GEOLOGICAL SURVEY CIRCULAR 500 

Potash Feldspar of Possible 

Economic Value in the Barstow 

Formation, San Bernardino County 

California 

Potash Feldspar of Possible Economic 

Value in the Barstow Formation 

San Bernardino County, California 

By Richard A. Sheppard and Arthur J. Gude, 3d 

Geological Survey Circular 500 

Washington 1965 
United States Department of the Interior 

STEW ART L. UDALL, SECRETARY 

Geological Survey 

THOMAS B. NOLAN, DIRECTOR 

Free on application to the U.S. Geological Survey, Washington, D. C. 20242 
Abstract----------------------------

Introduction ________________ -~-- _____ _ 

General geology of feldspar deposits __ _ 

Geology~ mineralogy~ and chemistry 

of potash feldspar- rich tuff ________ _ 

CONTENTS 

Page 

1 

1 

1 

2 

Economic considerations ____________ _ 

Comparable deposits elsewhere ______ _ 

References cited--------------------

ILLUSTRATION 

Figure 1. Geologic sketch map of the central part of the Mud Hills1 showing sample 

Page 

4 

6 

6 

Page 

locations-------------------------------------------------------------- 3 

TABLE 

Page 

Table 1. Chemical analyses and calculated mineral content of potash feldspar-rich 

tuff from the Barstow Formation---------------------------------------- 5 

III 

Potash Feldspar of Possible Economic Value in the Barstow 

Formation, San Bernardino County, California 

By 

Richard A. Sheppard and Arthur J. Gude, 3d 

ABSTRACT 

'!'uffs in the ~arstow Formation of Miocene age are altered 

m.a~nly t? zeohtes, potash feldspar, montmorillonite, and a 

sdtca ~meral. Potash feldspar is the major constituent of 

a consptcu?us tuff •. 1.5-4 .feet thick, in the central part of 

the Mud Hills. This chemically analyzed feldspar-rich tuff 

shows a range of 12.4-16.4 percent K20. The very high pot-

?-sh feldspar content suggests that this deposit or others like 

~t can ~ecome a source of feldspar for the glass and ceramic 

mdustnes. 

INTRODUCTION 

Potash feldspar and zeolites are the chief 

alteration products of rhyolitic vitric tuff in 

the Barstow Formation. of .middle to late 

Miocene age (Lewis. 1964). in the Mojave 

Desert region of California. Study of these 

alteration products. though directed mainly 

at the zeolites. has led to the discovery that 

at least one of the studied localities has a 

sizable body of rock containing about 90 percent potash feldspar. Deposits of such altered 

tuff have never been mined by the feldspar 

industry although their existence has long 

been recorded in geologic literature. The 

characteristics of this particular deposit so 

obviously suggest its economic value that 

this paper has been published to announce its 

existence and to describe it briefly. and at 

the same time to indicate that exploration for 

other deposits like it may be worth undertaking. How well the physical and chemical 

peculiarities of the feldspar in this deposit 

can be adapted to the needs of the glass and 

ceramic industries involves .many problems 

that go beyond the ability of a geologist to 

evaluate. For this reason. only the more 

obvious favorable and unfavorable aspects 

will be discussed here. 

The feldspar-rich tuff crops out in an area 

about 10 miles north of Barstow. the nearest 

principal town. The Union Pacific and the 

Atchison. Topeka. and Santa Fe Railroads 

serve Barstow. The Camp Irwin Road, a 

paved highway between Barstow and Camp 

Irwin, provides access to the area via the 

graveled Fossil Bed Road. The area is also 

served by unimproved dirt roads and jeep 

trails, but they will not sustain trucks unless 

improved. 

Acknowledgments.-Appreciation is expressed to R. G. Schmidt, who recognized the occurrence of authigenic zeolites and potash 

feldspar in tuffs of the Barstow Formation as 

early as 1954 and who suggested the present 

study. 

GENERAL GEOLOGY OF FELDSPAR DEPOSITS 

Most commercial feldspar is mined from 

pegmatites or granitic rocks that can be 

beneficiated to yield a nearly pure feldspar 

concentrate. Feldspathic materials are also 

obtained from quartz-feldspar sands and 

from aplite and nepheline syenite. Feldspar 

deposits are mined chiefly by open-pit methods although a few are mined by underground 

operations (Wells, 1965, p. 3). 

