of Ohio.

Some chert nodules are formed around skeletons of 

siliceous sponges (Moret, 1926, p. 63; Laird, 1935, p. 

257; McKee, 1938, p. 77-100), and others contain numerous sponge spicules (Lowenstam, 1942b, p. 825-828; 

Andrusov, 1932). Some nodules consist largely of replaced calcareous skeletal fragments (Fowler and 

others, 1934; Van Tuyl, 1912), or oolites (Bosazza, 

1937), whereas others are uniformly aphanitic, featureless in texture.

Chert is common in both limestone and dolomite. 

According to Chilingar (1956), the concentration of 

chert nodules, stringers, and beds in limestone increases 

as the Ca/Mg ratio of the limestone increases.

OTHEB SILICEOUS DEPOSITS

Included under this heading are siliceous sinter, silcrete, melikaria, and silicified wood. Most of these 

materials are more appropriately discussed in other sections, but analyses are listed in table 8 for comparison 

with the marine and lacustrine siliceous deposits.
NONDETRITAL SILICEOUS SEDIMENTS T5

MINERALOGIC COMPOSITION

The opal, chalcedony, and quartz s in the nondetrital 

siliceous sediments are admixed in varying amounts 

with the same clastic and authigenic minerals that are 

present in the adjacent sedimentary rock, and with organic matter. No mineral has been reported from chert 

that is not also present in other sedimentary rocks, and 

minerals common in other marine sedimentary rocks 

also occur in chert.

The crystal chemistry of the silica minerals is more 

complex than previously thought. Summaries of recent developments and references to original work are 

given in two papers by Eitel (1957; 1958, p. 66-73). 

Especially pertinent to this discussion is evidence by 

Buerger (1954, p. 604-606) that small amounts of 

A1+3 replace Si+4 in tridymite with the excess charge 

compensated by alkali or alkali-earth ions in the large 

interstitial spaces in the tridymite structure. According to Florke (1955a, 1955b), much low-temperature 

opal is not truly amorphous but contains inter-stratified 

cristobalite and tridymite layers, the tridymite layers 

resulting from disordering by aluminum, alkali, and 

alkali-earth ions. The quantity of the disordering cations may be considerable; Buerger and Lukesh (1942) 

report the approximate formula of tridymite from Las 

Plumas, Calif., as NaCaAlgSiisOse, and Koy and Roy 

(1959) have synthesized cristobalite-tridymite solid solutions at high temperature that contain not less than 2 

mole percent NaAlO2 . Quartz, on the other hand, can 

accommodate only Li+1 and possibly Be+2 and B+3 

in its much smaller interstices (Buerger, 1954, p. 

602). Keith and Tuttle (1952) have shown that aluminum probably substitutes for silicon in quartz with 

the charge compensated by lithium, and they suggest 

from consideration of valence requirements and ionic 

radii that titanium, too, can substitute for silicon, but 

their analyses of natural quartz (table 2) indicate that 

any substitution by any of these ions in quartz is very 

minor. In addition to these possible substitutions, 

Eitel (1954, p. 618) suggests that in chalcedony, the fibrous variety of quartz, ferric iron might substitute for 

silicon and hydroxyl for oxygen.

The silicon in siliceous organisms is in the form of 

opal that in diatoms, and presumably also in sponges 

and radiolaria, is amorphous (Mielenz and others, 1949, 

p. 56; Swineford and Franks, 1959, p. 117). Bramlette 

(1946, p. 17) states that the index of refraction in 

the opal of siliceous organisms varies little from 

1.440±0.002 which indicates a water content of about 

9 percent. The water content of opal in sponge

8 The fibrous-quartz varieties quartzine and lutecine and the cristobalite varieties lussatite and lussatine described in some European literature) (Braitsch, 1957) are not generally distinguished by American 

petrographers.

spicules ranges from 5 to 13 percent (Vinogradov, 1953, 

p. 184). As noted by Swinef ord and Franks (1959, 

p. 117), the opal of diatoms must be of high purity, for 

when diatomite is cooled from high temperature, tridymite does not form unless cations necessary to disorder 

the cristobalite structure have been added (Eitel, 1957, 

p. 146).

Mielenz, Witte, and Glanz (1949, p. 56) report cristobalite in opaline shale (but not in diatomite), and 

Swineford and Franks (1959, p. 117, 118) have obtained X-ray diffraction patterns of low cristobalite and 

tridymite from massive opal, opaline cement in sandstone, and silicified wood from the Pliocene of Kansas.

The meager data available on the relation between the 

mode of occurrence and the crystal structure of sedimentary opal will not permit generalizations, but they 

suggest that this, together with differences in composition that might be expected to accompany differences 

in crystal structure, would be a fruitful field for 

research.

A large part of both the siliceous tests and the matrix 

silica in deposits of Tertiary age is opaline, but nearly 

all of both the organic and inorganic silica in Paleozoic 

cherts is present as microcrystalline quartz and chalcedony.4 Opal, quartz, and chalcedony may all be 

found in Mesozoic cherts. It has long been concluded 

from these facts that most chert was originally opaline 

and that opal ages to chalcedony and quartz. However, factors other than age alone are involved: Cayeux 

(1929, p. 694) found no difference in the mineralogic 

character of the silica between cherts of Mesozoic and 

Tertiary age in the Paris basin, and Bramlette (1946, 

p. 54) cites evidence that both load and deformation 

further the conversion of opal to quartz and chalcedony. 

The structure and composition of the opal might have 

an effect on the ease of transformation; thus opal with 

a tridymite structure might be difficult to convert to 

quartz because of the large cations in the interstices 

of the lattice (Eitel, 1954, p. 617). Three analyses of 

nearly pure cherts are listed in table 1 as standards 

against which less pure cherts may be compared. Traceelement analyses of several speciments of igneous and 

hydrothermal quartz are listed in table 2 for comparison 

with chert analyses.

CHEMICAL COMPOSITION

The chemical analyses in tables 3, 4, 5, 6, 7, and 8 

have been selected from the more complete analyses 

available so as to represent a wide geographic and strat-

*For discussions of differences between microcrystalline quartz and 

chalcedony see Folk and Weaver (1950), Midgley (1951), and Pelto 

(1956). The recent tendency has been to discount the presence of any 

opal in the older cherts, but Hoss (1959) has advanced evidence for 

small amounts of opal in lower Carboniferous lydite of Germany.
T6 DATA OF GEOCHEMISTRY

igraphic range, but all appropriate analyses culled 

from the literature have been plotted in the diagrams.

TABLE 1. Analyses of three nearly pure cherts

TABLE 2. Spectrochemical analyses of igneous and 

hydrothermal quartz

[Analyses in parts per million. Modified from Keith and Tuttle, 1952, p. 224. Symbol: n.d., not determined]

[Samples not analyzed for elements other than those given]

SiO,. ................. ......

AlaOs _. _____. ._______.

FeO . _ ._

MsO ........ _. .. .

CaO ..... . .........................

NajO -._--.-....... ...__.._.-...._

K2O ......

HS0+ ._...__._ ..__

H2 0- . ....................................

COj -...................................

Total.... .... ...... ...............

1

99.82 

.11

.00 

.07 

.00 

.00 

.00 

.03 

.03 

.00 

.00

100. 06

2

99.95 

.00 

.00 

.06 

.00 

.00 

.00 

.01 

.01 

.00 

.00

100.03

3

99.86 

.00 

.00 

.06 

.00 

.03 

.01 

.01 

.07 

.00 

.00

100.04

Trace elements

[Parts per million]

Ac

Ge... ........................

Li............................................

Mn...........................................

Mo - .- . _...._--....

P.............................................

Ti _ ___ 

1.0 

.2 

2 

6 

2.6 

37 

82

0.7 

3.0 

0 

3 

1.6 

15 

0

0.4 

.4 

0 

7 

1.8 

22 

23

B ... 

Cu. 

K_... ...... -

Li....... 

ft/iff

Na 

Ti... __ .. ____________ -

1

10-100

n.d.

n.d.

10-100 1-6

10-100

2

«1

n.d.

10-50

<10? 1-5

n.d.

3

s»10

«1

n.d.

10-50

<10? 1-5

n.d.

4

«20

<1 5-50

100-1,000

<10?

10-300

n.d.

1. White novaculite from Arkansas Novaculite (Maxwell, 1953).

2. Chalcedony nodule from clay pit, Virginia (Maxwell, 1953).

3. Siliceous cement from chert breccia, Labrador (Maxwell, 1953).

NOTE. Al is present in all samples (10-100 ppm), but sample 4 is estimated to have 

about four times as much as sample 2. Ba and Fe are reported in small amounts in all 

four samples.

Ag, V, and Sr are doubtful trace elements; Mn, Or. Ca, Ni, Pt group, In, Oa, Zr. 

La, Nd, Y, Be, Rb, and Cs were looked for but not found. Ge and Au were not 

detected in 3 and 4 and not looked for in 1 and 2.

