DEPARTMENT OF THE INTERIOR

OF TIIK

UNITED STATES

No,. 2O

CONTRIBUTIONS TO THE MINERALOGY OF THE 

KOL'KY MOUNTAINS

WASHINGTON

GOVERNMENT PRINTING OFFICE

1885

A.33 VK JR T I S E Mi EJ N T.

[Bulletin No. 20.]

The publications of the United States Geological Survey are issued in accordance -with the statute, 

approved March 3,1879, which declares that 

'' The publications of the Geological Survey shall consist of the annual report of operations, geological 

and economic maps illustrating the resources and classification of the lands, and reports upon general 

and economic geology and paleontology.- The annual report of operations of the Geological Survey 

shall accompany the annual report of the Secretary of the Interior. All special memoirs and reports 

of said Survey shall be issued in uniform quarto series if deemed necessary by the Director, but otherwise in ordinary octavos. Three thousand copies of each shall be published for scientific exchanges 

and for sale at the price of publication; and all literary and cartographic materials received in exchange 

shall be the property of the United States and form a part of the library of the organization: And the 

money resulting from the sale of such publications shall be covered into the Treasury of the United 

States."

On July 7,1882, the following joint resolution, referring to all Government publications, was passed 

by Congress:

" That whenever any document or report shall be ordered printed by Congress, there shall be printed 

in addition to the number in each case stated, the 'usual number' (1,900) of copies for binding and 

distribution among those entitled to receive them."

Under these general laws it will be seen that none of the Survey publications are furnished to it for 

gratuitous distribution. The 3,000 copies of the Annual Keport are distributed through the document 

rooms of Congress. The 1,900 copies of each of the publications are distributed to the officers of the 

legislative and executive departments and to stated depositories throughout the United States.

Except, therefore, in those cases where an extra number of any publication is supplied to this office 

by special resolution of Congress, as has been done in the case of the Second, Third, Fourth, and Fifth 

Annual Eeports, or where a number has been ordered for its use by the Secretary of the Interior, as in 

the case of Mineral Resources and Dictionary of Altitudes, the Survey has no copies of any of its publications for gratuitous distribution.

v ANNUAL REPORTS.

Of the Annual Reports there have been already published:

I. First Annual Report to the Hon. 'Carl Schurz, by Clarence King. 1880. 8°. 79 pp. 1 map. A 

preliminary report describing plan of organization and publications.

n. Report of the Director of the United States Geological Survey for 1880-'81, by J. W. Powell. 

1882. 8°. Iv, 588pp. 61 pi. 1 map.

III. Third Annual Report of the United States Geological Survey, 1881-'82, by J. "W. Powell. 1883 

8°. xviii, 564 pp. 67 pi. and maps.

IV. Fourth Annual Report of the United States Geological Survey, 1882-'83, by J. "W. PoirelL 1884. 

8°. xii, 473 pp. 85 pi. and maps. 

The Fifth Annual Report is in press.

MONOGRAPHS.

Of the Monographs, Nos. n, III, IV, V, VI, VEI, and VIII are now published, viz:

II. Tertiary History of the Grand Canon District, with atlas, by Clarence E. Dutton, Capt., U. S. A. 

18e2. 4°. xiv, 264 pp. 42 pL and atlas of 24 sheets folio. Price $10.12.

III. Geology of the Comstock Lode and the Washoe District, with atlas, by George F. Beoker. 

1882. 4°. xv, 422 pp. 7.pl. and atlas of 21 sheets folio. Price $11.

IV. Comstock Mining and Miners, by Eliot Lord. 1883. 4°. xiv, 451 pp. 3 pi. Price $1.60.

V. Copper-bearing Rocks of Lake Superior, by Roland D. Irving. 1883. 4°. xvi, 464 pp. 15 1. 

29 pi. Price $1.85.

VI. Contribiitions to the Knowledge of the Older Mesozoic Flora of Virginia, by Wm. M. Pontaine. 

1883. 4°. xi, 144pp. 541. 54 pi. Price $1.05.

VTI. Silver-lead Deposits of Eureka, Nevada, by Joseph S. Curtis. 1884. 4°. TJH, 200 pp. 16 pi. 

Price $1.20.

VIII. Paleontology of the "Eureka District, by Charles D. Walcott. 1884. 4°. xiii, 298 pp. 24 L 

24 pi. Price $1.10.
ADVERTISEMENT.

The following are in press, viz:

IX. Brachiopoda and Lamellibranchiata of the Earitan Clays and Greensand Marls of New Jersey, 

by Eobert P. Whitfield. 1885. 4°. ix,338pp. 35 pi.

X. Dinocerata. A Monograph of an Extinct Order of Gigantic Mammals, by Othniel Charles Marsh. 

1885. 4°. , pp. 56 pi.

XI. Geological History of Lake Lahontan, a Quaternary Lake of Northwestern Nevada, by Israel 

Cook Kuasell. 1885. 4°. , pp. 46 pi.

The following are in preparation, viz:

I. The Precious Metals, by Clarence King. 

. Geology and Mining Industry of Leadville, with atlas, by S. F. Emmons.

Geology of the Eureka Mining District, Nevada, with atlas, by Arnold Hague.

Lake Bonneville, by G. K. Gilbert.

Sanropoda, by Prof. 0. C. Marsh.

Stegosanria, by Prof. 0. C. Marsh.

BULLETINS.

The Bulletins of the Survey will contain such papers relating to the general purpose of its work aa 

do not properly come under the heads of ANNUAL EEPOKTB or MONOGRAPHS.

Each of these Bulletins will contain but one paper and will be complete in itself. They will, however, be numbered in a continuous series, and will in time be united into volumes of convenient size. 

To facilitate this each Bulletin will have two paginations, one proper to itself and another which be 

longs to it as part of the volume.

Of this series of Bulletins Nos. 1 to 2'0 are already published, viz:

1. On Hypersthene-Andesite and on Triclinic Pyroxene in Augitic Eocks, by Whitman Cross, with 

a Geological Sketch of Buffalo Peaks, Colorado, by S. F. Emmons. 1883. 8°. 42pp. 2 pi. Price 10 cents.

2. Gold and Silver Conversion Tables, giving -the coining value of Troy ounces of fine metal, etc., by 

Albert Williams, jr. 1883. 8°. ii, 8 pp. Price 5 cents.

3. On the Fossil Faunas of the Upper Devonian, along the meridian of 76° 30', from Tompkins County, 

New York, to Bradford County, Pennsylvania, by Henry S.Williams. 1884. 8°.' 36pp. Price 5 cents

4. On Mesozoic Fossils, by Charles A. White. 1884. 8°. 36 pp. 9 pi. Price 5 cents.

5. A Dictionary of Altitudes in the United States, compiled by Henry Gannett. 1884. 8°. 325pp. 

Price 20 cents.

6. Elevations in the Dominion of Canada, by J. W. Spencer. ' 1884. 8°. 43 pp. Price 5 cents.

7. Mapoteca Geologica Americana. A catalogue of geological maps of America (North and South), 

1752-1881, by Jules Marcou and John Belknap Marcou. 1884. 8°. 184pp. Price 10 cents.

8. On Secondary Enlargements of Mineral Fragments in Certain Eocks, by E. D. Irving and C. E. 

Vanhise. 1884. 8°. 56 pp. 6 pi. Price 10 cents.

9. A Report of work done in the Washington Laboratory during the fiscal year 1883-'84. F. W. 

Clarke, chief chemist ; T. M. Chatard, assistant. 1884. 8°. ' 40 pp. Price 5 cents.

10. On the Cambrian Faunas of North America. Preliminary studies by Charles Doolittle Walcott. 

1884. 8°. 74pp. 10 pi. Price 5 cents.

11. On the Quaternary and Eecent Mollusca of the Great Basin; with Descriptions of New Forms, by 

E. Ellsworth Call; introduced by a sketch of the Quaternary Lakes of the Great Basin, by G. K. 

Gilbert. 1884. 8°. 66 pp. 6 pi. Price 5 cents.

12. A Crystallographic Study of the Thinolite of Lake Lahontan, by Edward S. Dana. 1884. 8°, 

34 pp. 3 pi. Price 5 cents.

13. Boundaries of the United States and of the several States and Territories, by Henry Gannett. 

1885. 8°. 135pp. Price 10 cents.

14. The Electrical and Magnetic Properties of the Iron-Carburets, by Carl Barus and Vincent 

Strouhal. 1885. 8°. 238pp. Price 15 cents.

15. On the Mesozoic and Cenozoic Paleontology of California, by Dr. C. A. White. 1885. 8°. 33 pp. 

Price 5 cents.

16. On the higher Devonian Faunas of Ontario County, New York, by J. M. Clarke. 1885. 8°. 

86 pp. 3 pi. Price 10 cents.

17. On the Development of Crystallization, etc., by Arnold Hague and J. P. Iddings. 1885. 8°. 

44 pp. Price 5 cents.

18. On Marine Eocene, Fresh-water Miocene, and other Fossil Mollusca of Western North America, 

by Dr. C. A. White. 1885. 8°. 26 pp. 3 pi. Price 5 cents.

19. Notes on the Stratigraphy of California, by George F. Becker. 1885. 8°. 28 pp. Price 5 cents.

20. Contributions to the Mineralogy of the Eocky Mountains, by Whitman Cross and W. F. Hillebrand. 1885. 8°. 114 pp. 1 pi. Price 10 cents.

Numbers 1 to 6 of the Bulletins form Volume I, and numbers 7 to 14 Volume n. Volume IH is not 

yet complete.

The following-are in press, viz:

21. The Lignites of the Great Sioux Reservation, by Bailey Willis. 1885. 8°. pp. 5 pi. Price 

 cents.
ADVERTISEMENT.

22. On New Cretaceous Fossils from California, by Charles A. White, M. D. 1885. 8°. pp. 5 pi. 

Price cents.

STATISTICAL PAPERS.

A fourth series of pnblications having special reference to the mineral resources of the United States 

is contemplated.

Of that series the first has been published, viz:

Mineral Resources of the United States, by Albert Williams, jr. 1883. 8°. xvii, 813 pp. Price 50 

cents. ' i

The second volume of this series, Mineral Resources 1883 and 1884, is in preparation and will soon 

be put to press.

Correspondence relating to the pnblications of the Survey, and all remittances, which must be by 

POSTAL NOTE or MONEY oiiDKB, should be addressed

TO THE DlRECTOB OF THB

UNITED STATES GEOLOGICAL SURVEY,

Washington, D. 0. 

WASHINGTON, D. C., May 25,1885.
DEPARTMENT OF THE INTERIOR

BULLETIN

OF THE

UNITED STATES

GEOLOGICAL SURVEY

No. 2O

I WASHINGTON

'GOVERNMENT PRINTING OFFICE 

1885

UNITED STATES GEOLOGICAL SURVEY

J. W. POWELL DIRECTOR

CONTRIBUTIONS

TO THE

MINERALOGY OF THE ROCKY MOUNTAINS

BY

WHITMAN CROSS and W, F. HILLEBRAND

WASHINGTON

GOVERNMENT PRINTING OFFICE 

1885
.LETTER OF TBANSMITTAL.

UNITED STATES GEOLOGICAL SUEVEY,

DIVISION OP THE EOCKY MOUNTAINS,

Denver, Colo., March 1,1885.

