I~ 

/ 

Zeolites and Associated Authigenic Silicate 

Minerals in Tuffaceous Rocks of the Big 

Sandy· Formation, Mohave County, Arizona 

By RICHARD A. SHEPPARD and ARTHUR J. GUDE 3d 

GEOLOGICAL SURVEY PROFESSIONAL PAPER 830 

Physical properties, chemistry, and origin of 

silicate minerals formed in tuffaceous rocks 

of a Pliocene lacustrine deposit 

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON: 1973 
UNITED STATES DEPARTMENT OF THE INTERIOR 

-;f.r 

ROGERS C. B. MORTON, Secretary 

GEOLOGICAL SURVEY 

V. E. McKelvey, Director 

Library of Congress catalog-card No. 73-600206 

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

Washington, D.C. 20402 - Price $1.05 (paper cover) 

Stock Number 2401-02404 
CONTENTS 

Page 

Abstract _______________ ---- ~----------- Authigenic minerals- Continued 

Introduction ____________________________ _ Phillipsite _______________ --- __ - ____ --

Location _ __ _ __ __ _ _____ __ ___ ___ ___ ___ I Potassium feldspar _____________________ _ 

Previous work _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 2 Quartz _______________ - _ --- __ -------

Scope of investigation--------------------- 2 Diagenetic facies _________________________ _ 

Laboratory methods _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 2 Distribution _________________________ _ 

Acknowledgments _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 3 Field description _______________________ _ 

Geologic setting _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 3 Petrography _________________________ _ 

Stratigraphy and lithology of the Big Sandy Formation _ _ _ _ 4 Nonanalcimic zeolite facies ______________ _ 

Conglomerate, sandstone, and siltstone _ _ _ _ _ _ _ _ _ _ _ 4 Analcime facies _· ____________________ _ 

Mudstone _ _ __ __ __ __ ____ ___ ___ ______ _ 6 Potassium feldspar facies _______________ _ 

Limestone _______________ -------- ____ 6 Genesis of authigenic silicate minerals _____________ _ 

Tuff_______________________________ 8 Interpretation of a saline, alkaline depositional 

Authigenic minerals _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 8 environment for parts of the Big Sandy Formation __ _ 

Analcime____________________________ 8 Correlation between the water chemistry of the 

Chabazite ______________ ...! _ _ _ _ _ _ _ _ _ _ _ _ 10 depositional environment and the authigenic silicate 

Clay minerals ---------·---------------- 12 'mineralogy ..... _________ ---------------- Clinoptilolite _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 13 Formation of zeolites from silicic glass __________ _ Erionite _ ___ __ __ __ ___ ___ ___ ___ ___ ____ 15 Reaction of alkalic, silicic zeolites to form analcime ___ _ 

Harmotome -------------------------- 16 Reaction of zeolites to form potassium feldspar _____ _ 

Mordenite --------------------------- 17 References cited ______________ --- ___ - ----- Opal __ __ __ __ _ __ __ ____ __ __ ___ ___ ___ 17 

ILLUSTRATIONS 

Page 

FIGURE I. Index map showing the distribution of the Big Sandy Formation _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 2 

2. Diagrammatic sketch showing X-ray diffractometer patterns of authigenic silicate minerals _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 3 

3. Map of the Big Sandy Formation, showing sample localities -------------------------------- 5 

4. Generalized columnar section of the Big Sandy Formation __________ ..:_______________________ 6 

5-8. Photomicrographs of analcime, showing: 

5. Thin section of analcimic tuff and individual crystals and clusters of crystals _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 9 

6. Pseudomorphs after prismatic clinoptilolite _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ I 0 

7. Pseudomorphs of shards _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 10 

8. Irregular patches _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ t'l 

9. Histogram showing the distribution of Si: AI ratios of analcime in tuff _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ II 

10. Scanning electron micrograph of chabazite-rich tuff, showing rhombohedral morphology of the chabazite _ _ _ _ _ _ _ 12 

II -18. Ph9tomicrographs: 

II. Veinlet of prismatic clinoptilolite _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 14 

12. Cavity lined with phillipsite and clinoptilolite ----------------------------------- 14 

13. Sandstone cemented by finely crystalline clinoptilolite _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 15 

14. Prismatic erionite --------------------------------------------------- 16 

15. Fibrous erionite _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 16 

16. Radial aggregates of harmotome _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 17 

17. Stubby prismatic crystals of phillipsite --------------------------------------- 18 

18. Spherulitic phillipsite _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 19 

19. Stereographic pair of electron micrographs of potassium feldspar __________ -:-___________________ 20 

20. Plot of the band c dimensions of potassium feldspar ------------------------------------ 22 

21. Photomicrograph of spherulitic quartz _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 23 

22. Map showing the diagenetic facies for a composite of all the tuffaceous rocks in the Big Sandy Formation _ _ _ _ _ _ 24 

23. Map showing the diagenetic facies for the lower marker tuff of the Big Sandy Formation ___ .:... _ _ _ _ _ _ _ _ _ _ _ _ 25 

24-27. Photographs: 

24. Natural. exposure of nonanalcimic zeolitic tuff that consists of erionite and clinoptilolite and minor amounts of 

chabazite_____________________________________________________ 30 

Ill 

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18 

19 

21 

21 

21 

21 

23 

23 

31 

31 

32 

33 

33 

33 

34 

35 

35 
IV CONTENTS 

FIGURES 24-27. Photographs - Continued 

25. Natural exposure of chabazite-rich tuff _______________________ - ___ -----------

26. Natural exposure of erionite-rich upper marker tuff _____ -,- _________________ -------

27. Natural ezposure of analcime-rich lower marker tuff __________________________ ----

28-29. 

30. 

Photomicrographs of nonanalcimic zeolitic tuff, showing preservation of vitroclastic texture _______ ----

Photomicrograph of nonanalcimic zeolitic tuff, showing pseudomorphs of shards --------------------

TABLE I. 

2. 

3. 

4. 

5. 

6. 

7. 

8. 

9. 

10. 

II. 

12. 

13. 

14. 

TABLES 

Mineralogic composition of mudstone, as estimated from X-ray diffractometer patterns of bulk samples ______ -----· 

Semiquantitative spectrographic analyses of mudstone ______________________ -- ____ ----------

Formulas of selected alkalic zeolites __________________________________ ---_----------

Checklist of associated authigenic silicate minerals in tuffs of the Big Sandy Formation ___________________ _ 

Chemical analysis and composition of unit cell of analcime ______________________________ -----

Chemical analysis and composition of unit cell of chabazite ________________________________ ---

Semiquantitative spectrographic analyses of chabazite-rich and clinoptilolite-rich tuffs ____________________ _ 

Chemical analysis and composition of unit cell of clinoptilolite _______________________________ ---

Chemical analysis and composition of unit cell of erionite _________________________________ ---

Chemical analysis and composition of unit cell ofharmotome _________________________ ---------

Chemical analysis and composition of unit cell of phillipsite _____________________________ ------

Semiquantitative spectrographic analyses of potassium feldspar-rich tuffs __________________ ----------

Unit-cell parameters and boron content of authigenic potassium feldspar ___________ -----------------

Mineralogic composition of tuffaceous rocks of the Big Sandy Formation, as estimated from X-ray diffractometer patterns of 

bulk sa1nples ______________________ ---------------------------:--------

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\ 
ZEOLITES AND ASSOCIATED AUTHIGENIC SILICATE MINERALS 

. IN TUFFACEOUS ROCKS OF THE BIG SANDY FORMATION, 

MOHAVE COUNTY, ARIZONA 

By RICHARD A. SHEPPARD and ARTHUR J. GuDE 3D 

ABSTRACT 

The Big Sandy Formation of Pliocene age covers an area of about 30 

square miles in southeastern Mohave County. The formation consists 

chiefly of nearly flat lying lacustrine rocks that have a maximum exposed 

thickness of about 245 feet. Lacustrine rocks are mainly mudstone with interbedded tuff and limestone. Mudstone interfingers ·with coarser clastic 

rocks in the marginal parts of the formation, and some of these coarser 

clastic rocks, including sandstone and conglomerate, may be fluviatile. 

Tuffs make up about 2-3 percent of the exposed stratigraphic section, and 

they are about 0.5-40 inches thick, although most are less than 6 inches 

thick. Most tuffs were originally vitric and consisted mainly of silicic, fine 

to very fine grained ash and a. variable percentage of crystal and rock 

fragments. All the originally vitric material in the tuffaceous rocks is completely altered. This report summarizes the physical properties, chemistry, 

distribution, and genesis of those silicate minerals that formed in the tuffaceous rocks during diagenesis. 

Zeolites, monoclinic potassium feldspar, clay minerals, and silica 

minerals now compose the altered tuffs. The zeolites are mainly analcime, 

clinoptilolite, erionite, and chabazite. Phillipsite, mordenite, and harmotome, a rare barium zeolite, are much less abundant. Authigenic clay 

minerals are nearly ubiquitous and occur in trace to major amounts 

associated with each of the other silicate minerals. Monomineralic beds of 

zeolites, especially analcime, and potassium feldspar were recognized, but 

most zeolitic tuff consists of two or more zeolites. Analcime is associated 

with each of the other zeolites, and potassium feldspar is associated with 

analcime and most of the other zeolites. Textural evidence indicates that 

the zeolites, except analcime, formed directly from the silicic glass by a 

solution-precipitation mechanism. Neither analcime nor potassium 

feldspar seems to have formed directly from the silicic glass. Analcime 

formed from the early zeolite precursors, and potassium feldspar formed 

from analcime, as well as from the other zeolites. 

Three diagenetic facies are recognized in the tuffaceous rocks of the Big 

Sandy Formation. Those tuffaceous rocks nearest the margin of the formation are characterized by zeolites other than analcime and are termed the 

"nonanalcimic zeolit.e facies." Tuffaceous rocks in the central part of the 

ancient lake basin are characterized by potassium feldspar and are termed 

the "potassium feldspar facies." Those tuffaceous rocks intermediate in 

position between the nonanalcimic zeolite facies and the potassium feldspar 

facies are characterized by analcime and are termed the "analcime facies." 

The boundaries between the facies are iaterally gradaiional. Although no 

relict glass was recognized in any of the facies, vitroclastic texture is commonly preserved, especially in tuffs of the nonanalcimic zeolite facies. The 

distribution and the gradational character of the facies are undoubtedly due 

to a chemical zonation of the pore water during diagenesis, and this zonation was probably inherited from the chemical zonation that existed in the 

ancient lake during deposition of the tuffaceous rocks. Those tuffaceous 

rocks that contain zeolites other than analcime were deposited in the least 

saline and least alkaline water, near the margin of the lake. Farther 

basinward, these same rocks are represented by the analcime and 

potassium feldspar facies because they were deposited in water of increasing salinity and alkalinity. The lake water was probably moderately to 

highly saline with a pH of 9 or higher, except near the lake margin. 

Solution of si.licic glass by saline and alkaline pore water during 

diagenesis provided the materials necessary for the formation of the 

zeolites and, subsequently, the potassium feldspar. The paragenesis of 

silicate minerals in the tuffaceous rocks is attributed to chemical variables 

of the pore water, such as the Na++K+:H+ ratio, the Si:AI ratio, the 

proportion of cations, and the activity of H20. 

INTRODUCTION 

LOCATION 

The Big Sandy Formation of Pliocene age is chiefly a 

lacustrine deposit and is restricted to low elevations in the 

valley of the Big Sandy River in southeastern Mohave 

County (fig. 1). Most of the formation is in the east half of 

T. 16 N., R. 13 W., and the northwestern part ofT. 15 N., 

R. 12 W. The nearest settlement is Wikieup, a small desert 

town along U.S. Route 93. Kingman is the nearest principal 

city and is about 40 airline miles to the northwest. The area 

is shown as a part of the ?Y2-minute topographic maps of the 

Greenwood Peak, Gunsight Canyon, Tule Wash, Wikieup, 

and Wikieup NW quad ranges by the U.S. Geological 

Survey. 

The Big Sandy Formation is in the Basin and Range 

physiographic province, which is characterized by generally 

north- to northwest-trending isolated ranges separated by 

alluvial desert plains. That part of the Basin and Range 

province in northwestern Arizona has been termed the 

"Mohave section". by Hayes (1969, p. 35), and the Big 

Sandy Formation is in the southeastern part of this subprovince. The Big Sandy Formation occupies an intermontane basin which lies between the south end of Hualapai 

Mountain on the west and Aquarius Cliffs on the east. Most 

of the peaks surrounding the basin rise to elevations of 

5,000-7,000 feet. 

The Big Sandy Formation has a northwestward extent 

along the Big Sandy River of about 12 miles and a width 

that ranges from about 1.5 to 5.5 miles. The formation underlies an area of about 30 square miles. The lowest exposures, at an elevation of about 1,800 feet, are along the 

Big Sandy River at the southernmost extent of the· formation; the highest exposures, at an elevation of about 2,500 

feet, are near the gravel-capped pediments just south of 

Boner Canyon. 
2 ZEOLITES AND AUTHIGENIC SILICATE MINERALS, BIG SANDY FORMATION, ARIZONA 

0 Kingman 

ARIZONA 

) 

~) 

34°L---L-----------------------~--------~ 

0 10 20 30 MILES 

I i .I 

I I 

0 10 20 .30KILOMETERS 

FIGURE I.- Distribution ofthe Big Sandy Formation (shaded). 

PREVIOUS WORK 

Although the lacustrine deposits of late Tertiary age 

along the Big Sandy River near Wikieup were briefly mentioned as early as 1908 by Lee, the deposits have since 

received only cursory study. Morrison .(1940), as part of a 

ground-water study of the Big Sandy valley, mapped 

sedimentary deposits in the valley and included the 

lacustrine strata in a widespread unit he called "older fill." 

Ross ( 1928, 1941) described the zeolite analcime in tuffs of 

the Big Sandy Formation near Wikieup, and he (1941, p. 

627) also described a partial stratigraphic section, about 80 

feet thick, of the formation. The formation was formally 

named and described by Sheppard and Gude (1972a). Short 

reports on other zeolites in the Big Sandy Formation have 

been published as part of the present study (Sheppard, 1969; 

Sheppard and Gude, 1971 ). 

The Big Sandy Formation contains a rich vertebrate 

fauna, but we are unaware of any published reports on the 

fossils other than that prepared in conjunction with the present study (Sheppard and Gude, 1972a). Several paleontologists from !the Frick Laboratory of the American 

Museum of Natural History have studied the vertebrate 

fossils from the Big Sandy Formation, but no reports have 

been published (Ted Galusha, written commun., 1971). 

SCOPE OF INVESTIGATION 

This investigation of the Big Sandy Formation was made 

primarily to study the distribution and formation of zeolites 

and associated authigenic silicate minerals in the tuffaceous 

beds. Zeolites are common authigenic minerals in tuffaceous rocks of Cenozoic age throughout the desert regions 

of the Western United States (Sheppard, 1971a). The tuffaceous rocks of the Big Sandy Formation were chosen for 

· detailed study for the following reasons: ( 1) The formation 

was subjected to very shallow burial and shows only slight 

deformation; (2) exposures of the formation are good, and 

tuffs can be traced throughout most of the extent of the formation; and (3) reconnaissance in 1966 showed an abundance and variety of authigenic silicate minerals in the tuffs. 

The common occurrence of authigenic analcime and 

potassium feldspar in the tuffs provided the opportunity to 

study the genetic relationships of these minerals to the other 

alkalic, silicic zeolites. Although authigenic clay minerals 

are common in the tuffaceous rocks, their mineralogy 

received only cursory examination in this investigation. 

Sampling was confined to surface outcrops and weighted 

heavily in favor of tuffs, although the other rock types were 

sampled sufficiently to obtain r~presentative · material. 

:Weathered surface outcrops were avoided. No cores were 

available to this investigation. 

LABORATORY METHODS 

X-ray diffractometer patterns were made of all bulk 

samples of tuffs. The samples were first ground to a powder, 

packed in aluminum sample holders, and then exposed to 

nickel-filtered copper radiation. Relative abundances of 

authigenic minerals were estimated from the diffractometer 

patterns by using peak intensities. Estimates are probably 

less reliable for mixtures containing opal because this 

material yields a rather poor X-ray record. 

Optical studies, made by using immersion oil mounts and 

thin sections, supplemented the abundance data obtained by 

X-ray diffraction and provided information on the age 

relationships of the authigenic minerals. All measurements 

of the indices of refraction are considered accurate to 

±0.001. 

Most samples of altered tuff contain more than one 

authigenic mineral. In order to identify each mineral in the 

diffractometer patterns of bulk samples, the patterns were 

compared with a "sieve." The sieve, such as that, illustrated 

in figure 2, was prepared from pure mineral separates at the 

same scale as the patterns of the bulk samples. One mineral 

at a time could then be sieved from the bulk patterns until 

all lines were identified. This procedure served to render the 

l. 

( j 
~:'".f ' 

GEOLOGIC SETTING 3 

20, IN. DEGREES 

40 3@ 20 10 o· 

I I I I I I I I I 

I Analcime I I I I 

• 11 I I I Chabazite 

I I I I I I I ,, I I I I 

Ill ' II I II ' .. I Clinoptilolite 

II, oil I I I II. d I 

II I I II I I I 

Erionite 

I I 111 I I Ill.. I I. I I 

II II I J. Harmotome II I I I I 1l1 I I I 

I I I II I I I I I. I I II I I I I I I I .I 1 

Mordenite 

I I I I I Phillipsite I I I II I I I I 

till I 1. . I .~ I Potassium feldspar I I II I II •• Ill I I I. 

, I , I I I I I I I I I I I I I I I I I II II I II II I II II I II II I II II'" IIIII "'""I I I I I I I I I II II I I I I I ~.0 2:5 3.0 3.5 4.0 5.0 6.0 7.0 8.0 9.0 10 15 20 30 50 100 

Cuka,IN ANGSTROMS 

FIGURE 2. - X-ray diffractometer patterns of authigenic silicate minerals. Copper radiation with nickel filter .. Relative intensities 

indicated by height of lines above base line. All samples are from the Big Sandy Formation, except the mordenite, which is from an 

altered tuff of the Barstow Formation, near Barstow, Calif. (Sheppard and Gude, 1969a). 

identifications routine and to help the analyst recognize 

minor or trace amounts of constituents. 

The "pure" mineral separates were prepared for chemical 

analysis from nearly monomineralic tuffs. The zeolites were 

separated by crushing the tuff and then disaggregating it in 

an ultrasonic bath. The zeolites were then concentrated by 

repeated centrifuging in a heavy-liquid mixture of 

bromoform and acetone, utilizing the technique described 

by Schoen and Lee ( 1964 ). 

ACKNOWLEDGMENTS 

Grateful appreciation is expressed to those in the U.S. 

Geological Survey who provided technical assistance during 

this study. B. W. Lanthorn, Violet M. Merritt, Wayne 

Mountjoy, Harriet G. Neiman, George 0. Riddle, Van E. 

Shaw, and Vertie C. Smith performed the chemical 

analyses. Mahmood-Uddin Ahmad and Toribio Manzanares, Jr., prepared samples for X-ray diffractometer 

analysis. Melvin E. Johnson prepared the thin sections. 

Louise S. Hedricks exercised great patience in the preparation of the photomicrographs. 

GEOLOGIC SETTING 

The Big Sandy Formation was deposited in a closed basin 

which formed as a result of the damming of the ancestral; 

Big Sandy River. The mountain ranges surrounding the 

basin are chiefly Precambrian granitic rocks, although 

silicic to basaltic volcanic rocks of Tertiary age are common 

in the mountains along the eastern and southern parts of the 

basin. '!he lower slopes of the Aquari~s Cliffs are underlain 
4 ZEOLITES AND AUTHIGENIC SILICATE MINERALS, BIG SANDY FORMATION, ARIZONA 

by tilted Tertiary sedimentary rocks, locally interbedded 

with basalt flows. The tilted Tertiary sedimentary rocks include both fluviatile and lacustrine deposits, some of which 

have thick interbeds of gypsum at Burro Wash, about 5.5 

miles north of Wikieup. A thick fanglomerate of Tertiary 

age overlies the granitic rocks on the eastern flank of 

Hualapai Mountain. This fanglomerate is probably older 

than the Big Sandy Formation (Sheppard and Gude, 

1972a). 