1. Quartz crystal, Brazil.

2. Pegmatitic quartz, South Dakota*

3. Drusy incrustation on barite or celestite, Colorado.

4. Pale-green quartz, Iceland.

MAJOR CONSTITUENTS

The frequency distributions of four types of chert 

within the major compositional triangle SiO2-(Al,Fe) 

2O3 -(Ca,Mg)CO3 are plotted on figure 1. The major 

differences between types may be explained largely by 

differences in lithologic association. Eadiolarian rocks

TABLE 3. Analyses of diatomaceous rocks

SiOj. ...._......_

FesOs -

FeO. .. .

MgO_ . ....

CaO. ...............

NasO _______ . ...

KjO. __ .............

HiO+-. ..........

H2 0- . ...........

TiOj_ . __ ..........

P2 05. ...............

MnO __________

Diatom ooze

1

60.14 

13.01 

5.96

2.34 

1.87 

1.97 

2.04

1 8.01

.53 

.12

.74

> 98. 13

2

61.80 

9.25 

3.43

2.82 

4.19 

3.10 

1.45

.42

.17

* 86. 66

3

82.36 

4.87 

2.23

1.84 

7.85 

Tr. 

Tr.

.09 

.10

899.36

Diatomite

4

71.80 

5.02 

2.45 

.35

1.69 

1.46 

1.81 

3.55 

f 5.50 

I 4.64

.17

4 99. 77

5

89.70 

3.72 

1.09

.65 

.35

} .82

3.70 

.10

100. 13

6

79.55 

8.18 

2.62

1.30

.25

1.31

5.80 

.70

99.71

7

71.99 

3.00 

1.12

2.30 

8.15

.63

12.68 

.13

100. 00

8

71.20 

12.67 

5.65 

.38

.40 

1.35 {""-:«-

7.91

« 100. 27

9

79.7 

6.4 

1.1

Tr.

.5 

.08

.06

I ~5.~6" 

7.4 

.3

.01

100. 55

10

86.25 

.62 

.80

.31 

.45

} 5.74 

5.48

99.65

11

83.21

2.96 

.33

Tr. 

.20 

.20 

.17

{ 8.81

4.00 

.09

99.97

12

73.16 

9.08 

1.44

.23

.50 

1.20 

1.40

7.20 

5.41 

.21

99.83

13

78.6 

5.7

> "

1.4 

.8 

1.1

.25

Diatomaceous 

chert

14

87.20 

1.86 

f 1.06 

\ .33 

1.14 

.05 

.53 

2.75 

2.23 

2.78

.22

« 100. 31

i Includes COj, 0.20; C, 1.20.

3 Includes SrO, 0.033.

«Inc-ludes ZrOj, 0.01.

< Includes CL 1.34; a small amount of C present.

«Includes SOa, 0.26.

 Includes Cl, 0.16; a small amount of C present.

1. Diatom ooze, North Pacific (Revelle, 1944, p. 59). Sharp-Schurtz Co., analysts.

2. Diatomaceous sediment with volcanic ash layers (Ooldberg and Arrhenius, 1958, 

p. 170).

3. Average of six Arctic diatom oozes (Sujkowski, 1952).

4. Composite sample of 10 diatomaceous rock1!, Monterey Formation (Miocene), 

California (Bramlette, 1946, p. 13). R. C. Wells, analyst.

5. Diatomite, Monterey Formation, California (Cummins and Mulryan. 1949).

6. Diatomite (marine), Tertiary, Maryland (Cummins and Mulryan, 1949).

7. Dintomite (marine), Miocene, Algeria (Cummins and Mulryan, 1949).

8. Diatomite, Tertiary, Siberia (Maleev, 1937).

9. Diatomite (lacustrine). Tertiary, Queensland, Australia (Bonner, 1951).

10. Diatomite (lacustrine), Miocene. Washington (Glover, 1936).

11. Diatomite (lacustrine), Pleistocene, New Zealand (Grange, 1937). F. T. Seelye, 

analyst.

12. Diatomite (lacustrine), Pleistocene, New Zealand (Grange, 1937). F. T. Seelye, 

analyst.

13. Average of analyses 4 through 12.

14. Composite sample of 10 chert shales, Monterey Formation (Miocene), California 

(Bramlette, 1946, p. 13). R. 0, Wells, analyst.
NONDETRITAL SILICEOUS SEDIMENTS T7

50 percent Si02

DIATOMITE AND DIATOMACEOUS CHERT 

(38 analyses)

50 percent Si02 

SPICULAR CHERT 

(24 analyses)

50 percent Si02 

RADIOLARIAN CHERT 

(48 analyses)

50 percent Si02 -

NODULAR CHERT IN CARBONATE ROCK 

(57 analyses)

Only this part of 

triangle is shown

EXPLANATION

(AI.Feyj, (Ca.Mg) C03 30-50 0-10

FIGURE 1. Frequency diagrams of four types of nonfragmental siliceous sedimentary rocks. Analyses were plotted in the SiO2-(Al,Fe) 2O3- 

(Ca,Mg)CO3 compositional triangle, tallied by use of a 1-percent-area triangle, and contoured. Only that part of the triangle containing 

more than 50 percent SiO2 is shown.
T8 DATA OF GEOCHEMISTRY 

TABLE 4. Analyses of radiolarian rocks

SiOs.__ .............

AUCh._ .............. ..

FejOa.. . ........ ....

FeO_._ .............

MgO..-- - ... .

CaO... ......... .........

Na3O_ - ..- 

K2 0_.. . ...-. 

HsO+. .-.-... ......

H2 0-..-.-. -..____.....

Loss on ignition ____

TiOa... ........... ..

P20t._..............._.

MnO. . .-. .

COs-. ......... . ...

C.. . . .. .

Total............

Radiolarian ooze

1

66.67 

14.82 

6.51

2.58 

2.26 

1.66 

2.54

.63 

.14 

.28 

.51 

1.32

199.94

2

64.34 

15.37 

6.85

3.58 

1.86 

.98 

3.75

.73 

.46 

.29 

.70 

.89

J99.93

Black radiolarian chert

3

95.94 

1.39 

.69 

.05

.26 

.00 

.13 

.53

.06 

.42

Tr. 

.02 

.01 

.00 

.30

'99.80

4

97.6

.8 

.15

Tr. 

Tr. 

.02 

.1 

.60 

.08

.02 

.44 

.04

99.85

5

91.06 

3.79 

2.01

.46 

.45 

.28 

.84 

.97 

.32

Tr. 

Tr.

Tr.

100.18

6

86.9 

4.6 

2.7

.8 

.1 

.4 

1.0 

2.3 

.3

.14 

.04 

.03

.65

99.96

7

89.6 

4.8 

1.6

.4 

.2 

.3 

.8 

2.3 

.1

.10 

.04 

.10

.13

100.47

8

89.15 

3.45 

.58 

2.19 

1.05 

.24 

.22 

.53 

1.17

.22 

.04 

.03

.11

< 99. 71

Red and green radiolarian chert (radiolarian jasper)

9

76.54 

10.65 

4.02

.79 

.48 

440 

1.03 

.70 

.00

.57 

.13 

.61 

.00

8 99. 92

10

83.67 

3.30 

7.74

.50 

.40 

1.00 

1.42 

.85 

.10

.40 

.10 

.30

99.78

11

94.90 

2.31 

1.19

.30 

.30 

.50

J 1.35

.10 

Tr.

100.95

12

88.20 

4.40 

3.91

1.25 

.30 

.60

1.25

.20 

Tr.

100.11

13

95.00 

1.70 

.78 

.11

.23 

.41 

.09 

.33 

f .71 

\ .08

.08 

.20 

.18 

.06

 99.97

Av. 

(3-13)

14

89.9 

3.7 

2.3

.5 

.3

.7 

.7

.2 

.9 

.1

' Includes ZrOa, 0.02.

* Includes ZrOs, 0.13.

»Also FeS2, trace.

< Includes ZrO2, 0.59; S, 0.14.

> BaO, 0.00.

«Includes L^O, 0.01.

1-2. Radiolarian ooze from North Pacific (Revelle, 1944, p. 58, 59). Recalculated to 

sea-salt-water and water-free basis. Sharp-Schurtz Co., analysts.

3. Black radiolarian chert, Upper Silurian. Carnic Alps, Austria (Heritsch and 

Heritsch 1943).

4. Black radiolarian chert. Silurian, Altmannsgrun, Saxony, Germany (Hoss, 

1957, p. 81).

5. Black radiolarian chert, Devonian, New South Wales, Australia (David and 

Pittman, 1899). J. C. H. Mingaye, analyst.

6. Black radiolarian chert, lower Carboniferous (Culm), Wallace, Hesse, Germany 

(Hoss, 1957, p. 65).

TABLE 5. Analyses of spicular chert

SiOs- _____

AljOs .... 

FeO - 

MgO.. ... -

CaO... ... ..

Na2O- .....

KjO 

H2 0+. .... .

H2O- _ .. .

TiOs-- - -

PaOs -

COj. .

Total....

1

94.10

1.85

1.65

.01

.05

~~2.~45~

.......

100. 11

2

94.6

1.8

.36

.28

.64

.49

.15

.37

.77

. vy 

.07 

.24

.60

1 100. 49

3

82.94

.1

3.4

.19

1.60

.65

1.40

}

QQ .33

.27 

.8

.40

292.38

4

98.60

.39

91

.26

.11

.11

99.68

5

94.75

1.30

.55

Tr.