SIE : I have the honor to transmit herewith a paper by Messrs. W. 

Cross, assistant geologist, and W, F. Hillebrand, chemist, representing 

work that has been done by them in the office and laboratory of this 

division, at intervals of leisure from their regular duties, during the 

past three years. Believing that the results of their investigations form 

a valuable contribution to the mineralogy of the Eocky Mountains, I 

would respectfully suggest that they be published in the form of a bulletin, so that they may be made immediately available to those interested in this science.

Very respectfully, your obedient servant,

S. F. EMMONS,

Geologist in Charge. 

'Hon. J. W. POWELL,

Director United States Geological Survey,

(223) 6

^2303

CONTENTS.

Letter of transmittal........................................................ 5

Introductory remarks....................................................... 11

I. Minerals from the basalt of Table Mountain,' Golden, Colorado, by Whitman Cross and W. F. Hillebrand ....................J................. 13

Description of Table Mountain .......................................... 13

Manner of occurrence of the minerals............................ 14

Order of deposition.............................................. 15

Zeolites. First group.. ..,................................................. 15

General......................................................... 15

Lauinontite.......................................................... 16

Description.............................................. . >-.-- 16

Chemical composition............................................ 16

Mixed Zeolites...................................................... 17

General description ............................................. 17

Chemical composition............................................ 18

Thomsonite spherules ............................................... 18

Chemical identification........................i................. 18

Zeolites. Second group................................................. 19

Slilbite. ("Desmin" German.)...................................... 19

General......................................................... 19

Crystal form and optical properties .............................. 19

Analysis........................................................ 23

Chabazite................ ........................................... 23

General......................................................... 23

Chemical composition........................................... 24

Thomsonite ......................................................... 24

Occurrence and general description.............................. 24

Chemical composition........................................... 25

Discussion of analyses................... ........................ 26

Relation to "mesole"............................................ 26

Analcite ............................................................ 27

General description................................................ 27

Optical behavior.................................. .............. 27

Chemical composition............................................ 29

Apophyllite......................................................... 29

General description ............................................. 29

Optical properties............................................... 29

Chemical composition........................................... 33

Alteration .................................................. .... 34

Mesolite............................................................ 35

General description ............................................. 35

Chemical composition........................................... 35

Natrolite ... v ...................................................... 36

Description and analysis ........................................ 36

Scolecite.................. .......................................... 36

Description and analysis ........................................ 36

(225) . 7
8 CONTENTS.

Page.

I. Minerals from the basalt of Table Mountain, Golden, Colo., etc. Cont'd.

Zeolites. Second group Continued.

Levynite ........................................................... 37

General description.............................................. 37

Chemical composition............................................. 38

Other minerals...................... r ................................... 38

Bole................................................................ 38

Description and analysis ......................................... 38

Calcite ............................................................. 39

Occurrence and description...................................... 39

II. Minerals from the neighborhood of Pike's Peak, by Whitman Cross and

W.F. Hillebrand...................................................... 40

General............................................................. 40

List of species known ........................................... 40

Mode of occurrence.............................................. 41

Cryolite ............................................................ 41

Locality........................................................ 41

Occurrence and association.............................. ^....... 41

Purely scientific value of the discovery .......................... 42

Recent literature of cryolite and its alteration products........... 42

General description ............................................. 43

Twin structure.................................................. 43

Chemical composition........................................... 48

Alteration of cryolite............................................ 48

Pachnolite.......................................................... 49

From the thin walls.... ........ % ................................ 49

From the bluish massive alteration product ...................... 50

. Crystallographical determinations-...............'............... 50

Chemical investigation.......................................... 52

Other forms of pachnolite ....................................... 55

Thomsenolite ....................................................... 55

Occurrence and description...................................... 55

Ralstonite ........................................................... 56

Probable identification.......................................... 56

Elpasolite, a new mineral ........................................... 57

Gearksutite ...................... .................................. 58

General description ............................................. 58

Chemical investigation.......................................... 58

Evigtokite....................................................... 61

Prosopite........................................................... 62

Occurrence ..................................................... 62

Crystalline form and physical properties ......................... 63

Chemical investigation.......................................... 63

Zircon.............................................................. 66

General occurrence...........^.................................. 66

Zircon from the Eureka tunnel.................................. 66

Kaolinite ........................................................... 67

Phenacite........................................................... 68

From Crystal Park............................... .............. 68:

Phenacite from near Florissant .................................. 69!

Topaz ............................................-.1............... 701

Crystal Park...... ...................~............... ............ 70

Florissant ...................................................... 71

Topaz from Devil's Head Mountain.............................. 72

(226)
CONTENTS. 9

.Page.

II. Minerals from the neighborhood of Pike's Peak, etc. Continued.

Appendix............ ................................................... 73

Notes upon the occurrence of topaz at Devil's Head Mourftain,by W.

B. Smith...... .................................................. 73

Topaz .......................................................... 73

Microcliue ...................................................... 74

Cassiterite...................................................... 74

Fluorite ........ ................................................ 74

III. On the lustre exhibited by sanidine in certain rhyolites, by Whitman

Cross ............................................................. 75

Sanidiue iu rhyolite from Chalk Mountain ........................... 75

Sanidine in rhyolite from Ragged Mountain.......................... 77

Previous description of lustre in feldspar ............................ 78

Lustre upon other sanidiues ......................................... 80

Conclusion ................................................... ...... 80

IV. An unusual occurrence of topaz, by Whitman Cross .................... 81

y. Associated rare minerals from Utah, by W. F. Hillebrand................ 83

Olivenite ........................................................... 83

Conichalcite ........................................................ 84

Chenevixite............................................ ............ 85

A hydrous cupri-calcium arseniate ................................... 86

Jarosite............................................................. 86

The massive ore..................................................... 86

VI. Miscellaneous mineral notes, by W. F. Hillebrand ...................... 89

Lollingite ........................................................... 89

Occurrence ..................................................... 89

Description...... ......................:........................ 89

. Chemical composition........................................... 92

Zinckenite.......................................................... 93

Cosalite .......... ..............................................:... 95

Hiibnerite .1........................................................ 96

Bindheimite .......................................... ............. 97

Kaolinite ........................................................... 97

Chemical composition............................................ 98

A chromiferous pseudomorph........................................ 99

Native lead......................................................... 99

VII. New mineral species from Colorado, by W. F. Hillebrand............... 100

Zunyite ............................................................ 100

Guitermanite....................................................... 105

A probably new mineral......... .......... .......................... 107

ILLUSTEATIONS.

PLATE I. Colorado minerals................................................. 114

Figs. 1, 2. Twin structure of stilbite.

3. Twin structure of phillipsite.

4. 5, 6. Optical anomalies of apophyllite. 

7, 8, 9, 10. Twin structure of cryolite. 

. 11. Prosopite. Saint Peter's Dome.

12.. Phenacite. Crystal Park.

13. Sanidine. Chalk Mountain.

14-16. Lolliugite. Gunnison Comnty.

17-21. Khoinbic arsenides associated with lollingite.

(227)

CONTRIBUTIONS TO THE MINERALOGY OF THE 

ROCKY MOUNTAINS.

By WHITMAN CROSS and W. F. HILLEBRANB.

INTRODUCTORY REMARKS.

A large part of the subject-matter contained in the following pages 

has already appeared in print, at various times during the past four 

years, in the American Journal of Science or the Proceedings of the 

Colorado Scientific Society. As opportunity has offered, the studies 

'have been extended upon the old or upon new and better material, so 

that much of that which has been previously published is here presented 

in a revised or enlarged form. The desirability of collecting in one 

place the notices of minerals from the same general region has led to 

the reproduction of some descriptions unaltered.

The more purely mineralogical parts of Sections I and II, for which 

the first-named author is chiefly responsible, does not claim to be so 

thorough and exact in many cases as the nature of the material may 

render desirable. This is partially explained by a want of the proper 

instruments for use in determining certain optical and physical properties of the minerals, but still more fully by the fact that the geological 

investigations in progress have left but little time for pure mineralogy.

In regard to the chemical part of the work a few remarks are necessary. 

From the first establishment of a laboratory in Denver a special aim has 

been to make the analytical work as thoroughly accurate as possible 

even though the amount accomplished should in consequence be lessened. 

As the main part of the laboratory work consists in investigations 

upon eruptive rocks, an exact knowledge of whose composition is at 

present deemed of great importance, it was sought to reduce the errors 

ordinarily incident to analyses of such rocks to the smallest possibly 

limits. To this end none of the ordinary reagents employed in any quantity are used without being first subjected to careful analysis. If they 

are found to contain sufficient impurity to influence even to a slight 

extent the result of an analysis, they are either rejected altogether or 

purified, or the percentages of impurities present are estimated and deducted from each analysis, for which weighed or measured quantities 

of these reagents are employed. Thus the very sma'll quantities of

(229) 11
12 MINERALOGY OF THE ROCKY MOUNTAINS. [BULL. 20.

silica, ferric oxide, alumina, and lime, almost invariably to be found in 

the purest of sodium carbonate, in a measure due to dust that has collected in the process of manufacture and packing, and which will gen. 

erally influence the result of an analysis from 0.1 to 0.2 per cent., are 

allowed for. Ammonia, which, after being kept in carboy for some 

length of time, often contains large amounts of silica aud other foreign 

matter, is redistilled and collected in pure water every few weeks.

By taking such precautions and using wherever possible platinum 

vessels, with proper care a high degree of accuracy is attainable. Especially is this so when no solid reagents enter into an analysis, as in 

the case of zeolites, of which a large number of analyses appear on subsequent pages and in few of which the sum total of percentages exceeds 

-100.1. A long series of analyses of eruptive rocks has been made in 

which, during the past two years, it has been the rare exception for an 

analysis to foot up over 100.2.

Without these explanatory remarks the close approximation to 100 

per cent, shown by so many analyses might rather inspire distrust than 

confidence. .

(230)
I. MINERALS FROM THE BASALT OF TABLE MOUNTAIN, 

GOLDEN, COLORADO.

By WHITMAN CROSS and W. F. HI^LEBRAND.

DESCRIPTION OF TABLE MOUNTAIN.

Table Mountain is a plateau or mesa with an area of from 4 to 5 square 

miles, situated upon the border of the3 great plains, 12 miles west of

Denver, approaching so closely to the abruptly rising foot-hills, com-, 

posed of Arch&an rocks, that the intervening space is not more than 1 

mile in width. Within this space, however, are exposed the upturned 

edges of strata of the Triassic, Jurassic, and Cretaceous ages, including 

in the latter the coal-bearing Laramie formation, all dipping steeply eastward. The mountain owes its existence to a sheet, or rather, in most 

places, to two sheets of basalt, which have in a measure protected the 

underlying soft Tertiary beds from erosion, which has removed the upturned Mesozoic strata to the west, until a valley several hundred feet 

deep has resulted, separating Table Mountain from the foot-hills. The 

Tertiary strata below the basalt are horizontal, and seem at first glance 

unconforrnable with the Mesozoic, but this is largely due to the location 

of the valley of erosion in a sharp fold; in other places apparent conform ability is shown.

Clear Creek issues from the foot-hills opposite the mountain, and has 

cut a gorge directly through it, dividing it into what are known as North 

and South Table Mountains, which have an average elevation above the 

creek bed of about 700 feet. On the banks of the creek behind the 

mountain is situated the town of Golden.