Until recent years feldspar was mined 

chiefly from zoned pegmatites and then was 

hand-cob bed to obtain a high-quality perthitic 

microcline. Feldspar obtained from zoned 

pegmatites contains some soda, which is 

mainly in the intimately associated sodic 

plagioclase but is also chemically combined 

in the potash fel_dspar. In mines where feldspar is the main product, only 25-50 percent 

of the rock is recovered as potash feldspar 

(J. J. Norton, 1965, written commun.). The 

other rock constituents, mainly quartz and 

plagioclase are discarded. 

At the present time the feldspar m1n1ng 

industry depends mainly on large bodies of 

1 
2 POTASH FELDSPAR, BARSTOW FORMATION, SAN BERNARDINO C0UNTY, CALIFORNIA 

nearly homogeneous pegmatitic rock or on 

finer grained feldspathic igneous rock that 

cannot be hand-cobbed or belt picked but can 

be beneficiated by flotation. Unlike handcobbed feldspar, the flotation concentrate 

contains all the plagioclase of the rock as 

well as all the potash feldspar, and the K20 

content of flotation feldspar is thus less than 

that of hand-cobbed feldspar. 

GEOLOGY, MINERALOGY, AND CHEMISTRY OF 

POTASH FELDSPAR-RICH TUFF 

The feldspar-rich tuff crops out in a range 

of hills known locally as the Mud Hills, about 

10 miles north of Barstow, San Bernardino 

County, California. In this area the Barstow 

Formation is well exposed in the Barstow 

syncline. The formation consists of about 

3, 000 feet of fluviatile and lacustrine rocks 

that unconformably overlie the Oligocene(?) 

to Miocene(?) Pickhandle Formation (Bowen, 

1954). An additional thickness of unknown 

magnitude was eroded before the deposition 

of the overlying Quaternary alluvium. 

In the vicinity of Rainbow Basin and Owl 

Canyon (fig. 1), the axis of the Barstow syncline trends nearly east, and the beds on 

each limb dip 20°-35°. Several northwestward-trending faults offset the beds and 

locally cause steeper dips. Differential erosion of the more resistant rock, such as 

sandstone, conglomerate, carbonate rocks, 

and altered tuff has produced hogbacks. 

Areas underlain hy thick sequences of claystone are reduced to badlands. 

Although tuffs make up only a small part 

of the Barstow Formation in the Mud Hills, 

more than 30 individual tuff layers, less than 

an inch to several feet thick and mostly in 

the upper half of the formation, can be recognized in the vicinity of Rainbow Basin. 

The tuffs originally were mainly rhyolitic 

vitric tuffs containing varying amounts of 

crystal and lithic fragments. All now are 

altered to some degree, and most contain 

only a small quantity of relict glass, if any 

at all. Zeolites are the most abundant of the 

authigenic silicate minerals formed by alteration of the tuffs, but some beds of tuff are 

rich in montmorillonite, opal, or potash feldspar. Locally some altered tuffs are monomineralic, although most consist of two or 

more authigenic minerals. 

The feldspathized tuff is part of one of the 

most conspicuous and continuous tuffs in the 

formation and is ·herein called the lower 

marker tuff, a name given informally by 

T. W. Dibblee, Jr. (1963, written commun.). 

The tuff, consisting of several beds that are 

less than 1 inch to 2 feet thick, has a total 

thickness of 1. 5-4 feet within the mapped 

area (fig. 1). The tuff thins gradually eastward to the edge of the mapped area; however, it then thickens farther eastward and is 

as much as 7 feet thick at the east end of the 

Mud Hills. Ordinarily, the upper 6-12 inches 

consists of thinly interbedded tuff and greenish claystone. The lower marker tuff generally is white to light gray but locally is 

partly or wholly pale yellow or green. The 

rock below and above the tuff is generally 

claystone. 

Throughout the Mud Hills the lower marker 

tuff is altered. Although zeolites, mainly 

clinoptilolite, are the common authigenic 

minerals, potash feldspar is the dominant 

authigenic mineral in the eastern part of 

Rainbow Basin and for approximately 1 mile 

eastward along the strike. Pods and lenses 

of clinoptilolite or analcime are locally 

present, particularly in the vicinity of Rain-

-bow Basin and Owl Canyon; however, except 

in these zeolitic pods and lenses, the tuff 

generally consists of BQ-100 percent potash 

feldspar. 