Although the ancestral Big Sandy River supplied most of 

the impounded water in which the Big Sandy Formation 

was deposited, several major tributaries must have contributed significant quantities of water and detritus. These 

major tributaries were near the present Natural Corrals 

Wash on the west and Bull Canyon, Boner Canyon, and 

Sycamore Creek on the east (fig. 3). As the basin filled with 

sediment, the lake began to overflow, and the Big Sandy 

River cut through the barrier. The lake was eventually 

drained, and the lacustrine sediments were subsequently dissected by the Big Sandy River and its tributaries. 

Erosion and dissection of the Big Sandy Formation has 

proceeded to such a degree that now the area is 

characterized by badlands and dissected gravel-capped 

pediments. The Big Sandy River and its mile-wide alluviumfilled channel transects the formation north of Wikieup, but 

it forms the west boundary of the formation south of 

Wikieup (fig. 3). Natural exposures of the Big Sandy Formation are mainly in badland areas adjacent to the Big 

Sandy River or in the steep sides of the numerous washes 

that head eastward from the river. 

Nowhere in the axial part of the basin has the Big Sandy 

River or its tributaries cut through the basal beds of the Big 

Sandy Formation. However, small patches of volcanic 

rocks crop out beneath the formation in marginal parts of 

the basin near Bitter Creek and midway between Sycamore 

Creek and Gray Wash (fig. 3). These inliers of older 

volcanic rocks were probably islands in the lake during 

much of the deposition of the Big Sandy Formation. 

The Big Sandy Formation is only slightly deformed, and 

it dips generally less than 2°. However, dips up to I 0° were 

measured in Natural Corrals Wash, about 0.5 mile west of 

U.S. Route 93. Normal faults of slight displacement cut the 

formation, particularly north of Wikieup. The greatest displacement measured is only 14 feet. 

STRATIGRAPHY AND LITHOLOGY OF THE 

BIG SANDY FORMATION 

The Big Sandy Formation, of probable late Pliocene age 

(Sheppard and Gude, 1972a), consists chiefly of lacustrine 

rocks that have a maximum exposed thickness of about 245 

feet. However, the maximum thickness of the formation is 

necessarily greater than 245 feet because the basal beds are 

not exposed. The original thickness must have been even 

greater because an unknown thickness of the formation was 

eroded prior to the deposition of the overlying Quaternary 

gravel. The formation unconformably overlies Precambrian 

granitic rocks and unnamed sedimentary and volcanic rocks 

of Tertiary age. 

Green or brown mudstone or a silty, sandy, or calcareous 

variant is the predominant lithology of the Big Sandy Formation. Limestone and altered tuff beds compose a minor 

part of the formation, but they are generally very resistant 

and form conspicuous ledges. The mudstone interfingers 

marginward with coarser clastic rocks. Some of the coarse 

clastic beds may be fluviatile rather than lacustrine. 

A generalized columnar section of the exposed part of the 

Big Sandy Formation is shown in ·figure 4. Detailed 

measured sections of the formation have been published by 

·Sheppard and Gude (1972a). Two of the thickest and most 

continuous tuffs are in the lower part of the formation and 

have been given informal field names- lower marker tuff 

and upper marker tuff. The upper marker tuff is about 35 

feet above the lower marker tuff. 

CONGLOMERATE, SANDSTONE, AND SILTSTONE 

Conglomerate, sandstone, and siltstone occur chiefly in 

the marginal parts of the formation, especially at its 

northern) exterit. These coarse clastic rocks interfinger 

basin ward with mudstone. Thin beds of siltstone and, rarely, 

sandstone occur locally in the mudstone of the central part 

of the basin. 

Most of the conglomerate is medium to thick bedded and 

poorly indurated, except where cemented by calcite or 

zeolites. The pebbles are angular to subrounded, and most 

are less than 2 inches in diameter. Some beds, however, contain boulders that are as much as 12 inches across. The composition of the pebbles is variable from place to place and 

reflects the differences in the local source areas. Most beds 

contain a mixture of volcanic and granitic pebbles, but the 

volcanic pebbles generally predominate. Some beds contain 

only volcanic pebbles. 

Sandstone and siltstone are brown, green, or gray, and 

thin to thick bedded, and most are poorly indurated. 

Cementation is local. The following cements occur, listed in 

the approximate order of decreasing abundance: Calcite, 

clay minerals, zeolites (chiefly clinoptilolite or analcime), 

and opal. Sedimentary structural features other than bedding are rare, but ripple marks and crossbedding are present 

locally. 

The framework constituents of sandstone and siltstone, as 

well as the sand-size matrix of conglomerate, consist of 

varying amounts of mineral grains and rock fragments. 

Sorting is poor, and the clasts have an estimated roundness 

of 0.2-0.4. The detrital minerals. are feldspar and quartz 

and lesser amounts of biotite, hornblende, epidote, 

muscovite, magnetite, zircon, apatite, tourmaline, garnet, 

and sphene, listed in the approximate order of decreasing 

abundance. Feldspar generally exceeds quartz, and sodic 

plagioclase exceeds alkali feldspar. Rock fragments are 

volcanic and lesser amounts of granitic rock, gneiss, schist, 

I. 

(, 
0 

0 

113° 37'30" 

21 

34° 42'30"-

Big Sandy Formation 

o52 

Sample locality 

~ 

Inlier of volcanic rocks 

2 

STRATIGRAPHY AND LITHOLOGY 

27 

34° 40' -

113° 35' 

35 

3 Ml LES 

.r 

2 3 Kl LOME TEAS R.13W. R . 12W. 

....... 

FiGURE 3.- Sample localities in the Big Sandy Formation. X-ray analysis of samples given in table 14. 

5 
6 ZEOLITES AND AUTHIGENIC SILICATE MINERALS, BIG SANDY FORMATION, ARIZONA 

EXPLANATION 

E3 

Mudstone 

BJ 

Siltstone, sandstone, and 

conglomerate 

8 

Tuff 

10 

20 

30 

40 

50 

FIGURE 4. - Generalized columnar section of the Big Sandy 

Formation. Base of formation is not exposed; top is eroded. 

and quartzite. Zeolite pseudomorphs after sand- and siltsize shards are locally common. The matrix of sandstone 

and siltstone is generally less than 15 percent and is chiefly 

clay minerals. On the basis of the classification of Pettijohn 

( 1957, p. 291 }, the sandstones and siltstones are arkose or 

subgraywacke, depending on whether feldspar or rock 

fragments predominate. 

MUDSTONE 

Mudstone is the predominant rock in the Big Sandy Formation. It has an earthy luster and is pastel shades of 

brown, gray, and green. Most of the mudstone is even 

bedded and medium to thick bedded. Fresh mudstone 

breaks with a conchoidal or subconchoidal fracture, but, 

where weathered, it has a typical punky "popcorn" coating 

·several inches thick. Nodular to lenticular calcareous concretions are ·common in much of the mudstone. Some 

mudstone contains numerous disseminated crystal molds, 

0.2-2.0 mm long, that are filled or partly filled with calcite. 

The shape of some of the molds resembles that of gaylussite 

(CaC03·Na2C03·5H20). Calcite occurs in the molds as 

clusters of anhedral to subhedral crystals, and it apparently 

precipitated in cavities that formed by solution of a readily 

soluable saline mineral. 

Most mudstones contain, in addition to clay minerals, 

detrital sand and silt, calcite, and authigenic zeolites or 

potassium feldspar. The mineralogic composition of eight 

representative mudstones, as determined by X-ray diffraction of bulk samples, is given in table 1. The sand and silt 

fraction is about 1 to 40 percent but generally is less than 20 

percent of the mudstones. Most of these relatively coarse 

grains are angular to subangular and include both mineral 

and rock fragments. The mineralogic composition of the 

sand and silt fraction of the mudstones is similar to that of · 

the framework portion of the sandstones and siltstones. 

Quartz and feldspar are the predominant clasts. Vitroclastic 

texture is very rare in the mudstones, but a few samples contain pseudomorphs of small shards that consist of 

authigenic silicate minerals. 

Authigenic zeolites and potassium feldspar are common 

in the mudstones, where they generally comprise 20 percent 

or less of the rock and only rarely comprise as much as 50 

percent of the rock. Some mudstones contain both 

authigenic potassium feldspar and a zeolite, but others contain either potassium feldspar or a zeolite (table 1 ). 

Analcime is, by far, the most common zeolite in the 

mudstones. Clinoptilolite was the only other zeolite identified in the mudstones by X-ray diffraction of bulk samples. 

Neither authigenic potassium feldspar nor a zeolite occurs 

in some mudstones. 

Semiquantitative spectrographic analyses of eight 

representative mudstones are given in table 2. The sodium 

and potassium contents of these mudstones are higher than 

generally reported for pelitic rocks (Shaw, 1956) but are 

similar to abundances reported for mudstones from saline 

lacustrine deposits (VanHouten, 1965; Sheppard and Gude, 

1969a). Authigenic analcime and potassium feldspar in the 

mudstones of the Big Sandy Formation probably account 

for the relatively high alkali contents. The mudstones also 

seem to have abundances of boron, barium, cerium, lithium, 

neodymium, and strontium that are higher than those of the 

average shale reported by Turekian and Wedepohl (1961). 

LIMESTONE 

In addition to nodular or lenticular calcareous concretions in mudstone, bedded limestone occurs in the Big 

Sandy Formation, particularly along the east margin of the 

(, 
~ 

.,;, 

~ 

~ 

., 

STRATIGRAPHY AND LITHOLOGY 7 

TABLE I. -Mineralogic composition of mudstone, as estimated from X-ray diffractometer patterns of bulk samples 

( ___ ,looked for but not found: Tr., trace. Clay, lOA includes muscovite, biotite, and illite; clay, 14A includes montmorillonite and mixed-layer montmorillonite-illite] 

X-ray analysis (parts of I 0) 

Field Sample Clay, Clay, Potassium 

No. description lOA 14A Quartz Plagioclase Hornblende feldspar Analcime Calcite 

SEIASWIA sec. 18, T. 15 N., R. 12 W. 

SW-1-1 ---- Brown mudstone ------ 7 2 I 

SW-1-7 ---- _-----do-------- I 2 Tr. Tr. 4 2 

SW-1-11 --- Greenish-gray mudstone __ 3 I 3 Tr. 3 Tr. 

SEIASW1A sec. 24, T. 16 N., R. 13 W .

SW-3-IA --- Brown mudstone ------ 3 2 3 I Tr. Tr. 

SW-3-10A Gray mudstone _______ 5 2 2 

SW-3-15B ___ Green mudstone ------ 3 5 2 

NWIANEIA sec. II, T. 16 N., R. 13 W. 

SW-13-1 Brown mudstone ------ 3 3 2 Tr. 2 

SW-13-IOB: __ ______ do ________ 2 4 2 2 Tr. Tr. 

TABLE 2.- Semiquantitative spectrographic analyses of mudstone 

(Analyst: Harriet G. Neiman. Localities for samJ?les are ~Jiven in table I. Results are to be identified with geometric brackets whose boundaries are 1.2, 0.83, 0.56, 0.38, 0.26, 0.18, 0.12, and so forth, but are reported arbitranly as m1dpoints of these brackets, I, 0.7, 0.5, 0.3, 0.2, 0.15, 0.1, and so forth. The precision of a reported value is arcproximately ~Ius or minus one bracket at 68-percent c~nfidence, or two brackets at 95-percent confidence. G, greater than 10 percent; N, not detected. The following e ements were ooked for but not detected: Ag, As, Au, B1, Cd, Eu, Ge, Hf, In, Mo, P •. Pd, Pr, Pt, Re, Sb, Sm, Sn, Ta, Te, Th, Tl, U, W, and Zn] 

Field No------------ SW-1-1 SW-1-7 SW-1-11 SW-3-IA SW-3-IOA SW-3-15B SW-13-1 SW-13-IOB 

Lub. No ------------ 0142240 0142241 0142242 0142243 0142244 0142246 0142247 0142248 

Weight percent 

Si ----------- G G G G G G G G 

AI ----------- 10 10 10 7 10 10 7 7 

Fe ----------- 7 7 7 7 7 7 3 5 

Mg --·--------- 3 2 2 3 3 3 2 3 

Ca ----------- 3 5 5 5 3 1 G 7 

Na _.:....~-------- 1.5 3 2 3 3 1 3 2 

K ----------.-- 7 7 7 5 5 5 5 5 

Ti -----------. .5 .5 .5 .7 .5 .5 .5 .5 

Parts per million 

B ____________ 700 200 500 150 200 300 70 100 

Ba ----------- 1,000 1,500 700 1,000 1,000 700 500 1,000 

Be ----------- 2 3 2 2 2 2 1.5 1.5 

.Ce 200 150 150 150 150 150 200 N 

Co =~========= 20 15 20 20 15 20 15 20 

Cr , ___________ 150 150 150 200 150 150 50 150 Cu ___________ 100 50 50 50 30 100 30 30 Ga ___________ 30 20 30 20 30 30 20 30 

La ----------- 150 100 150 70 100 70 100 100 

Li ----------- 700 500 500 500 500 700 100 300 

Mn ___________ Nb 1,500 1,000 1,000 700 1,000 700 1,000 700 ___________ 10 10 15 15 15 10 10 10 

Nd _ ---------- 150 70 150 70 70 100 100 N 

Ni ----------- 50 30 30 100 70 70 30 70 

Pb ----------- 30 20 30 20 15 15 30 15 

Sc ----------- 20 20 20 20 20 20 20 15 

Sr ----------- v ____________ 1,000 1,500 1,000 2,000 2,000 1,000 1,000 1,500 

y ____________ 300 200 700 200 300 700 100 200 

30 30 30 30 20 20 50 30 Yb ___________ 3 3 3 3 3 2 3. 3 

Zr ----------- 70 100 100 150 150 70 150 150 

deposit. The bedded limestones are light brown or light 

green, thin to thick bedded, and commonly vuggy and wavy 

bedded. Beds range in thickness from 0.5 inch to 3 feet, and 

limestone units are as much as 15 feet thick. Most of the 

limestone beds contain detrital grains or authigenic silicate 

minerals. This noncarbonate fraction ranges from less than 

1 percent to about 30 percent of the rock. Detrital grains are 

in all the limestones, but authigenic zeolites and opal are 

fairly rare. The limestones are finely crystalline, but most 

have veinlets or cavity fillings of coarsely crystalline calcite 

that is euhedral to subhedral and white to yellow. No fossils· 

were recognized in any of the limestones. 
8 ZEOLITES AND AUTHIGENIC SILICATE MINERALS, BIG SANDY FORMATION, ARIZONA 

TUFF 

Tuffs in the Big Sandy Formation make up about 2-3 

percent of the exposed stratigraphic section (fig. 4). At least 

13 tuffs were recognized, and they are about 0.5-40 inches 

thick, although most are less than 6 inches thick. The 

thicker tuffs are generally more continuous than the thinner 

ones. Thin tuffs are commonly single beds, but. tuffs more 

than several inches thick generally consist of multiple beds. 

The original textural and structural features of the tuffs 

are generally preserved even though no vitric material 

remains. Most tuffs are even bedded; ripple marks or ripple 

laminations are present but not common. Individual beds of 

either single bedded or multiple bedded tuffs are commonly 

graded, being coarser at the base. The lower contact of a 

tuff is generally sharp, whereas the upper contact is commonly gradational into the overlying rock, regardless of its 

lithology. 

Most of the tuffs originally were vitric and consisted 

mainly of fine to very fine grained ash and a variable 

percentage of crystal and rock fragments. The vitric 

material was of two types - platy bubble-wall shards that 

formed from the walls and junctions of relatively large 

broken bubbles, and pumice shards that contained small 

elongated bubbles. Most tuffs contained both types of 

shards, but the platy bubble-wall shards were predominant. 

Most of the crystal and rock fragments in the tuffs are 

angular; the fragments range from less than I percent to 

about 50 percent of the rock. Most of the tuffs, however, 

contain less than 20 percent crystal and rock fragments. 

Crystal fragments are in excess of rock fragments. Because 

no fresh glass is attached to the crystal fragments, pyrogenic 

crystals cannot be positively distinguished from epiclastic 

ones. However, quartz, sodic plagioclase, biotite, 

hornblende, sanidine, clinopyroxene, zircon, apatite, and 

magnetite are presumed to be pyrogenic. Crystal fragments 

of epiclastic origin are epidote, muscovite, microcline, garnet, chlorite, and sphene, which were probably derived from 

the granitic terranes surrounding the basin. Many of the 

presumably pyrogenic crystals listed above could also have 

been derived from the older volcanic and granitic rocks that 

are marginal to the Big Sandy Formation. 

The rock fragments are volcanic and granitic rocks and a 

minor amount of gneiss. Volcanic rock fragments are 

spherulitic and hyalopilitic lavas. The rock fragments could 

have been torn from the vent area during eruption of the 

ash, or they could be epiclastic. 

Some tuffs and the lower part of some tuffs are the result 

of ash falls directly into a lake. Other tuffs (particularly the 

upper part of most tuffs) consist of reworked ash mixed with 

epiclastic grains derived from the highlands surrounding the 

basin. Most of these tuffs, or parts of tuffs, contain an abundance of granitic rock fragments and crystal fragments of 

epidote and microcline. 

The original composition of the ash is unknown, but the 

presumed pyrogenic crystal fragments in the tuffs indicate a 

silicic composition, probably rhyolitic or dacitic. 

The two marker tuffs (fig. 4) are the thickest and most 

continuous tuffs in the Big Sandy Formation. The lower 

marker tuff crops out from the NE14 sec. 30, T. 15 N., R. 12 

W., northward to the NE~ sec. 14, T. 16 N., R. 13 W., and 

can be recognized wherever its stratigraphic interval is exposed. The thickness of the lower marker tuff is 6-39 inches 

but commonly is 18-24 inches. The tuff is at least 30 inches 

thick in sec. 18 and the NV2 sec. 19, T. 15 N., R. 12 W. The 

upper marker tuff occurs about 35 feet stratigraphically 

above the lower marker tuff and crops out from the NW14 

sec. 29, T. 15 N., R. 12 W., northward to the NW14 sec. 25, 

T. 16 N., R. 1.3 W. Although the stratigraphic interval of the 

upper marker tuff is exposed farther north, the upper 

marker tuff was not recognized north of sec. 25, T. 16 N., R. 

13 W. The thickness of the upper marker tuff is 9-40 

inches, and it seems to gradually decrease from south to 

north. 

AUTHIGENIC MINERALS 

ANALCIME 

Analcime, commonly referred to as analcite, is one of the 

. more abundant zeolites in sedimentary rocks. Analcime has 

an ideal formula of NaA1Si20 6·H20, but the analcime of 

sedimentary rocks is generally more siliceous (table 3). 

Since its discovery in the Green River Formation (Bradley, 

1928) and in the tuffs of the Big Sandy Formation (Ross, 

1928), analcime has been reported in sedimentary rocks that 

are diverse in age, lithology, and depositional environment 

(Hay, 1966). Analcime occurs in rocks that range in age 

from Pennsylvanian to Holocene, but it is especially common relative to the other zeolites in rocks of Mesozoic age, 

particularly those older than Cretaceous. Saline lucustrine 

deposits, regardless of age, very commonly contain 

analcime. Analcime, unlike the other zeolites in sedimentary rocks, does occur in rocks that lack evidence of vitric 

material, and is apparently a common constituent of saline, 

alkaline soils, such as those in .southern California (Baldar 

and Whittig, 1968). 

TABLE 3.- Formulas of selected alkalic zeolites 

[Formulas are standardized in terms of a sodium end member that has one aluminum atom) 

Name 

Analcime _______ _ 

Chabazite _______ _ 

Clinoptilolite _____ _ 

Erionite --------- Harmotome ______ _ 

Mordenite _______ _ 

Phillipsite _______ _ 

Dominant 

cations 

Na -----------

Na,Ca,K -------

Na,K,Ca -------

Na, K,Ca -------

Ba, Na, K ------- Na, Ca. K ______ _ 

Na,K,Ca ______ _ 

Formula 

NaAISil.;-2 .• o~.o-u•0.8-1.3H 0 

NaAISiu-•. 10s.o- 1o.2'2.7 -4.7H20 

NaAISiJ•-s.sOu-IJ.o'2.5 -4.0H20 

NaAISil.•-J.H07.K-9.h'2.4- 3.4Hl0 

N aAISil.o-l.<Oo.0-7.o'2.5- 3.0Hl0 

N aAISi4.5-~.JOII.O-Il.o'3.2- 3.5Hl0 

NaAISiu-JAO•.o-<.<'1.7- 3.3H20 

Analcime is a very common zeolite in the tuffs of the Big 

Sandy Formation, where it ranges from trace amounts to 

nearly 100 percent of the rock. The analcime is associated 

with each of the other zeolites, but its association with 

mordenite and chabazite is rare (table 4). Analcime is also 

commonly associated with authigenic potassium feldspar, 

\ 

(. 

r. 
AUTHIGENIC MINERALS 9 

TABLE 4.- Checklist of associated authigenic silicate minerals in tuffs of 

the Big Sandy Formation 

(X. minera l pair associated; 0 , mineral pair not associated . Data compiled from X-ray diffrac- tometer palterns of bulk samples. Clay minerals include lOA and 14A types: quartz includes epiclastic, pyrogenic, and authigenic crystals] 

] ~ e e u ;g .!l u E ~ 0 

-~ e Q. " u 0 ~ =>c. N ·c; -g .5 ·;: E "E ~ -~ -0 

" ,., 0 ~ g:§ " < 0 " ~ :r 0 :;: 0 0 0 ::;: 0 0.. 0.. 