The source of the basalt is in certain dikes situated to the north and 

northwest, whence the lava spread out in sheets and flowed to the southsoutheast. The lower sheet averages 100 to 115 feet in thickness and 

possesses the structure of a stream which has flowed upon the surface. 

Adjacent to the underlying strata is a layer of a very porous structure 

about 1 foot in thickness, then follows massive compact rock for 70 

feet, while the upper 40 to 50 feet show many cavities, large and small, 

more or less flattened and drawn out, and the surface is rough and 

jagged. The first sheet was covered by a second, of identical composition, before erosion or decomposition had produced noticeable effects.

(231) 13
14 MINERALOGY OP THE ROCKY MOUNTAINS. [BULL. 20.

Of the second sheet only the massive lower part remains, and its thickness, as well as the lateral extension of both sheets, can only be a matter 

of coDJecture. The rock is a feldspar basalt of very simple composition, 

rather coarsely crystalline in its massive parts, and in the porous part 

with a groundmass which becomes finer grained as it approaches the 

contact or the surface. A glassy base, now much devitrified, was 

formerly present in the porous parts.

In the cavities of the upper portion of the lower sheet are many beautifully crystallized zeolites, associated with calcite and aragonite. The 

mode of occurrence varies somewhat in different parts of the mountain, 

and a few species seem to ,be locally restricted, but most of those to b« 

described can be found in abundance and well developed.

At a point on the southern face of North Table Mountain, where the

greatest number of species occur together, the students in the School

, of Mines at Golden began blasting for specimens several years ago.

During the present investigations the locality was still further opened

and absolutely fresh and clear material was obtained.

The only previous notice of this mountain is embodied in the report 

of Arch. E. Marvine, in the Annual Eeport of the United States Geological and Geographical Survey of the Territories for the year 1873, pp. 

129-131, but the information given is exceedingly meager and in part 

incorrect.

The Survey is indebted to Prof. A. Lakes, of the School of Mines, for 

calling special attention to Table Mountain.

MANNER OP OCCURRENCE OF THE MINERALS. The following mineral species have been identified in the cavities of the basaltic sheet, 

viz.: analcite, apophyllite, chabazite, levynite, thomsonite, mesolite, natrolite, scolecite, stilbite, laumontite, calcite, and bole. Of the occurrence of these species a few remarks will be in place before proceeding 

to detailed descriptions.

Primarily one can distinguish between the minerals occurring in fissures and those)in the roundish cavities of the amygdaloidal zone. On 

both mountains are many fissures and irregular cavities having outward communication, in which calcite, bole, and reddish zeolites are 

almost always deposited. Occasionally colorless zeolites (analcite or 

natrolite) appear in fissures, but it is much more characteristic to find 

them in the closed cavities. On the other hand a reddish, horizontally 

stratified zeolitic deposit is found in many amygdaloidal cavities, filling 

the smaller ones completely or forming a floor in the larger ones. As 

the minerals developed here are in part the same as those found in adjacent fissures, and as these reddish deposits always precede in time 

the formation of the colorless zeolites, it seems probable that all the 

cavities containing the minerals in question were formerly penetrated 

by fissures. Some such explanation is necessary, for cavities containing the reddish zeolites occur side by side with those in which only 

members of the other group are present, In some few cases, small fis-

(232)
CKOS8 AND HILLEBUAND. I ZEOLITES FIKST GROUP. 15

sures, now filled, were found leading into cavities containing the stratified deposits.

The zeolites are then naturally divisible into two groups, according to 

mode and time of formation, the first containing laumonfcite, stilbite, 

and thomsouite; the second, stilbite and thomsonite, with all the other 

species of the above list. They will be thus considered in the following 

description.

ORDER OF DEPOSITION. Considering all the species which occur in 

associations allowing inferences as to relative age, the following may 

be given as the order observed, beginning with the oldest:

1. Laumontite. \

2. Stilbite. > Eed or yellowish.

3. Thomsonite. ;

4. Calcite (yellow).

5. Stilbite.

6. Chabazite. ,

7. Thomsouite.

8. Analcite.

9. Apophyllite.

10. Calcite (colorless).

11. Mesolite.

Chabazite and thomsonite were also formed again in very small 

quantity, probably between 9 and 10. Natrolite, scolecite, and levynite 

do not occur in direct association with most of the above, so that their 

places in the series are unknown.

. . ZEOLITES. FIRST GROUP.

GENERAL. The minerals of this group are best developed in the 

stratified deposits of the amygdaloidal cavities, where also the order 

and manner of deposition can most clearly be seen.

In a large cavity containing a floor of the reddish-yellow mixture of 

the minerals of this group, it is at once noticed that the roof and sides 

above the level of the stratified mass show no trace of any one of these 

species. From this fact and from the structure of the mass the inference is warranted that the formation began at the bottom and proceeded very rapidly to its close. Usually the lower portion of such 

masses is composed of a reddish-yellow mineral in irregular grains, 

forming a compact aggregate in which lie isolated spherules of a similarly colored radiate mineral. These spherules are seldom more than 

2mm in diameter and are very perfect spheres. They increase in number upward and finally compose the greater part of the deposit,

(233)
16 MINERALOGY OF THE ROCKY MOUNTAINS [BULL. 20.

In one cavity, 6 to 8 feet in horizontal diameter and about 2 feet in 

height, the deposit is quite different. Here the main mass is loosely 

granular, and is formed chiefly by a bright greenish-yellow mineral, 

while a stratified appearance is produced by layers of a white or colorless substance.

Some of the light layers are chiefly made up of easily recognizable 

stilbite, and the same mineral in distinct tablets forms the upper layer 

of the whole deposit. There are also irregular seams of white running 

through the yellow material.

LATTMONTITE.

DESCRIPTION. If the loose sand from the above-mentioned cavity 

be placed under the microscope with a. power of about 15 diameters, 

it is seen to consist of prismatic grains, mostly with broken terminations. Many of the grains are clear and transparent, with the greenishyellow color mentioned, while others are dull. The clear prisms polarize 

strongly, and extinction upon a prismatic plane takes place at an angle 

of 35° to 40° with the vertical axis:

On splitting open some of the white layers, surfaces are obtained 

showing minute stout prismatic crystals, which seen under the microscope present the same habit as the yellow grains. The prism angles 

are nearly 86° and 94°, and the termination is usually formed by an 

oblique plane, like a hemidome of the inonocliuic system. The optical 

orientation is the same as in the yellow crystals and corresponds also 

to the requirements of the monoclinic system so far as can be determined. The properties given agree with those of laumontite, and in 

the light of the chemical analyses the identification of both yellow and 

white crystals with that mineral seems entirely justifiable.

CHEMICAL COMPOSITION. The analysis gives the following results:

SiOz...... ........... .....

AlzOs .. ...................

FesOs. ....................

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

KsO. ........... ..... ....

tfazO..... ................

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

( W. F. Hillebrand.)

I. Yellow 

grains.

51.43

21.52

0.94

11.88

0.35

0.19

13.81

100. 12

II White 

crystals.

52.07

21.30

11.24

0.42

0.48

14 58

100.09

Oxygen ratios:

RO : E2O3 : SiO2 : H2O

I. 1 : 2.97 : 7.83 : 3.50

II. 1: 2.94 : 8.15 : 3.81 

(In all calculations of ratios 27 is taken as atomic weight of Al.)

These analyses represent the composition of air-dried material, and 

the percentages were calculated from the analyses published in the

(234)
CU08S AND HILLEBBAND.] LAUMONTITE MIXED ZEOLITES. 17

American Journal of Science. 1 The latter were made after drying over 

sulphuric acid, it having been observed that at 100° C. an unexpectedly large loss took place, steadily increasing as the temperature rose 

above 100°. Even when simply dried over sulphuric acid the loss in 

the case of I was 0.60 per cent., and in the case of II was 1.45 per cent. 

These abnormally large losses, coupled with still larger ones observed 

subsequently in analyzing other zeolites, seemed to indicate that all, or 

at any rate nearly all, the water removed by sulphuric acid should be 

counted with the water of crystallization, especially as when this was 

done the oxygen ratios generally more nearly approached that required 

by theory; for example, in II the ratio for material dried over sulphuric 

acid is only I : 2.94 : 8.15 : 3.42, instead of L: 2.94 : 8.15 : 3.81 as above 

given. Keceiit investigations by Jannasch 2 on heulaudite and epistilbite tend to confirm us in this opinion.

The ratio of II agrees fairly well with the theoretical requirements of 

laumontite, 1:3:8:4, especially as it can hardly be supposed that the 

material was absolutely pure. It is quite probable that a small amount 

of stilbite was included with the material analyzed, which would explain the rather high value for SiO2 .

In regard to the amount of water found it is only necessary to suppose that the dull particles have lost a part of their water while the 

transparent grains are entirely fresh in order to explain the relation of 

water to the other constituents as shown in the above ratios, a supposition in full accord with the characteristic tendency of laumontite. to 

lose its water on exposure.

The mineral is not quite so easily fusible before the blow-pipe as 

typical laumontite should be according to the textbooks, but the difference is not sufficiently pronounced to be considered abnormal.

MIXED ZEOLITES.

GENERAL DESCRIPTION. Turning now to the more compact reddish-yellow deposits, which correspond so closely to the one described 

above, the same constituent minerals .were sought for. Some small 

cracks or fissures were noticed, usually ending blindly in the yellow 

mass, some of which were only partially filled with minute white crystals. On splitting the mass open along such a half-filled crack two 

surfaces were obtained, coated with minute but exceedingly perfect 

clear crystals, easily recognizable under the microscope as laumontite 

and stilbite. The little crystals of the former show occasionally the 

clinopinacoid and a steep positive orthodome in addition to the prism 

and base.

1 III, Vol. XXIII, p. 135.

2 Neues Jabrbuch fur Mineralogie, etc., 1884, II, 20Q, 

. 20 2 (235)
18 MINERALOGY OF THE ROCKY MOUNTAINS. [BULL. 20.

The sand obtained by simple fracture of the yellow massive portion 

on being placed under the microscope is seen to consist largely of fragments of tabular crystals, the angles of which, so far as they are determinable, correspond to stilbite. The grains which are not evident 

fragments of tablets .are in part roughly prismatic, though seldom 

showing definite faces; neither could the optical action be satisfactorily 

determined.

CHEMICAL COMPOSITION. Chemical analyses were made from two 

different specimens of the yellow granular mass, care being taken to 

exclude all reddish spherules. The results are given under III and IV 

below.

SiOz....... ..................

AlzOs...--... ................

Fe«03 .. .....................

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

K20....... ..................

NasO. .......................

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

(W.F.Hillebrand.)

ni.

54.20

17.26

0.77

8.35

0.17

1.38

18.09

100. 22

rv.

53.87

17.26

0.74

8.27

0.07

1.48

18.44

100. 13

Oxygen ratios:

KO:B2O3 :SiO2 : H2O

III. 1:3.01 :10.43: 5.80

IV. 1:3.03 :10.42: 5.95

Analyses III and IV were published in the American Journal of Science, with this difference, that they represented the composition of dried 

material. Inasmuch as III lost 2.14 per cent, of moisture in two days 

over sulphuric acid (no further loss in three days) and IV 1.69 per cent, 

under similar conditions, the whole is counted as water of crystallization for the reasons given in discussing the analyses of laumontite.