.37

.21 

2.35

99.53

6

94.63

2.23

1.74

.18

.91

} 18 / 1H

.10

99.97

7

85.70

4 $25!

9 O7

49

1.05 f .20

\ .68 

5.80

.30 

Tr.

100.17

8

64 00

K O3

2.47

.81

11.67

.36

.08 

6.45

.30 

.10 7 on

99.37

9

QQ 7

2

1

1.5

.4

2 n

.5

.2

......

1 Includes MnO, 0.03.

2 Includes F, 0.10; S, 0.14; VsOj, 0.06.

1. Lacustrine?, Stephanian, France (Cayeux, 1929, p. 299). Laboratorie de Chimie 

de la Prefecture de Police, M. Lassieur, director.

2. Pumpernickel Formation (Lower Permian), Antler Peak quadrangle, Nevada 

(R, 3. Roberts, U.S. Geological Survey, unpublished data). K. White, H. F. 

Phillips, P. W. Scott, and F. S. Boms, analysts.

3. Phosphoria Formation (Permian), Utah (Smith and others, 1952, p. 12). Analysis 

by Tennessee Valley Authority.

4. Jurassic, Poland (Morawiecki, 1955).

5. "Spongolithe", Cretaceous, France (Cayeux, 1929, p. 416). Laboratorie de Chimie 

de la Prefecture de Police, M. Lassieur, director.

6. Lgota Beds, Cretaceous, Poland (Kamienski and Tokarski, 1958).

7. "Gaize", Cretaceous, France (Cayeux, 1929, p. 259). Laboratorie de Chimie de la 

Prefecture de Police, M. Lassieur, director.

8. "Gaize", Cretaceous, Belgium (Cayeux, 1929, p. 212). Laboratorie de Chimie 

de la Prefecture de Police, M. Lassieur, director.

9. Average of analyses 1 through 8.

are most abundant in argillaceous sequences and both 

radiolarian and diatomaceous rocks are very commonly 

associated with pyroclastics; they are therefore somewhat more aluminous that the spicular cherts which are 

more commonly associated with sandstone or carbonate 

rocks. The similarity between spicular and nodular 

cherts reflects their common origin in relatively shallow 

water in which clay is not so likely to accumulate.

7. Black radiolarian chert, Harz Mountains, Germany (Hoss, 1957, p. 81).

8. Red and green radiolarian chert, Pumpernickel Formation (Lower Permian), 

Antler Peak quadrangle, Nevada (R. J. Roberts, U.S. Geological Survey, 

unpublished data). M. K. Carron, analyst.

9. Bright red radiolarian chert, Jurassic, Val d'Err, Switzerland (Jakob, 1925).

10. Red radiolarian chert, Jurassic, Val d'Err, Switzerland (Jakob, 1925).

11. Red radiolarian jasper, Jurassic(?), Borneo (Cayeux, 1929). Laboratorie de 

Chimie de la Prefecture de Police, M. Lassieur, director.

12. Red radiolarian jasper. Eocene, Tuscany, Italy (Cayeux, 1929). Laboratorie de 

Chimie de la Prefecture de Police, M. Lassieur, director.

13. Radiolarian chert, Franciscan Formation, Jurassic near Oakland, Calif. (Maxwell, 1953).

14. Average of analyses 3 through 13.

The relations between SiO2 and A12O3 are further 

illustrated by figure 2 on which SiO2 is plotted against 

the ratio SiO2/Al2O8. The radiolarian rocks fall along 

a well-defined trend that is marked by curve A, the 

theoretical change in composition that would result 

from the addition of SiO2 to a siliceous ooze of the composition of the average of the six reported by Kevelle 

(1944, p, 58). The line would fit the trend of the radiolarian rocks equally well if plotted from either the average pelagic clay or the average shale. The trend reflects the occurrence of radiolarian chert in carbonatepoor very argillaceous rocks.

The spicular rocks form a somewhat less well-defined 

trend, most of the samples having a higher SiO2/Al2O8 

ratio than radiolarian rocks with the same SiO2 content, 

as one might expect from the common association of 

spicular chert with sandstone. Curve B, similar to 

curve A, but plotted from the composition of the average sandstone (Clarke, 1924, p. 30), fits the trend fairly 

well.

Part of the wide spread of the diatomaceous rocks on 

figure 2 results from the high content of organic matter of some, particularly those from high-latitude 

lacustrine deposits, and the high-water content of 

others.

No regular relationship is apparent between SiO2 

and the ratio SiO2/Al2O8 for nodular chert on figure 2. 

Curve C is the change in composition that would result 

from the addition of SiO2 to the average limestone, the 

composition of which is taken from Clarke (1924, p. 30).
NONDETRITAL SILICEOUS SEDIMENTS T9

100

90

80

70

60

o

QL 

UJ Q- 50

O '(/)

40

30

20

10

/-* * a°

H D

\Average sandstone 

(Clarke, 1924)

Curve A

° °

Average of six siliceous oozes / 

(water-free; Revelle, 1944)\ '

_ A

+ / 

/ 

/ 

/ 

/

v/^Average of nine pelagic clays 

(water-free; Revelle, 1944)

Curve D f 

I

/ 

/ Curve C

! /

I /

I /

/ /

EXPLANATION

D 

Diatomaceous rocks

A.

Radiolarian rocks

Spicular rocks

+ 

Nodular chert in carbonate rock

Average limestone 

(Clarke, 1924) -

I i i i i i i i i i i i i i i riii

10 100 1000

Si02 /AI203

FIGUKB 2. Relation between SiO2 and the ratio SiO2/Al2Oa in chert and related rocks.

It is not surprising that many analyses lie above curve C 

inasmuch as many nodular cherts exhibit replacement 

textures, but it is surprising that all lie above the curve. 

Clark's average limestone may be too low in SiO2 and 

A12O3 , or nodular chert may develop preferentially in 

rock more sandy or argillaceous than the average limestone, but most of the points remain above the curve if 

it is constructed from any reasonable initial composition. Curve D is the change of composition that would

result from volume-for-volume replacement of calcite 

of the average limestone by quartz. The curve at least 

falls in the midst of the points, but there is no similarity 

between the arrangement of the points and the trend of 

the line. The absence of any trend in these analyses 

may be explained partly by a wide range in the composition of the parent rock. Furthermore, even cherts 

with evident replacement textures probably have resulted from both replacement and pore filling so that
T10 DATA OF GEOCHEMISTRY

TABLE 6. Analyses of bedded cherts containing lew or no siliceous skeletal remains

Si02.-..__ ............

AljOs - . ...

FejOj... ...

FeO _ ................

MaO.. ................

CaO. - ........... ..

Na2 0.. ................

KjO...... .......

H,0+ ..... ... ...

HsO ...... ...........

TiOj -... .-. 

P,0,-...._....-....___

MnO.. .

COi. _ ... ....

C... . .........

SOi-.. _ ..........

Total.. ......_...

1

99.43

.01

.03

.16

.01

.08

Nil

Nil

.16

.01

.06

Nil

99.95

2

61.42

.10

30.64

3.23

.20

.48 | . 

.08

1.79

.66

99.54

3

96.39

.78

} " 43

.05

.23

{

f)4 .04

.16

.051

.071

.01

.31

99.48

4

95.89

1.95

f .24

1 13

.05

04

.04

.30

i 0°.

.15

.091

047

.00

.15

100.11

6

QQ 4.7

.23

nn

.09

.00

.00

.01

.05

.07

.01

.01

QQ 04

6

QQ fifi

.03

nn

i<\

.00

.00

.01

.01

.11

.02

.00

QQ QQ

7

Q? sn

.60

nfi

.23

.03

.18

.03

.15

en

.14

.105

00

QQ JW

8

99.33

.01

.08

.23

.01

.00

.01

.03

.17

.05

.034

.00

99.95

9

74.56

3.23

.00

3.60

6.26

Tr.

} .05

Tr.

.00

.01

5.85

1.30

100.09

10

93.75

2.63

1.43

00

Tr.

1.36

.00

f .00

.00

.00

.02

1 00

.00

100.19

11

92.86

1.95

} 2.28

.10

.27

} .77

1 23

/ *

2.03

100.49

12

80.59

8.29

1.83

.34

.70

. Jw

.53

6.55

100.65

13

97.74

.44

1 .09

I .70

.25

.33

(

151

.07

Nil

Nil

100. 15

14

85.40

2.06

1.43

.14

.12

4.56

f .25

I .35

1.80

.10

.15

1.62

.01

2.06

100. 05

Chert band, Soudan Iron-Formation, Precambrian, Minnesota (Maxwell, 1953).

Chert band from iron-formation, Precambrian, India (Spencer and Percival, 1952)

Bedded chert, Maravillas Formation, Ordovician, Texas (Maxwell, 1953).

Huntersville Chert of Price (1928), Devonian, West Virginia (Maxwell, 1953).

Gray Arkansas Novaculite, Devonian. Arkansas (Maxwell, 1953).

Milky-white novaculite, lower novaculite member of Caballos Formation, Devonian, Texas (Maxwell, 1953).