Analcime ----------- - X X X X X X X X X X 

Chabazite ----------- X - X X X X 0 0 X X X 

Clay minerals --------- X X - X X X X X X X X 

Clinoptilolite --------- X X X - X X X X X X X 

Erionite ------------ X X X X X X X X X X 

Harmotome __ _ _______ X X X X X - 0 0 0 0 X 

Mordenite ----------- X 0 X X X 0 - 0 0 0 X 

Opa l -------------- X X X X X 0 0 - 0 X X 

Phillipsite ----------- X X X X X 0 0 0 - X X 

Potassium feldspar ------ X X X X X 0 0 X X - X 

Qua rtz ------------- X X X X X X X X X X -

quartz, and clay minerals. The association of analcime with 

potassium feldspar is particularly common. 

Analcime has three modes of occurrence in the tuffs of 

the Big Sandy Formation - (I) subhedral to euhedral 

crystals, (2) pseudomorphs of shards and early authigenic 

silicate minerals, and (3) irregular patches. Subhedral to 

euhedral crystals are by far the most common occurrence of 

analcime. The subhedral to euhedral crystal~ (fig. 5) range 

in size from 5J.Lm to 50J.Lm, although most are 20J.Lm to 401-'m. 

The ana!Gime is pale tan in transmitted light and generally 

milky in reflected light, owing to abundant minute inclusions. Analcime pseudomorphs after prismatic clinoptilolite (fig. 6) and analcime pseudomorphs of shards (fig. 7) 

are sparse in the altered tuffs. Petrographic evidence indicates that the shards were first pseudomoq)hed by an 

earlier zeolite, generally clinoptilolite, and then were 

replaced by analcime. The irregular patches of analcime are 

colorless and are as much as about I mm (fig. 8). This 

analcime replaced earlier authigenic silicate minerals, completely obliterating the vitroclastic texture. 

The index of refraction of analcime from the Big Sandy 

Formation ranges from 1.483 to 1.488. Saha (1959) showed 

that the index of refraction of synthetic analcimes decreases 

with increasing Si:Al ratio. The above indices are consistent 

with fairly high Si:Al ratios. 

A new chemical analysis of analcime from the Big Sandy 

Formation is given in table 5. The analcime was separated 

FlGURI: 5.- Subhedral to euhedral a nalcime . A, Thin section of analcime tuff. Irregula r light a reas are pores in the tuff. Unpolarized light. 8 , lndivid ual crystals and clusters of crystals separated from an analcime tuff. Unpolarized light. 
10 ZEOLITES AND AUTHIGENIC SILICATE MINERALS, BIG SANDY FORMATION, ARIZONA 

FIGURE 6.- Analcime pseudomorphs after prismatic clinoptilolite. Light 

areas are quartz. Unpolarized light. 

from a nearly monomineralic portion of the lower marker 

tuff. The analyzed analcime contained less than 2 percent 

minute clay mineral inclusions, but the analysis was not corrected for them. The composition of the unit cell based on 

96 oxygen atoms is also given in table 5 and shows a 

Si:Al + Fe+3 ratio of 2.49. Sodium is greatly in excess of the 

other cations. 

Ross ( 1928) has published two analyses of analcime 

separated from a tuff collected near Wikieup. The exact 

locality and stratigraphic position of the tuff are unknown, 

but the tuff probably was the lower marker tuff. Both 

separates contained minor impurities of clay minerals and 

opal. The uncorrected analyses showed Si·Al+Fe+3 ratios of 

about 2.6 and 2.8. 

The composition of analcime from 55 other samples was 

determined indirectly by measurement of the displacement 

of the (639) peak, utilizing the data of Saha (1959, 1961) for 

synthetic analcimes and the determinative curve of Sheppard and Gude (1969a). Saha showed that the (639) peak 

falls at higher angles (degrees 28, CuKa1 radiation) for 

analcimes of higher silicon content. Displacement of the 

(639) peak of analcime was measured against the (331) peak 

FIGURE 7. - Analcime pseudomorphs of shards (dark). Light areas are 

quartz. Unpolarized light. 

of a silicon internal standard. The analcimes from tuffs of 

the Big Sandy Formation show a compositional range from 

about (NaAI) 14 . 2Si 33 . 80 96·nH20 to (NaAI) 12 •7Si 35 •30 96·nHp. 

The Si:Al ratio of the analcimes ranges from about 2.4 to 

2.8; the distribution for the 55 samples is shown in figure 9. 

Nearly half the samples have a Si:Al ratio of 2.5-2.6. 

Coombs and Whetten (1967) studied analcimes from many 

sedimentary environments and determined a range in Si:Al 

of about 2.0-2.7. Analcimes in tuffs of the Eocene Green 

River Formation of Wyoming have Si:Al ratios of about 

2.0-2.9 (lijima and Hay, 1968), and analcimes in tuffs of 

the Miocene Barstow Formation of California have Si:Al 

ratios of about 2.2-2.8 (Sheppard and Gude, 1969a). 

CHABAZITE 

Chabazite was unknown in sedimentary deposits before 

1964, when it was discovered by Hay ( 1964, p. 1377) in tuffs 

and tuffaceous clays at Olduvai Gorge, Tanzania. Since 

then, authigenic chabazite has been recognized in tuffs from 

California, Nevada, Oregon, Wyoming, and several 

localities in Arizona. Most of the occurrences are in 

lacustrine rocks of ·late Cenozoic age. Chabazite has an 

ideal formula of Ca 2Al 4Si 80 24 '12H20, but natural 

• 
AUTHIGENIC MINERALS 11 

FIGURE 8. - Irregular patches of analcime (light), which have replaced 

erionite and chabazite pseudomorphs of shards. The vitroclastic texture 

is preserved where analcime is absent. Unpolarized light. 

chabazites show considerable variation in cation content 

and in Si:AI ratio (table 3). 

The chabazite in the Big Sandy Formation occurs in 

nearly monomineralic beds, but generally it is associated 

with clay minerals, other zeolites, or potassium feldspar of 

authigenic origin (table 4). Chabazite has not been 

recognized in association with opal or mordenite, and its 

association with potassium feldspar or analcime is rare. 

Erionite and clinoptilolite are the zeolites that are most 

commonly associated with chabazite. The chabazite occurs 

as aggregates of equidimensional crystals that are anhedral 

to euhedral. Some of the chabazite crystals have a rhombohedral morphology (fig. 10), as shown by electron 

microscopy. The crystals range in maximum dimension 

from less tq,an 2J.Im to 40J.Im, but most are less than 20J.Im . 

The mean index of refraction of chabazite from the Big 

Sandy Formation ranges from 1.468 to 1.474, and the 

birefringence is about 0.002. This compares with a range of 

1.470- 1.494 given by Deer, Howie, and Zussman (1963 , p. 

387) for chabazite from nonsedimentary environments. The 

indices for the Big Sandy chabazites are, however, similar to 

TABLE 5. - Chemical analysis and composition of unit cell of analcime 

{Analyst: Vertie C. Smith, except for Na20, K20, and SrO determined by atomic ab- sorption by Violet Merritt and for BaO determ ined gravimet rically by V. E. Shaw. The Al 20 3 content includes P20 5, and the Fe20.J content represents total iron. Field No. SW-3-2A. Lab. No. DI 3898 1. Loc. 3 (lig. 3), NE ~N 1< sec. 25, T. I6 N., 

R. 13 W.J 

Chemical analysis 

Constituent Weight percent 

t~: ~ ~ ~: :::: ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~~~ ~ ~ ~ ~ ~ ~: ~: !l 

CaO ____ ___ __ ___ _ _ __ _ _ __ __ _ _ _ ___ .15 

BaO ____ _ _ __ _ ____ __ _ _ _ __ _ ____ ___ .02 &o ___ ___ _______ ____ ________ ___ .m 

~l.~~ ~~ ~~~ ~ ~ ~~~ ~ ~ ~~ ~~ =~~~~ ~ ~ ~ ~ ~ F~ Total _____ ____ __________ _ ____ 99.02 

Composition of unit cell 

[Ti was omitted in calculation of the unit cell] 

A toms per Constituelll unit cell 

Si ----------------------------- 34.32 

AI ----------------------------- 13.37 Fe+• _ __ _ __ ____ _ _ _ ________ _ _ _____ .42 

Mg___ ________ _ _ _____________ ___ .W 

Ca ----------------------------- .® Ba ___ _ __ _ ___ _ __ _ _ _ ______ _ __ ____ .00 

Sr _ _ _ _ __ ____ _ _ __ _ __ _ _ ___ _ _ __ __ _ .01 

Na ----------------------------- 12.49 K ___ ___ _ ___ _ ___ ____ _ _ __ _ _ ___ __ _ .28 

H,O + ----------------------- ---- 15.45 

H,O - --------------------------- .60 

0 ------------------------------ 96.00 

Si+Al+Fe+' ------------------- ---- 48.11 Si:Al+Fe+' _ __ _ ___ _ ____ _ _ __ _ ____ _ _ _ 2.49 

1- 50 

z -

UJ 

u 

a: 

~ 40 

z 

UJ 

u di 30 

a: 

a: 

::J 

u 

g 20 

u. 

0 

>-

u 

z 10 UJ 

::J 

0 

UJ 

a: 

-

-

-

-

u. 0 

2.3 

I 

2.4 

I I l I 2 .5 2 .6 2 .7 2.8 

Si:Al 

FIGURE 9. - Distribution of Si:Al ratios of analcime in 55 

samples of tuff from the Big Sandy Formation. The Si:Al 

ra tios were determined from X-ray diffractometer data by 

measurement of the displacement of the (639) peak of 

analcime. 

those for siliceous chabazites from silicic tuffs (Sheppard 

and Gude, 1970). 

A chemical analysis of chabazite from the Big Sandy Formation is given in table 6. The chabazite was separated from 
12 ZEOLITES AND AUTHIGENIC SILICATE MINERALS, BIG SANDY FORMATION, ARIZONA 

FIGURE 10. - Scanning electron micrograph of chabazite-rich tuff, 

showing rhombohedral morphology of the chabazite. Prismatic crystals 

(bottom) are erionite. Electron micrograph by Frederick A. Mumpton . 

a nearly monomineralic part of a thin tuff stratigraphically 

higher than the upper marker tuff. The analysis was 

calculated into atoms per unit cell, on the basis of 72 oxygen 

atoms, and is also given in table 6. Divalent cations exceed 

monovalent ones, and the Si:Al+Fe+3 ratio is 3.27. 

Ideal chabazite has a Si:Al+ Fe+3 ratio of 2, and most of 

the chabazites from mafic igneous rocks have a ratio near 2. 

The few analyzed chabazites from sedimentary rocks, 

however, have Si:Al+Fe ' 3 ratios greater than 3. A calcic 

chabazite from a silicic tuff in the John Day Formation of 

Oregon was recently analyzed and has a Si:Al + Fe+3 ratio of 

about 4. 1 (Sheppard and Gude, 1970), higher than that for 

any previously analyzed chabazite. 

Chabazite from the Big Sandy Formation has higher 

potassium and magnesium contents than previously analyzed chabazites from sedimentary rocks. Semiquantitative 

spectrographic analyses (table 7) of five chabazite-rich tuffs 

from the Big Sandy Formation suggest that the relatively 

high potassium and magnesium contents are characteristic 

for these chabazites. The spectrographic analyses were performed on bulk samples that contained at least 90 percent 

chabazite. The spectrographic analyses also confirm that 

the divalent cations are in excess of the monovalent ones, 

although the sodium contents are higher than the sodium 

T ABLE 6. - Chemical analysis and composition of unit cell of chabazite 

{Analyst: George Riddle, except for BaO and SrO determined by atomic absorption by Wayne Mountjoy. Field No. W7-6A. Lab. No. DI02734. Loc. 6 (fig. 3), 

SE V.N WY. sec. 13, T. 16 N., R. 13 W.J 

Chemical analysis 

Constituent Weight percent 

SiO, ---------------------------- 56.39 

~~§: MgO _ = __ ==== ___ == __ === __ _ _ _ = === __ = _ _ ======== __ __ ___ = _ === ___ 1~:~! 2.79 

CaO ---------------------------- 2.46 BaO _ _ _ _ _ _ _ _ __ _ _ _ _ __ _ ___ _ _ _ _ _ _ _ _ .03 

SrO _ _ _ _ _ _ _ _ _ _ _ _ __ _ _ _ ___ _ __ _ __ _ _ .13 

Na,O ------- -------------------- .72 

~~t-~=mmm~~~~~~~mmm ~l~ Total ____________ ___ _________ 99.48 

Composition of unit cell 

[Fe+2 , Ti, P, and Mn were omitted in calculation of the unit cell] 

Atoms per Constituem unit cell 

Si ----------------------------- 27.46 

AI ----------------------------- 7.67 

Mg ~ _____________________________ --- ------------------------- 2.00 .M 

Ca _ _ _ _ __ _ _ _ _ _ _ _ _ _ _ _ __ __ _ _ _ _ _ ___ 1.28 

Ba ----------------------------- .01 

Sr ----------------------------- .04 

Na ----------------------------- .68 

K ------------------------------ 1.55 H,O + ____ _ ______________________ 20.79 

H20 - --------------------------- 9.39 

0 ------------------------------ 72.00 

Si +Al+Fe+' - ---------------------- 35.87 

Si:AI+Fe+> ------------------------ 3.27 

content given in table 6. The barium content of sample No. 

W8-95B seems anomalously high for a chabazite from any 

geologic setting (Passaglia, 1970). 

Cell parameters for the analyzed Big Sandy chabazite 

were obtained by a least-squares refinement of X-ray 

powder diffractometer data, utilizing the U.S. Geological 

Survey's FORTRAN IV Computer Program W9214. The 

hexagonal cell parameters are a= 13.735±0.004 A, 

c= 14.840±0.006 A, and V=2,424.3± 1.2 N. These cell 

dimensions are smaller than those of chabazites from mafic 

igneous rocks. Most chabazites from mafic igneous rocks 

have a cell volume of 2,470-2,490 N, but siliceous 

chabazites from silicic tuffaceous sedimentary rocks have a 

cell volume of 2,410-2,430 N (Sheppard and Gude, 1970). 

Thus, the relatively small cell of the Big Sandy chabazite is 

consistent with a siliceous composition. 

CLAY MINERALS 

Most tuffs in the Big Sandy Formation contain 

authigenic clay minerals, but no attempt was made to study 

the clay mineralogy in detail. The clay minerals are 

associated with all the other authigenic silicate minerals, 

and their content is generally less than 40 percent of the tuff. 

Examination of X-ray diffractometer patterns of bulk 

samples indicated that lOA and 14A clay minerals occur in 

the tuffs. The l4A clay minerals are probably mont-

' ' 
~I 

~· .. 

-:-

~ 

AUTHIGENIC MINERALS 13 

TABLE 7. -Semiquantitative spectrographic analyses of chabazite-rich and c/inoptilo/ite-rich tuffs 

(Analyst: Harriet G. Neiman. Results are to be identified with geometric brackets whose boundaries are 1.2, 0.83, 0.56, 0.38, 0.26, 0.18, 0.12, and so forth, but are reported arbitrarily us midpoints of these brackets, I, 0.7, 0.5, 0.3, 0.2, 0.15, 0.1, and so forth. The precision of a reported value is' approximately plus or minus one bracket at 68-percent 

confidence, or two brackets at 95-percent. confidence. G, greater than 10 percent; N, not detected but below limit of determination. The following elements were looked for but not detected: Ag, As, Au, 81, Cd, Eu, Ge, Hf, In, Mo, P, Pd, Pr, Pt, Re, Sb, Sm, Sn, Ta, Te, Th, Tl, U, W, and Zn] 

Chabazite-rich tuff Clinoptilolite-rich tuff 

10 II 

Weight percent 

Si ------- G G G G G G G G G G G 

AI ------- 7 5 7 7 7 7 7 7 10 10 7 

Fe _______ ... 

Mg 3 2 2 2 2 I 3 2 2 2 I _______ 1.5 1.5 1.5 2 I .5 1.5 I 1.5 I .3 

Ca ------- 5 3 3 3 3 1.5 2 5 3 3 1.5 

Na ------- 2 2 I 2 3 .7 2 3 2 3 3 

K·-------- 2 3 I 2 2 5 3 3 3 3 2 

Ti ------- .3 .15 .2 .15 .2 .I .3 .2 .I .2 .I 

Parts per million 

B -------- N 20 N L N 

Ba ------- 300 1,500 150 300 15,000 

Be ------- I 3 N N I 

Ce ------- L 150 N N N 

Co ------- 5 5 7 5 5 

Cr ------- 50 50 15 ·20 7 

Cu ------- 20 10 10 15 15 

Ga ------- 20 10 10 15 10 

La ------- 50 50 N 30 50 

Li ------- 70 N N 70 N 

Mn _______ 300 300 150 200 300 

Nb ------- L 10 L N N 

Nd ------- 70 N N N N 

Ni ------- 5 10 10 15 5 

Pb ------- 15 15 L 10 10 

Sc ------- 15 7 10 10 10 

Sr ------- 2,000 3,000 1,000 1,000 7,000 

v -------- 100 100 70 200 15 

y -------- 30 15 10 10 20 

Yb ------- 5 I 1.5 1.5 3 

Zr ------- 150 150 200 150 150 

Analysis Field No. Lab. No. Locality 

I. W7-14B 0142252 NEY-INEltl.t sec. II, T. 16 N., R. 13 W. 

2. W7-19B 0142253 NWY-ISEY-1 sec. 2·, T. 16 N., R. 13 W. 

3. W8-89A 0142260 SEY-ISWY-1 sec. 12, T. 16 N., R. 13 W. 

4. W8-89C 0142261 SEY-ISWY-1 sec. 12, T. 16 N., R. 13 W. 

5. W8-95B 0142262 NEY-INEY-1 sec. 4, T. 16 N., R. 1'3 W. 

6. SW-26-98 0142249 NEY-ISEY-1 sec. 7, T. 15 N., R. 12 W. 

morillonite and mixed-layered montmorillonite-illite. Examination of thin sections of tuffs proved that much of the 

lOA clay mineral shown in ·the X-ray diffractometer 

patterns is biotite of detrital or pyrogenic origin. Some of 

the 1 OA clay mineral, however, is authigenic illite, inasmuch 

as the (00 1) peak is broad, and biotite is absent in the thin 

sections. Montmorillonite seems to be the most abundant 

authigenic clay mineral in the tuffs. 

CLINOPTILOLITE 

Clinoptilolite is a member of the heulandite structural 

group. Although there is still disagreement on the distinction between these closely related zeolites, most workers 

have considered clinoptilolite to be the silica-rich (Hey and 

Bannister, 1934; Mumpton, 1960) and alkali-rich (Mason 

and Sand, 1960) member (table 3). Indices of refraction and 

response to thermal treatment have also been used to dis100 50 50 30 20 70 

1,500 1,000 3,000 1,500 1,500 15,000 

2 1.5 I I I 2 

200 N N N N L 

N 7 5 L 3 N 

7 100 50 15 10 1.5 

5 20 70 10 10 I 

15 15 15 15 20 15 

150 50 30 30 N 70 

200 100 300 300 500 100 

100 500 300 150 200 100 

10 10 N N L 15 

70 N N N N N 

N 10 7 7 5 N 

10 15 30 10 10 15 

5 15 10 7 15 N 

30,000 1,500 15,000 5,000 1,500 15,000 

100 150 1,000 70 300 30 

20 15 20 10 20 20 

2 1.5 3 L 3 1.5 

150 100 100 100 200 150 

Analysis Field No. Lab. No. Locality 

7. SW-67-2 0142250 NWY-ISWY-1 sec. 29, T. 15 N., R. 12 W. 

8. SW-67-9A 0142251 NWY-ISWY-1 sec. 29, T. 15 N., R. 12 W. 

9. W7-28A 0142256 SEY-INWY-1 sec. 8, T. 15 N., R. 12 W. 

10. W7-36B 0142257 SWY-ISEY-1 sec. 20, T. 15 N., R. 12 W. 

II. W7-42B 0142258 SEY-INEY-1 sec. 36, T. 16 N., R. 13 W. 

tinguish clinoptilolite from heulandite. However, some 

members of the heulandite structural group from sedimentary rocks display anomalous optical properties and thermal 

behavior and cannot be classified conveniently as clinoptilolite or heulandite (Shepard, 1961; Hay, 1963). Furthermore, siliceous, but calcic, clinoptilolite has recently been 

discovered in volcanic rocks of Bulgaria (Kirov, 1965) and 

Italy (Alietti, 1967). 