The potash feldspar phase of the lower 

marker tuff generally can be distinguished in 

the_ field from both the clinoptilolite and 

analcime phases. The tuff is soft, powdery, 

and friable where composed mainly of potash 

feldspar; it can easily be disaggregated with 

the fingers. Clinoptilolite-rich tuff is hard 

and commonly breaks with a conchoidal 

fracture. Analcime-rich tuff has a sugary 

texture and individual euhedra commonly can 

be seen with a hand lens. Tuff consisting of 

a mixture of potash feldspar and clinoptilolite or analcime can be correctly indentified 

only by microscopic or X-ray examination. 

The authigenic potash feldspar forms 

rather nondescript low-birefringent aggregates of irregular crystals that range in size 

from 2-10 microns. The aggregates superficially resemble chert but are similar to 

authigenic potash feldspar described by Hay 

and Moiola (1963) from tuffaceous beds of 
117"02' 

0 14 '12 MILE 

EXPLANATION 

Windblown 

~ sand 

~ Alluvium 

Older alluvium 

UNCONI"ORMirY 

0:: >-

<( 

z 

0:: 

w 

~ :::> 

0 

w{ ~b }>- z 0:: w <( 

(.) t -

~ Barstow Formation ffi 

t, lower marker tuff 1--

Contact, approximately located 

~ 0 

Fault 

Dofltld whtlrtl conctlaled, u, upthrown 

sidti;D, downfhrown sldtl, arrows 

show rBiotive horizontal movtlmenf 

I 

f 

Syncline 

Dotted wht1re concealed 

20 

Strike and dip of beds 

7 

• 

Analyzed sample (See table I) 

,-------", ~\ I. "" / Area of ' 

1 ) report "" 

r ,\ 

I ' I SAN BERNARDINO COUNTY '\ 

I / 

<;-~---- -J __ ___/" 

Geology by T.W. Dibblee, Jr., 1951, and 

R.A. Sheppard and A.J. Gude, 3rd, 1961 

INDEX MAP OF CALIFORNIA 

SHOWING SAN BERNARDINO CO. 

Figure 1.--Map of the central part of the Mud Hills, San Bernardino County, Calif., showing sample locations. 

C'l 

T. "" 

~ 

-~ 11 

N. 

~ 

~ 

~ 

~ 

~ >-l "'

~ 

0 

.., 

0 "" 

~ 

!t 

~ 

~ :xl 

' C! 

@ 

>-l 

!;i 

.., 

CAl 
4 POTASH FELDSPAR, BARSTOW FORMATION, SAN BERNARDINO COUN1Y, CALIFORNIA 

Searles Lake. The mean inu~.A of refraction 

is 1.518 (±0.001), which suggests nearly pure 

potash feldspar. Other optical consta;nts 

could not be measured from the very small 

crystals. 

Study of X-ray diffractometer powder data 

indicates that the potash feldspar is monoclinic and has the following cell constants as 

refined on a digital computer by leastsquares analysis: a= 8. 593± 0. 002 A; 

b= 12.967±0.003 A; 

c = 7.165±0.001 A; 

~ = 116° 3. 3' ± 1. 01

; cell volume=717.25±0.19 A3 • If the 

feldspar from the tuff is comparable to common boron-free feldspar, the composition can 

be estimated from the a cell edge to be 95 

percent KAlSiaOs. The structural state estimated from the b and c cell edges is that of 

sanidine, but the cell seems to be distorted 

because the composition indicated by the b 

and c edges is very different from that indicated by the a edge (D. B. Stewart, 196 5, 

written commun. ). 

The original vitroclastic texture of the tuff 

generally is poorly preserved by the authigenic feld$par. Both field and petrographic 

evidence indicate that most, if not all, the 

potash feldspar formed, not directly from 

vitric material but from clinoptilolite or 

analcime. The pods and lenses of clinoptilolite or analcime probably are remnants of an 

earlier alteration. Relicts of analcime and 

clinoptilolite can be seen in some thin sections of altered tuff consisting mainly of 

potash feldspar. Inasmuch as the vitroclastic 

texture is generally obliterated by analcime, 

those parts of the feldspar-rich tuff that lack 

relict vitroclastic texture probably formed 

from an analcime precursor, whereas those 

parts that have relict texture formed from a 

clinoptilolite precursor. 