As will be seen later, pure crystals of colorless stilbite from Table 

Mountain do not possess, as regards SiO2 and H2O, quite the theoretical composition of that mineral (see analysis VI, p. ). If, however, 

that analysis represents the composition of all stilbite from this locality, 

these analyses III and IV correspond remarkably well to mixtures of 

much stilbite with a little laumontite, as was surmised from microscopical examination of the material.

It seems remarkable that the material from two different cavities 

should contain the two minerals in so nearly the same proportions as 

is indicated by the analyses.

THOMSONITE SPHERTJXES.

CHEMICAL IDENTIFICATION. Concerning the reddish spherules no 

data of importance could be obtained except by chemical apalysis,

(236)
CROSS AND HILLBBRAND.J THOMSONITE SPHERULES ZEOLITES. 19

Under V is given the composition found for this substance in material 

which was apparently very pure.

SiOs.. .......................

AhOs.---.. .................

' FezOg........ ................

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

Na50.. ......................

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

(W. F. Hillebrand.)

. V.

40.52

29.22

0.79

12.43

4.31

19 70

100. 00

The oxygen ratio for this is:

EO : B2O3 : SiO2 : H2O 

1: 3.00 : 4.63 : 2.44

These figures agree so well with those obtained for the colorless 

thomsonite (see page 25) that in the absence of anything to the contrary the identity of the two substances can scarcely be doubted. It 

was noticed here, as in the other thomsonite, that about 2 per cent, of 

the water could be expelled only at a very high temperature. The ferric oxide in all these minerals seems to replace a portion of the alumina.

Thomsonite in the form of these reddish spherules has been deposited 

locally in great abundance in irregular cavities on the upper surface of 

the lower sheet of basalt and also in the angular spaces formed where 

the scoriaceous crust of the flow has been broken or crumpled. It is 

here deposited alone, free from stilbite and laumontite, but the spherules are exactly similar in size and appearance to those formed in the 

cavities below.

ZEOLITES. SECOND GROUP. 

STILBITE ("DESMnST" GERMAN).

GENERAL. As has been already mentioned, stilbite occurs occasionally in clear, colorless crystals, as well as in the manner characteristic of 

the first series. It is noteworthy that in all such cases as yet observed 

the clear stilbite is either deposited upon the colored zeolites of the group 

described, or in close proximity to them, although it may be associated 

with chabazite or clear thomsonite, species having no such limitation. 

When these three minerals are associated it is sometimes difficult to 

assign an order of deposition, as they seem to have been nearly contemporaneous. The tablets of stilbite are usually attached by an edge, projecting at various angles from the underlying surface, and rarely appear 

so abundantly as to form a crust.

CRYSTAL FORM AND OPTICAL PROPERTIES. The largest crystals 

seen measure about 1.5cm in longest diameter and 2.3mm in thickness,

(237)
20 MINERALOGY OF THE ROCKY MOUNTAINS. [BULL. 20.

These crystals, however, are made up of several plates, which are not 

in exactly coincident orientation, and their surfaces are not very smooth 

or glistening, from which causes they are not available for either crystallographical or optical studies. For these purposes only the minute 

transparent tablets which are occasionally found intermingled with the 

others could be used.

These tablets have the usual rhombic symmetry which has been explained by von Lasaulx as the result of a double twinning of a monoclinic groundform isomorphous with those of harmotome and phillipsite, and according to the laws observed in those species. The isomorphism thus pointed out has been advocated from the chemical side by 

Fresenius.3 The Table Mountain stilbite presents some structural and 

optical properties not fully in accord with the statements of von Lasaulx, 

and yet the material is not perfect enough to show the full significance 

of the disagreement. A description of the observed variation may lead 

to an explanation based upon the study of other and better material.

Assuming the isomorphism stated, the predominant face is coPSo, 

while o> P and 0 P are always present, and -f P w occasionally. The 

front prism angle was measured at 118° 22', by attaching small flakes 

of mica to the dull surfaces of a large crystal, while approximate measurements in the othodiagonal'zone could be made under the microscope.

For optical examination a number of small tablets were mounted in 

balsam, lying upon the predominant pinacoidal face; others were 

mounted in the same position after a little grinding, which was intended 

simply to. remove impurities from the surface. All exhibit the same 

optical action. The larger crystals could not be used for the reasons 

stated above.

Fig. 1 of the plate represents the structure described by von Lasaulx4 j 

in crystals examined by him, the figure being copied from his article, 

with a simple inversion to correspond with Figs. 2 and 3. On examining a crystal of tabular form, mounted as above described, between 

crossed nicols, there appears a division into four quadrants, a a and b 

ft, by lines passing through the centre parallel and normal to the clino- ? 

axis. By parallel position of these lines with th(^principal sections of 

the uicols all four portions appea-r equally dark, but the maximum of 

extinction is only obtained by a revolution of about 5° from this position, for two diagonally opposite quadrants when the revolution is to 

the right, for the other two when to the left. There is therefore a dif- . 

ference of about 10° in extinction of adjoining quadrants. According 

to von Lasaulx the bisectrix is inclined 5° to the clino axis, while the 

optical normal makes an angle of 34° with the vertical axis. Reference 

will be made to this point later. A distinct zonal structure parallel to ' 

the outlines of OP, and cc P is described, and a very faint subdivision of

sZeitschriftfiir Krystallographie, III, 42, 1878. i 

4 "Ueber den Desmin." Zeitschrift fiir Krystallograpliie, II, 576, 1878.

(238)
CROSS AND HILLHBRASD.J STILBITE COMPLEX TWINNING, 21

each quadrant by this zonal structure is mentioned, but it is distinctly 

stated that no corresponding optical division exists. It is noted, 

however, that in a given quadrant the extinction adjoining d maybe 

slightly less than that near c. Aside from this division into quadrants, 

which is in agreement with the supposed symmetry and twinning of 

the mineral as isomorphous with harmotome and phillipsite, there are 

. often four other fields, c c and d d. The portions e c are diverging 

bundles of a somewhat fibrous, colorless mass, producing in all positions 

brilliant aggregate polarization. The parts d d are made ilp of bars 

placed perpendicularly to the line of 0 P, the area thinning out wedgelike toward the centre. Sections situated in the orthozone show coincident extinction throughout, so that these irregular aggregates (c and d} 

seem to consist of stilbite substance having at least the orthoaxis in 

common with the rest. In all the many occurrences examined by von 

Lasaulx this division is more or less distinct. .The portions c and d, 

termed by him "inverse substance," in contrast to the normal quadrants 

a and &, sometimes predominate largely, while d at least is occasionally 

very subordinate. With this action as given by von Lasaulx will now 

be compared that exhibited by the Table Mountain stilbite.

Fig. 2 represents the optical behavior of a crystal from Table Mountain, and is typical of that in all examined. It is in parallel position 

with Fig. 1, the dome -f P co~"being added while at one end is a repetition of oo P and P «T. The same primary divisions are here seen as 

in Fig. 1, but each quadrant, «, is clearly subdivided when seen in 

polarized light by the zonal structure, which in the octants a and & 

runs parallel to the outline of oo P, in a' and &' parallel to 0 P. The 

two systems meet in an irregular line which usually runs from the 

angle between 0 P and oo P to the centre of the crystal. The bands of 

the two systems do not cross each other, as represented in Fig. 1, and. 

a very small but appreciable variation in optical orientation may be 

seen. The direction of extinction in a' and &' measures about 4° 15' 

from the edge of 0 P, while in a and & it is 5°-5° 30' from the same 

direction. This corresponds to the statement of von Lasaulx that 

there seemed to be in some cases a difference between the extinction of 

a near the space d and that near c, the latter being greater. So far 

the action might be considered as slightly more intense than usual, 

whereby the subdivision of the quadrants is plainer. However, the 

position of the optical normal as given by von Lasaulx demands that 

the bisectrix should cut the clino axis, i. e., the line of OP in the 

figure, at an angle of about 5° and the vertical axis at about 56°, while 

the bisectrix in the present case is inclined 5° to the clino axis and 

about 46° to the vertical axis, the normal consequently intersecting the 

latter at about 44°. In all crystals and in each quadrant the bisectrix 

lies in a dome which is steeper than the basal plane by about 5°, and 

hence truncates the angle between 0 P and oo P, bringing the optical 

normal to an inclination of about 44° with the vertical axis. The close

(239)
22 MINERALOGY OF THE ROCKY MOUNTAINS. [BULL. 20.

agreement in other respects suggests the possibility that the position 

of the bisectrix relative to the cliuo axis may have been transposed by 

von Lasaulx.

The portions lettered c in Fig. 2 correspond in position and character to those of Fig. 1. An attempt has been made to indicate their 

irregular form and their relation to other parts. Usually based upon 

the outline of Poo", they may spring from any part of the line of oo P, 

and universally run toward the centre, often wedging out before reaching it and'never penetrating segments a' or &'. Parts corresponding to 

d d in the Fig. 1 are here represented by a few bars at right angles to 

OP,but, although most numerous near the sharp line between a' and &', 

they do not appear in sufficient quantity to form a distinct field, as d in 

Fig. 1. These interpositions seem most probably to be portions of a' 

included in b' and vice versa. The lower part of Fig. 2 shows the irregular relation of b' to a1 in some cases, the dividing line being sharp 

while very much broken. In &', which is thus enlarged, are numerous 

interpositions which are most sharply defined and apparently thickest 

on the side opposite a', while thinning out toward that area. Some 

bars in &' seem to have a thin wing-like appendage on the side next a'. 

The orientation of these interposed bodies cannot be definitely ascertained, but they seem to correspond closely to the adjacent division of 

the next quadrant.

The areas c c often contain stripes corresponding to a and b and also 

more rarely of b' or a'. Fig. 2 shows how each repetition of oo P is 

accompanied by portions which are banded parallel to its outline and 

correspond optically to all other parts of the same position. In some 

crystals a close examination shows a delicate zonal structure, parallel 

to that of a or 6, in small irregularly shaped parts of c, and as these 

are almost always thin and underlaid by substance of other orientation, 

so that a uniform extinction does not take place, it seems quite probable

that these portions showing aggregate polarization are made up of an 

intergrowth of thin flakes of a and 6 with the ortho axis in common, 

but not in fully coincident position otherwise; corresponding thus to 

the known tendency of the mineral in larger crystals and which is characteristic of those from this locality. Von Lasaulx also suggests this 

explanation, but thinks the brilliant and strongly contrasted polarization of parts whose extinction angles should so nearly coincide is antagonistic. The interference of light in passing numerous laminae and 

possible tension arising from the manner of intergrowth assumed seem, 

however, sufficient to account for this strong action.

During the study of the twin structure in phillipsite, Trippke 5 made 

a section through the centre of a double twin crystal, parallel to the 

clinopinacoid of one of the simple twins and obtained thus a form cor-

 - « : 

b P. Trippke. " Beitrage zur Kenntniss der schlesischen Basalte und ihrer Mineralien." Breslau, 1878. (Dissertation.)