The original description of clinoptilolite is of material 

from amygdales in a basaltic rock from Wyoming (Pirsson, 

1890; Schaller, 1932). Subsequent occurrences of clinoptilolite have been reported chiefly from sedimentary rocks, 

especially those originally rich in silicic vitric material. 

Clinoptilolite is the zeolite most often reported from 

sedimentary rocks in recent years, and it occurs in many 

rock types from lacustrine, fluviatile, and marine environments. Although clinoptilolite is most abundant in 
14 ZEOLITES AND AUTHIGENIC SILICATE MINERALS, BIG SANDY FORMATION, ARIZONA 

FIGU RE II. - Veinlet of prismatic clinoptilolite (light) in zeolitic tuff 

consisting chiefly of finely crystalline phillipsite (dark). Unpolarized 

light. 

rocks of Cenozoic age, it has been reported in New Mexico 

in rocks as old as Jurassic (Sheppard, 1971b). 

Clinoptilolite is a very common zeolite in the tuffs of the 

Big Sandy Formation, and it is associated with all the other 

authigenic silicate minerals. The clinoptilolite content 

ranges from trace amounts to nearly 100 percent of the 

tuffs. Clinoptilolite occurs as prismatic (fig. II) or platy 

(fig. 12) crystals that are 21-'m to 3751-'m long; most, 

however, an~ IO~J.m to 301-'m long. The clinoptilolite occurs 

as pseudomorphs after shards and as fillings of veinlets or 

irregular cavities in the tuffs. Small prismatic clinoptilolite 

also serves as a cement in some sandstones (fig. 13). 

Most of the clinoptilolite has a mean index of refraction 

of 1.475-1.483 and a birefringence of about 0.003 . The 

clinoptilolite has parallel extinction and is length slow. 

Some large clinoptilolite crystals, particularly those larger 

than about 801-'m, are length fast or zoned, having a lengthslow core and a length-fast rim. The rim of zoned crystals 

commonly has an index of refraction that is as much as 

0.006 higher than that of the core. Rarely, large crystals of 

clinoptilolite show oscillatory zoning. 

FIGU RE 12. - Irregular cavity that was first lined with fibrou s to 

spherulitic phillipsite (P) and then filled by platy clinoptilolite (cl). Unpolarized light. 

An analysis of clinoptilolite from the Big Sandy Formation is given in table 8. The clinoptilolite was separated from 

a nearly monomineralic part of a thin tuff that is 

stratigraphically higher than the upper marker tuff. The 

analysis was calculated in atoms per unit cell, on the basis of 

72 oxygen atoms, and is also given in table 8. Divalent 

cations exceed monovalent ones, and the Si:Al + Fe+3 ratio is 

4.03. Most clinoptilolites from sedimentary rocks are 

alkalic and have Si:Al+ Fe +1 ratios of 4-5 (Sheppard, 

1971b). Thus, this specimen from the Big Sandy Formation 

is unusual because of its high calcium and magnesium contents. 

Semiquantitative spectrographic analyses of six bulk 

samples of clinoptilolite-rich tuffs are given in table 7. All 

the tuffs contain at least 90 percent clinoptilolite. The spectrographic analyses suggest that the chemical analysis given 

in table 8 is not characteristic of the clinoptilolites in the Big 

Sandy Formation. Most of the spectographic analyses show 

clinoptilolite to be rich in alkalis, rather than in alkaline 

earths. The spectrographic analyses also show that the 

clinoptilolite-rich tuffs contain as much as 1.5 weight percent barium and as much as 3.0 weight percent strontium. 

The strontium content of clinoptilolites separated from 

" r 
AUTHIGENIC MINERALS 15 

F IGURE 13.- Sandstone cemented by finely crystalline clinoptilolite (d). 

Unpolarized light. 

the strontium-rich tuffs was determined by semiquantitative 

spectrographic analysis and showed a range of 0. 7-3.0 

weight percent. The mean index of refraction of these 

strontium-rich clinoptilolites is 1.488-1.496, which is 

significantly higher than that for clinoptilolites containing 

less than 0.5 weight percent strontium. 

ERIONITE 

Erionite was considered to be an extremely rare mineral 

before the work of Deffeyes (1959a, b) and Regnier (1960), 

who showed it to be a common authigenic zeolite in the 

altered silicic tuffs of lacustrine deposits in north-central 

Nevada. Since then, erionite has been recognized in silicic 

bedded tuffs from many of our Western States (Sheppard 

197la). Erionite, like chabazite, has not been reported from 

sedimentary rocks older than Eocene. Most occurrences of 

erionite are in upper Cenozoic lacustrine deposits. 

Erionite in the tuffs of the Big Sandy Formation occurs as 

nearly monomineralic beds or in association with the other 

zeolites, clay minerals, opal quartz, or potassium feldspar of 

authigenic origin (table 4). The association of erionite with 

clinoptilolite is especially common, but the associations 

T ABLE 8. - Chemical analysis and composition of unit cell of 

c/inoptilo/ite 

(Analyst: George Riddle, except for BaO and SrO determined by atomic absorpt ion by Wayne Mountjoy. Field No. W7 - 6B. Lab. No. 0102735. Loc. 6 (fig. 3), SE~NW~ sec. 13, T. 16 N., R. 13 W.] 

Chemical analysis 

Constituent Weight percent 

SiO, ______________ ___ ------ _____ 62.78 

AI,03 --------------------------- 12.33 

Fe,O, - ·- ------------------------- 1.41 

FeO ---------------------------- .00 MgO _ _ ____ _ _ _ _ __ __ __ _ ___ _ ___ __ _ _ 1.99 

CaO ---------------------------- 3.10 BaO _ _ ___ _ ____ __ __ ___ _____ ____ _ _ .13 

SrO _ ____ __ _ ___ _ _ ___ ___ __ _ _ ____ _ .40 

Na,O --------------------------- .63 K,O __ _ _ _ __ __ __ _ _ __ __ __ _ __ __ __ __ 1.67 

H,O + -------------------------- - 9.08 H,O - ___________________________ 5.36 

E~6 ============================ Tota l _____________ ___ __ _ ____ 99.:~~ 28 

Composition of unit cell 

[Ti, P, and Mn were omitted in calcu lation of the unit cell] 

Atoms per 

Constituent unit cell 

Si - ------------------ ---------- 28.76 

AI __ __ -------- ___ -------- _ _ _ __ _ 6.65 

Fe+> __ ___ _____ _____ -------- __ ___ .48 

~g============================= Ba __ _ _ __ ______ _ _______ ___ _ _ _ ___ u~ .02 

Sr _ __ _ _ _ ___ _ _ _ _ ___ _ ___ ____ _ _ ___ .II 

Na _____________________________ .56 

K _ _ ___ ___ ____ __ _____ _ _ _ _ _ _ _ _ _ __ .97 

~- ~ ~ -=~ ~ ~ -=~ ~ _= ~ ~ _=_=_=_=_= ~ _=_= ~ _= ~ ~ ~ ~-= ~u~ Si +AI+Fe"'' ____________ ___ ____ ---- 35 .89 

Si:AI+Fe+' ___ _ ____ ------ ______ - --- 4.03 

with mordenite, opal, and potassium feldspar are rare. 

Unlike the woolly-appearing erionite from the type locality 

near Durkee, Oreg. (Eakle, 1898), most of the Big Sandy 

erionite is prismatic (fig. 14) or acicular (fig. 15). The 

erionite commonly forms a network of unoriented prismatic 

crystals or aggregates of radiating acicular crystals. 

Spherulites of erionite are relatively rare in the tuffs of the 

Big Sandy Formation. Individual crystals range in length 

from lOJ.Im to 130J.Im, but most are 20J.Im to 60J.Im long. 

Indices of refraction of the Big Sandy erionite are: 

w= 1.464-1.467 and E = 1.467-1.4 70; birefringence is 0.003. 

Erionite has parallel extinction and is length slow. The indices are in the upper part of the range, 1.458-1.470, given 

by Sheppard and Gude (l969b) for other erionites from 

silicic tuffs. 

A chemical analysis of erionite that was separated from a 

nearly monomineralic part of the upper marker tuff is given 

in table 9. The analysis was corrected for minor calcite impurities associated with the erionite. The corrected analysis 

was then calculated into atoms per unit cell, on the basis of 

72 oxygen atoms, and is also given in table 9. Monovalent 

cations exceed divalent ones, and the Si:AI + Fe+3 ratio is 

3.77. The molecular ratio AlP3+Fep3: (Ca, Mg, Ba, Sr, 

Na2 , K2) 0 for zeolites should be unity; however, this ratio 
16 ZEOLITES AND AUTHIGENIC SILICATE MINERALS, BIG SANDY FORMATION, ARIZONA 

FI GU RE 14.- Network of prismatic erionite. Unpolarized light. 

for the Big Sandy erionite is about 0.6. Thus, the cation oxides are greatly in excess of Al 20 3+Fep3, and the analysis 

is unfortunately of poor quality. Compared with analyses of 

other erionites from silicic tuffs (Sheppard and Gude, 

1969b ), the Big Sandy erionite has high contents of 

magnesium and strontium. 

Cell parameters for the analyzed Big Sandy erionite were 

obtained by a least-squares refinement of X-ray powder diffractometer data, utilizing the U.S. Geological Survey's 

FORTRAN IV Computer Program W9214. The hexagonal 

cell parameters are a= 13.219±0.002 A, c= 15.040±0.005 

A, and V=2.276.0± 1.0 N. Inasmuch as the cell volume of 

erionite seems to decrease with increasing Si:Al + Fe+3 ratio 

(Sheppard and Gude, 1969b ), this cell volume for the Big 

Sandy specimen is compatible with a relatively high 

Si:Al+Fe+3 ratio. 

HARMOTOME 

Harmotome, probably the most common of the bariumrich zeolites, has been reported from a variety of 

metamorphic and igneous rocks throughout the world (Deer 

and others, 1963, p. 399). It is also commonly associated 

with metallic ore deposits. Although harmotome is a 

relatively rare zeolite in sedimentary rocks, it has been 

FIGU RE 15. - Fibrous erionite in zeolitic tuff. Vitroclastic texture is 

vaguely preserved. Unpolarized light. 

reported from deep-sea sediments (Morgenstein, 1967) and 

from lacustrine rocks in the Green River Formation and the 

Big Sandy Formation (Sheppard and Gude, 1971). 

Harmotome occurs in tuffs of the Big Sandy Formation 

in amounts ranging from a trace to about 40 percent of the 

rock. It is associated with authigenic clay minerals and one 

or more of the following zeolites: analcime, chabazite, 

clinoptilolite, and erionite. X-ray diffractometer patterns of 

harmotome-bearing tuffs also show quartz, but examination 

of thin sections indicated that the quartz is pyrogenic or 

detrital rather than authigenic. 

The harmotome in tuffs of the Big Sandy Formation occurs as prismatic or acicular crystals that are about 21-'m to 

301-Lm long. The crystals are commonly in radial aggregates 

(fig. 16) or small spherulites that are 201-'m to 301-'m in 

diameter. The harmotome has a mean index of refraction of 

1.506 and is length fast. 

A chemical analysis of harmotome from the Big Sandy 

Formation was corrected for analcime impurities (Sheppard 

and Gude, 1971) and is given in table 10. The harmotome 

was separated from a thin tuff stratigraphically higher than 

the upper marker tuff. The corrected analysis was 

calculated into atoms per unit cell, on the basis of 32 oxygen 

r 
AUTHIGENIC MINERALS 17 

T ABLE 9. - Chemical analysis and composition of unit cell of erionite 

· [a column. uncorrected analysis; b column, analysis corrected fo r C01 plus equi vale_nt CaO to. make ca lcite. Analyst: George Riddle, except for BaO and SrO determtned by atom1c absorption by 

Wayne Mountjoy. Field No. SW-26- 4C. Lab. No. 0102733. Lac. 26 (fig. 3), NEI'SEI' sec. 7. 

T. 15 N., R. 12 W.] 

Chemical analysis 

a Constituent (weight percent) 

b (weight percent) 

Si02 ---------------------- 58.37 Al,0 3 _ _ _ _ _ ___ _ _ _ _ ___ ____ _ _ 12.23 

~~§3 .:.:::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::: 6~ MgO ---------------------- 3.98 CaO _ ____ _ _ _____ _ _ ____ _ _ __ 1.72 

BaO ---------------------- .13 

SrO ---------------------- l.l4 

Na,O --------------------- 1.72 K,O __ :... ____ .:._ ______ _ _ ___ __ 6.12 

H,O + --------------------- 6.22 

H,O - --------------------- 4.96 

co, 5~6 ----------------------

====================== :.l1 76 

59.93 

12.55 

1.48 

.09 

4.08 

.77 

.13 

1.17 

1.76 

6.28 

6.39 

5. 10 

. 14 

.II 

.02 

-::-::-:-:---:-:-:--::-:--

Total ------------------ 99. 15 100.00 

Composition of unil cell 

[Fe+2 , Ti, P, and Mn were om itted in calcu lation of the unit cell I 

Constituent 

·si __ _ ____________ --- _ ----

AI _________ --------------

Mg ~~ _ ----------------------_____________________ _ 

Ca ______________ ---------

Ba _____ ------------------ Sr ______ ----- __ - ---------- Na ______________________ _ K _______________________ _ 

H,O+ ---------------------

0 H,O- _ ______________________ ---------------------_ 

Si+Al+Fe+' _ _______________ _ 

Si:Al+Fe+' ------------------

Atoms per 

unit cell 

27.47 

6.78 

.51 

2.79 

.38 

.02 

.31 

1.56 

3.67 

9.77 

7.80 

72.00 

34.76 

3.77 

atoms, and is also given in table 10. Monovalent cations are 

in excess of divalent ones, and the Si:AI +Fe +J ratio is 2.47. 

The ideal formula for harmotome is Ba2A14Si 120 32· 12H20, 

but most of the natural specimens contain substantial 

amounts of alkalis, mainly sodium. This harmotome from 

the Big Sandy Formation is the most sodium-rich and 

barium-poor harmotome thus far reported from any 

geologic environment. The deviation in composition of the 

Big Sandy harmotome from the ideal formula can be approximated by about 0.54 Na2(K2) replacement of 0.54 

Ba(Sr,Ca,Mg), and by about 0.69 Na(K)AI(Fe+3

) replacement of 0.69 silicon. 

Cell parameters for the Big Sandy harmotome were obtained by a least-squares refinement of X-ray powder diffractometer data, utilizing the U.S. Geological Survey's 

FORTRAN IV Computer Program W9214. The resulting 

monoclinic cell parameters for the analyzed specimen are 

a=9 .921 ±0.004 A, b= 14.135±0.009 A, c=8.685±0.006 

A, {3= 124°55'±2', and V=998.59±0.76 N. 

MORDENITE 

Mordenite has been confused with clinoptilolite or 

heulandite in sedimentary rocks because of similar indices 

of refraction and chemistry. X-ray diffractometer techniques, however, are adequate for positive identification (fig. 

FIGURE 16. - Radial aggregates ofharmotome, Unpolarized light. 

2). In recent years, mordenite has commonly been identified 

in Cenozoic tuffaceous rocks of the Western United States 

(Sheppard, 1971 a). 

Mordenite is the least common zeolite in tuffs of the Big 

Sandy Formation, and it has been recognized only from Xray diffractometer patterns of bulk samples. The mordenite 

ranges in abundance from trace amounts to about 30 percent of the tuff and is associated with authigenic clay 

minerals, analcime, clinoptilolite, erionite, and quartz. 

Mordenite is most commonly associated with clinoptilolite 

and quartz. 

Inasmuch as mordenite occurs in small amounts and is invariably associated with some other authigenic zeolite in the 

tuffs, no attempt was made to separate material for 

chemical analysis. Mordenites generally have a range in 

Si:AI+Fe+3 ratio of about 4.5-5.3 and generally have 

alkalis in excess of alkaline earths. 

OPAL 

Opal is difficult to recognize in the tuffs because of its 

isotropic and nondescript character. The opal is colorless to 

pale brown in thin section and has an index of refraction of 

1.43-1.46. Most of the opal is milky in reflected light. Most 

identifications of opal in tuffs of the Big Sandy Formation 
18 ZEOLITES AND AUTHIGENIC SILICATE MINERALS, BIG SANDY FORMATION, ARIZONA 

TABLE I 0. - Chemical analysis and composition of unit cell of 

harmotome 

(Analyst: Vertic C. Smith, except for SrO determined by atomic absorption by Violet 

Merritt. The Al 20 3 content includes P20, and the Fe20} content represents total irop. Analysis was corrected for analcime impurities ana recalculated to 100 percent (Sheppard and Gude, 1971). Field No. W7 - 44. Lab. No. 013893. Loc. 44 (fig. 3). SW\ISE\1 sec. 26, T. 16 N., R. 13 W.] 

Chemical analysis 

Constituent Weight percent SiO, ____________________________ 49.97 

Al 20 3 --------------------------- 15.15 

Fe,O, --------------------------- 3.15 MgO _ ______ _ ___ ____ _______ ___ _ __ 1.52 

CaO ________ ------ _ ---------- _ __ .64 

BaO ---------------------------- 8.75 SrO ·_ _ _ _ __ _ __ _ ____ _ _ __ _____ _ _ _ _ _ .10 

Na,O --------------------------- 3.33 

K,O ---------------------------- 2.24 

H,O+ -------------------------- 8.72 

H,O- -------------------------- 6.16 TiO, _ _ ____ _ __ ____ _ _ ___ ____ _ _ _ _ __ .27 

Total ________________________ 100.00 

Composition of unit cell 

[Ti was omitted in calculation- of the unit cell) 

Atoms per CoiiStituent unit cell Si ________________ _________ ____ 11.31 

AI ______ _ _ __ _ _ _ ___ _ _ _ __ ____ _ _ _ _ 4.04 

h +J ---------------------------- .~ Mg_____________________________ .51 

Ca ____ ___ _ __ __ _ __ _ _ _ _ _ _ _ ___ ___ _ .16 

Ba _ _____ __ __ _ __ ___ _ __ __ ____ ___ _ .78 

Sr _____________________ -------- .01 

Na _ ______ ___ _ _ _ ___ _ _ ____ ___ ____ 1.46 

K ___ _ _ __ _ _ ___ _ _ ___ _ _ __ _ _ __ _ ___ _ .65 

H,O+ --------------------------- 6.58 

H20- --------------------------- 4.65 

0------------------------------ 32.00 

Si+AI+FeT' ----------------------- 15.89 

Si:Al+Fe+• ------------------------ 2.47 

are based on X-ray diffractometer data of bulk samples. 

The opal has characteristically broad peaks at the following 

d spacings: 4.28 A, 4.08 A, and 2.50 A. Opal is associated 

with authigenic clay minerals, potassium feldspar, quartz, 

and each of the zeolites except harmotome, mordenite, and 

phillipsite. Associations of opal with analcime, clinoptilolite, and potassium feldspar are especially common. The 

abundance of opal ranges from trace amounts to about 70 

percent of the tuffs; however, most tuffs contain no more 

than 20 per~ent opal. 

PHILLIPSITE 

Phillipsite has long been known to occur in deposits on 

the sea floor (Murray and Renard, 1891, p. 400-411). Since 

the discovery by Deffeyes (1959a) of phillipsite in lacustrine 

tuffs of Nevada, this zeolite has been commonly reported as 

a rock-forming constituent in tuffaceous rocks of the 

Western United States. Phillipsite occurs in sedimentary 

rocks that range in age from Cretaceous to Holocene, but it 

is especially common in lacustrine deposits of late Cenozoic 

age, particularly those deposits of saline, alkaline lakes. 