Banded chert, upper chert member of Caballos Formation, Devonian, Texas 

(Maxwell, 1953).

White to light-buff novaculite, upper novaculite member of Caballos Formation, 

Devonian, Texas (Maxwell, 1953).

9-10. Fort Payne Chert, Mississippian, Georgia (Hurst, 1953). L. H. Turner, 

analyst.

11. Kanawha flint, blocky phase, Pennsylvanian, West Virginia (Price, 1921). J. B. 

Krak, analyst.

12. Kanawha flint, shaly phase, Pennsylvanian, West Virginia (Price, 1921). J. B. 

Krak, analyst.

13. Light to dark-gray chert interbedded with greenstone and argillite, Fergusson 

Series, Permian(?), British Columbia (Cairnes, 1937). R. J. C. Fabry, analyst.

14. Chert interbedded with limestone, siltstone, and phosphorite, Jurassic, Zacatecas 

Mexico (Rogers and others, 1956, p. 19). Alberto Obregon, analyst.

TABLE 7. Analyses of chert nodules, lenses, and layers in carbonate rock

SiOS . ...

AhOs. .... _

FesOi _ . ...........

FeO...................

MgO.. -- .._ _.

CaO _ ... .............

Na2O ..................

K2 0. -- . ..-..._

HjO+. -. ..

H2 0-.. ...............

TiO» . .. . 

PsO*. ...

MnO... __ . ___ .

COS - ............

C......................

Total _____ ..

1

OS Sfi

1.85

.04

.07

.02

.22

Nil

Nil

100. 50

2

95.00

4.47

.61

.07

.01

.32

Nil

Tr.

100.48

3

QQ 4.7

.06

nn

.17

.06

.01

.03

19

.02

00

.03

100. 04

4

f\Q CO

12

.00

09

4>;

.01

no

iq

08

.25

.03

5

95.11

.14

40

44

.71

1.11

<.01

.01

OK

.43

.03

.01

.01

1

OO

.05

i inn 9Q

6

Q.E 79

00

no

.12

91

1 9*

O4.

.10

.55

.11

.027

009

002

1.17

.04

7

^

70

45

.02

.30

1.88 19 on

.05

.06

.48

00

.03

.16

.02

19 flJ.

.33

a inn no

8

64.55

1.67

1 03

5.45

10.80

1 ,, .*

| 1.70

Tr.

IQ on

99.63

9

96.45

.07

.07

.06

.49

1 9f;

f .01

1 04

(

tn

.03

.018

.033

1.20

100. 07

10

86.11

1 Q9

.88

.20

5.40

.42

[ .»

4.10

QQ Q°.

11

98.36

.12

.00

.08

.01

.16

.04

.04

(

84

.11

.023

.07

.02

99 87

12

92.30

.35

.60

.10

2.25

.29

1 2.05

Tr.

Tr.

1.45

99.39

13

97.54

.52

.19

Nil

Nil

{--"«

1.12

99.65

14

91.4

.9

.3

.2

.8

2.7

.1

.05

.02

.03

3.6

i Includes FeR2 0.21, SO3 <0.01.

8 Includes Zr02<0.01, FeS2 0.27, 80s <0.01.

1-2. Chert bands, dolomite series, Precambrian, South Africa (Bosazza, 1937).

3. Oolitic chert, mines Dolomite, Cambrian, Pennsylvania (Maxwell, 1953).

4. Chert, Ellensberger Group, Ordovician, Texas (Maxwell, 1953).

5. Chert lay«,r in dolomite, Bisher Formation, of Foerste (1917), Silurian, Ohio 

(Stout and Pchoenlaub, 1945). Downs Schaaf, analvst.

6. Chert, Keyser Limestone, Devonian, West Virginia (Maxwell, 1953).

7. Chert nodule, Delaware Limestone, Devonian, Ohio (Stout and Schoenlaub, 

1945). Downs Schaaf, analvst.

8. Chert from dolimite, Carboniferous, France (Cayeux, 1929, p. 533). Laboratorie 

de Chimie de la Prefecture de Police, M. Lassieur, director.

two parent rocks with the same initial composition but 

different porosities would, on silicification, yield cherts 

of different composition.

The assumption has been made in this discussion that 

most of the aluminum occurs in terrigenous clays with 

some contribution from feldspars and other aluminum 

silicates. This is generally confirmed by petrographic 

studies (for example, see Bramlette, 1946, p. 17-18, and 

Hoss, 1957). However, Robertson and Twedily (1953) 

report that late Pleistocene or Eecent diatomite from 

Skye contains 5 to 60 percent of an alumina-ferric 

oxide-silica gel, which might partly explain the scatter 

of the diatomaceous rocks on figure 2, and aluminum

9. Ch^rt, Bird Spring Formation, Pennsylvanian, Nevada (Maxwell, 1953).

10. Chert nodule, Jurassic, France (Cayeux, 1929, p. 495). Laboratorie de Chimie de 

la Prefecture de Police, M. Lassieur, director.

11. Flint nodule, Dover Chalk, Cretaceous, England (Maxwell, 1953).

12. Flint nodules, Cretaceous, France (Cayeux, 1929, p. 437). Laboratorie de 

Chimie de la Prefecture rte Police, M. Lassieur, director.

13. Chert, Amuri Limestone, Cretaceous(?), New Zealand (Wellman, 1945). L. R. 

L. Dunn, analyst.

14. Average of analyses 1 through 13.

may substitute for silicon in the cristobalite-tridymite 

lattice of opaline chert. Vinogradov (1953, p. 103, 

180, 181) lists analyses of siliceous sponges in which 

the combined Al2O3-Fe2O3 is as much as 10 percent of 

the total ash, but inasmuch as sponges are filter feeders, 

much of the alumina may be in foreign clay particles.

MINOR CONSTITUENTS 

IRON

Nodular chert generally contains less than 1 percent 

total iron as F^Os,' most bedded chert contains more 

than 1 percent Fe2O3 , and the content of some red radiolarian cherts ranges up to nearly 9 percent (Jakob,
NONDETRITAL SILICEOUS SEDIMENTS Til

TABLE 8. Analyses of silcrete and other siliceous materials

SiOj-.....-... ......

AljOi . _ 

FeO.-...... .... ...

MgO ..............

CaO_ .-_.. . ....

NajO. .. .

K2O 

HzO-K~ 

H2O-........ .....

TiOj.. ..... ..........

PS 06 .. .--.. - ... ...

MnO. ............ ...

COj...___.... . _

Total. 

1

95.35 

.36 

1.81

.09 

.33 

Nil 

.02

.73 

1.26

99.95

2

94.72 

.55 

1.74

.23 

.63

.34 

2.13

100.34

3

99.95 

.00 

.00 

.06

.00 

.00 

.00 

.01 

.01 

00

.00

100.03

4

85.2 

1.1 

.26 

.20

.48 

5.7 

.18 

.16 

1.0

.04

.24

.02

4.8

99.4

5

96.84 

.02 

.00 

.05

.11 

1.54 

.01 

.01 

.26 

.03

.64

J 99. 57

6

83.50 

.78 

.32

1.82 

3.85 

.21 

.27

} 6.40

2.60

99-75

7

85.58 

.74 

.09

.01 

.64 

.58 

.28

{ 5.50 

6.17 

.03 

.01 

.02 

.00

« 99. 77

8

92.6 

1.0 

.23 

.14 

.07 

.36 

.41 

.21

5.5 

.04 

.02 

.42

101.0

I Includes C 0.06.

» Includes S 0.09, BaO 0.03.

1. Silcrete, Australia (Williamson, 1957). B. C. Terrell, analyst.

2. Silcrete overlying lower Dwyka Shale, South Africa (Frankel and 

Kent, 1937). J. J. Frankel, analyst.

3. Chalcedony nodule in clay, Virginia (Maxwell, 1953).

4. Silicifled oolite from beneath tuff bed, Twin Creek Limestone, Jurassic, Lincoln County, Wyoming (B. R. Cressman, U. S. Geological 

Survey, unpublished data). S. D. Botts, M. D. Mack, and H. H. 

Thomas, analysts.

5. Petrified wood, Arizona (Maxwell, 1953).

6. Chert nodule from gypsum, Eocene, France (Cayeux, 1929, p. 672). 

Laboratorie de Chimie de la Prefecture de Police, M. Lassieur, 

director.

7. Siliceous sinter, New Zealand (Grange, 1937, p. 118). F. T. Seelye, 

analyst.

8. Primary opaline sinter, Steamboat Springs, Nevada (D. E. White, 

U.S. Geological Survey, unpublished data). H. F. Phillips, 

Leonard Shapiro, and Katrine White, analysts.

1925) .5 Much of the iron in the red radiolarian jaspers 

is in the form of hematite (Cayeux, 1929, p. 324), in unweathered black radiolarian chert as pyrite (Hoss, 1957, 

p. 62; Cayeux, 1929, p. 333), and in spicular chert as 

glauconite or pyrite or both (Cayeux, 1929, p. 255-301). 