The lower marker tuff locally contains 

small percentages of authigenic montmorillonite, chalcedonic quartz, and calcite in addition to the zeolites or potash feldspar. 

Chalcedonic quartz is most commonly concentrated at the top and bottom of the tuff, 

although thin veinlets and spherical segregations are present locally in the interior. 

Most of the tuff also contains about 1 percent 

crystal fragments of plagioclase, quartz, 

sanidine, biotite, hornblende, zircon, and 

apatite. All these crystals are presumably 

pyrogenic. 

Analyses of bulk samples of the potash 

feldspar-rich tuff are given in table 1. Except for No. 4, the analyses are remarkably 

similar. The K20 content ranges from 12.4-

16.4 percent, and the NatO content ranges 

from 0.39-0.82 percent. Optical and X-ray 

study indicates that most of the Na20 is in 

analcime rather than in solid solution with 

the potash feldspar. The percent of B203 is 

high for natural potash feldspar, and the 

percent of Al203 is somewhat lower than 

average; therefore, B203 is assumed to replace part of the Al20J. No boron mineral 

has been recognized by optical or X-ray 

study, but further study thereon is in 

progress. Those components other than K20, 

Al203 (~Oa), and Si02 essential for pure potash feldspar probably are contained in minor 

amounts of analcime, chalcedonic quartz, 

montmorillonite, calcite, and iron oxides. 

The chemical analyses were recalculated 

as modal minerals, and these minerals are 

also given in table 1. The potash feldspar 

content of the tuff ranges from about 8'7-94 

percent. Analysis 4 was not recalculated 

because its content of impurities was high. 

This sample contains only 12.4 percent K20 

and was collected from the top of the lower 

marker tuff where there are thinly interbedded feldspar-rich tuff and greenish claystone rich in montmorillonite. 

ECONOMIC CONSIDERATIONS 

The most obvious merit of this deposit is 

its very high content of potash feldspar. 

Whether the very high K20 content of the 

feldspar is also a merit is less certain because the feldspar presently used has less 

~0 and much more Na20 than does this 

feldspar; furthermore, the Al20a content is 

unusually low, and its place is in part taken 

by B203. An obvious need is to test how these 

chemical properties influence the behavior 

of the feldspar with respect to its use in 

glass or ceramics. The very fine grain size 

and friability seem to be advantageous because grinding costs would be low; however, 

it is uncertain whether feldspar of this unusual physical character would cause difficulties in manufacturing processes. 

Feldspar should be low in iron oxides for 

most glass and ceramic uses. Glass-grade 

feldspar generally should not contain more 

than 0. 05 percent iron oxide, though amber 

glass may contain as much as 0. 50 percent 
ECONOMIC CONSIDERATIONS 5 

Table 1.-Chemical analyses and calculated mineral content of potash feldspar-rich tuff from the Barstow Formation, Mud Hills, 

Opal Mountain quadrangle, California 

Analysis number ____________ 1 2 3 4 5 6 7 

Laboratory number _________ 164953 164956 164957 164958 D100508 164955 164952 

Chemical analyses 

[Analyses 1-4, 6-7: rapid rock analyses by Paul Elmore, Samuel D. Botts, and Lowell Artis. Analysis 5: standard rock analysis by EllenS. 

Daniels. BaOs determined as B by quantitative spectrographic analysis by Janet D. Fletcher] 

Si0

2 

_______________________ 65.1 65.3 64.2 66.9 65.41 65.4 65.1 

Al20a --------------------- 16.6 16.6 17.2 14.0 16.64 16.2 16.6 

B203---------------------- .55 .97 .58 .90 .55 .93 .68 

Fe20 3 --------------------- .69 .51 .63 1.6 .10 .06 .41 

FeO ___ ----- _- _---------- -- .04 .04 .08 .16 .09 .04 .04 ~go _______________________ .10 .00 .00 1.4 .04 .00 .10 CaO _______________________ .23 .08 .06 .10 .13 .58 .15 

N a2 0 ______________________ .82 .41 .41 .69 .41 .50 .39 

K 20 _______________________ 14.8 15.8 16.4 12.4 15.47 15.3 15.8 H

2

o+ ______________________ 1.0 . 75 .53 1.2 .66 .63 .47 - H20 ---------------------- .27 .25 .28 1.0 .12 .28 .32 