Phillipsite in the Big Sandy Formation occurs in nearly 

monomineralic beds, but most of it is associated with 

authigenic clay minerals, potassium feldspar, quartz, or 

FIGURE 17.- Stubby prismatic crystals of phillipsite. Unpolarized light. 

other zeolites (table 4). Phillipsite has not been recognized 

in association with harmotome, mordenite, or opal and its 

association with potassium feldspar is rare. Clinoptilolite is 

the zeolite that is most commonly associated with phillipsite 

in tuffs of the Big Sandy Formation. The phillipsite occurs 

as stubby prismatic crystals or as spherulites. The prismatic 

crystals (fig. 17) range in length from less than 2J..Lm to 

25J..Lm, but most are less than 15J..Lm long. The spherulites 

(fig. 18), some of which are hollow, are 25J..Lm to IOOJ..Lm in 

diameter. Some spherulites show concentric zoning. 

The mean index of refraction of the Big Sandy phillipsite 

is 1.459-1.468, and the birefringence is about 0.002. The 

phillipsite has parallel extinction and is length slow. Indices 

of refraction for phillipsites from various rock types range 

from about 1.44 to 1.51 and seem to vary inversely with the 

Si:AI + Fe+3 ratio (Hay, 1964). The indices of the Big Sandy 

phillipsites are consistent with those of siliceous phillipsites 

from saline lacustrine deposits. 

A chemical analysis of phillipsite from the Big Sandy 

Formation is given in table 11. The phillipsite was separated 

from a nearly monomineralic thin tuff that is 

stratigraphically higher than the upper marker tuff. The 

analysis was calculated into atoms per unit cell, on the basis 
) 

AUTHIGENIC MINERALS 19 

FIGU RE 18.- Spherulitic phillipsite. Unpolarized light. 

of 32 oxygen atoms, and is also given in table II. 

Monovalent cations greatly exceed divalent ones, and the 

Si:Al+Fe +3 ratio is 3.37. The high Si:Al+Fe+J ratio, the 

high contents of alkalis, and the excess of sodium over 

potassium are characteristic of authigenic phillipsites 

formed in silicic tuffs of saline lacustrine deposits (Sheppard 

and others, 1970). 

POTASSIUM FELDSPAR 

Potassium f~ldspar occurs as an authigenic mineral in 

sedimentary rocks that are diverse in lithology, depositional 

environment, and age (Hay, 1966). The authigenic 

potassium feldspar is a pure or nearly pure potassium 

variety and occurs as authigenic crystals, overgrowths on 

detrital or pyrogenic feldspars, and replacements of detrital 

and pyrogenic plagioclase. In the tuffs of the Big Sandy Formation, the potassium feldspar occurs chiefly as authigenic 

crystals and only rarely replaces plagioclase. The authigenic 

potassium feldspar occurs in nearly monomineralic beds or 

is associated with authigenic clay minerals, opal, quartz, 

and each of the zeolites except harmotome and mordenite 

(table 4). The association of authigenic potassium feldspar 

with analcime is especially common. 

Potassium feldspar occurs in the tuffs as low birefringent 

T ABLE II.- Chemical analysis and composition of unit cell of 

phillipsite 

!Ana lyst: George Riddle, except for BaO and SrO dete rmined by atom ic absorption 

by Wayne Mountjoy. Field No. W7-25A. Lab. No. 01 02736. Loc. 25 (fig. 3), 

SE~NE~ sec. 7. T. 15 N., R. 12 W.l 

Chemical analysis 

Constituellf Weigh t percent Si02 

____________________________ 56.55 

AI,0 3 ___________________________ 13.23 

Fe,0 3 _ _ __ _ __ _ _ _ _ _ _ _ _ _ _ __ ___ __ __ _ 1.67 

FeO ---------------------------- .07 

MgO ---------------------------- 2.47 CaO _ _ _ __ _ ___ _ _ ___ _ _ _ _ _ _ ____ _ __ _ .48 

BaO _ _ ____ _ _ _ _ _ _ ___ _ _ _ _ _ __ _ _ _ __ _ .35 

SrO ---------------------------- .39 Na,O _ ____ ___ _ _ ____ _ _ _ __ _ _ _ _ ___ _ 4.14 

K,O _ ____ _ __ _ _ __ _ __ ____ _ _ _ _ _ _ ___ 5.69 

H20 + ___________________________ 6.83 

H,O - --------------------------- 6.74 TiO, _ __ __ __ _ _ _ __ _____ _ ___ _ _ _ _ _ _ _ .20 

P,O, ---------------------------- .19 MnQ ___________ _ ________________ ~2 

Total ________________________ 99.02 

Composition of unit cell 

[f e+2 , Ti, P, and Mn were omitted in calculation of the unit cell] 

Consrituent 

Atoms per unit cell 

Si _____________ _ _______________ 12.02 

AI ----------------------- ------ 3. 31 

Fe+' ---------------------- ------ .26 

Mg ----------------------------- .78 Ca _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ . I I 

Ba _ _ _ _ _ __ _ _ _ _ _ _ _ __ __ _ _ ____ _ _ _ _ _ .03 

Sr _ _ _ _ _ ____ _ _ _ _ _ ____ _ _ _ __ __ ___ _ .05 

Na _ ___ _ _ __ _ _ _ _ _ _ __ __ _ _ ___ ___ _ __ 1.70 

K ------------------------------ 1.54 

H,O + --------------------------- 4.84 

H,O - ---------- ----------------- 4.78 

0 ------------------------------ 32.00 

Si+ Al + Fe+' ----------------------- 15.59 

Si:AI + fe+' ------------------------ 3.37 

aggregates of crystals. These crystals range in maximum 

dimension from about 2,LLm to 14,LLm ; however, most are 

4,LLm to 8,LLm long. Paul D. Blackmon, using electron 

microscopy, has shown that the crystals are subhedral to 

euhedral (fig. 19). The feldspar is identical in habit and size 

with authigenic potassium feldspar from altered silicic tuffs 

of Pleistocene Lake Tecopa, Calif. (Sheppard and Gude, 

1968), and altered tuffs of the Miocene Barstow Formation 

(Sheppard and Gude, 1969a). The mean index of refraction 

is about 1.522 and indicates a pure or nearly pure potassium 

feldspar. Other optical parameters could not be determined 

because of the small size of the feldspar crystals. 

Semiquantitative spectrographic analyses of six bulk 

samples of potassium feldspar-rich tuff are given in table 12. 

All the samples contain more than 90-percent feldspar, as 

determined by X-ray diffraction. The analyses confirm that 

the feldspar is highly potassic and also show that the 

samples are relatively rich in boron. Quantitative spectrographic analyses for boron for the six bulk samples are 

given in table 13. The boron content ranges from 660 to 

2,300 ppm, but it is generally greater than I ,500 ppm. The 

absence of a boron-rich mineral from these nearly 

monomineralic tuffs suggests that the boron is in the 

authigenic potassium feldspar. 

Cell parameters for the six specimens of authigenic 
20 ZEOLITES AND AUTHIGE!-IIC SILICATE MINERALS, BIG SANDY FORMATION, ARIZONA 

FIGURE 19.- Stereographic pair of electron mic r ographs, s h owing s ubhedra l to e uh edra l au thigen ic potassium 

feldspar in the lower marker tuff. E lectron micrographs by P a ul D. Blackmon. 

T ABLE 12. - Semiquantitative spectrographic analyses of potassium 

feldspar-rich tuffs 

{Analyst B. W. Lanthorn. Results are to be identified with geometric brackets whose boundaries are 1.2. 0.83, 0.56, 0.38, 0.26, 0.18, 0. 12, and so forth , but are reported arbitrarily as mid-points of 

these brackets, I, 0. 7, 0.5, 0.3, 0.2, 0. 15, 0.1, and so fo rth . The precision of a report ed value is approxim ately plus or minus one bracket at 68-percent confidence, or two brackets at 95-percent 

confidence. G, greater than 10 percent; N, not detected; L, detected but below limit of determina- tion . The following elements were looked for but not detected: Ag, As, Au. Bi. Cd. Eu , Ge, Hf, In, 

P. Pd. Pr, Pt, Re, Sb, Sm. Sn, Ta, Te, Th, Tl, U, W, and Znl 

4 

Weight percent 

Si ----------------- G G G G G G AI ----------------- 10 7 10 10 G 7 

Fe ----------------- Mg 3 2 3 2 2 I _________________ .3 .3 .7 .7 .3 .15 

Ca ----------------- .3 .15 .3 1.5 .7 .2 

Na ----------------- .2 .7 .5 .3 .7 .5 

K ----------------- 7 7 10 10 10 7 Ti ----------------- .07 .03 .2 .05 .05 .03 

Parts per million 

B ----------------- 1,000 1,000 300 1,500 700 1,000 

Ba ----------------- !50 70 !50 150 700 150 

Be ----------------- 7 5 2 3 5 3 Ce ----------------- 150 150 N 200 L L 

Co ----------------- 7 N 7 N 5 N 

Cr ----------------- 15 5 15 7 10 20 Cu ----------------- 30 10 7 10 50 20 Ga ----------------- 30 20 30 30 30 20 La ----------------- 150 100 70 !50 50 100 Li ----------------- 500 200 200 500 200 200 

Mn _________________ Mo ____________ ___ 500 300 300 300 500 !50 __ 7 7 10 5 7 5 Nb ----------------- 30 20 L 20 15 20 Nd ----------------- 70 70 N 100 70 70 

Ni ----------------- 10 N 7 5 7 L Pb ----------------- 15 10 20 15 15 L 

Sc ----------------- 7 5 10 5 5 N 

Sr ----------------- 500 200 !50 300 500 150 

v ----------------- 500 200 70 150 !50 30 y ----------------- 20 50 10 30 15 L Yb ----------------- 1.5 7 1.5 3 1.5 I Zr ----------------- 150 200 !50 150 100 150 

NUM BERS AND LOCALITIES OF SAMPLES 

I. FieldNo. SW -2- IB.Lab.No.DI41570. Locality: NE\4 NE \4sec. l8, T. l5 N .. R. 12 W. 

2. Field No. W7 - 40A. Lab. No. 0141 571. Loca lity: SE1ASE\4 sec. 36, T. 16 N .. R. 13 W. 

3. Field No. W7 - 41A. Lab. No. 0141572 . Locality: SW1

ANW\4 sec. 31, T. 16 N .. R. 12 W. 

4. Field No. W7 - 45B. Lab. No. 014 1574. Locality: SW\4 NW\4 sec. 36, T. 16 N .. R. 13 W. 

5. Field No. W8 -54D. Lab. No. 0141575. Loca lity: SW\4SE\4 sec. I, T. 15 N .. R. 13 W. 

6. Field No. W8-72D. Lab. No. 0141577. Locality: SW 1

ANE\4 sec. 18. T. 15 N .. R. 12 W. 

potassium feldspar from tuffs of the Big Sandy Formation 

are given in table 13. The monoclinic cell parameters were 

obtained by a least-squares refinement of X-ray powder diffractometer data, utilizing the U.S. Geological Survey's 

FORTRAN IV Computer Program W9214. The cell 

parameters show the following range: a= 8.570-8.591 A, 

b=l2.960-12.990 A, e=7.163-7 .173 A , 

{3= 115°54.7' -116°4.6', and V= 715.61-718.99 N . 

The b and e cell dimensions for the six Big Sandy 

authigenic potassium feldspars are plotted in figure 20, the 

potassic portion of Wright and Stewart's (1968) b-e 

quadrilateral for alkali feldspars. All the authigenic 

feldspars plot near the high sanidine corner but well within 

the quadrilateral. This plot shows that the Big Sandy 

feldspars are anomalous; otherwise, the feldspars would 

have plotted at the high sanidine corner because of their 

potassic composition and measured a dimension (Wright 

and Stewart, 1968). The measured a dimension is 

8.570-8.591 A, but the a dimension inferred from the b-e 

plot is about 8.30-8.40 A . Thus, the Big Sandy feldspars 

have b that is shortened by as much as 0.06 A and e that is 

shortened by as much as 0.01 A. 

Authigenic potassium feldspars with similar anomalous 

cell dimensions have been reported from tuffs in the 

Pleistocene Lake Tecopa deposits and tuffs in the Miocene 

Barstow Formation (Sheppard and Gude, 1965; Martin, 

1971). These feldspars also have relatively high boron contents, and Martin ( 197 I) suggested that the anomalies a re 

caused by the partial substitution of boron for aluminum in 

the feldspar structure. Feldspars of the series 

KAISip8 -KBSip8 that were synthesized by Martin (1971) 

seem to confirm the effect of boron on the cell dimensions. 
DIAGENETIC FACIES 21 

TABLE 13.- Unit-cell parameters and boron content of authigenic potassium feldspar 

[Cell parameters were obtained by a least-squares refinement of X-rar powder diffr~cto_meter data, utili.zing the _U.S. Geological Survey's FORTRAN IV Computer _Program W9_214. _The boron content was determmed by quantitative spectrographic analys1s by J. C. Hamilton on bulk samples of tuff. Locality datu are g1ven m table 12) 

Purumeter 

or content 

a ______ (A)__ 8.589±0.003 8.583±0.004 

12.974±0.003 

7.167±0.002 

116°0.6'±1.8' 

717.18±0.33 

1,800 

8.578±0.004 8.589±0.002 8.589±0.002 8.573±0.003 

b ______ (A)__ 12.976±0.003 12.976±0.004 12.984±0.002 12.982±0.002 12.986±0.004 

c ------(A)__ 7.164±0.001 

fJ ---------- 115°59.2'±1.2' 

7.170±0.003 7.169±0.002 7.168±0.002 7.167±0.002 

116°3.2' ± 1.4"115°59.3' ± 1.4' 115°55. 7' ± 1.0' 116° 1.4' ± 1.1' 

V ______ (N)__ 717.70±0.23 0717.57±0.31 718.65±0.23 718.80±0.19 715.91±0.30 

Boron __ (ppm) _ _ 2,300 

QUARTZ 

Authigenic quartz is a common constituent in the altered 

tuffs of the Big Sandy Formation. Quartz is associated with 

all the other authigenic silicate minerals, as determined by 

studies of X-ray diffractometer patterns of bulk samples. 

Studies of the altered tuffs in thin sections, however, have 

confirmed the association of authigenic quartz with only 

clay minerals, potassium feldspar, opal, analcime, clinoptilolite, and mordenite. The association of authigenic quartz 

with analcime and potassium feldspar is especially common. 

The abundance of quartz in part·s of the altered tuffs ranges 

from trace amounts to about 90 percent. · 

Quartz occurs either as aggregates of anhedral, nearly 

equidimensional crystals or as aggregates of fibers. Both 

varieties occur in irregular, clear patches or they locally line 

irregular cavities. Individual crystals in the anhedral 

aggregates are from less than 2}-&m to 80}-&m in diameter and 

generally have wavy extinction. The fibrous variety is about 

l 0}-&m to 125}-&m long and is either length slow or length fast. 

Quartz also occurs as spherulites, as much as 250}-&m in 

diameter. Clusters of mutually interfering spherulites commonly fill irregular cavities (fig. 21). Most of the quartz is 

chalcedonic, inasmuch as the indices of refraction are below 

1.54. 

DIAGENETIC FACIES 

DISTRIBUTION 

Three diagenetic facies can be recognized in the tuffs of 

the Big Sandy Formation. Tuffs nearest the margin of the 

formation are characterized by zeolites other than analcime 

and are herein termed the "nonanalcimic zeolite facies." 

Tuffs in the central part of the lake basin are characterized 

by potassium feldspar and are termed the "potassium 

feldspar facies." Those tuffs intermediate in position 

between the nonanalcimic zeolite facies and the potassium 

feldspar facies are characterized by analcime and are 

termed the "analcime facies." No relict fresh glass was 

recognized in any of the tuffaceous rocks of the Big Sandy 

Formation. 

The boundaries between the facies are laterally 

gradational and difficult to recognize in the field. X-ray 

powder diffractometer data of bulk samples, coupled with 

thin-section study, are considered essential for positive identification and placement in the proper facies. 

660 2,200 1,500 1,900 

A map showing the diagenetic facies for a composite of 

all the tuffaceous rocks in the Big Sandy Formation is given 

in figure 22, and a map showing the facies for only the lower 

marker tuff is given in figure 23. The boundary between the 

nonanalcimic zeolite facies and the analcime facies was 

placed at the first appearance of analcime, and the boundary between the analcime facies and the potassium feldspar 

facies was placed at the first appearance of authigenic 

potassium feldspar. Most sample localities shown on the 

maps represent more than one sample (table 14). As many 

as 25 samples were collected and studied from tuffaceous 

units at certain localities, and as many as six samples of a 

single tuff were examined from certain localities. Therefore, 

each locality shown on the maps does not represent an equal 

quantity of mineralogical data. 

The diagenetic facies in plan are elongated parallel to the 

depositional basin. The nonanalcimic zeolite facies and the 

analCime facies are broadest at the northern part of the 

basin which was the inajor inlet of the ancient lake. The 

nonanalcimic zeolite facies is also broad and extends 

basinward near the other inlets. In a general way, the nonanalcimic zeolite facies and the analcime facies narrow 

where the basin narrows. About 3 miles southeast of 

Wikieup, where the basin was narrowest, both the nonanalcimic zeolite and analcime facies are absent along the 

eastern margin (fig. 22); the potassium feldspar facies is in 

contact with rocks older than the Big Sandy Formation for 

a distance of about 0.2 mile. These features suggest that the 

chemical depositional environment affected, if not controlled, the distribution of the diagenetic facies. 

FIELD DESCRIPTION 

The altered tuffs of the Big Sandy Formation are 

generally white to pale gray or pastel shades of yellow, 

brown, pink, or green with a dull or earthy luster. Most of 

these tuffs are resistant and form ledges. Original sedimentary structures, such as bedding and ripple marks, are 

generally preserved in the altered tuffs. Although no relict 

glass was recognized in any of the tuffaceous rocks, the 

original vitroclastic texture is commonly preserved, especially in the nonanalcimic zeolite facies. Preservation of 

these features is convincing evidence that the present 

differences in composition and mineralogy of the tuffs are 

due to postdepositional processes. 
22 ZEOLITES AND AUTHIGENIC SILICATE MINERALS, BIG SANDY FORMATION, ARIZONA 

7.23~--~----~----~----~--~-----.----.-----.----.~---.-----.----.-----.----,----, 

7.22 

7.21 

7.20 

Q)" 

·v.~ ~, 

"'i " 

Maximum microcline 

Q)'\ 

-~~ 

Q)'\ "' '\ -~~ -v '\ 

" 

0" \. -v '\ \. 

" " " " 

'\ '\ " '\ 

" 

'\ '\ " '\ 

" " 

" '\ " '\ 

" " 

'\ '\ " '\ '\ '\ 

" " " 

" '\ '\ '\ 

'\ '\ " '\ " '\ '\ '\ 

~ 7.19 " " " 

\ \ \ \ u \ \ \ 

\ 

7.18 

7.17 

\ 

\ 

\ 

\ 

\ 

\ 

\ \ 

\ \ \ \ 

\ 

\ 

\ 

\ 

\ \ 

\ \\ 

\ \ 

\ 

\ 

\ \ 

\ \ \ \ 

\ 

\ 

High sanidine 

7.15~--~-----L~--~----~--~--_£~----~----L---~~--~-----L----~----L---~----~ 

12.90 12.95 13.00 13.05 

b (A) 

FIGURE 20. - Potassium-rich portion of Wright and Stewart's (1968) b- c quadrilateral for alkali feldspars, which has been contoured for a (dashed 

lines). The b-e dimensions are plotted for the six specimens given in table 13. Error bars represent plus or minus one standard deviation. 

The authigenic silicate minerals in the altered tuffs 

generally cannot be positively identified in the field because 

of the very small size of the crystals. Where the altered tuff 

is nearly monomineralic, certain gross physical properties of· 

the rock may aid field identification. Tuffs of the nonanalcimic zeolite facies are generally more resistant and 

show better preservation of the vitroclastic texture than 

tuffs of the analcime or potassium feldspar facies. Most 

nonanalcimic tuffs break with a platy or subconchoidal to 

conchoidal fracture (figs. 24-26). Tuffs rich in chabazi~e 

are commonly white to pale yellow and break with a platy 

or subconchoidal fracture (fig. 25). Erionite-rich tuffs are 

yellow to orange and generally break with a platy fracture 

(fig. 26). Tuffs rich in clinoptilolite are generally white, 

gray, or pale yellow and break with a conchoidal fracture. 