In those cherts containing admixed pyroclastic material, iron may occur in augite, hornblende, magnetite, 

and ilmenite, and the work of Eobertson and Twedily 

(1953) suggests that much iron in the younger diatomaceous rocks may be in an alumina-ferric oxidesilica gel.

The iron content of bedded chert is generally less than 

that of the associated sediments. For example, the average Fe2O3 content of 13 samples of black radiolarian 

chert from the Carboniferous of Germany is 2.4 percent, 

whereas six interbeds of argillite average 3.6 percent 

(Hoss, 1957, p. 65, 67). Even the high-iron content 

of the red radiolarian chert analyzed by Jakob is less 

than that found in many red clays (Clarke, 1924, p. 

516; Ishibashi and Harada, 1938).

On figure 3, the total iron as Fe2O3 is plotted against 

A12O3 for analyses of radiolarian chert. The Fe2O3/ 

A12O3 ratio in most of the radiolarian cherts is about

0 Chert from iron formations of Precambrian age may, of course, contain much more iron.

10

UJ

O

cc

UJ 

Q_

CC

< 

O

x 

x x

Average of nine pelagic clays 

(water-free; Revelle, 1944)

-X Average of six siliceous oozes 

(water-free; Revelle, 1944)

4 6 8 10 12 14 

AI 2O3 , IN PERCENT

FIGURE 3. Relation of Fe2Og to Al2Og in 46 radiolarian cherts.

16 18
T12 DATA OF GEOCHEMISTRY

the same as in modern pelagic clay and siliceous ooze, 

and the iron content may be explained by the addition 

of SiO2 , either as radiolarian tests or as inorganic silica, 

to typical marine lutite. However, a few radiolarian 

jaspers contain considerably more iron than can be explained in this manner. Inasmuch as these high-iron 

cherts are associated with volcanic rocks, the iron may 

have had a local source.

Excluding the sample from the Phosphoria Formation, the Fe2O3/Al2O3 ratios of the spicular chert listed 

in table 3 are all less than 1 and average 0.53, only 

slightly more than 0.44, the ratio in the average shale 

(Clarke, 1924, p. 30). Spicular chert of the Phosphoria 

Formation at one locality in Montana contains 2.8 to 

4.9 percent Fe2O3 , about the same as in interbedded 

mudstone, but the Fe2O3/Al2O3 ratio in the chert averages 3.1 as compared with 0.61 in the mudstone (Swanson and others, 1953, p. 29). The iron in chert of the 

Phosphoria Formation is now present as pyrite, but 

inasmuch as these cherts occur in the upper part of a 

highly carbonaceous black shale sequence, the immediate source of much of the iron may have been organic 

matter, for marine plants are known to concentrate 

iron (Harvey, 1955, p. 144).

Too few analyses are available to compare the iron 

content of chert nodules with that of the country rock, 

but a few such analyses (Bosazza, 1937, p. 182; Cayeux, 

1929, p. 495, 498; Lamar, 1953, p. 26) suggest that the 

content does not differ markedly. However, Newell 

and coworkers (1953, p. 162) note that chert lenses and 

nodules in the Bone Spring Limestone (Permian) of 

Texas commonly contain more pyrite than the surrounding limestone.

MANGANESE

The manganese content of chert is of particular interest because of the association of sedimentary manganese deposits with radiolarian chert. A number of 

radiolarian cherts, both lydites and jaspers, contain 10 

or 20 times as much manganese as the average igneous 

rock or the average shale (fig. 4 and table 4), but none 

of the cherts for which analyses are available is more enriched than much of the siliceous ooze and clay of the 

oceanic basins. However, Taliaferro and Hudson 

(1943, p. 23Y) describe manganiferous opal in chert 

of the Franciscan formation that must contain considerably more manganese than any samples on figure 4 

or table 4.

The analyses of the Arkansas and Caballos Novaculites are all much lower in manganese than are those of 

other bedded cherts, the highest value reported being 

0.0011 percent Mn. However, the upper part of the 

Arkansas Novaculite in parts of Oklahoma and Arkansas contains as much as 0.41 percent Mn in the form

of either manganiferous calcite or rhodochrosite (Miser, 

1917, p. 80; Goldstein and Hendricks, 1953, p. 430; 

Crittenden, in Hewett and others, 1956, p. 188).

The manganese content of chert in carbonate rock is 

generally quite low, nearly all samples containing less 

than 0.01 percent Mn. Pieruccini (1951a, p. 52) lists 

the manganese contents of 17 chert layers and nodules 

from Mesozoic limestone of the central Apennines; the 

average content is 0.0052 percent Mn (0.0067 percent 

MnO) and the highest value 0.020 percent Mn (0.026 

percent MnO). Pieruccini's samples are therefore 

somewhat more manganiferous than the nodular cherts 

plotted on figure 4, but they are considerably less manganiferous than most bedded cherts. The few available analyses show that chert nodules contain considerably less manganese than the surrounding carbonate 

rock (Pieruccini, 1951a, p. 52; Bosazza, 1937, p. 182), 

as might be expected if most of the manganese were 

originally present in the calcite of the parent rock.

RELATION OP IKON TO MANGANESE

The iron and manganese contents of chert and related 

siliceous sediments are plotted on figure 4. In general, 

the iron content increases but the ration of Fe/Mn decreases as the manganese content increases. The 

Fe/Mn ratio is higher in nonvaculite and nodular chert, 

both of which are associated with sublittoral sediments, 

than it is in radiolarian chert. Correns (1937) reports 

a higher Fe/Mn ratio in shallow-water sediments than 

in deep-water sediments in the equatorial Atlantic. 

Comparison of the ratios in radiolarian rocks (the average Fe/Mn ratio of all radiolarian cherts in table 4 

is 20) with those in the following table, recalculated 

from Correns' data, supports the interpretation of most 

radiolarian cherts as bathyal or abyssal deposits:

TABLE 9. Relation of iron and manganese to depth of water in 

sediments of the equatorial Atlantic Ocean 

[Recalculated from Correns, 1937, p. 231]

Fe - 

Mn.........

Fe/Mn.....

Values for iron and manganese for indicated depth range in meters

0-200

2.60 

.0294 

88.0

200-2,000

4.27 

.0573 

75.0

2,000-3,000

4.98 

.394 

12.6

3,000-4,000

5.64 

.320 

17.6

4,000-5,000

4.77 

.238 

20.0

5,000-6,000

4.79 

.525 

9.0

The explanation of the concentration of manganese 

relative to iron in deep-sea sediments that was originally advanced by Murray and Irvine (1895) and was 

recently supported by Krauskopf (1957, p. 78) is that 

manganese oxide precipitated in shallow-water sediments is reduced in the presence of organic matter, 

redissolved, transported to deeper water, and concentrated in deep-sea sediments where the content of organic matter is small. Iron is less readily reduced; if
NONDETRITAL SILICEOUS SEDIMENTS T13

10.0 r:~ 1 I 1 1 I 1 1 1 [ 1 1 1 1 1 1 1 1

:

-

-

_ _» > /

: //

<$>y

/ o

-

9 + '* © e + ^/

-~ + /* $'/

" + /f> ^/

- * / y

/ / 

- / /

/ /

/ / / /

/ 

/

i i i i i i i i !/ i i i i i i i i

 i i i i i i i >-] i i i i \~\\y\ \ i i r rr

/ Average igneous / 

/ rocks (Green, 1953) / * 

/ V A *

/ x * */ *\

/ o Average shale / &

^ (Vinogradov, 1956) /

°/° ° o / A

/ ° /

/ o / o

/ e o ° / A ° EXPLANATION /

/ A 

J/ A Red and green radiolarian chert

/ °

/ Black radiolarian chert

/ »

/ Novaculite

/

/ ° o +

Nodular chert

7

Pelagic clay (Rotschi, 1952)

V

Siliceous ooze (Revelle, 1944)

i i i i i i i i 1 i i i i i i i i 1 i i i i i i

TT

1

-

-

~

-

-

_

_

-

_

, ,

1.0

UJ

o

cr

UJ 

Q_

0.1

0.01

0.0001 0.001 0.01 0.1

Mn, IN PERCENT

FIGURE 4. Relation of iron to manganese in chert and related rocks.

1.0 10.0

reduced, it is more likely to be precipitated as pyrite and 

is thus deposited more readily in shallow-water sediments. It is therefore surprising that the Fe/Mn ratios 

of the black and somewhat carbonaceous lydites plotted 

on figure 4 are not notably higher than those of the 

radiolarian Jaspers; in fact, the average Fe/Mn ratio 

of the lydites listed in table 4 is only 7.2, considerably 

lower than 29.8, the average ratio for the radiolarian 

jaspers in the same table. Planktonic foraminifera are 

apparently able to extract manganese from sea water 

(Goldberg and Arrhenius, 1958, p. 195), and manganese may have been added to some black radiolarian 

sediments in organic remains.

TITANIUM

The relation of TiO2 to A12O3 in the nondetrital siliceous rocks is shown on figure 5. No marine or lacustrine siliceous sediment is enriched in titanium with 

respect to either the average igneous rock or the average 

shale, but the ratio TiO2 /Al2O3 ranges widely from that 

of the average shale, mostly on the side of high titanium. 