(240)
CllOSS AtiD HILLEBKANb.1 STILBITE' CHABAZITE. 23

responding to the crystals of stilbite. Fig. 3 is a reproduction from his 

work showing the optical division of the section. Its formal correspondence with that described for stilbite is noteworthy. The segments 

a and b correspond to a' and b' of Fig. 2, even to the interposed bars at 

right angles to 0 P, which are interpreted by Trippke as inclusions of a 

substance in &, and the reverse (loc. cit., p. 39). The areas c, d', /, e1 

represent, however, four distinct individuals which do not correspond 

to a and b of Fig. 2, except in form. Likewise the wedge-shaped portions a' and b' do not correspond to c of the stilbite, for they represent 

substance whose basal plane falls parallel to coP«> of a and b. If the 

various parts of the stilbite crystals do possess the ortho axis in common, as indicated by the observations of von Lasaulx and by a single 

section secured parallel to 0 P in a Table Mountain crystal, then the 

structural correspondence between Figs. 2 and 3 is meaningless except 

for the segments based upon 0 P. These are actual equivalents.

The material thus far obtained from Table Mountain does not permit 

of crystallographic measurements of sufficient accuracy to determine 

definitely whether the division into octants, indicated by the optical 

behavior, can be traced in the outer form or not. The incomplete results obtained have been given in detail because it seems probable that 

the material examined by von^Lasaulx does exhibit in less distinct form 

the same action. It is hoped that an attempt to secure better specimens from Golden may be successful, so that further examination may 

be made.

ANALYSIS. Pure crystals gave on analysis the following:

Si02 ...... ..................

AlsO....... .................

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

Na?0...... ............ ....

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

(W. F. Hillebrand.) -

VI.

5467

16.78

7.98

1.47

19.16

100. 06

Oxygen ratio: 

EO : B2O3

2.97

3.00

formula.

SiO2 : H2O

10.97 : 6.41, instead of 

; 12.00 : 6.00, as required by the ordinarily accepted

CHABAZITE.

GENERAL. With the exception of stilbite this is the oldest of the 

colorless zeolites. In most cases where several zeolites occur together 

chabazite forms the lining of the cavity and the others are deposited 

upon it. It is often found alone, however, and excellent specimens are 

abundant.

The glassy white, or rarely pinkish, crystals have the usual rhoinbohedral form and the faces are occasionally as much as lcm in diameter.

(241)
24 MINERALOGY OF THE ROCKY MOUNTAINS. | BULL. 20.

The crystals are usually twins of interpenetration. In some of the 

smaller cavities are subdividing walls of chabazite or miniature columns composed of many small crystals. A second generation of chabazite came after thomsonite and analcite, but the crystals are few and 

very minute.

CHEMICAL COMPOSITION. Chemical analysis of clear crystals gave 

as follows: :

SiOz. .......................

AhOs. ......................

FesOa.-..-- .................

CaO. ...................... I

SrO....... ............ ....5

KifO ........................

NasO.... ..................

HsO ................ .... ; ...

(W. F. Hillebrand.)

VII.

47.86

19.30

*0. 12

9.94

O P^

0.52

22.07

100. 16

vni.

47.18

19. 67

f Q 7/1

I 0.43

n wi

0.51

22.15

100. 05

* From attached limonite.

Loss on drying over sulphuric acid. 

Total loss at 100° C...... -.......-...

Total loss at about 300° C...........

Loss above 300° C"..................

Per cent. 

2.66 

4.76

... 18.45 

3.70

From the above analyses it is impossible to deduce a formula strictly 

in accordance with that of Eammelsberg6 or that of Streug.7 Assuming part of the alkaline earths to be replaced by alkalies, the following 

oxygen ratios are obtained :

BO: AlA, : SiO2 : H2O 

VII. 1 : 3.05 : 8.57 : 6.59 

VIII. 1: 3.04 :8.27 : 6.47 _ .' 

It is highly probable that a part of the water is basic. The presence 

of strontia in such quantity is noteworthy. 

The material was riot examined microscopically.

THOMSONITE.

OCCURRENCE AND GENERAL DESCRIPTION. This zeolite followed 

closely upon the chabazite ; Indeed its earliest aggregates are so intimately associated with that mineral as to make it evident that the deposition of the one had begun before that of the other had ended. The 

mineral occurs in very minute rectangular blades, which are placed upon 

each other like the leaves of a closed fan, and the very compact combinations of such aggregates are usually arranged in a more or less distinct radiate manner. Sometimes spherical forms result, in other cases 

columns, by radiation from an axis, or, less frequently, walls, the blades 

standing at right angles to the central plane. Where crystals of yellow

e Zeitschrift d. D. geol. Ges., XXXVI, 220, 1884. 

7 Berichte d. oberliess. Ges., etc., XVI, 74, 1877.

(242)
cuoss AXD MILLEBBAND.] THOMSONITE CHEMICAL COMPOSITION. 25

calcite were not covered by chabazite the thomsonite has never failed 

to coat them, the blades being approximately perpendicular to the crystal faces. When a large surface of chabazite has been completely 

coated by'the more or less radiate aggregates of thomsonite, forming aii 

undulating surface, the whole has a most delicate silken lustre, while 

that on a fractured surface of a spherical mass is more satin-like. The 

aggregates are white when pure and single blades are transparent.

It is difficult to obtain isolated leaves, and they are then so thin as to 

affect polarized light but slightly, still it was definitely determined that 

the direction of total extinction between crossed nicols is parallel to the 

longitudinal axis. By examination of the ends of the blades under the 

microscope with a power of 90 diameters, it could be seen that the vertical edges were formed in many cases by a plane at right angles to the 

dominant surface. Occasionally a prism was found with angle very 

near 90°, and in a few cases both forms together were seen. These 

planes correspond to the macropinacoid (dominant) prism and bracliypinacoid of thomsonite, as given by all authorities. The termination 

seems to be the basal plane. The average thickness of these blades is 

aboutO Olmm . Toward the close of the zeolitic formation a second generation of thomsonite was deposited. The blades are in this case longer 

than in those of the first while the other dimensions remain about the 

same. In combination with the base upon the crystals of this latter 

growth are apparent brachydomes, whose angles with the base \yere 

most frequently measured at about 145° or 135°.

The blades of the second generation, when deposited upon those of 

the first, have the same crystallographic orientation and serve simply 

as prolongations of the latter. Through the usual slight yellow tinge of 

the recent growth, the line between the two is clear. The long blades 

of the second growth of thomsonite often form bundles resembling rough 

prismatic crystals, and these bundles arranged in a loosely and irregularly radiate manner form bunches an inch or. more in diameter upon 

which the delicate needles of mesolite have a special tendency to de 

posit themselves.

The thomsonite of Table Mountain, was first identified through a quantitative analysis by Garlton H. Hand, at the time a student in the School 

of Mines at Golden. The analysis was not published and has been lost.

CHEMICAL COMPOSITION. The following results were obtained by 

the analysis of different specimens of thomsonite from Table Mountain:

SiOs ............... ...............

AlsOs...... ........................

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

Na«0.-.. .................. ........

mo...............................

(W. F. Hillebrand.)

IX.

40.88

29.68

11.88

4.72

12.91

100. 07

3

a 

40. 68

30.12

11.92

4.44

12.86

100.02

b 

40.70

29.75

11.89

........

X

a 

41.21

29.71

11.34

5.62

12.20

100. 08

I.

b 

41.17.

11.38

........

X]

a 

42.66

29.25

10.90

4.92

12.28

100. 01

[I.

6

29.29

10.90

12.34

xin.

41.63

........

(243)
26 MINERALOGY OF THE ROCKY MOUNTAINS. |BULL.20. 

Oxygen ratios: *

IX ....................

X, mean of a and 6 ......

XI, mean of a and &..... 

XII, mean of a and b ....

RO : E2O3 : SiO2 : H2O 

..1: 3.03: 4.73: 2.49

..1: 3.09: 4.77: 2.51

. .1: 2.98: 4.68: 2.31 

. . 1 : 3.14 : 5.19 : 2.50

DISCUSSION OF ANALYSES. In all of these analyses the figures under 

6 denote repeated determinations. Analysis IX was made upon material taken from the purest and finest specimen of thomsonite as 

yet obtained. Separation from the underlying thin layer of chabazite 

was complete. The material for X was also selected with the greatest 

care from a very pure specimen. Imperfectly spherical aggregates 

were broken up quite finely, and each particle appropriated for analysis was first closely examined with a strong lens in order to detect any 

trace of chabazite. Thinking it possible that a small amount of chajbazite might have escaped notice, a second portion of thomsonite from 

the same specimen was procured by breaking off the ends of the 

blades, and this was found to contain 41.63 per cent, of SiO2 (XIII). 

A microscopical examination of this material showed that these blades 

of thomsonite contained very small, irregularly rounded particles imbedded in the outer surfaces. These particles, which are clear or 

slightly yellowish, do not affect polarized light perceptibly and are not 

crystalline in form. They are present in varying quantity toward the 

termination of nearly all blades, but are usually entirely wanting in 

the lower portions of all aggregates. In the material yielding IX they 

were present in less quantity than usual, and even if they consisted of 

pure silica could have affected the result but slightly.

Analyses XI and XII were made upon substance known to be slightly 

contaminated by delicate hairs of mesolite which could not be fully removed, Both represent tliomsonite from bunches of the kind mentioned 

above.

RELATION TO " MESOLE." In the hope of throwing some light upon 

the cause of the difference between the composition of normal thomsonite (oxygen ratio 1: 3 : 4 : 2£) and the variety sometimes called 

"mesole" (oxygen ratio well represented by those of the foregoing 

analyses)*, the ratios for all the analyses of mesole given in Dana's 

System of Mineralogy, and of such others as could be obtained, were 

calculated and the results examined.

Intermixture of free silica or of mesolite has been generally considered the cause of the excess of silica in mesole. While the presence 

of either or, both of these substances may be a sufficient explanation in 

some instances, and in two of the above analyses (IX and X) un. 

doubtedly is, to some extent at least, a true one, it will not answer for 

a majority of the published analyses examined. Only one of these, on

(244)
ctioss AND HiLLKBKAiJD.I THOMSONITE ^ANALCITE. 27

Nova Scotia material, by How, affords a ratio very near that furnished 

by. IX and X above.

While positive proof is wanting of the total absence of free silica in 

the purest of the Golden thomsonite analyzed, the most thorough microscopical examination failed to reveal its presence or that of any 

other foreign matter.

Mesolite cannot be the disturbing element here, because in order to 

raise the silica 3 per cent, above that of normal thomsonite there would 

be required an admixture of not far from 50 per cent, of mesolite, 

which amount would also have raised the oxygen value for water. It 

seems indispensable to a solution of this question that numerous and 

accurate analyses should be made of this variety of thorasonite from as 

many localities as possible, and that careful microscopical examination 

should in every case furnish as far as possible a guarantee of the purity 

of all material taken for analysis.

AN AI, CITE.

GENERAL .DESCRIPTION. Analcite follows thomsonite in time of deposition. At the locality mentioned on North Table Mountain its crystals are pure white or transparent and vary in size from very small ones 

to those nearly an inch in diameter. The predominating form is the 

common trapezohedron 202 having its octahedral edges evenly trun-. 

cated by fO. The appearance of fO is very characteristic of the Table 

Mountain analcite, though the form is never prominent and is usually 

represented by an exceedingly narrow line. According to Zirkel8 the 

form fO has been observed but once on analcite, viz., by Laspeyres 

on that from the Kerguelen Islands. A second generation of analcite 

was. observed, analogous to that of chabazite, tbe crystals being very 

small and clear. They were deposited upon apophyllite.