Tuffs rich in other zeolites of the nonanalcimic zeolite facies 
' 

DIAGENETIC FACIES 23 

FIGU RE 21. - Spherulitic quartz, which has filled an irregular cavity in the 

lower marker tuff. Much of the dark area of the photomicrograph consists of finely crystalline authigenic potassium feldspar. Crossed nicols. 

do not seem to have distinctive megascopic properties that 

help their identification. 

Tuffs that consist mostly of analcime are generally green 

or greenish yellow and are porous and friable. Their most 

characteristic features are a sugary texture and the poor 

preservation or absence of the original vitroclastic texture. 

The analcimic tuffs gen'erally resemble well-sorted siltstone 

to the unaided eye. However, analcime euhedra are commonly visible with the aid of a hand lens. Analcimic tuffs 

break with an irregular or blocky fracture (fig. 27). 

Tuffs altered chiefly to potassium feldspar are generally 

white or pale yellow, porous, and very friable. If minor or 

no authigenic quartz is associated with the feldspar, the tuff 

can easily be crumbled in one's hand. Potassium feldsparrich tuffs commonly show poor preservation of the original 

vitroclastic texture and break with an irregular fracture. 

PETROGRAPHY 

The mineralogy of the tuffaceous rocks was determined 

by study of X-ray powder diffractometer data of bulk 

samples (table 14), supplemented by thin-section study. 

Thin sections were especially useful for determining age 

relationships of the authigenic minerals but were generally 

not examined until the mineralogy of the samples was 

known by X-ray methods. Optical identification of the 

zeolites is difficult because of their small crystal size and 

similar optical properties and morphology. 

Crystal fragments, unlike the original vitric materials, are 

generally unaltered in the tuffaceous rocks. Authigenic 

potassium feldspar, however, locally replaced plagioclase; 

and calcite locally replaced detrital and pyrogenic crystal 

fragments, as well as the authigenic silicate minerals, including analcime and potassium feldspar. 

NONANALCIMIC ZEOLITE FACIES 

The vitroclastic texture is generally well preserved in tuffs 

of the nonanalcimic zeolite facies (figs. 28 and 29). Some of 

the zeolitic tuffs lack the relict texture or have only vague 

ghosts of shards, where the zeolite is coarsely crystalline or 

where authigenic clay minerals are absent. Typical 

pseudomorphs of shards consist of a thin marginal film of 

montmorillonite, several micrometers thick, succeeded inwardly by crystals of one or more zeolites. The thin montmorillonite film emphasizes the pseudomorphs, especially if 

a thin section is viewed under crossed nicols (fig. 30). The 

pseudomorphs may be either solid or hollow, and both types 

can be recognized in some thin sections. Hollow 

pseudomorphs seem to have formed from relatively large 

vitric particles and are generally less abundant than solid 

ones. 

Nearly monomineralic tuffs of chabazite, clinoptilolite, 

erionite, and phillipsite were recognized in the Big Sandy 

Formation, but most tuffs consist of two or more zeolites in 

addition to the nearly ubiquitous authigenic clay minerals. 

The tuffs consist very commonly of two zeolites, less commonly of three zeolites, and rarely of four zeolites. The 

following two-, three-, and four-zeolite associations are 

recognized in the nonanalcimic zeolite facies: 

Zeolite Associations 

(Ch, chabazite; Cl, clinoptilolite; E, erionite; H, harmotome; M, mordenite; P. phillipsite] 

Two Three Four 

zeolites zeolites zeolites 

Ch+Cl Ch+Cl+E Ch+Cl+E+H 

Ch+E Ch+Cl+P 

Ch+P Ch+E+P 

Cl+E Cl+E+P 

Cl + M Cl+E+H 

Cl+P Cl+E+M 

E+ P 

The most common associations of two zeolites are clinoptilolite plus erionite, followed by clinoptilolite plus phillipsite. The most common associations of three zeolites are 

chabazite plus clinoptilolite plus erionite, followed by 
24 ZEOLITES AND AUTHIGENIC SILICATE MINERALS, BIG SANDY FORMATION, ARIZONA 

34° 4 5'-

113'' 37'30" 

21 

34"42'30"-

EXPLANATION 

Facies boundary 

27 

Dashed where approximately located 

Nonanalcimic zeolite facies 

0 

Analcime facies 

Potassium feldspar facies 

0 36 

Sample locality 

@ 

Inlier of volcanic rocks 

2 

34" 40'-

0 3 KILOM ETERS 

. .__. 

34 37'30"-+ 

···./""'"' 

3 Ml L ES 

R.13W R 12W. 

FIGU RE 22. Diagenetic facies for a composite of all the tuffaceous rocks in the Big Sandy 

Formation. X-ray analysis of samples given in table 14. 
113° 37'30" 

27 

8 

DIAGENETIC FACIES 

113° 35' 

35 

_,-r··· 

.r ··" 

10$ · · ·ios ... -' _._~ 

/ 

lo4~' \ / .. ~ 

.-,:.'''t-1\ --·~· · 

-+·. __ ·.:::---~==s~~~~+l--+-'---l---··_· 1-4-li~··c.;···-l\~~-1-3-~r--\::;-ct·L 

EXPLANATION 

Facies boundary 

Dashed where approximately located 

Nonanalcimic zeolite facies 

Analcime facies 

Potassium feldspar facies 

0 

.n 

Sample locality 

~ 

Inlier of volcanic rocks 

2 3MILES 

! 

0 3KILOMETERS R.13W. R . 12 W. 

~..- . 

· · ·../"'"" 

FIGURE 23. - Diagenetic facies for the lower marker tuff of the Big Sandy Formation. X-ray analysis of samples 

given in table 14. 

25 
26 ZEOLITES AND AUTHIGENIC SILICATE MINERALS, BIG SANDY FORMATION, ARIZONA 

TABLE 14.- Mineralogic composition of tuffaceous rocks of the Big Sandy Formation, as estimated from X-ray diffractometerpatterns 

of bulk samples 

1- __ looked for but not found; Tr., trace. Clay I OA: authigenic illite, pyrogenic and detrital biotite, and detrital muscovite. Quartz includes authigenic, pyrogenic, and detrital varieties. Plagioclase and hornblende are pyrogenic and detrital. Other: chiefly dolomite; sample C from Loc. 42 contains a trace of barite; samples B and D from loc. 37 contain 

a trace of gypsum; and sample SW-2-6 from loc. 2 contains a trace of halite. Sam pie taken: Tu, upper marker tuff; Tl, lower marker tuff; L, below lower marker tuff, but 

exact stratigraphic position unknown; M, between lower marker tuff and upper marker tuff but exact stratigraphic position unknown; U, above upper marker tuff but exact stratigraphic position unknown; Ms, mudstone; Ss, sandstone; St, siltstone; T, tuJf] 

Loc. 

(fig. 3) Field No. 

SW-1-11 

IOF 

IOE 

IOD 

IOC 

lOB 

lOA 

9 

8 

7 

6 

5 

4B 

4A 

3 

2B 

2A 

I SW-2-8B 

SA 

7 

6 

4 

2 

IC 

IB 

lA SW-3-15B 

15A 

14C 

c 

B 

A 

F 

E 

D 

c 

B 

A 

c 

B 

A 

A 

c 

B 

A 

c 

B 

A 

10 A 

II B 

A 

12 E 

D 

c 

B 

A 

F 

14B 

14A 

13B 

13A 

120 

12C 

12B 

12A 

lOB 

lOA 

9C 

9B 

9A 

8 

7 

5 

4 

2C 

2B 

2A 

IB 

lA 

Sample taken 

3ft above Tl, Ms _ ------ _______________ _ 

Tl, 31 in. above base ______ ----- __________ _ Tl, 23 in. above base _____________________ _ 

Tl, 16 in. above base __ ------ _____________ _ 

Tl, 13 in. above base _______ --- ___________ _ Tl, 8 in. above base _____________________ _ 

Tl, at base ___________ - --------------- 2ft below Tl, Ms ______________________ _ 6ft below Tl, T _______________________ _ 

21ft below Tl, Ms ______________________ _ 

26ft below Tl, St ______________________ _ 

31ft belowTI, Ms ----------------------- 35ft below Tl, T, at upper part _______________ _ 35ft below Tl, T, at lower part _______________ _ 38ft below Tl, Ms ______________________ _ 

. 42ft below Tl, T, at upper part _______________ _ 

42ft below Tl, T, at lower part _______________ _ 

48ft below Tl, Ms ______________________ _ 

75ft above Tl, T, at upper part ____ --,- ________ _ 75ft above Tl, T, at lower part _______________ _ 

62ft above Tl, Ms ______________________ _ ·55ft above Tl, T _______________________ _ 

51 ftaboveTI, T _ _: _____________________ _ 

24 ftaboveTI, Ms ----------------------- TI, at top ___________________________ _ 

Tl, 14 in. above base _____________________ _ 

Tl, at base __________ -.- ______ --------- 148ft above Tu, Ms _____________________ _ 120ft above Tu, Ms _____________________ _ 

108ft above Tu, Ms _____________________ _ 

103ft above Tu, T _ _ _ _ __ _ _ _ _ _ __ _ ___ __ ___ _ Tr. 

99ft above Tu, T _ _ _ _ _ _ _ _ _ _ __ __ ____ ___ _ _ Tr. 

94ft above Tu, T, at upper part _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ Tr 

94ft above Tu, T, at lower part _______________ _ 83ft above Tu, Ms _____________________ _ 58 ft above Tu, T, at upper part _______________ _ 

58ft above Tu, T, at lower part _______________ _ 

48ft above Tu, T ______________________ _ 

21 ftaboveTu, T ----------------------- 16ft above Tu, Ms _____________________ _ 

Tu, at top _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ Tr. 

Tu, 2 in. above base _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ I 

Tu, at base___________________________ Tr. 5 ft below Tu, Ms _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 2 II ft below Tu, T _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ I 

13 ftaboveTI, Ss ----------------------- I 12ftaboveTI, T ------------------------ Tr. Tl, at top____________________________ Tr. 

Tl, 9·in. above base ---------------------- Tr. Tl, at base ----- _ __ _ _ _ _ _ _ __ _ _ _ _ _ _ _ _ _ _ _ Tr. 

3ft below Tl, Ss _ _____ __ _ _ _ _ _ _ _ _ _ _ _ _ _ ___ 2 

6ft below Tl, Ms _ _____ __ _ _ _ _ _ _ _ _ _ _ __ _ _ _ 3 

r~t ~J!:=+r.~s = = = = = = = = = = = = = = = = = = = = = = = = ir U, T, at top ___ ----------- _ _ ___ _ __ _ ___ I 

U, T,46in.abovebase -------------------- 1 U, T, 35 in. above base _ _ __ _ __ ____ ____ __ __ _ 3 

U, T,22in.abovebase -------------------- 2 

U, T,l2in.abovebase -------------------- 2 

~~~~~-------------------------- U, T, at top -------------------------- U, T, near middle ______________________ _ 

U, ~~~~~-------------------------- Ss ________ ---- __ _ _ _ _ _ _ _ __ _ _ __ __ _ Tr. 

H ~\~~~~e:~~;e-====================== T{' Tl, at lower part _ _ _ _ ___ _ _ _ ____ __ _ _ ___ _ _ _ 2 

Tl, at upper part _______________________ _ 

Tl, near middle _______________________ _ 

Tl, at lower part _ _____ _____ __ _ _ __ ___ _ _ __ Tr. 

Tl, at upper part _______________________ _ 

U,T ------------------------------ U, T- ~----------------------------- Tr. 

Tr . 

Tr. 

I 

Tr. 

Tr. 

Tr. 

Tr. 

U,T,atupperpart ---------------------- 2 Tr. 

U,T,atlowerpart ---------------------- Tr. I 

U, T,attop -------------------------- Tr. 2 U,T,nearmiddle ----------------------- Tr. 2 U, T, at base ___ ------------___________ Tr. 2 

U, T ------------------------------ Tr. Tr. 

Tr. 

Tr. 

2 

3 

4 

6 

9 

7 

7 

Tr. 

3 

8 

I 

9 

I 

10 

10 

Tr. 

8 

Tr. 

7 

8 

8 

10 

Tr. 

Tr. 

9 

9 

Tr. 

6 

4 

3 

8 

8 

I 

Tr. 

7 

8 

8 

9 

OJ 

-~ 

~ u 

I 

10 

OJ 

;g 

0. 

.5 

0 

3 

5 

Tr. 

Tr. 

2 

10 

9 

5 

0 

0 

E 

:J: 

X-ray analysis (parts of 10) 

OJ 

~ :c 

0.. 

3 

5 

5 

4 

2 

8 

6 

2 

I 

4 

4 

6 

3 

2 

8 

7 

2 

4 

3 

8 

4 

8 

10 

9 

2 

Tr. 

4 

Tr. 

Tr. 

Tr. 

Tr. 

I 

4 

5 

4 

3 

Tr. 

Tr. 

Tr. 

I 

-; 

c. 

0 

Tr. 

4 

4 

6 

I 

Tr. 

Tr. 

Tr. Tr. 

Tr. 

2 

Tr. Tr. Tr. 

I 

Tr. 2 Tr. 6 

2 Tr. Tr. 

Tr. 

Tr. 

Tr. 

I 

Tr. 

Tr. 

I 

I 

Tr. 

Tr. 

Tr. 

Tr. 

Tr. 

Tr. 

Tr. 

I Tr. 

Tr. Tr. Tr. Tr. Tr. 

Tr. 

Tr. 

Tr. 

I Tr. 

Tr. 

Tr. 

I 

Tr. 

Tr. 

Tr. 

Tr. 

I 

Tr. 

I 

Tr. 

I 

Tr. 

Tr. 

Tr. 

2 

Tr. 4 I Tr. 2 Tr. 

Tr. I 

Tr. I 

4 

Tr. 

2 Tr. 3 

Tr. 

Tr. 

I 

Tr. 

Tr. 

4 

3 

-. 

"I 

·~ I 
DIAGENETIC FACIES 

TABLE 14.- Mineralogic composition of tuffaceous rocks of the Big Sandy Formation as estimated from X-ray diffractometer patterns 

of bulk samples - Continued 

Loc. 

(fig. 3) Field No. 

13 SW-13-108 lOA 

9 

88 

SA 

78 

7A 

6 

48 

4A 

14 c 

B 

A 

15 A 

16 c 

8 

A 

17 c 

B 

A 

18 B 

A 

19 B 

A 

20 A 

21 c 

B 

A 

23 c 

8 

A 24 8 

A 

25 B 

A 

2B 

2A 

I 

26 SW-26-10 

98 

28 B 

A 

29 A 30 c 

B 

A 

31 A 

33 E 

0 

c 

B 

F 

A 

G 

9A 

8 

6 

5 

4C 

48 

4A 

3 

2 

I 

34 SW-34-9 

BE 

80 

sc 

88 

SA 

36 c 

B 

A 

37 0 

c 

8 

6 

58 

SA 

4C 

48 

40 

4E 

4A 

3 

28 

2A 

Sample taken 

U. Ms ----------------------------- 2 U,Ms ----------------------------- 4 U,Ss------------------------------ I 

U, T ------------------------------ Tr. U, T ------------------------------ Tr. U, Ms -------------------------- ___ 2 U, Ms ----------------------------- 2 U, Ss _____ ------ __ ----- ____ -------- 2 U, T, at top ___________ _:______________ Tr. 

U, T, at base ________ ---- _________ ----_ 

U, T, at upper part _____________________ _ 

~~~~~-------------------------­ u. U, Ms ----------------------------- T, at upper part _____________________ _ 

U, T, near middle _·:.. ____________ ----- ___ _ 

u.~~~~-------------------------- u. T ------------------------------ Tr. 

U, T ------------------------------ Tr. U, T ------------------------------ I 

U. T ------------------------------ Tr. 

U,T ------------------------------ U, T ------------------------------ Tr. 

U, T ------------------------------ Tr. 

U, T ------------------------------ Tr. 

U, T ------------------------------ I U, T ------------------------------ Tr. Tr. U, T ------------------------------ Tr. Tr. U. T ------------------------------ Tr. 2 U, T, at top -------------------------- 2 2 U, T, near middle -----·------------------ Tr. 

U. T. at base-------------------------- I Tr. U, T, ut top -------------------------- I Tr. 

U, T,ut upper part ---------------------- Tr. ·Tr. 

U, T, at lower part ---------------------- 2 U, T, at upper part _____________________ _ 

U, ~:i·~~~~========================== T ------------------------------ 97ft ubove Tu, Ms _ ------ _ ---- __ ----- __ _ 75ft above Tu, T, at upper part _______________ _ 

75ft above Tu, T, at lower part _______________ _ 

62ft ubovcTu, Ms ---------------------- I 30ft above Tu, Ss __ ---- ___ ----- _ _ _ _ _ _ _ _ _ I 

4ft above Tu, Ms _ ------ __ ----- _ _ _ _ _ _ ___ I Tu, ut top _____ ---- _____________ ---- _ Tr. 

Tu, near middle _ ------ _ ----- __________ _ Tu, at buse __________________ -·- ______ _ 2ft below Tu, Ms ______________________ _ 

6ft below Tu, T _________ ----- _________ _ 

10ft belowTu, Ms ----------------------

U, T ------------------------------ 2 U, u.ss T ------------------------------ _____________________________ _ Tr. 

Tu, at top __ --- _ __ _ ____ _ _ _ _ _ _ ____ _ _ _ _ Tr. Tu, near middle _ __ _ _ ___ _ _ _ _ _ __ ___ _ _ _ _ _ _ Tr. Tu,otbase ___________________________ Tr. Tr. 

M, T ------------------------------ Tr. Tl, at top _______ -----_------_________ Tr. 

Tl, 31 in. above base______________________ Tr. Tr. Tl, 26 in. above base _____ ---- _______ -----_ Tr. Tl,l3in.abovebase ______________________ Tr. 

Tl, II in. above base ________ ------ _______ _ Tl, at base ____ ------ _ _ __ ____ _ _ _ _ _ _ _ __ Tr. 

2ft belowTI, Ms ----------------------- 2 Tr. 13ft aboveTu, Ss ----------------------- Tr. 

Tu,attop --------------------------- Tr. Tu, 24 in. above base --------------------- Tr. Tu, 18 in. above base _ __ _ _ __ _ _ __ _ _ _ _ _ _ _ _ _ _ Tr. 

Tu, 8 in. above base _____________________ _ Tu, at base ____ -- ____________________ _ 

5 ft below Tu, T ____________ ----- _ _ _ _ _ _ _ Tr. Tr. 

18ftbelowTu,Ss ----------------------- Tr. 2 

21ft belowTu, Ms ---------------------- 2 ~ Tl, at top __________ ---- ___ ------_____ 1 Tl, near middle _ __ _ _ _ __ _ _ _ _ ____ _ _ _ _ _ _ _ _ I Tr. 

Tl,ncurmiddle ------------------------ Tr. Tl, near middle _______ ---- _ _ _ _ _ _ ____ __ _ 1 

Tl,atbuse --------------------------- Tr. 9ft below Tl, Ss ______________ ----- ____ _ 

12ft below Tl, T ------------------------ Tr. 

13ft below Tl, Ss _ _ _ _ _ ___ __ _ _ _ _ _ ___ _ _ _ _ _ I 

U,Ss------------------------------ I 

U, T,ut upperpurt ---------------------- Tr. U, T, at base ___ ----- _________________ _ 

U, T ------------------------------ Tr. 

~·.~ ·::::::::::::::~:::::~::::·~~~~= i~·. 

Tr. 

2 

Tr. 

Tr. Tr. 

... 

·~ 

r) 

~ 

... 

;g 

c.. 

.5 

0 

Tr. Tr. 

Tr. 

2 

Tr. 

.o 

8 

10 

9 

2 

10 

10 

8 

Tr. 

6 

7 

8 

4 

9 

2 

10 

2 

Tr. 

10 

9 

4 Tr. Tr. I Tr. 2 Tr. 2 

Tr. 

Tr. 

I 

I 

Tr. 

10 

Tr. Tr. 

Tr. 

Tr. 

Tr. 

2 

9 

3 

9 

9 

I Tr. Tr. 

Tr. 