Ti02 ---------------------- .00 .00 .00 .13 .02 .00 .00 

P20s ---------------------- .07 .09 .07 .11 .01 .07 .07 ~no _______________________ .04 .03 .02 .10 .02 .03 .04 

C02 ----------------------- .09 <.05 <.05 .05 .15 .22 .09 

Cl------------------------- -------- -------- -------- --------- .01 -------------- F-------------------------- -------- -------- -------- --------- .01 -------- -------

Total-------------------- 100 101 100 101 99.84 100 100 

Calculated mineral content 

Potash feldspar a ____________ 87.1 93.0 94.4 --------- 91.0 89.7 92.6 

Analcimeb ----------------- 5.7 3.1 3.1 --------- 3.1 3.5 2.6 Quartz _____________________ 5.3 3.1 1.2 --------- 4.5 5:0 3.4 

Other (by difference)-------- 1.9 .8 1.3 --------- 1.4 1.8 1.4 

Total ____________________ 100.0 100.0 100.0 --------- 100.0 100.0 100.0 

a b The potash feldspar content includes KA1Si 3 0s and KBSi 30 8 • 

Analcime has an ideal formula of NaAlSi206"H20, and this was used in these calculations: however, analcime from rhyolitic vitric tuffs 

is known to be more siliceous (Ross, 1928, p. 196: Wilkinson and Whetten, 1964, p. 544), and hence, the analcime content may be slightly 

higher and the quartz content slightly lower than indicated here. 

1-5. Rainbow Basin, sec. 24, T. 11 N., R. 2 W. 

1. NW!NE! sec. 24. 

2. Base of lower marl<er tuff. NE!NE! sec. 24. 

3. Middle of lower marker tuff. NE!NE! sec. 24. 

4. Tor, of1lower marker tuff. Nf4Nf4 sec. 24. 

5. Sf4NE4 sec. 24. 

6. Owl Canyon, NE!SW! sec. 19, T. 11 N., R. 1 W. 

7. Canyon half a mile east of Owl Canyon SW!SW! sec. 20, T. 11 N., R. 1 W. 
6 POTASH FElDSPAR, BARSTOW FORMATION, SAN BERNARDINO COUNTY, CALIFORNIA 

iron oxide (Wells, 1964, p. 2). Bulk samples of 

the potash feldspar-rich tuff from the Barstow Formation contain an average of 0.46 

percent total iron oxides if sample 4 is not 

included. This iron oxide content is high 

compared with that in hand-cobbed feldspar. 

Perthites from pegmatites of the Black Hills, 

South Dakota, for example, average only 0.09 

percent FE!20s (Higazy, 1949, p. 559). Alaskite, containing about 0. 3 percent Fe20s (Olson, 1944, p. 23), currently is mined for feldspar near Spruce Pine, N. C. Subsequent 

treatment by flotation and magnetic separation yields a usable product. The feldsparrich tuff described herein has only a slightly 

higher content of iron oxides, and much of 

this iron is contained in montmorillonite 

which probably can be removed by simpl~ beneficiation processes. 

COMPARABLE DEPOSITS ELSEWHERE 

Authigenic potash feldspar is known to occur in sedimentary rocks of various lithologies and ages (Tester and Atwater, 1934; 

Baskin, 1956). Although the authigenic feldspar content of these rocks generally is less 

than 10 percent, there are exceptions. Gruner 

and Thiel (193 7) described shales and siltstones of Ordovician age that consist mainly 

of potash feldspar. Siltstone in the upper 

member of the Dripping Spring Quartzite of 

Precambrian age in southeastern Arizona 

consists of 60--90 percent feldspar (Granger 

and Raup, 1964, p. 36-38). Authigenic potash 

feldspar forms as much as 80 percent of 

Ordovician bentonitic tuffs from Minnesota 

(Weiss, 1954) and constitutes as much as 50 

percent of tuffaceous beds of Searles Lake, 

Calif. (Hay and Moiola, 1963, p. 323; Smith 

and Haines, 1964, p. 24-25). 