On the eastern side of North Table Mountain analcite is often present 

alone, filling small cavities completely and developed in immense crystals in the larger ones, some being nearly 2 inches in diameter. The 

faces of such large crystals are often uneven through depressions or 

other irregularities bounded by faces of 202.

On South Table Mountain analcite is more abundant than any other 

zeolite. Large cavities have a floor of analcite but always in quite 

small crystals. Natrolite is almost invariably deposited upon it and 

frequently small cracks are filled with the same mineral associated with 

calcite or natrolite. Analcite was also found in spaces between the 

pebbles of a conglomerate bed, not far below the basalt, the pebbles 

being of basic eruplive rocks.

OPTICAL BEHAVIOR. The anomalous optical properties oi1 much

analcite have been the subject of careful investigation by numerous

able mineralogists, some of whom have sought the explanation in a complicated twin structure by which a substance of lower degree of sym8 Naumaun-Zirkel, "Elemeute der Mineralogie." Leipzig, 1881.

(245)
28 MINERALOGY OF THE ROCKY MOUNTAINS. [BULL. 20.

metry may imitate a higher, while others have referred the phenomenon 

to double refraction arising from inner tension. Since the exhaustive 

researches of Ben-Sande 9 few have opposed the latter view, according 

to which all optical action in analcite, which is abnormal for a mineral 

crystallizing in the regular system, is regarded as secondary and produced by molecular disturbances due to changes of temperature. The 

mode of formation of the mineral and the crystal forms developed determine the character of the anomalous action.

In the preliminary description of the Golden zeolites 10 it was stated 

that the analcite of Table Mountain " is doubly refractive, but so irregularly that it cannot be well used in confirmation of the interesting observations of Ben-Saude." At about the time of this publication a suite 

of the Golden zeolites was sent to Professor Carl Klein, of Gottingen, 

the foremost in the group of those who have sought to explain many 

optical anomalies in crystallized minerals by the theory of inner molecular tension due to secondary causes. The thorough examination of 

the Table Mountain analcite by Professor Klein, the results of which 

were published in the Neues Jahrbuch fur Mineralogie, etc. (1884,1, 

250), shows that the above statement is correct only for the larger crystals, while the smaller and most perfect ones agree entirely with the 

observations and conclusions of Ben-Saude. Renewed examination by 

us upon minute and carefully-selected crystals fully confirms this testimony.

Professor Klein also subjected our material to investigation in a direction recently followed by him in regard to many minerals with eminent 

success, particularly in the cases of boracite11 and leucite.12 By means 

of an apparatus devised for the purpose the effect of heat upon the optical properties of a given mineral can be observed under the microscope. 

The application of this method of research to the Table Mountain analcite enables Professor Klein to state that in sections parallel to ccO GO 

and oo 0 the doubly refractive action of the various segments into which 

the crystal is divided becomes less and less, and finally disappears entirely, leaving an isotropic field. By thin sections this change is effected 

rapidly, while in the thicker ones it is retarded, and in some cases ;was 

not wholly successful. These investigations seem to demonstrate clearly 

that analcite is a regular mineral, whose anomalous optical properties 

are due to molecular disturbances produced by a decrease in temperature from that prevailing at the time of formation of the mineral.

s " Ueber den Analcim." Neues Jahrbuch fur Mineralogie, etc., 1882, I, 41.

10 Am. Jour. Sci., III, XXIII, p. 452r 1882.

11 Neues Jahrbuch fiir Mineralogie, etc., 1882,1, 235.

12 Ibid., 1884, 11,49.

(246)
dices AND HiLLEBRAND.] ANALYSES OP ANALCITE APOPHYLLITE. 29

CHEMICAL COMPOSITION. Analyses of crystals, apparently pure, 

which were, however, not examined microscopically, gave as follows:

SiOz. ...... .................

AhOs. ......................

NanO. ......................

HzO. .......................

(W. F. Hillebrand.)

XIV.

55.82

22 42

13.48

8.38

100. 10

XV.

55.80

22.45

13.45

8.35

100. 05

Oxygen ratios:

Na2O:Al2O3 :SiOa :H2O

XIV. 1:3.03 :8.56 :2.14

XV. 1:3.04 :8.57 :2.14

The excess in silica and water is most probably due to presence of 

hydrated silica.

APOPHTLLITE.

GENERAL DESCRIPTION. This mineral occurs in well-developed 

crystals of prismatic habit with co P oo and P predominating, while OP 

is in most cases quite subordinate or wanting entirely. The larger 

crystals which are occasionally half an inch in diameter, are often of a 

greenish tinge, sometimes quite pronounced, and possess more or less 

uneven surfaces produced by a repetition of the crystal faces, so that 

the termination is made up of a large number of small pyramids. 

The prismatic surfaces are roughened by depressions or elevations 

bounded by prism and pyramid planes. This feature is very prominent 

in all large crystals, while the smaller ones are in contrast sharp and 

clear with smooth, brilliant faces. Especially noticeable on these small 

and clear Crystals, though not peculiar to them, is a replacement of the 

pole edge of the pyramid by a small re-entering angle formed by pyramid 

faces. This angle is nowhere prominent, yet may be easily identified on 

all clear crystals, both large and small. No corresponding irregularity 

of any kind could be detected on the dimetric prism of these crystals.

As a rule the largest crystals occur in the small cavities, and their 

growth has been more or less hemmed by the walls, while the more 

perfect crystals are present in the large cavities, and are usually small 

and numerous.

OPTICAL PROPERTIES. Apophyllite is another of the group of minerals exhibiting in many cases an optical behavior not in accordance 

with the outward symmetry, and the mineral from Table Mountain shows 

this anomalous action in typical form. The thorough investigation of 

such minerals having become within the past, few years a work for the 

specialist, with appliances not at our disposal, we shall confine ourselves to a simple statement of observed facts. We are able, however, 

to refer to the published results obtained by Professor Klein from an 

examination of material from Table Mountain. Unfortunately but a

(247)
30 MINERALOGY OF THE ROCKY MOUNTAINS. [BULL. 20.

few small crystals of this locality are suitable for such study, owing to 

the irregularities of form common to the larger ones, so that a satisfactory suite of specimens could not be placed at Professor Klein's disposal. His results are contained in the same article with those upon 

analcite.13 '

The mere observation of the optical anomalies of apophyllite is no 

difficult matter, provided good crystals are available, for the easily-obtained sections parallel to the perfect basal cleavage planes are most 

suitable for the purpose. It is, however, a significant fact that only the 

most perfect and symmetrically developed crystals exhibit the peculiar 

action in sufficiently simple form to permit a satisfactory description. 

With all apparent, and sometimes, it must be confessed, without visible 

irregularities in form, there appear variations and distortions of the 

more regular action about to be described.

The Table Mountain apophyllite crystals are bounded by oo P co and 

P with 0 P as a frequent addition. If a regular crystal of this form be 

divided into a number of sections parallel to the basal cleavage plane, 

there will be small ones of square outline, situated in the pyramid near 

the apex; larger ones of octagonal form through the intersection of 

both pryamid and prism; and still lower, square ones again from the 

prism alone. Such sections, ground to the desired thinness and mounted 

in Canada balsam, show the following peculiarities when examined in 

parallel polarized light. Unless otherwise stated the examination takes 

place between crossed nicols, and the position in which the diagonals of 

the pyramidal section are parallel to the planes of vibration in the nicols 

is designated as position A, that produced by revolving the crystal section through 450, as position B.

Figs. 4, 5, and 6, represent the relation in a crystal examined and 

described by Professor Klein, 14 all of them in position A. Fig. 4 illustrates the appearance in a section near the apex of a crystal having 

0 P and showing the small re-entering angles above mentioned. In the 

centre is a dark field, whose outlines are only approximately parallel to 

those of the pyramid. The outer zone is then divided in segments 

based upon the four sides, the opposite pairs having the same optical 

orientation. Fig. 5 represents the division in the octagonal section cutting oo P oo and P. The central field is here much smaller find the segments upon P consequently larger. Based upon co P GO are low triangular 

spaces of still different optical action. Fig. 6 shows the relations in a 

section of the same crystal taken in the prism. The central field is 

here very small, while those areas corresponding to the outlines of 

co P co have increased very markedly. The optical behavior of these 

divisions in position A i^usually as follows: The central field is nearly 

or quite dark, the sectors based on outlines of P are light and equal,

13 Neues Jahrbuch fiir Mineralogie, etc., 1884, I, 253. 

l* These figures taken from the cited article.

(248)
CROSS AND HILLEBBAND.] OPTICAL ANOMALIES OF APOPHYLLITE. 31

while those upon oo P GO are not homogeneous in action. The areas 

based upon P are optically biaxial, the plane of the axes lying normal 

 to the outline of P adjoining. When a gypsum plate producing red 

light of higher order is inserted, and so situated that the lesser axis of 

elasticity runs from the upper left-hand to the lower right-hand quadrant, the blank sectors appear yellow, the dotted ones blue, while the 

inner field has more or less perfectly the red color of the outer field of 

vision. The sectors based upon co P co are usually variegated in 

color, red, blue, or yellow, as will be described further on. In position 

B the whole becomes dark except the irregular sectors adjacent to

CO P CO .

The statements of Professor Klein are chiefly directed to show that 

the optical properties observed are, to a very large degree, dependent 

upon the crystal faces developed. Thus the crystal whose sections are 

figured had a well-developed basal plane, to which fact is attributed

the presence of the central field, while the decrease in size, as the sections are taken deeper in the crystal, corresponds to the distance from 

0 P. He states that in a crystal without a basal plane the central field 

is wanting. The appearance of the prism co P oo as a boundary of a 

section is accompanied by the appearance of the low triangular spaces 

of irregular optical behavior. The biaxial fields seem definitely related 

to the outlines of P.

The examination of several crystals with reference to this relationship 

between outer form and optical action has shown us that any generalization with regard to 0 P and the central field is impracticable. In 

several crystals showing no base at all the dark central field is present, in one case being large near the apex and very small in the prism; 

in another case the reverse; also in crystals with 0 P developed this 

field is sometimes smallest near that plane, and again it does not vary 

materially in size from the pyramid to the prism. In no case, however, 

has the prism GO P co appeared as a boundary of a section, without an adjacent field in which the action is often complex, the complexity increasing as the section is taken lower in the crystal. No sector in this position has ever been seen independent of the development of oo P co.

The figures of Professor Klein are intended to illustrate the most regular action observed, and it is quite natural to assume that this simple 

relation of optically different parts is largely dependent upon the regularity in the development of the crystal form. The deviations from this 

simple relation and action of individual parts have never been fully described, but in the series of sections we have examined these variations 

are very numerous and seem quite as important in considering the cause 

of the optical phenomena as the more regular condition occasionally 

seen.