I Tr. I I 

4 I 

2 

6 

9 

3 

7 

8 

7 

X-ray analysis (parts of 10) 

E 

0 

0 

E 

:l: 

4 

Tr. 

Tr. 

I 

Tr. 

... 

~ :.c 

Q, 

Tr. 

Tr. 

Tr. 

Tr. 

4 

Tr. 

Tr. 

Tr. 

Tr. 

I 

Tr. 

Tr. 

2 

I 

Tr. 

Tr. 

Tr. 

I 

Tr. 

Tr. 

Tr. 

... 

g "' 

-~ 

c:: 

Tr. 

Tr. 

Tr. 

I 

Tr. 

Tr. 

Tr. 

Tr. 

Tr. 

Tr. 

Tr. 

I Tr. Tr. Tr. Tr. 

Tr. 

4 

Tr. 

Tr. 

Tr. 

Tr. 

Tr. 

Tr. 

Tr. 

I 

Tr. 

Tr. 

Tr. 

I 

I 

I 

Tr. 

I Tr. 

2 

I 

Tr. Tr. 

Tr. 

Tr. 

Tr. 

Tr. 

Tr. 

2 

Tr. 6 

Tr. Tr. 

Tr. 

Tr. 

Tr. 

I 

Tr. 

I Tr. 

Tr. Tr. 

Tr. Tr. Tr. 3 Tr. Tr. Tr. 

Tr. 

2 Tr. 

Tr. 

... 

-5 

0 

27 

Tr. 

Tr. 

Tr. 

Tr. 

Tr. 

Tr. 
28 ZEOLITES AND AUTHIGENIC SILICATE MINERALS, BIG SANDY FORMATION, ARIZONA 

TABLE 14. - Mineralogic composition of tuffaceous rocks of the Big Sandy Formation as estimated from X-ray diffractometer patterns 

of bulk samples - Continued 

Loc. 

(fig. 3) Field No. 

37 A 

38 A 

39 8 

A 

40 D 

c 

8 

A 

41 8 

A 

42 c 

8 

A 

E 

D 43 A 

44 A 

45 D 

c 

8 

A 

46 c 

8 

A 

47 A 

48 c 

8 

A 

49 A 

50 8 

A 

51 A 

52 A 

53 A 54 G 

F 

E 

D 

c 

8 

A 55 8 

A 

58 A 

59 8 

A 

60 8 

A 

61 c 

8 

A 62 c 

8 

A 

63 E 

D 

c 

8 

A 

64 B 

A 65 D 

c 

8 

A 

66 A 

67 SW-67-9C 

98 

9A 

7 

60 

6C 

68 

68 B 

A 69 c 

8 

A 71 G 

F 

E 

D 

c 

6A 

58 

5A 

4C 

48 

4A 

2 

Sample taken 

U, T ------------------------------ I Tl, at lower part _ __ _ _ _ _ _ _ _ _ __ _ __ _ _ __ ___ _ Tr. 

Tl, at upper part________________________ Tr. 

Tl, at lower part _ _ _ __ __ __ _ _ _ _ _ _ __ _ _ _ _ _ _ _ Tr. 

TI, T~d~P---------------------------- 20 in. above base _____________________ _ 

Tl, 13 in. above base______________________ Tr. 

Tl, 4 in. above base _ ------ _ --------- ____ _ 

L, T, at upper part----------------------- L, T, at lower part ______________________ _ 

Tl, at top____________________________ Tr. Tl, near middle _______________________ _ 

Tl, at base ____ ----------------------- Tr. 

25ft below Tl, T, at upper part _ _ _ _ __ _ _ _ _ _ _ _ _ _ _ Tr. 

25ft below Tl, T, at lower parL __ 

U, T ------------------------------ Tr. 

U,T ------------------------------ TI, at top:.. __ '-________________________ Tr. 

Tl, 9 in. above base _____________________ _ Tl, 3 in. above base _____________________ _ Tl, at base __________________________ _ 

Tl, at top____________________________ Tr. Tl, at upper part _______________________ _ 

Tl, at base __________________________ _ 

U, Ms ----------------------------- U, T, at top _________________________ _ 

U, T, near middle ______________________ _ 

U, T, at base-------------------------- Tr. 

U, T ------------------------------ I U, T, at upper part ---------------------- Tr. U, T, at base__________________________ Tr. 

U, T ------------------------------ I 

U, Ms ----------------------------- Tr. 

U,T ------------------------------ 18ft above Tl, T, at upper part _______________ _ 18ft above Tl, T, at base __________________ _ 

Tl, at top---------------------------- Tr. Tr. Tl, 18 in. above base _____________________ _ 

Tl, 15 in. above base______________________ Tr. 

Tl,8in.abovebase ---------------------- 2 Tr. Tl, 2 in. above base _ _ _ _ _ _ _ _ _ _ __ _ _ _ _ _ _ _ _ _ _ I Tr. 

U, T, at upper part _ _ _ __ _ _ _ __ _ __ _ __ _ _ _ _ _ _ Tr. U, T, at lower part _ _ _ ____ _ _ _ _ _ _ _ __ __ _ _ __ Tr. 

U, Ss _ _ _ _ _ _ _ __ _ _ _ _ _ _ _ _ _ _ __ __ _ _ _ _ _ _ _ Tr. 

M, T,atupperpart ---------------------- I M, T, at lower part _ _ __ __ _ _ _ _ _ _ _ _ _ __ __ _ _ _ I Tl, at upper part _______________________ _ 

Tl,atlowerpart ------------------------ 3 Tl, at upper part________________________ Tr. Tr. Tl, 15 in. above base _____________________ _ Tl, at base _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 4 

U, T ------------------------------ Tr. Tr. U, T, at top _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ Tr. Tr. 

U, T, at base ________ ---------- _______ _ 

U,T ------------------------------ U, T, at upper part _____________________ _ U, T, near middle ______________________ _ 

U, T, at lower part _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ Tr. Tr. 

U, T ------------------------------ Tr. Tl, at upper part________________________ Tr. Tl, at lower part _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ Tr. 

Tu, at upper part _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ Tr. Tu, near middle _ _ _ _ _ _ _ _ _ _ __ _ _ _ _ _ _ _ _ _ _ _ _ Tr. Tr. 

Tu, at lower part ______________________ _ 5 ft below Tu, T _______________________ _ 

23ft below Tu, Ss _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ Tr. Tr. 

104ft above Tu, Ss _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ Tr. 

98ftaboveTu,Ss ----------------------- Tr. 93 ft above Tu, T ______________________ _ 

58ft above Tu, Ss _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ Tr. 55 ft above Tu, T ______________________ _ 40 ft above Tu, T _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ I 

36 ft above Tu, Ss _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ Tr. 

23ftaboveTu,Ss ----------------------- Tr. Tr. 12ft above Tu, Ss ________ ------- _ _ _ __ _ _ _ I 10ft above Tu, T _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ Tr. 

Tu, at top _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ Tr. Tu, near middle _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ Tr. Tu, at base _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ Tr. 

5 ft below Tu, T _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ Tr. 

U. T ------------------------------ I U, T _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ Tr. 

Tl, at top _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 2 

Tl, near middle _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ Tr. Tl, at lower part _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ Tr. 75ft above Tl, T _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ Tr. 

Tl, a't top____________________________ Tr. Tl, 22 in. above base _____________________ _ 

Tl, 18 in. above base _____________________ _ Tl, II in. above base _____________________ _ 

Tr. 

Tr. 

Tr. 

4 

Tr. 

Tr. 

8' 

6 

7 

5 

10 

Tr. 

3 

2 

2 

3 

Tr. 

3 

7 

I 

10 

6 

10 

Tr. 

2 Tr. 

Tr. 

Tr. 

Tr. 

2 

4 

I 

Tr. 

10 

3 

8 

8 

8 

9 

10 

Tr. 

Tr. 

I 

10 

2 

E 

0 

0 

E 

:1: 

X-ray analysis (parts of 10) 

I 

3 

10 

10 

9 

10 

10 

10 

2 

9 

10 

3 

4 

10 

4 

7 

7 

5 

3 

9 

10 

10 

10 

8 

9 

9 

8 

10 

7 

8 

9 

6 

I 

]. 

0 

I Tr. 

2 4 

4 6 

8 2 

9 

8 

2 

Tr. 

4 

., 

·;:; 

-;;; 

u 

Tr. 

., 

u "' 

0 

·~ 

c::: 

Tr. Tr. Tr. 

Tr. 

I 4 

Tr. 

Tr. Tr. 

Tr. 

Tr. 

I 

I Tr. Tr. 

Tr. 

Tr. 

Tr. 

Tr. 

Tr. 

Tr. 

Tr. 

6 

4 

I 

10 

Tr. 

Tr. 

Tr. 

Tr. 

Tr. 

Tr. 

Tr. 

Tr. 

Tr. 

Tr. 

Tr. 

Tr. 

.. 

6 

Tr. 

Tr. 

• '· 
DIAGENETIC FACIES 

TABLE 14.- Mineralogic composition of tuffaceous rocks of the Big Sandy Formation as estimated from X-ray diffractometer patterns 

of bulk samples - Continued 

Loc. 

(fig. 3) 

71 8 

A 

72 E 

D 

c 

8 

A 75 8 

A 

76 A 77 8 

A 

78 8 

A 

79 A 

80 A 

81 8 

A 

82 A 

84 A 

!IS A 86 A 

87 8 

A 88 A 

89 c 

8 

A 90 A 

91 A 

92 A 

93 A 

94 A 

95 c 

8 

A 

D 96 8 

A 

97 A 

98 A 

99 A 100 8 

A 101 8 

A 

102 c 

8 

A 

103 8 

A 

Field No. Sample taken 

Tl, 6 in. above base ----- _ _ _ _ _ __ ___ __ _ _ ___ 3 Tr. Tl, at base ____ ------ _ _ __ __ ___ __ _ _ _ ___ I 

Tl, at top_----_______________________ Tr. 

Tl, 20 in. above base _____________________ _ 

Tl, 12 in. above base---------------------- Tr. Tl, II in. above base ___ ---- ________ ----___ 2 

Tl, at base --------------------------- 2 

U,T ------------------------------ 4 U, T ------------------------------ Tr. Tr. U, Ss ____ ------ _____ ---- __ - _ _ _ ____ _ Tr. 

U,T ------------------------------ U, T ------------------------------ 2 

L, T ------------------------------ Tr. 

L, Ss _ _ _ _ _ _ _ _ _ _ _ _ _ __ _ _ _ _ __ __ _ _ _ _ _ _ _ Tr. 

U, T ------------------------------ 4 U, Ms _______ ---- ______ ----- _ _ _ _ _ _ _ 2 Tr. 

Tl, at upper part_-------________________ Tr. Tl, at lower part _ ------ ________________ _ 

U, Ms ----------------------------- 3 U, T ------------------------------ Tr. U,Ss------------------------------ I 

U, Ms ----------------------------- 4 U, T,at upper part ----------------------

U, T, at lower part _ _ _ _ _ _ _ __ _ _ __ _ _ _ _ _ _ _ _ _ 3 

U, Ss ------------------------------ Tr. Tr. 

U, T,ut top -------------------------- I U, T, near middle ----------------------- 4 U, T, at base----------'---------------- Tr. 

U, T ------------------------------ Tr. Tr. U, T ------------------------------ Tr. Tr. U, Ss ________ ----- _ _ _ _ _ __ __ _ _ _ _ _ ___ Tr. 

U,Ss------------------------------ Tr. Tr. U, Ss _ --------- ______________ --- __ _ I 3 

U, T, at top --------~----------------- Tr. U, T,nearmiddle ----------------------- Tr. I 

U, T, at lower part ---------------------- I 1 U, T,at base-------------------------- I Tr. U, T, at upper part _ ____ _ _ _ _ _ __ _ _ _ _ ____ _ _ I I 

U, T, at lower part ---------------------- Tr. 

U, Ss ------'------------------------ .I 2 U, Ss ------------------------------ I 3 U, Ss ------------------------------ I I L,SS·------------------------------ 2 Tr. 

L, Ms ----------------------------- 3 2 U, Ms ----------------------------- 2 I U,Ms ----------------------------- 2 I Tl, at top____________________________ I Tr. 

Tl, 14 in. above base---------------------- Tr. Tr. 

Tl,'atbase --------------------------- 3 Tr. Tl, at upper part------------------------ 2 

104 SW-104-9 

8 

Tl, at lower part _______________________ _ 

78ft ubove Tl, Ms __________ ----- _______ _ 60ft above Tl, Ms _________ ----- ________ _ 

70 51 ftaboveTI, T ------------------------ 3 2 7C SOft above Tl, T _ __ __ _ _ _ _ _ _ _ _ _ _ _ __ _ _ _ _ _ _ 3 2 

78 48ftaboveTI,T ------------------------ I I 7A 42 ftaboveTI, T ------------------------ 2 2 6 38ft above Tl, Ms _ _ _ _ _ __ _ _ _ _ _ _ _ _ _ _ _ _ _ __ _ 2 I 

58 26ftaboveTI,Ss ----------------------- I I SA 18ftaboveTI,St ----------------------- I I 4 3ftaboveTI,T ------------------------ Tr. Tr. 3 I ft above Tl, St _ _ _ _ _ _ ___ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 3 

2 Tl ------------------------------- Tr. 

II ft below Tl, Ms _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ __ _ _ _ _ _ 2 

105 8 Tl ------------------------------- Tr. A Tl _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 2 

106 SW-106-7 92ft above Tl, Ss ______________________ _ 

107 A 

108 c 

B 

A 

109 B 

A 110 A Ill A 

112 A 

6 

SF 

SE 

SD 

sc 

58 

SA 

4C 

48 

4A 

3 

28 

2A 

I 

89ftaboveTI, T ------------------------ 71ft above Tl, Ss ______________________ _ 

45ft above Tl, T _ --------------- __ ------ 42ft above Tl, T, at upper part _______________ _ 42ft above Tl, T, at lower part _______________ _ 

ISftaboveTI,Ss ----------------------- Tr. 

II ft above Tl. T _______________________ _ 

Tl, at upper part _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ I Tl. near middle _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ Tr. 

r~ abte\~:e+ts: = = = = = === = = = = = = = = = = = = = = = = ~ 19ft belowTI, T, at upper part ---------------- 19ft below Tl, T, at lower part _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ I 22 ft below Tl, St _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 2 

U, T ------------------------------ Tr. U, T ------------------------------ I 

U. U,St T ------------------------------

______________________________ Tr. I 

U, T,at upper part ---------------------- U, T, at base _________________________ _ 

U. Ss--- _----- _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ Tr. 

U, T ------------------------------ I Tr. U. Ss _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 2 Tr. 

3 

3 

10 

9 

6 

Tr. 

Tr. 

Tr. 

Tr. 

3 

Tr. 

Tr. 

Tr. 

10 

Tr. 

10 

2 

9 

Tr. 

10 

" 

! 

.5 

0 

Tr. 

Tr. 

I 

Tr. 

Tr. Tr. 

Tr. 

4 Tr. 

Tr. 

2 

Tr. 

Tr. 2 

Tr. 

-T-;..- 1 

9 

4 

Tr. 3 

Tr. 

Tr. 

Tr. 

10 

I 

10 

X-ray analysis (parts of 10) 

e 

0 

0 

E 

"' :I: 

Tr. 

7 

8 

10 

10 

10 

8 

8 

3 

Tr. 

Tr. 

4 

Tr. 

Tr. 

4 

5 

7 

4 

2 

Tr. 

Tr. 

Tr. 

3 

2 

Tr. 

Tr. Tr. 

2 

2 

Tr. 

I Tr. 

3 

3 Tr. Tr. 

5 

4 

4 

4 

4 

4 

Tr. 

4 Tr. Tr. 

Tr. 

3 

I 

Tr. 

Tr. 

2 Tr. Tr. 

I 

4 

I Tr. Tr. 

I Tr. 

Tr. 

4 

I 

Tr. 

Tr. 

Tr. 

I 2 Tr. 5 Tr. Tr. Tr. I 3 Tr. 2 3 Tr. Tr. 3 Tr. 

Tr. Tr. 

Tr. 

2 

4 Tr. 

Tr. 

Tr. 

Tr. 

Tr. 

Tr. 

Tr. 

Tr. 

29 

" ..c 

0 
30 ZEOLITES AND AUTHIGENIC SILICATE MINERALS, BIG SANDY FORMATION, ARIZONA 

FIGURE 24. - Natural exposure of light-yellow nonanalcimic zeolitic tuff 

along northeasterly tributary to Boner Canyon, about 3.2 miles 

northeast of Wikieup. Tuff consists of erionite and clinoptilolite and 

minor amounts of chabazite. 

FIGURE 25. - Natural exposure of white chabazite-rich tuff along 

northeasterly tributary to Boner Canyon, about 3.4 miles northeast of 

Wikieup. Tuff grades upward into brown sandstone. 

clinoptilolite plus erionite plus phillipsite. Absence of other 

seemingly possible zeolite associations in tuffs of the Big 

Sandy Formation may be, in part, due to our inability to 

identify small quantities of a constituent by optical or X-ray 

techniques. 

The paragenesis of authigenic silicate minerals in the 

zeolitic tuffs can be ascertained by studying the sequence of 

filling of shard cavities, by contrasting the mineralogy of the 

pseudomorphed shards with the mineralogy of the matrix, 

and by studying the mineralogy of the relatively late fillings 

in vugs and along fractures. The mineral in the interior of a 

pseudomorph presumably formed later than the minerals 

nearer the periphery of the pseudomorph. Those minerals in 

the finely crystalline matrix are presumed to have 

FIGURE 26. - Natural exposure of yellow erionite-rich upper marker tuff 

along northeasterly tributary to Gray Wash, about 5 miles southeast of 

Wikieup. Tuff is platy, resistant, and 20 inches thick. 

FIGURE 27. -Natural exposure of green analcime-rich lower marker tuff 

along unnamed tributary to the Big Sandy River, about 2 miles east of 

Wikieup. 

crystallized prior to the minerals that compose the relatively 

large pseudomorphs. The following sequences of crystallization were determined by using the above criteria: 

Paragenesis of authigenic silicate minerals 

[Earliest mineral listed on leftJ 

Montmorillonite-phillipsite-clinoptilolite 

Montmorillonite-harmotome-chabazite 

Montmorillonite-clinoptilolite-quartz 

Montmorillonite-clinoptilolite-erionite 

Montmorillonite-chabazite-clinoptilolite 

These relationships indicate that montmorillonite was consistently the earliest mineral to form in the tuffs. Phillipsite, 

chabazite, and harmotome are relatively early zeolites; and 

clinoptilolite and erionite are relatively late zeolites. Other 

age relationships, particularly those concerning mordenite, 
' . 

DIAGENETIC FACIES 31 

FIGU RE 28. - Nonanalcimic zeolitic tuff, showing preservation of 

vitroclastic texture. Tuff consists of clinoptilolite and a minor amount of 

erionite. U npolarized light. 

are unkown because the critical textural relations were not 

recognized in thin sections. Replacement of one zeolite by 

another was not observed in tuffs of the nonanalcimic 

zeolite facies, although more than one zeolite commonly occurs in the same sample. 

ANALCIME FACIES 

Tuffs of the analcime facies characteristically lack 

evidence of a vitroclastic texture, or they show poor preservation of the texture. Destruction of the vitroclastic texture 

is especially common in those tuffs that consist entirely of 

subhedral to euhedral analcime. Some analcime crystals 

enclose "ghosts" of shards that are outlined by a thin film of 

montmorillonite. 

X-ray diffractometer study has shown that analcime is 

associated with each of the other zeolites, and thin-section 

study has shown that analcime replaced each zeolite except 

mordenite. Analcime may also have replaced mordenite, 

but mordenite was not recognized in any of the thin sections. 

Replacement of authigenic montmorillonite by analcime is 

FIGU RE 29. - Nonanalcimic zeolitic tuff, showing preservation of 

vitroclastic texture. Tuff consists of chabazite and a minor amount of 

clinoptilolite. Unpolarized light. 

commonly observed in thin sections. Thus, analcime seems 

to have formed from preexisting authigenic silicate 

minerals, chiefly other zeolites. There is no petrographic 

evidence to suggest that analcime formed directly from the 

silicic glass shards in the tuffs. 

POTASSIUM FELDSPAR FACIES 

Tuffs of the potassium feldspar facies are characterized 

by finely crystalline authigenic potassium feldspar that occurs in trace to major amounts. The potassium feldspar is 

associated with each of the zeolites except harmotome and 

mordenite. The association of the authigenic feldspar with 

analcime is especially common in the Big Sandy Formation. 