The titanium content of pelagic clay in the oceans has 

been found to be relatively constant. Arrhenius (1952, 

p. 31) determined a value of 0.73 percent TiO2 in pure 

lutite of the Eastern Pacific which is the same as the 

TiO2 content of the average shale (Vinogradov, 1956). 

High concentrations of titanium in pelagic sediments invariably result from the admixture of mafic pyroclastics (Goldberg and Arrhenius, 1958, p. 189; Correns, 

1937).

Some of the deviations of the TiO2/Al2O3 ratios of 

chert from that of the average shale may also be explained by differences in the composition of the admixed elastics. Felsic volcanic ash probably accounts 

for the low ratios in the black radiolarian chert of 

Hesse (Hoss, 1957), and many of the radiolarian and 

diatomaceous cherts in which the ratio is relatively 

high are associated with and probably contain mafic 

pyroclastics.

The relatively high TiO2 content of other cherts cannot be accounted for so easily. The spicular cherts, for 

example, are certainly not directly associated with volcanics. Kaminskaya (1944) found that many marine 

organisms concentrate titanium, that plants generally 

contain more than animals, and that organisms having 

high calcium, silicon, and iron contents generally also 

have a higher titanium content, and titanium is apparently concentrated by some siliceous sponges (Bowen 

and Sutton, 1951) and diatoms (Griel and Kobinson, 

1952). It is therefore possible that the high 

TiO2/Al2O3 ratios in the spicular cherts and carbonaceous radiolarian cherts of Thuringia reflect the presence of biogenous titanium. Biogenous titanium
T14

10.0 IT

DATA OF GEOCHEMISTRY

1.0

0.1

o i0.01

I I I I I I I I

Average igneous 

rocks (Green, 1953)

A*/ Average shale 

(Vinogradov, 1956)

s

0.001

0.01

\ S\ ill

EXPLANATION

D

Marine diatomite

 

Fresh-water diatomite

A

Radiolarian chert

A

Black radiolarian chert, 

Carboniferous, Hesse, Germany

i

Black radiolarian chert, 

Silurian, Thuringia, Germany

e

Spicular chert, 

Late Jurassic, Poland

Spicular chert, 

Paris Basin

Spicular chert, 

Permian, Nevada

Novaculite, 

Arkansas and Texas novaculites

Other bedded chert

Nodular chert

0

Silicrete

0.1 1.0 10.0 

AI203 , IN PERCENT

5^ Relation of T1O2 to A12O3 In chert and related rocks.

100

might, conceivably, be substituting for silicon in the 

opaline tests; however, Goldberg (1957, p. 351) suggests that the titanium is scavenged by colloidal iron 

that is taken up by the organisms.

The higher TiO2/Al2O3 ratio in those nodular cherts 

with higher A12O3 contents is puzzling, but the number 

of analyses is too small and the possibility of analytical 

bias too great to be certain whether or not the differences in the ratio are significant.

Pieruccini (1951b, p. 66) has found the titanium content of chert of Mesozoic age from the Apennines to be 

of the same order of magnitude as in the associated 

limestone. The average TiO2 content of his chert samples is 0.030 percent as compared with 0.044 percent 

TiO2 in the limestone. Pieruccini (1951b, p. 70) believes that the titanium is present as orthotitanic acid 

which is soluable in a weak alkaline solution containing CO2 ; thus the titanium content should be low in 

limestone but high in noncalcareous shale.

The titanium content of silcretes is generally about 

twice that of the average igneous rock, the average 

shale, and the clay in which they occur. Most of the 

titanium is in rutile (Williamson, 1957; Mountain 

1952; Frankel, 1952; Frankel and Kent, 1937). The 

exact manner in which silcretes originate is not known, 

but they are undoubtedly inorganic and probably can be 

deposited from either surface or ground waters in areas 

of tropical weathering (Bassett, 1954; Mountain, 1952; 

Frankel and Kent, 1937), probably where the water 

passes from a weathering environment with a pH 

greater than 9.8 to a less alkaline environment (Siever, 

1957, p. 832).

SODIUM AND POTASSIUM

The alkali-metal content is generally high in those 

siliceous rocks with a high-aluminum content and low 

in those with a low-aluminum content; most of the potassium and much of the sodium is undoubtedly present
NONDETRITAL SILICEOUS SEDIMENTS T15

in clay minerals. The median value of the ratio K2O/ 

Na2O in sedimentary rocks is approximately 1.7 (Green 

and Poldevaart, 1958, p. 105) and the average ratio 

in clay and shale is about 3.1 (Vinogradov, 1956). 

K2O exceeds Na2O in most chert analyses although the 

ratio ranges widely. In some cherts, however, the 

Na2O content nearly equals that of K2O and in a few 

analyses actually exceeds it. Relatively high sodium 

contents in some radiolarian and diatomaceous rocks result from admixed volcanics. This is clearly shown 

in analyses of radiolarian cherts of Carboniferous age 

of Hesse (Hoss, 1957); sodium is the dominant alkali 

metal of tuffaceous chert in which it is present in albite, 

but potassium is more abundant in those cherts with 

little or no volcanic component. In some diatomaceous 

rocks, the sodium may be an exchangeable base in an 

alumina-ferric oxide-silica gel (Robertson and Twedily, 

1953). No explanation has been advanced to explain 

the low K2O/Na2O ratios in some spicular and nodular 

cherts, but they may result from the presence of authigenic albite or, in the opaline rocks, from the presence 

of sodium in the interstices of the tridymite lattice. 

Whatever the explanation, the sodium content does not 

seem greater than in many carbonate rocks.

TRACE ELEMENTS

Few cherts have been analyzed for trace elements. 

The analyses that are available (table 10) indicate that 

although certain cherts are enriched in some trace elements with respect to the average igneous rock, the enrichment can generally be ascribed to the admixed 

material.

The only cherts showing clear evidence of enrichment 

are the black cherts. At least some of the black radiolarian cherts are enriched in copper, molybdenum,

nickel, lead, and vanadium, and the black chert sample 

from the Maravillas Chert may be slightly enriched in 

arsenic. The samples showing the most enrichment are 

those from Thuringia which are also the most carbonaceous. All these elements are commonly enriched in 

black shales (Krauskopf, 1955), so their enrichment in 

black chert probably results from the presence of organic matter. The form in which these metals occur is 

not known. Some may be present as metal-organic compounds (Krauskopf, 1955, p. 421); the vanadium may 

occur in clay minerals or micas (W. W. Rubey, quoted 

in Krauskopf, 1955, p. 421) or in the iron oxide minerals 

(Hoss, 1957, p. 71).

The trace-element content of radiolarities from three 

localities in Switzerland were determined by semiquantitative methods by Grunau and Hiigi (1957). One 

group of samples was enriched in chromium and titanium, another group was chromium-free and titaniumpoor, and the third was enriched in copper, lead, and 

strontium. The chromium and titanium in the first 

group were thought to be caused by the presence of clastic serpentine and peridotite particles which were also 

thought to be the cause of the green color of the chert.

Giannini and associates (1950) found the Ni/Co ratio 

to average 0.37 in chert nodules of Mesozoic age from 

the Apennines and 0.52 in the surrounding limestone as 

compared to 2.5 or even 10 or 20 in eruptive rocks. 

They interpret the lower ratio in limestone and chert 

as resulting from the activity of organisms that require 

cobalt in metabolism.

ISOTOPIC COMPOSITION 

SILICON

The relative abundances of Si28 and Si30 have been 

investigated by Marsden (in Rankama, 1954), Reynolds

TABLE 10. Trace-element content of chert in parts per million

Element

As. 

Co... .... - 

Or..-- 

Cu 

Ga.... ... .... -

Ge . 

La ... ... -

Li ... ...

Mo... ... 

Ni ....- -

Pb. - 

V - - -

Zn .

Zr .... ... 

Igneous 

rocks 1

2 

25 

120 

60 

18 1-2 

40 

40 1-2 

60 

16 

30 

80 

170

Sandstone *

1

.3 

35 

10-20 

12 1-2 

30 

15 

<1 

2 

7 

10-20 

12 

200?

Limestone *

1

.2 

11 

5 

4 

.2 

1-10 

5 

0. 1-0. 5 

10 

10 

20 

4 

20?

Shale »

 10 

"20 

»90 

50 

20 

2 

40-90 

60

82

»70 

»20 

«130 

90 

160

Radiolarian chert

Black

Carboniferous, 

Germany *

Average

15

80

100

165

Maximum

20

150

180

270

Black tuffaceous

Carboniferous, 

Germany *

Average

25

>150

80

670

Maximum

30

150

160

970

Black

Carboniferous, Germany !

150

210

1,100

Red

Jurassic, California 

0.5

.9

26 

4.4

Other bedded chert

Precambrian, 

Minn.8

0.6

.7

8 

3.2

Upper Ordovician, 

Texas'

10.1

.0

9 

11.4

Arkansas and 

Caballos 

Novaculites '

Average

0.8

.4

3.0 

1.0

Maximum

1.0

1.5

13 

3.0

Nodular chert 

in carbonate 

rock 7

Average

1.0

.3

20

2.4

Maximum

1.6

2.0

36 

3.4

i Green, 1953, aud Fleischer, written communication, 1960.