The central core is very variable in form. Within a given crystal it 

often changes perceptibly from section to section either in size or in 

outline. As lias been stated, it may be largest near the apex of the

(249)
32 MINERALOGY OF THE ROCKY MOUNTAINS. [BULL. 20.

crystal (whether 0 P is developed or not) and steadily decrease in size 

downwards, or its apex may be in that of the pyramid, and in some 

cases it runs as an inner prism through the whole observed part of the 

crystal. Its section is but rarely square, although rectangular in many 

cases, and this variation has no observable relation with the prominence 

of adjacent pyramid faces. The more perfectly rectangular it's outline 

the sharper its boundaries are, and the more homogeneous its optical 

action. Variations from the rectangle are produced by broken side-lines, 

by the deviation of its angles from 90°, and by an increase in size until 

it can no longer be inscribed within the prism co P co. With all such 

irregularities are combined disturbances in the optical action of the 

centre. In the simpler instances, by position A the field is not wholly 

dark and several faint black crosses are seen whose arms are parallel 

to the diagonals of the pyramid, and revolve with the section, disappearing more or less completely in position B. These arms rarely cross 

each other at exactly 90°, and especially where the side lines of the 

rectangle are broken the field is divided into numerous irregular areas, 

each having by position A a black cross whose arms may join at any 

angle. These revolve with the section and either disappear or become 

less distinct by position B. In jone section the optical division is quite 

regular, in that by position A the field is composed of a mosaic of light 

and dark squares or rectangular blocks, whose sides are parallel to the 

outlines of the prism co P co. In position B the same structure is visible with the dark squares as the light ones. The lighter areas are 

"very faint and shade off into the darker ones. With the insertion of 

the gypsum plate the place of the black cross is sometimes indicated by 

bushy indistinct blue and yellow arms, normal respectively to the adjacent blue and yellow segments on the outlines of P. In two or three 

cases one side of the central field is absent, and there is a gradual shading from the adjoining sector into the area of the centre. The opposite

side of the field is very sharp and clear in such instances. By using 

the gypsum plate the change is very distinct, from the normal red next 

to the sharp outline, by transition shades out to tbe distinct yellow or 

blue of the sector.

The segments based upon P are much less subject to variation than 

the central field. They are always present and usually prominent. 

Normally they appear equally light in position A, but opposite pairs 

differ in intensity upon a slight revolution, and are wholly dark in position B. On insertion of the gypsum plate, in position A, one pair appears blue, the other orange-yellow. In regular crystals the dark lines 

which separate them run from the angles of the pyramid, or normal to 

oo P co if its faces are developed, to the angles of the central field, as 

in Figs. 4,5, and 6. If the inner field is not regular, these lines must bend 

to meet the angles, and in fact they are often wholly irregular curved or 

broken lines, neither normal to each other nor to the outline of co Pco . 

&u optical variation of these segments is frequent, in that the outer

(250)
AKI> HiLLEBRANu.l CHEMICAL COMPOSITION OF APOPHYLL1TE. 33

portions or a broad band through the centre, parallel to the outline of. 

P, is much lighter than that portion near the central field. If the gypsum plate is inserted the color of the lighter parts is purer blue or yellow, and shades off into reddish hues toward the red centre. In position 

A indistinct dark figures are sometimes seen, and these usually spring 

from a point on the surface or from the angles of the central field. 

Fissures when present commonly furnish a number of centres for such 

disturbances.

Finally, the areas based upon co P oo are quite variable both in form 

and behavior. They are sometimes very low, perfect triangles, and in 

such cases their action is often simple. In position A' they are dark, 

in B light. With the gypsum plate inserted they are red in position 

A, while in B opposite pairs are respectively blue or yellow, as with the 

pyramidal segments in the former position. When complex they consist chiefly of .laminae parallel to oo P oo. In position B, with gypsum 

plate, a part of these laminae appear red, the remainder blue OF yellow,

The simple recital of the optical variations observed seems sufficient 

to deter any one from an attempt to explain,the anomalous action of 

.apophyllite on a theory of complex twinning. The insensible gradations 

and shadings between all. structures and optical conditions seen, are 

much more characteristic of the phenomena due to unequal tension or 

pressure in glass and colloidal substances, than of any complex twinning 

 definitely known in a mineral.

CHEMICAL COMPOSITION. In chemical composition this apophyllite 

is quite normal, the fresh substance yielding the following:

.

SK)2 ........................

AhOs. ......................

FesOs. ......................

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

KsO... ......................

Na*0.. ......................

HjO.. .......................

F..... ......................

OforF .....................

(W.F.Hillebrand.)

XVI.

51.89

1.54

0.13

24.51

3.81

0.59

16.52

1.70

100. 69 

0.72

99.97

.Considering all potassium and sodium as combined with fluorine, the 

following oxygen ratio is afforded:

EO:SiO2 :H2O 

1:3.95 :2.10

The theoretical ratio 1:4:2 would be still nearer approached were 

it not for a probable slight loss of silica and excess of water, scarcely 

to be avoided in analyses of silicates containing fluorine. The Fe2O3 

is undoubtedly owing to rninuto particles of limonite which could 

mot be completely removed. The A12O3 is much higher than in most 

Bull. 20 3 (261)
MINERALOGY OF THE ROCKY MOUNTAINS. [BULL. 20-

analyses, and the condition in which it is present seems undeterminable, o

ALTERATION. The Table Mountain apophyllite is frequently subject 

to alteration in a peculiar manner, which is, so far as we can ascertain, 

different from anything previously observed for that mineral. By this, 

alteration a pearly-white, very finely foliate substance is produced in 

the basal cleavage fissures of the apophyllite. The decomposition beginsat the surface and progresses in ward,-the flakes of the newly-formed 

substance lying parallel to the cleavage planes. Some crystals which 

are outwardly snowy white, show perfectly fresh substance within. 

When the outer surface of an altered .crystal is dull the resemblance to 

albine is marked, but on fracturing such a crystal the distinct foliation 

and lustre show the different nature of this substance.

As more or less apophyllite is usually mixed with the alteration product it was quite difficult to'ascertain its chemical composition. Material apparently very pure was finally obtained from the specimen in? 

which the decomposition was most advanced, by treatment in the following manner: The finely:powdered substance was stirred up in waterr 

and the finer portions were poured off from the heavier impurities; the 

material suspended in the water was allowed to settle, the clear liquid wa» 

decanted, and the residue evaporated, accidentally quite to dryness. It 

having been found that the air-dried material lost several per cent, of 

water over sulphuric acid, it was certain that some loss had been occasioned by drying on the bath; hence the drying was completed at 

C., and the following analysis was then made:

SiO* ........................

Al»0s.......... .............

FetO,. ......................

CftO......... ...............

H.gO. ................. ------

K& ........................

N»»0*...... ................

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

F. .........................

(W.P.HDlebrand.)

XVII.

67.86

8.48

1 (U

5.47

0.53

1.23

0.74

14.55

100. 00

* By difference.

The F^Oa comes from certain reddish flakes which could not be separated. The H2O is, from reasons above given, much too low, and the 

other figures are consequently too high.

Neglecting Fe2O3 and H2O the following oxygen ratio is obtained:

EO : A12O3 : SiO2 

1 :1.86 : 16.66

from which no satisfactory formula is deducible.

(252)
CBOSS AND HILltEBRAND.] MESOLITE. 35

It is plain that this alteration product has nothing in common with 

albine except the color, Knop 15 having proved, for many cases at least, 

that the latter substance is chiefly calcite.

MESOLITE.

GENERAL DESCRIPTION. Mesoliteis the last of the minerals deposited 

at the locality on North Table Mountain where all of the species thus 

far described occur so often together that their order of succession is 

plain. The mineral appears uniformly in masses composed of exceedingly delicate needles loosely grouped together, very much like the 

spicules of a fine sponge. Such light aggregates frequently fill the 

smaller cavities entirely. In the larger ones the bases of the rounded 

bunches, 1 to 2 inches in diameter, often touch each other. The 

very latest deposition, the finishing touch so to speak, is a thin film 

coating the whole mass. This is sometimes a continuous membrane, 

and in other cases more like a thick cobweb. The exquisite delicacy of 

some of these films is quite wonderful. In rare cases bunches on the 

upper and lower walls of a cavity are united by-such a membrane. 

Single needles are clear, but the aggregate appears pure white.

As was mentioned under thomsonite, the loose aggregates of the 

second generation of that mineral seem specially suited to attract the 

deposition of mesolite.

None of the mesolite needles are large enough to allow any determination of their crystal form, even under the microscope at a high power. 

They seem simply like very fine transparent hairs.

CHEMICAL COMPOSITION. The identification as mesolite rests upon 

the following chemical analysis:

SiOa..... ...................:

AhOg----- - - - - -- 

CaO..... .................... M-ftoO

H«O....... ...:.. ............

(W. P. Hillebrand.)

a.

46.14

26.88

8.77

6.19

12.17

100. 15

XVIII.

6.

46.02

26.87

12.17

e.

46.33

12.13

46.17

26.88

8.77

6.19

12.16.

inn 17

Oxygen ratio:

EO

1

E203 

3.08

SiO2 

6.00

H20

2.63

If mesolite be considered as a mixture of theisomorphous silicates contained inscolecite (CaAl2Si3Oi0-f3 aq) and natrolite (Na2Al8Si3Oi0+2 aq), 

the present occurrence would answer very nearly to the requirements 

of the combination of 2 of scolecite + 1 of natrolite, the percentage of 

which would be: SiO8 46.32, A12O3 26.40, CaO 9.61, Na8O 5.32, H,O 

12.35=100.00._________________________________

16 In Blum, Die Pseadomorphosen, etc.; Dritter Nachtrag, 1863, p. 41.

(253)
36 MINERALOGY OF THE ROCKY MOUNTAINS. [BULL. 20.

NATROLITE.

DESCRIPTON AND ' ANALYSIS. Natrolite occurs much less abundantly than any of the species thus far described, and seems to be re 

stricted locally to the northern part of South Table Mountain. It usually appears in delicate prisms sparingly deposited upon analcite or 

associated with that mineral in fissures. It has also been observed upon 

yellow calcite, chabazite, and thomsonite.

The crystals show only co P and P; they extinguish light exactly parallel to the prism, and are therefore of the normal rhombic type. The 

microscope shows many crystals to be partially coated with calcite, which 

explains.the presence of CaCO3 in the following analysis of the needles:

sio*..

Alz03 

CaO.

H20. 

CDs.

XIX.

43.66 

24.89 

4.87 

14.66 

*8.09 

t3.83

100 00 

__ JW. F. Hillebrand.)

* By difference. t Calculated for total CaO.

There being much less than half a gram of material at disposal for 

analysis, no attempt at a direct water determination was made. On 

treating with acid there was a strong effervescence of CO2 ; therefore in 

calculating the following oxygen ratio the CaO was assumed to be 

present entirely as CaC03. 

Oxygen ratio:

Na^O : A12O3 : SiO2 : H2O 

0.98: 3.02:6.00 : 1.85 

A study of the ratio time thus obtained, however, renders it probable

that a small part of the CaO was combined with silica, in which case the

COj would be less and the HaO consequently higher, bringing the ratio 

still nearer to the theoretical 1:3:6:2.

SCOLECITE.

DESCRIPTION AND ANALYSIS. Scolecite occurs sparingly in a zone 

just above that containing a great number of the zeolites. It appears 

in small spheres or segments of spheres with a radiate structure, and 

greatly resembles thomsonite, though easily distinguished by the brilliant white color and satin-like lustre. Toward the centre of the aggregates there is often a greenish color.