In addition to its occurrence in tuffs of the 

Barstow Formation and at Searles Lake 

authigenic potash feldspar has been reported 

in tuffs from the following formations of the 

western conterminous United States: Eocene 

Tepee Trail Formation in Wyoming (Deffeyes, 

1959, p. 603), Eocene Green River Formation 

in Colorado and Wyoming (Milton and others, 

1960, p. 179-180; Hay, 1965), Jurassic Trowbridge Formation in Oregon (Dickinson, 196 2, 

p. 259-260), Miocene and Pliocene Esmeralda 

Formation in Nevada (Moiola, 1964), and upper part of the Oligocene(?) and Miocene 

Tropico Group at the Kramer borate district, 

California (Hay, 1965). Further mineralogical study of altered tuffaceous rocks of 

Cenozoic age from the southwestern United 

States probably will reveal additional deposits rich in authigenic potash feldspar. Some 

of these deposits may have commercial potential for use in the glass and ceramics industries or even a.s a source of potash for 

fertilizer (Everest and others, 1964). 

REFERENCES CITED 

Baskin, Yehuda, 1956, A study of authigenic 

feldspars: Jour. Geology, v. 64, p.132-155. 

Bowen, 0. E., 1954, Geology and mineral deposits of Barstow quadrangle, San Bernardino County, California: California Div. 

Mines Bull. 165, p. 1-185. 

Deffeyes, K.S., 1959, Zeolites in sedimentary 

rocks: Jour. Sed. Petrology, v. 29, p. 602-

609. 

Dickinson, W. R., 196 2, Metasomatic quartz 

keratophyre in central Oregon: Am. Jour. 

Sci., v. 260, p. 249-266. 

Everest, D. A., Napier, E., and Wells, R. A., 

1964, Extraction of potassium from adularia shale: Chern. and Ind., v. 40, p.l684-1685. 

Granger, H. C., and Raup, R. B., 1964, Stratigraphy of the Dripping Spring Quartzite, 

southeastern Arizona: U.S. Geol. Survey 

Bull. 1168, 119 p. 

Gruner, J. W., and Thiel, G. A., 1937, The occurrence of fine grained authigenic feldspar in shales and silts: Am. Mineralogist, v. 22, p. 842-846. 

Hay, R. L., 196 5, Zeolites and zeolitic reactions in sedimentary rocks: Geol. Soc. 

America Special Paper [in press]. · 

Hay, R. L., and Moiola, R. J., 1963, Authigenic 

silicate minerals in Searles Lake, California: Sedimentology, v. 2, p. 312-332. 

Higazy, R. A., 1949, Petrogenesis of perthite 

pegmatites in the Black Hills, South Dakota: Jour. Geology, v. 57, p. 555-581. 

Lewis, G. E., 1964, Miocene vertebrates of 

the Barstow Formation in southern California, in Short papers in geology and hydrology: U.S. Geol. Survey Prof. Paper 

475-D, p. Dl8-D23. 

Milton, Charles, Chao, E. C. T., Fahey, J. J., 

and Mrose,. M. E., 1960, Silicate mineralogy of the Green River Formation of Wyoming, Utah, and Colorado: Internat. Geol. 

Cong., 21st, Copenhagen 1960, Rept., pt. 21, 

p. 171-184. 

Moiola, R. J., 1964, Origin of authigenic silicate minerals in the Esmeralda "Formation• of western Nevada[abs.], in Abstracts 

for 1963: Geol. Soc. America Spec. Paper 

76, p. 116-117. 
REFERENCES CITED 7 

Olson, J. C., 1944, Economic geology of the 

Spruce Pine pegmatite district, North Carolina: North Carolina Dept. Conserv. Devel. 

Bull. 43, pt. 1, 67 p. 

Ross, C. S., 1928, Sedimentary analcite: Am. 

Mineralogist, v. 13, p. 195-197. 

Smith, G. I., and Haines, D. V., 1964, Character 

and distribution of nonelastic minerals in 

the Searles Lake evaporite deposit, California: U.S. Geol. Survey Bull. 1181-P, 

58 p. 

Tester, A. C., and Atwater, G. I., 1934, The 

occurrence of authigenic feldspars in sediments: Jour. Sed. Petrology, v. 4, p. 23-31. 

Weiss, M. P., 1954, Feldspathized shales 

from Minnesota: Jour. Sed. Petrology, v. 24, 

p. 27Q-274. 

Wells, J. R., 1965, Feldspar: in Mineral facts 

and problems, 196 5 ed.: U.S. Bur. Mines 

Bull. 630, 7 p. [preprint]. 

Wilkinson, J. F. G., and Whetten, J. T., 1964, 

Some analcime-bearing pyroclastic and 

sedimentary rocks from New South Wales: 

Jour. Sed. Petrology, v. 34, p. 543-553.