» Krauskopf, 1955, p. 416; Pettijohn, written communication, 1960 (sandstone); 

Turekian and Wedepohl, 1961.

« Vinogradov, 1956, Krauskopf, 1955; Turekian and Wedepohl, 1961. 

«Hoss, 1957.

s Hoss, 1957, 1 sample.

« Maxwell, 1953, 1 sample.

? Maxwell, 1953, 7 samples.

s Enriched in black shale.

9 Possibly enriched in black shale (Krauskopf, 1955, p. 420).
T16 DATA OF GEOCHEMISTRY

and Verhoogen (1953), and Allenby (1954), and the results are summarized and discussed by Rankama (1954, 

p. 273). Most of the available data for the nondetrital 

siliceous sediments are listed in table 11; inasmuch as 

the different investigators used different standards, 

their results are not strictly comparable (Rankama, 

1954, p. 273) and are therefore listed in separate 

columns.

TABLE 11. Relative abundance of Si isotopes in nonfragmental 

siliceous sedimentary rocks

Do.......... ...__-_.......__.___--..-..-

Flint, Dover Chalk, England. _____ . __ .

Silicifled wood...... __ ................... 

Do...-...-...-..-......-....... . .

Do.. - _ . -- 

St. Peter Sandstone, Wisconsin _______

Marsden, 

in 

Rankama, 

1954 (Si28/Si30)

29.34 

29.55 

29.56 

29.59 

29.48

29.54

29.41 

29.50

29.21

Allenby, 

1954

(Si28/Si80)

29.73

30.10

30.02 

29.86

Reynolds 

and 

Verhoogen, 

1953 («)i

-1.6 

+.5

+1.0 -1.8

-2.1

-.1 

-1.1 -1.1

1 & 100.(Si30/Si28)_ (Si30/Si*8)0 whnro fammnn ln ^ , n,Mnn «^^

In a theoretical discussion of the partition of silicon 

isotopes, Grant (1954, p. 240) concluded that heavier 

isotopes should favor the precipitated phase and that 

silica precipitated from aqueous solutions either organically or inorganically should therefore contain concentrations of Si30 . The results of Allenby and Reynolds 

and Verhoogen indicate that marine accumulations of 

siliceous organisms are enriched in Si30 , which is in accord with Grant's conclusion, but Reynolds and Verhoogen (1953, p. 233) attribute the concentration to selective organic processes. However, Marsden's data 

from Lake Windermere indicate that at least one genus 

of diatoms concentrates the lighter isotope. Reynolds 

and Verhoogen (1953, p. 233) believe the enrichment 

of the fresh-water diatomite in Si28 may have resulted 

from a volcanic source of the silica and cite the isotope 

ratio in siliceous sinter as supporting evidence. If their 

conclusion is correct, the marked enrichment of the one 

analyzed sample of radiolarian chert from the Franciscan Formation in Si30 is of considerable interest inasmuch as the silica in the Franciscan has generally been 

ascribed to a volcanic source. The enrichment of the 

flint from the Dover chalk in Si28 is anomalous and Reynolds and Verhoogen did not attempt an explanation. 

The equilibrium constant of the isotope-exchange reaction is a function of temperature, and silica deposited 

from cool water might be expected to contain a higher 

proportion of Si30 than silica deposited from warm 

water, but the few data and the uncertainty as to the 

isotopic composition of the liquid phase preclude any 

evaluation of the temperature effect.

OXYGEN

The O18/O16 ratio has been determined for a few samples of chert and diatomite by Baertschi (1950), Silverman (1951), Clayton and Epstein (1958), and Engel, 

Clayton, and Epstein (1958). Their results are listed 

in table 12 along with a few determinations of the ratio 

in quartz from igneous rocks; the standard for all determinations is Hawaiian sea water 6. The concentration of O18 in the siliceous sediments is evident. The 

oxygen-isotope ratio in silica precipitated from marine 

water might be expected to vary in the same manner as 

the ratio in carbonates (that is, O18 would be more concentrated in silica deposited from cold water than warm 

water), but a silica-oxygen temperature scale has not 

been worked out for the range of temperatures in the 

marine environment, and it may not be possible to do so 

(Urey and others, 1951, p. 402).

Hydrothermal alteration decreases the O18/O16 ratio; 

thus Engel and others (1958) found that in chert occuring in the unaltered Leadville Limestone of Mississippian age, 8 ranged from 28.0 to 29.4 whereas in chert 

from hydrothermally altered areas 8 ranged from 22.2 to 

24.2. Metamorphism also decreases the ratio (H. L. 

James, oral communication, 1958).

TABLE 12. Relative abundance of oxygen isotopes in nonfragmental siliceous sedimentary rocks

Sample

5. Flint, Dover Chalks...... __ .. __________________ . _

6. Black chert in fine-grained limestone; Mississippian, Colorado 2 . ..

 a (/,s(rri l)l,000, where^S;

\R (standard) / O18

«"

34.1

30.3

29.4

29.4

29.3

29.2 

28.6

28.0

10.4

9.6

8.9

2 Clayton and Epstein, 1968.

» Silverman, 1951.

* Engel and others, 1958.

SOLUBILITY OF SILICA AT LOW TEMPERATURES

Reliable experimental determinations of the solubility of quartz at room temperatures have not been 

made, but the extrapolation of Kennedy's (1944) curves 

for the solubility of quartz under hydrothermal conditions indicates extremely low solubilities at tempera6 The Hawaiian sea water has a 8=0.2 relative to mean ocean water 

(Clayton and Epstein, 19&8, p. 359).
NONDETRITAL SILICEOUS SEDIMENTS T17

tures prevailing at the surface of the earth. Thermodynamic calculations of Siever (1957, p. 825) yielded 

results of 7.25 and 14 parts per million for the solubility 

of quartz in pure water at 25 °C. Although many surface waters are undoubtedly supersaturated with respect to quartz, the attainment of equilibrium is very 

slow, and no direct evidence exists that quartz is precipitated directly from waters in the sedimentary environment except during diagenesis (Siever, 1957, p. 834).

The amount of SiO2 dissolved from amorphous silica 

in pure water is 60 to 80 ppm at 0°C, 100 to 140 ppm at 

25°C, and 300 to 380 ppm at 90° C (Krauskopf, 1956, 

p. 23; Okamoto and others, 1957, p. 125, determined 

solubilities about 50 to 70 percent greater than those 

of Krauskopf). Below about pH 9 the dissolved silica 

is nearly all in the form of monosilicic acid, H4SiO4 

and the solubility is little affected by changes of pH, 

but above pH 9 the solubility increases rapidly as the 

alkalinity increases (Krauskopf, 1956, p. 23). The 

amount dissolved is about the same in artifical sea water 

as in fresh water (Krauskopf, 1956, p. 24). Bruevich 

(1953) concluded from the average maximum silica 

content of interstitial waters in unconsolidated sediments that the solubility of silica in sea water is about 

70 parts per million, which agrees fairly well with 

Krauskopf's experimental results.

The apparent solubility of silica in water is greatly 

reduced by the addition of either aluminum oxide or 

powdered aluminum, probably by the formation of an 

insoluble aluminum silicate on the surface of the silica 

phase (Her, 1955, p. 14). Okamoto and others (1957, 

p. 130) report that the addition of aluminum sulfate 

also reduces the solubility of silica with the greatest 

reduction in solubility for a given amount of aluminum 

being between pH 8 and 9.

The oceans and nearly all rivers contain much less 

silica than the saturation values determined in the 

laboratory for amorphous silica, the maximum content 

reported in the oceans being 26.7 ppm SiO2 (Bruevich, 

1953), so direct inorganic precipitation of silica should 

not be expected. However, Bien and others (1958) have 

found that most of the dissolved silica in Mississippi 

River waters is precipitated, mostly by inorganic processes, when the river water mixes with water of the 

Gulf of Mexico. Bien and his coworkers conclude that 

the process is largely an adsorption of soluble silica 

on suspended matter as it comes in contact with electrolytes of the Gulf water, although some is probably 

removed by co-precipitation with aluminum ions.

ORIGIN

The very common association of deposits of siliceous 

organisms, particularly diatoms, with volcanic ash has

been noted by many authors (Bramlette, 1946, p. 39). 

This association has led Taliaferro (1933, p. 54) and 

Bramlette (1946, p. 41) among others to suggest that 

much of the silica and perhaps much of the other nutrients utilized by the organisms may have been released 

by the weathering of volcanic ash. Trask (1932, p. 

237) emphasizes the necessity of adequate nitrate for 

high organic activity, as in areas of turbulence or upwelling (Harvey, 1955, p. 99-101). Much of the nitrate 

and phosphate must thus be available through the 

cycle of renewal and upwelling, but unusual supplies of 

silica from the volcanics might be critical for long-continued extraction of silica that is being permanently 

removed as the opaline tests of diatoms (Bramlette, 

written communication, 1958).