Vitroclastic texture is poorly preserved iri tuffs or those 

parts of tuffs where potassium feldspar is abundant. The 

vitroclastic texture is recognizable by remnants of clinoptilolite pseudomorphs after shards and by remnants of 

montmorillonite that vaguely outline shards. 

Thin section study of the potassium feldspar-bearing tuffs 

shows that the feldspar has formed chiefly from precursor 
32 ZEOLITES AND AUTHIGENIC SILICATE MINERALS, BIG SANDY FORMATION, ARIZONA 

FIGURE 30.- Nonanalcimic zeolitic tuff, showing pseudomorphs of shards 

that consist of an outer film of montmorillonite (light) and a filling of 

chabazit.e and a minor amount of erionite (dark). Crossed nicols. 

zeolites. Feldspar replacements of subhedral to euhedral 

analcime crystals, clinoptilolite pseudomorphs after shards, 

and phillipsite spherulites were recognized in thin sections. 

Authigenic potassium feldspar also probably has replaced 

other associated zeolites, but the textural relations with the 

other zeolites were not observed in thin sections. Replacement of analcime by potassium feldspar is especially common in the Big Sandy Formation. All stages of the replacement are recognizable, from marginal replacement that 

commonly gives the analcime crystals a ragged appearance 

to complete pseudomorphs of finely crystalline potassium 

feldspar. Where completely replaced by feldspar, the crystal 

outlines of the analcime precursors are recognizable by clay 

minerals or irresolvable opaque material. 

Authigenic potassium feldspar rarely occurs as 

replacements of pyrogenic or detrital plagioclase in some of 

the feldspar-rich tuffs. The replacements are hollow, and 

some show a boxwork structure similar to that of 

pseudomorphed plagioclase in tuffs of the Barstow Formation in California (Sheppard and Gude, 1969a, p. 21 ). All 

the replacements consist of untwinned, optically continuous 

potassium feldspar. 

GENESIS OF AUTHIGENIC SILICATE MINERALS 

Zeolites of authigenic origin occur in sedimentary rocks 

that are diverse in lithology, depositional environment, and 

age throughout the world (Hay, 1966). The zeolites and 

associated authigenic silicate minerals formed by the reaction of a variety of aluminosilicate materials with interstitial 

pore water. Silicic volcanic glass, however, is the 

aluminosilicate material that most commonly served as a 

precursor for the authigenic zeolites, although clay 

minerals, feldspars, feldspathoids, and gels have also 

reacted locally to form zeolites. The zeolites and associated 

authigenic silicate minerals form during diagenesis by reaction of the volcanic glass with interstitial water, which may 

have originated either as meteoric water or as connate water 

of a saline, alkaline lake. 

Factors that may control the formation and distribution 

of zeolites and other authigenic silicate minerals in sedimentary rocks were summarized by Hay (1966) as composition, 

permeability, and age of the host rock, metastable 

crystallization, temperature, pressure, and chemistry of the 

pore water. Inasmuch as nearly all the authigenic silicate 

minerals in the Big Sandy Formation occur within a given 

tuff, differences in the composition, permeability, and age of 

the host rock cannot explain their distribution pattern. The 

Big Sandy Formation was subjected to only shallow burial; 

therefore, the temperature and pressure during diagenesis 

was relatively low. Besides, the difference, if any, in the 

depth of burial between the nonanalcimic zeolite facies and 

the potassium feldspar facies was seemingly not great 

enough to cause the observed pattern. The present 

authigenic silicate mineralogy of the tuffs and the pattern of 

distribution of the diagenetic facies probably reflect 

differences in the chemistry of the pore water during 

diagenesis. 

Experimental work by others indicates that the activity 

ratio of alkali ions to hydrogen ions and the activity of silica 

are the major chemical parameters of the pore water that 

control whether clay minerals, zeolites, or feldspars will 

form under those conditions approximating surface 

temperatures and pressures (Hemley, 1959, 1962; Garrels 

and Christ, 1965, p. 359- 370; Hess, 1966). Zeolites and 

feldspars are favored over clay minerals by relatively high 

alkali ion to hydrogen ion activity ratios and by relatively 

high silica activities. The high alkali ion to hydrogen ion activity ratio necessary for the formation of zeolites in a tuff 

can be attained in the depositional environment of a saline, 

alkaline lake or in the postdepositional environment by 

hydrolysis and solution of silicic vitric material by subsurface water. The formation of the authigenic silicate minerals 

and their distribution pattern in tuffs of the Big Sandy Formation are believed to have been controlled by entrapped 

saline, alkaline lake water. 

r 
GENESIS OF AUTHIGENIC SILICATE MINERALS 33 

INTERPRETATION OF A SALINE, ALKALINE 

DEPOSITIONAL ENVIRONMENT FOR PARTS OF 

THE BIG SANDY FORMATION 

The obvious evidence for a saline, alkaline depositional 

environment - bedded saline minerals - has not been 

found in the Big Sandy Formation, The chemistry of the 

water must be inferred from the sedimentary rocks of the 

formation. Disseminated crystal molds that resemble 

gaylussite occur in some mudstones and suggest saline conditions during deposition. The molds are most common in 

mudstones of the potassium feldspar facies, are less common in mudstones of the analcime facies, and are absent in 

mudstones of the nonanalcimic zeolite facies. The absence 

of diatomites and unaltered glass in the Big Sandy Formation also suggests that the lake water was at least 

moderately saline and alkaline. However, the coarse clastic 

rocks in the marginal parts of the Big Sandy Formation 

suggest an influx of relatively fresh water, particularly at the 

northern part of the depositional basin. These rather coarse 

clastic rocks either lack authigenic zeolites and potassium 

feldspar or contain zeolites other than analcime. 

A saline, alkaline depositional environment for parts of 

the Big Sandy Formation can be inferred from the occurrence of certain of the authigenic silicate minerals. Such 

zeolites as clinoptilolite and mordenite occur in either fresh 

or saline water; however, such zeolites as erionite and 

phillipsite are found almost exclusively in saline-lake 

deposits (Hay, 1964, 1966). The occurrence of analcime and 

potassium feldspar in the tuffs and mudstones suggests a 

saline, alkaline depositional environment (Sheppard and 

Gude, 1969a; Surdam and Parker, 1972). The authigenic 

potassium feldspar in tuffs of the Big Sandy Formation contains anomalously high contents of boron. Studies of boronbearing authig~nic potassium feldspar from several closedbasin deposits suggest that these feldspars are unique to 

saline, alkaline lacustrine deposits (Sheppard and Gude, 

1972b). 

CORRELATION BETWEEN THE WATER CHEMISTRY 

OF THE DEPOSITIONAL ENVIRONMENT AND THE 

AUTHIGENIC SILICATE MINERALOGY 

Not only was the depositional environment of the Big 

Sandy Formation a saline, alkaline lake, but there is a 

strong correlation between the inferred areal variation of 

the water chemistry and the authigenic silicate minerals in 

the tuffs. In a general way, the diagenetic facies seem to 

have resulted from differences in the pH and the salinity of 

the lake water trapped during deposition of the tuffs. The 

lake water was probably moderately to highly saline with a 

pH of at least 9, except near the lake margin where runoff 

and the ancestral Big Sandy River and its tributaries 

probably kept the salinity and alkalinity at lower levels. 

Depending on the influx of fresh water versus the rate of 

evaporation, this areal chemical zonation of the lake water 

probably fluctuated during the deposition of the Big Sandy 

Formation. 

The areal destribution of authigenic silicate minerals in 

the tuffs from zeolites other than analcime to analcime and 

then to potassium feldspar was due to a chemical zonation 

of the pore water during diagenesis, and this zonation was 

probably inherited from the chemical zonation that existed 

in the lake water during deposition of the tuffs. Those tuffs 

that contain zeolites other than analcime were deposited in 

the least saline and alkaline water near the lake margin. 

Farther basinward, these same tuffs are represented by the 

analcime and potassium feldspar facies because they were 

deposited in water of increasing salinity and alkalinity. 

Studies of tuffs deposited in young saline lakes where 

water analyses are available have shown a strong correlation 

between the water chemistry and the authigenic silicate 

mineralogy (Hay, 1966; Surdam and Mariner, 1971). Tuffaceous sediments deposited in fresh-water parts of these 

lakes still contain unaltered glass, but those deposited in 

saline, alkaline water are altered and contain zeolites, 

potassium feldspar, or searlesite. Older lacustrine deposits 

that contain interbedded saline minerals also show a correlation between the inferred salinity of the depositional environment and the authigenic silicate mineralogy of the 

silicic tuffs. In the Pleistocene deposits of Lake Tecopa, 

Calif. (Sheppard and Gude, 1968), glass is unaltered in tuff 

deposited in fresh water; however, the tuffs consist of 

zeolites where they were deposited in moderately saline 

water, and of potassium feldspar and sear1esite where they 

were deposited in highly saline water. Tuffs in the Eocene 

Green River Formation of Wyoming (Iijima and Hay, 1968; 

Surdam and Parker, 1972) are altered to montmorillonite 

where they were deposited in fresh water; to clinoptilolite 

and mordenite, in slightly saline water; to analcime, in 

moderately saline water; and to potassium feldspar, in 

highly saline water. 

FORMATION OF ZEOLITES FROM SILICIC GLASS 

Solution of silicic glass by alkaline and slightly to 

moderately saline pore water provided the materials 

necessary for the formation of the zeolites except analcime. 

The genesis of analcime is discussed in a following section. 

Deffeyes (1959a) emphasized that zeolites form during 

diagenesis by solution of the shards and subsequent 

precipitation of zeolite from the solution, rather than by 

devitrification of the shards. Mariner and Surdam ( 1970) 

suggested that an aluminosilicate gel first precipitates from 

the solution, and then zeolites grow from the gel. A gel was 

recently recognized in Holocene tuffs at Teels Marsh, Nev., 

where the gell is associated with phillipsite (Surdam and 

Mariner, 1971 ). Gels or evidence for the previous existence 

of gels is probably not preserved in ancient zeolitic tuffs; 

thus, their importance has been overlooked. Laboratory and 

commercial synthesis of zeolites is commonly accomplished 

from ·gels (Zhdanov, 1971). 

Tuffs in the Big Sandy Formation are commonly interbedded with relatively impermeable mudstones and after 
34 ZEOLITES AND AUTHIGENIC SILICATE MINERALS, BIG SANDY FORMATION, ARIZONA 

deposition may have behaved as closed systems consisting of 

the silicic glass and the connate lake water. The early formation of montmorillonite was probably favored by a 

relatively low Naf+ +l(i+1

:H+ activity ratio (Hemley, 1962). 

This ratio would have been at its lowest value at the time of 

deposition. Subsequent solution of the glass or the formation of montmorillonite by an initial marginal hydrolysis of 

the glass would have caused a:n increase in the pH and the. 

. concentration of alkali ions (Hay, 1963), thereby increasing 

the Na+l + K+! :H1

+' activity ratio and providing a chemical environment more favorable for the formation of zeolites 

rather than additional mQntmorillonite. Except for 

analcime, the zeolites that subsequently formed in the tuffs 

did not replace the early-formed montmorillonite. 

The zeolites of the Big Sandy Formation differ 

significantly in chemical composition; therefor ... , the following factors may influence which zeolite will crystallize: activity of H20, Si:Al ratio, pH, and proportion of cations in 

the pore water. Where the relationships are clear, 

petrographic evidence indicates that phillipsite and 

chabazite crystallized before clinoptilolite. Phillipsite and 

chabazite have higher H20 contents and lower Si:Al ratios 

than clinoptilolite. In addition, all phillipsites have a 

relatively low content of calcium. Thus, phillipsite and 

chabazite should be favored over clinoptilolite by a 

relatively low Si:Al ratio and high activity of H20. Phillipsite should also be favored over clinoptilolite by a relatively 

low Ca:Na + K ratio of the pore water. Such conditions may 

have prevailed in the silicic tuffs during early diagenesis. 

Continued solution of the glass coupled with the early 

crystallization of phillipsite or chabazite in a tuff probably 

enriches the pore water in silicon and cations, particularly 

calcium. The Si:Al ratio may thus increase and the activity . 

of H20 decrease to levels suitable for the crystallization of 

clinoptilolite rather than phillipsite or chabazite. An increase in the Ca:Na + K ratio during solution would also 

favor the formation of clinoptilolite rather than phillipsite. 

Experimental work by Mariner and Surdam (1970) indicated that the Si:Al ratio of the zeolite is controlled by the 

Si:Al ratio of the solution from which the zeolite 

crystallized. Their experiments showed that the solubility of 

silicic glass increased and the Si:Al ratio of the solution 

decreased as the pH increased. 

REACTION OF ALKALIC, SILICIC ZEOLITES TO FORM 

ANALCIME 

Since the discovery of ana~cime in tuffaceous rocks, most 

workers have assumed that the analcime formed directly 

from the vitric material. The presence of vague vitroclastic 

texture and pyrogenic crystals in some analcimic tuffs 

seemed sufficient evidence (Ross, 1941); however, Hay 

( 1966) showed that these criteria do not necessarily prove 

that the glass altered directly to analcime. Hay (1966) concluded from a comparison of the authigenic mineralogy of 

tuffs in modern and ancient saline-lake deposits that 

analcime commonly formed at low temperatures by the 

reaction of alkalic, silicic zeolite precursors with the interstitial fluids. Sheppard and Gude ( 1969a) presented even 

stronger {(Vidence for this reaction by the recognition of 

analcime replacements of clinoptilolite and phillipsite in 

tuffs of the Miocene Barstow Formation. Furthermore, 

relict fresh glass has not bP~n confirmed in analcimic tuff; 

thus, there is doubt that analcime ever has formed directly 

from glass. Much, if not all, of the analcime in the tuffs of 

the Big Sandy Formation seems to have formed from 

alkalic, silicic zeolite precursors. 

Experimental work by others and theoretical considerations indicate that the reaction of an alkalic, silicic 

zeolite such as clinoptilolite to form analcime is favored b} 

a high Nat':H1+ ratio (Hess, 1966; Boles, 1971), a relatively 

low Si:Al ratio (Senderov, 1963), and, perhaps, a relatively 

low activity of H20 in the pore fluid. Simplified representations of the clinoptilolite-analcime and phillipsiteanalcime reactions are 

Na2K2CaA16Si300 72·24H20+4Na+----+-6NaA1Si201j·H20 

clinoptilolite analcime 

+ 18H20+ 18Si02+2K +Ca+ 2

• 

Na Al Si 12 32 ·1IH 0+2Na1+~4NaA1Si ·H 0 

phillipsite analcime 

+7H20+4Si02+2Ki+. 

The major changes are a gain of. sodium and losses of 

· potassium, calcium, silica, and water. If the driving force of 

the reaction is the increased concentration of sodium, the 

higher salinity of the depositional environment would certainly favor the reaction to form analcime. Additional 

sodium was also available to the pore water from the solution of the glass to form the alkalic, silicic zeolites. Increased· salinity may also lower the activity of water sufficiently to favor the transformation of alkalic, silicic 

: zeolites to analcime. A slight increase in the pH of the pore 

water would increase the Na+ :H.-H ration and decrease the 

Si:Al ratio of the pore water, and both conditions should 

favor the crystallization of analcime. 

The above arguments are based on the assumption that 

chemical factors alone are responsible for the formation of 

analcime; however, kinetic factors may be equally, or 

perhaps more, important. Analcime may simply form later 

than the other zeolites. 

Studies of the composition of analcime in sedimentary 

rocks have shown a range in Si:Al ratios of about 2.0-2.9 

(Coombs and Whetten, 1967; Iijima and Hay, 1968; Brobst 

and Tucker, 1972). Analcimes in tuffs of the Big Sandy Formation have Si:Al ratios of about 2.4-2.8, which fall in the 

siliceous part of the range. The analcime in the tuffs formed 

from precursor zeolites and not directly from silicic glass. 

The petrographic studies showed that analcime replaced all 

the other zeolites except mordenite. Studies of the analcimic 

tuffs in the Miocene Barstow Formation of California 

.... 
REFERENCES CITED 35 

(Sheppard and Gude, 1969a) suggested a correlation 

between the Si:Al ratio of analcime and the composition of 

the precursor zeolite. Analcime derived from a siliceous 

precursor, such as clinoptilolite, has a relatively high Si:Al · 

ratio, whereas, analcime derived from an aluminous precursor zeolite, such as phillipsite, has a relatively low Si:Al 

ratio. A similar correlation was recognized for analcimes in 

tuffs of the Big Sandy Formation. Analcime associated with 

phillipsite, erionite, and clinoptilolite has Si:Al ratios of 

2.50-2.58, 2.45-2.60, and 2.58-2.66, respectively. Thus, 

in a general way, the Si:Al ratio of the precursor zeolite 

seems to have influenced the Si:Al ratio of analcime. Experimental work by Boles (1971) confirmed this correlation 

by showing that the Si:Al ratio of analcime synthesized 

from natural zeolites is chiefly a function of the Si:Al ratio 

of the zeolite reactants. 

REACTION OF ZEOLITES TO FORM POTASSIUM FELDSPAR 

Formation of potassium feldspar from zeolite precursors 

in tuffs that were never deeply buried has been well 

documented in recent studies. Analcime is replaced by 

potassium feldspar in tuffs of the Eocene Green River Formation in Wyoming (lijima and Hay, 1968; Surdam and 

Parker, 1972). Analcime and clinoptilolite are replaced by 

potassium feldspar in tuffs of the Miocene Barstow Formation of California (Sheppard and Gude, 1969a). Phillipsite is 

replaced by potassium feldspar in tuffs of Pleistocene Lake 

Tecopa, Calif. (Sheppard and Gude, 1968). The formation 

of potassium feldspar in all of these examples has been correlated with a highly saline and alkaline depositional environment. Petrographic study of the feldspathic tuffs in the 

Big Sandy Formation has shown that the feldspar replaced 

analcime, clinoptilolite, and phillipsite. The other zeolites in 

the tuffs may also have served as precursors for potassium 

feldspar, but the textural evidence was not obsderved. 

Chemical factors that may affect the formation of 

potassium feldspar from precursor zeolites are a relatively 

low activity of H20, a relatively high K+' :H'+ rati.o, and a 

relatively high activity of Si02• Simplified representations 

of the analcime-potassium feldspar, phillipsite-potassium 

feldspar, and clinoptilolite-potassium feldspar reactions 

are 

NaA1Si 20 6"H20+Si02+ K +_.,KA1Si30 8+ H20+ Na+. 

analcime potassium feldspar 

Na 2K2Al 4Si 120 32 ·II H20+2K+-+-4KA1Si 30 8 

phillipsite potassium feldspar 

+llH20+2Na+. 

Na 2K2CaA16Si 300 72·24H20+4K +-+- 6KA1Si 30 8 

clinoptilolite potassium feldspar 

+24H20+ 12Si02+Na++Ca+2

• 

The major changes are a gain of potassium and losses of 

sodium and water. Depending on the composition of the 

zeolite, Si02 for the reaction may be in excess or deficient in 

the zeolite precursor. 

The increased salinity and alkalinity of the pore water 

trapped in the tuffs during deposition were probably the 

major. factors res.ponsible for the formation of potassium 

feldspar. The concentration of potassium was probably 

higher in the most saline part of the lake basin. Coupled 

with the high pH, the high potassium concentration would 

result in a relatively high K + :H+ ratio suitable for the 

crystallization of potassium feldspar. The high pH would 

also result in increased solubility of Si02 and contribute to 

the stabilization of potassium feldspar (Surdam and Parker, 

1972). A relatively high salinity would lower the activity of 

H20 and favor the formation of anhydrous potassium 

feldspar from hydrous zeolites, including analcime. 

Silicate reactions are generally regarded as sluggish at 

low temperatures, but potassium feldspar has been synthesized from a variety of aluminosilicate precursors at 

temperatures less than 250°C. Recently, a synthesis of 

potassium feldspar was accomplished from natural clinoptilolite in a saturated solution of KOH at about 80°C after 

44 hours (Sheppard and Gude, 1969a). Although this synthetic potassium feldspar was prepared at a higher 

temperature than that which prevailed during diagenesis of 

the Big Sandy Formation and was prepared in a chemical 

environment that probably did not even closely approximate 

the diagenetic environment, the synthesis does demonstrate 

the rapidity of the reaction of clinoptilolite to potassium 

feldspar in a favorable environment. 

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*u.s. GOVERNMENT PRINTING OFFICE: 1973-543-S?B/6