In addition to extracting soluble silica from water, 

some diatoms are capable of obtaining silica directly 

from aluminosilicate minerals (Murray and Irvine, 

1889; Hutchinson, 1957, p. 790). Gawel (1950) has 

noted that cherts (mostly radiolarian) in the Flysch of 

the Carpathians occur in argillaceous parts of the sequence but are uncommon in the more calcareous parts; 

he concludes that the siliceous organisms derived their 

silica from clays and that their growth was favored by 

periods of argillaceous deposition.

The apparently inorganic silica in bedded chert has 

undoubtedly formed in several different ways, but the 

relative importance of the different sources and processes cannot be assessed. Bramlette (1946, p. 50-52) 

has shown that much matrix silica in the Monterey 

Formation has resulted from the solution, migration, 

and redeposition of the silica in diatom f rustules. Arrhenius (1952, p. 85) has found such a process operative 

in some sediments of the East Pacific, and Sujkowski 

(1932, 1933b) has presented convincing evidence for a 

similar origin of matrix silica in radiolarian cherts of 

Poland. The common association of black shale and 

bedded chert indicates that many cherts such as the 

Fort Payne Chert that show no direct evidence of organic origin were deposited in areas of high organic 

activity and suggests that they may have resulted from 

the reorganization of organic silica.

Silica in bedded chert and siliceous shale can also be 

derived from the alteration of volcanic ash (Bramlette, 

1946, p. 44; Eubey, 1928, p. 168-169), probably during 

the early stages of diagenesis. Such a process may have 

been of great importance in the formation of chert from 

tuffaceous eugeosynclinal sediments such as those of the 

Paleozoic of central and western Nevada (E. J. Roberts, 

oral communications, 1959).

Inasmuch as sea water is undersaturated with respect 

to amorphous silica, the hypothesis of the origin of 

bedded chert by direct precipitation seems no longer
T18 DATA OF GEOCHEMISTRY

tenable except locally in areas of volcanism (Krauskopf, 

1956, p. 25). If the silica content of sea water is governed by a combination of adsorption processes and 

organic extraction, the silica content of the water may 

have varied widely through geologic time, particularly 

in response to evolutionary development of siliceous 

organisms.7 Siever (1957, p. 838) believes that radiolaria and sponges, and later diatoms, were able to hold 

down the silica concentrations in sea water sufficiently 

to prevent inorganic precipitation, at least from Paleozoic time on, basing his conclusion on the similarity of 

Paleozoic cherts to those of more recent geologic age. 

Inorganic precipitation may have been operative on a 

a larger scale in the Precambrian before evolution of the 

radiolaria (see also Kaleda, 1956).

The common association of radiolarian chert with 

volcanic rocks has led many investigators to conclude 

that silica was supplied either by the volcanics themselves (Krauskopf, 1957, p. 75) or by associated siliceous springs (Davis, 1918, p. 402) in amounts exceeding the solubility of amorphous silica in normal sea 

water. As the thermal waters would cool, the silica 

would be precipitated inorganically; any included 

radiolaria would be incidental. Stephens (1956, p. 

305) has proposed a slight modification of the theory to 

account for chert of Paleocene and Eocene age in 

Borneo. He proposes a volcanic source, but cites evidence to indicate that the chert resulted from postdepositional silicification of argillaceous sediments.

The close association of radiolarian chert and lava 

flows such as that in the Franciscan Formation of California (Taliaferro and Hudson, 1943) does strongly 

suggest a volcanic source for the silica, but the association does not in itself prove it. The function of the 

flows might have been merely the establishing of a 

marked thermal gradient which would facilitate solution, migration, and redeposition of disseminated silica 

in the sediment.

There is general, but by no means universal, agreement that nodular cherts in carbonate rock were formed 

by replacement of the host carbonate rock (PettiJohn, 

1957, p. 439). Certainly many chert nodules exhibit 

definite evidence of origin by replacement, but the field 

and petrographic evidence is inconclusive for many and 

perhaps most occurrences; the principal evidence 

against origin of these nodules by primary precipita7 Of the major silica-secreting organisms, sponges are known from the 

latest Precambrian, radiolarians from the earliest Paleozoic and possibly 

from the Precambrian, diatoms from the early Mesozoic, and silicoflagellates from the Late Cretaceous. According to Vinogradov (1953), 

siliceous sponges became less important during the middle Paleozoic 

when calcareous sponges evolved ; yet spicular cherts of considerable 

thickness and extent are known in rocks of late Paleozoic, Mesozoic, 

and Tertiary age.

tion is the recent experimental evidence indicating that 

sea water is undersaturated with silica.

According to Chilingar (1956), limestones with a 

high concentration of chert nodules and stringers generally have high Ca/Mg ratios, indicating that the 

high pH and temperatures that favor the deposition of 

dolomitic limestone do not favor the precipitation of 

chert. If the Ca/Mg ratio is higher in the chert bands 

than in the adjacent limestone bands, Chilingar interprets the cherts as probably being primary.

Giannini and others (1950) explain chert bands and 

layers of nodules in limestone of the central Apennines 

as having resulted from periodic solution of calcium 

carbonate from an original uniform siliceous-calcareous 

sediment, and Dunbar and Eodgers (1957, p. 248) describe light-colored vitreous chert that has resulted from 

the weathering of a dolomite containing 20 percent of 

finely divided silica.

Organic skeletal remains disseminated through the 

sediment were an adequate source of silica for some occurrences of nodular chert (Lowenstam, 1942b; Andrusov, 1932; Eichardson, 1919, p. 539). For others, the 

paucity of siliceous organisms in either the chert or 

the surrounding rock has been taken as strong evidence 

of an inorganic source (Biggs, 1957). The recent investigation of Bien and coworkers (1958) indicates that 

much inorganically precipitated silica is disseminated 

through sediments and would be available for redistribution, but most such silica would be in argillaceous 

deltaic sediments, an environment in which both bedded 

and nodular cherts are uncommon.

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NONDETRITAL SILICEOUS SEDIMENTS T19

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T20 DATA OF GEOCHEMISTRY

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NONDETRITAL SILICEOUS SEDIMENTS T21

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T22 DATA OF GEOCHEMISTRY

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INDEX

Page

Aluminum, relation to iron___________________________ Til-12

relation to silicon_______________________________ 6-10

Analyses ________... 5-6; tables 1-8, 10

Bedded nonfragmental deposits... ....................................... 2-4

- .- .. . 18

_______________________ 1

........__.__.__................. 5

....._.............................. 15

. ..-. ...-... .... - 15

Constituents in chert, major___________________________ 6-10

minor.. ...______________________________ 10-15

Calcium, relation to magnesium. 

Chert, defined _ .....

Cristobalite ____ . 

Chromium, in cherts............

Cobalt, relation to nickel... .

Copper, in cherts 

Crystal chemistry of silica minerals..

Diatom ooze __ . ___. 2

Diatomaceous chert .... _________________ 2

Diatomite.. ____ ....____........_............_.... 1,2

Iron content __ . ___.________ 7,10-12, 13; tables 1, 3-7 

Iron, relation to aluminum __________________________ 11-12 

relation to manganese____________________________ 12-13 

Isotopic composition of oxygen_________________________. 16 

Isotopic composition of silicon....... . __________________ 15-16

Jasper, radiolarian . ... . . ....__. 2,3

Lead, in cherts ._.... 15

Lgota beds, chert in ...______ .....____ 4

Lydite...... ........___...__......_................................ 2,3

Magnesium, relation to calcium_________________________ 18 

Manganese, relation to iron___________________________ 12-13 

Manganese deposits, accompanying radiolarian jaspers...__________ 3 

Menelitic shale, of the Carpathians_.......__________________ 2

Molybdenum, in cherts_____________________________ 15 

Monterey Formation of California, marine diatomite..____________ 2

Nickel, as a trace element in cherts, 

relation to cobalt _........

Page

Nodular chert in carbonate rock, occurrence T4 

origin..... ___ ___ .................................. 18

Opal____..__ . 5 

Opaline chert, conversion to quartz and chalcedony _ 5 

Organic skeletal remains in siliceous sediments 18 

Origin of siliceous deposits_______.. _ 17-18 

Oxygen isotopes. 16

Potassium, relation to sodium__ _.___ __ 14-15

Quartz.. 6

Radiolarian chert, association with volcanic rocks 18

occurrence___ . 2-3

Radiolarian ooze_____. ____.. . . __ 2

Radiolarite___._.__._-- ... . -. - 1,2

Shales, siliceous, defined . 1

Silcrete, analyses__ 11

defined..... . ........... . . ... 1

Silica, solubility of _ _ . . __-_.... 16-17

Silica, minerals, crystal chemistry_ .. 5 

Silicon, relation to aluminum_______.___..____._ . 6-10 

Silicon isotopes...... 15-16

Sodium, relation to potassium.. 14-15 

Solubility of silica__._.____ .... _.....__.... ... 16-17

Spicular chert_______.________...- ___ 3-4 

Spiculeooze 3 

Spiculite__..___............. . . . 1,3

Titanium, in cherts. .. ____ 15

relation to aluminum_______... __ 13-14

Trace elements in chert_..__.. 15

Tridymite___ 5

Vanadium, in cherts... 15

Water depth, in accumulation of radiolarian cherts ____.__ ... 3 

relation to concentration of iron and manganese __.... 12-13

o

T23