The mineral only occurs in very small cavities, which are often en-' 

tirely filled by it and seldom contain any other zeolite. Minute tablets 

of brown mica which are coated, as are the walls of the cavity, by a 

lavender-colored material, usually appear as the only associates of the 

scolecite. It occurs also in some cases with the next species to be described. Ohabazite and thomsonite may occur in larger cavities directly

(254)'
CKOB8 AXD HILLBBBAND.] SCOLECITE LEVYNITE. 37

adjacent to smaller ones containing scolecite, but they have never been 

found with the latter.

The mineral gelatinizes on treatment with hydrochloric acid and 

 was found to have the following composition:

_

SiOz ........................

AbOs.... ......... ..........

FesOs.- ......................

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

NasO. ......... ..............

K20...... ...................

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

(W. F. Hillebrand.)

XX.

46.03

25.28

0.27

12.77

1.04

0.13

*14. 48

100. 00

* Difiercnce.

No attempt at a direct water determination was made, owing to the

small amount of pure material available,

Oxygen ratio :

RO : A12O3 : SiO2 : H2O 

1: 3.02 : 6.23 : 3.26

It was impossible to free the mineral entirely from attached limonite 

and an insoluble silicate, which probably accounts for the high values 

for SiO2 and H2O in tbe oxygen ratio. The agreement with the theoretical ratio 1:3:6:3, is, in any case, close enough to establish the 

identity of the mineral as scolecite.

GENERAL DESCRIPTION. To the species levynite is referred a mineral occurring very sparingly in small cavities side by side with those 

containing scolecite, although the two have never been observed together. When but partially filling the cavity, white or colorless tabular crystals are developed, which resemble very closely the form usually 

given as characteristic of lovynite. Referring to the figures of Dana 

or Naumann-Zirkel, and adopting the? ground form of the latter, the 

Table Mountain crystals are formed of twins of interpenetration producing hexagonal tablets with 0 R and R as the chief faces, the reentering angle formed by £R being seldom distinct. R is always 

striated, often coarsely, parallel to the combination edge with £ R.

The faces of R and 0 R are not smooth enough to allow of good reflections, hence the following measurements are not very exact, although 

sufficiently so to prove the identity in crystal form with levynite:

GEAR...... ...............

BA JK. ..................

Measured.*

125°.10'

117° 38'

130° 22'

Theoretical.

125° 14'

117° 23'

129° 45*

* Average.

(555)
38 MINERALOGY OF THE KOCKY MOUNTAINS. [BULL. 20.

The crystals are attached by an edge, about half of the full crystal 

being developed free. They are extremely brittle, and fracture very 

easily at right angles to the horizontal edge of R, i. e., parallel to o> P 2, 

so that material suitable for optical observation could not be obtained.

Associated with thelevynite in some cavities or appearing independently in adjoining ones, is a fibrous mineral, dull white in color and 

never showing crystal faces. As seen below it is practically identical 

with the levynite in composition, although so different in formal development. It cannot be referred to any definite species from present data.

CHEMICAL COMPOSITION. Analysis'of the pure crystals of levynite 

gave XXI, while the allied substance has the composition XXII:

ao» ........................

ALpa ........ ...............

Cab..... ....... ............

1T«T>

Na«0. .....................

EM).... ........ ............

(W. F. Hillobrand.)

XXI.

46.76

21.91

n i9

0 91

1.34

18.65

99.99

XXIL

46.97

22.39

10.85

1 17

0.79

18.03

100. 20

Oxygen ratios:

EO : E2O3 : SiO2 : H2O

XXI. 1: 2.90 : 7.01 : 4.66

XXIL 1 : 3.01 : 7.15 : 4.58

The water lost in drying has been included in the oxygen ratios, for 

the reasons given under laumontite. The ratios for dried material are:

XXI. 1:2.90:7.01:4.03 

XXIL 1:3:01:7.15:3.94

OTHER MINERALS. 

«

BOLE.

DESCRIPTION AND ANALYSIS. In many irregular cavities in the scoriaceous crust of the lower sheet, and especially noticeable at about the 

centre of the northern faceof South Table Mountain, is a dark brown clay 

which probably comes under the above head. It is very dense and apparently homogeneous, and has the peculiar fracture characteristic of 

such masses. Placed in water it falls apart without decrepitation. It 

is often associated intimately with a brown massive calcite, and in other 

cases it alone fills cavities completely. Two specimens, one of a light 

(XXIV), the other of a dark brown color (XXIII), were subjected to 

analysis.

(256)
<CB088 AND HILLEBRAND.] BOLE CALCITE. 39

SiOa ........................

AbOa........ ................

~Fe>tOa ...... .................

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

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

KsO. .......................

NazO ...... ...............:.

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

(WMVHlllebrand.)

xxni.

42.63

18.76

11.88

2.59

3.39

0.35

. 0.24

20.21

100. 05

XXIV.

46.17

22.03

4.64

 2:30

2.42

? *2. 06

20.38

130. 00

* By difference. '

From these results no satisfactory ratio or formula can be deduced. 

They probably represent mixtures of different hydrous silicates.

CALCITE.

OCCURRENCE AND DESCRIPTION. The carbonate of calcium has had 

three periods of deposition in the basaltic cavities of Table Mountain,

two as calcite and one as aragonite. In the form of wine-yellow crystals it preceded even chabazite, being in all observed cases deposited 

directly on the basalt and coated usually by chabazite or thoinsonite. 

It is rarely found in those cavities to which water has had access through 

fissures, having been dissolved. The second deposit of calcite came 

after apophyllite. These crystals are colorless or slightly straw-yellow, 

and the form of both varieties is commonly that of a sharp scalenohe- 

 dron terminated by a low rhombohedron.

The aragonite is present only as a snow-white incrustation, apparently with a special tendency to deposition upon chabazite, though often 

noticed upon apophyllite and thomspnite. It was next to the last mineral deposited, only mesolite having been observed upon it.

The brown calcite mentioned as associated with bole is never present 

in the zeblitic cavities.

(257)
H. MINERALS FROM THE NEIGHBORHOOD OF PIKE'S 

' PEAK.

By WHITMAN CROSS and W. F. HILLEBRAND.

GENERAL.

The name of Pike's Peak has become well known the world over in 

connection with the large and perfect crystals of Amazon stone (microcline) which have found their way into almost every mineral collection 

of importance, and yet the stranger who ascends the mountain from 

Manitou may see no sign of that or of any other of the numerous species accredited in a general way to the region, it may be well, therefore, to preface this description with a few remarks concerning the mode 

of occurrence and the distribution of the Pike's Peak minerals. ',

The mountain proper rises to a height of 14,147 feet, and is surrounded by many lesser peaks which reach 10,000 feet. The same 

coarse reddish granite which forms the greater part of all these points 

extends in a northerly direction for at least 35 miles. Owing to a lack 

of gold and silver bearing ores the granitic formation has not been thor. 

oughly explored, the region is uninhabited, excepting on certain routes 

of travel, and the great majority of the mountains and streams are 

unnamed. Hence it is that minerals found in many remote spots are 

afterwards labelled simply as from Pike's Peak. For many of the species the inaccuracy is unimportant, as throughout the entire granitic 

area some of them are surely to be found upon search.

LIST OF SPECIES KNOWN. Up to the year 1882 the following minerals had been identified with certainty, viz.: Microcline, albite, biotiter 

muscovite, quartz (smoky and clear), fluorite, columbite, gothite, hematite and limonite (pseudomorph after siderite), arfvedsonite, astrophyllite, zircon, bastnasite, and tysonite. The species described in thi& 

article have been identified by us. since that time, viz: topaz, phenacite, 

kaolinite, cryolite, pachnolite, thomsenolite, gearksutite, ralstonite (?), 

prosopite, and elpasolite.

Another series of minerals now in the course of investigation embraces several salts of cerium, yttrium, etc., belonging to species not asyet fully determined, although xenotime and yttrotantalite are probably 

present. Oassiterite also occurs in small quantity. (See p.- 74.)

(258) 40
CBOSS AND HILLEBBAND.] MINERAL OCCURRENCES NEAR PIKE'S PEAK. 41

MODE OF OCCURRENCE. The reddish granite of the region belongs 

to a type common in the Colorado range of the Rocky Mountains, and 

is supposed to be a part of the Archaean formation. c It consists of a 

largely predominant reddish feldspar, to which are added brilliant 

black biotite and quartz, the latter subordinate, and occurring in small 

grains. The feldspar consists largely of an intergrowth of orthoclase 

and albite, somewhat after the manner of perthite.

Throughout the granite body, though much more abundant in some 

places than in others, are drusy cavities or " pockets " of very variable 

size, and often distorted by movements of the rock mass. Lining these 

druses, or entirely filling them in some cases, are crystals of feldspar 

and smoky quartz, in the first degree, with fluorite, topaz, phenacite, 

zircon, gothite, hematite, and limonite, as more or less constant companions.

The granite disintegrates rapidly through the action of the weather

into a coarse, gravel-like mass, and many of the mountain slopes are

covered by such material, with solid rock appearing here and there. On 

fiudiug fragments of crystal in the debri$ the prospector for minerals, 

with pick and shovel in hand, endeavors to find the original cavity from 

which the fragments came. One of these druses has been known to 

yield more than a ton of crystallized specimens of Amazon stone, smoky 

quartz, etc.

Vein-like masses, composed chiefly of white quartz and reddish inicrocline, are also locally abundant, and in these are sometimes found 

small masses of cryolite and its alteration products, with zircon, astrophyllite, and columbite as observed associates.

CRYOLITE.

LOCALITY. The point at which cryolite and its alteration products 

have been found is at the northeastern base of Saint Peter's Dome, a 

minor peak due west of Cheyenne Mountain and near the toll-road from 

Colorado Springs to the Seven Lakes, at the southern base of Pike's 

Peak. The spot lies nearly on the southeastern border of the extensive 

region within which Amazon stone and its associates occur, and may be 

thus considered within the "Pike's Peak region," although several miles 

distant from the mountain proper. The fluorides were first shown in a 

prospect shaft and in a neighboring tunnel, but visits made to the locality since the first publication have proven the presence of cryolite masses 

in several of the small irregular veins north and west of Saint Peter's 

Dome.

OCCURRENCE AND ASSOCIATION. iThe manner of occurrence and 

the relationship of the fiuoride masses can now be stated much more 

clearly than -was possible in our first notice. Cryolite, in the massive 

form to be described, was deposited in the veins of secretion which are

(259)
42 MINERALOGY OF THE ROCKY MOUNTAINS. [BULL. 20.

so abundant in the granite country rock, in small but pure and homogeneous masses. Some of these veins have certainly had two periods 

of secretion, as is shown in the Eureka tunnel, Saint Peter's Dome. This 

tunnel penetrates for about 200 feet an irregular mass, consisting largely 

of white quartz and reddish microcline. The greater part of the quartz 

is the common white vein material containing no included minerals, but 

a portion of it, appearing in sharply defined angular blocks, is full of 

the transparent zircon to be hereafter described. Small particles of 

microcline are also disseminated through this quartz, while in the body 

of the vein it presents huge individuals, sometimes several feet in diameter. An examination of the tunnel walls shows here and there faces 

of pure massive fluorides 5 or 6 feet across and sharply defined against 

both pure and zircon-bearing quartz, the spaces filled being very irregular and angular. No contemporaneous minerals of importance accompany the zircon and cryolite in this vein.

The purity or homogeneity of the white quartz, zircon-bearing quartz, 

and fluoriue masses, together with their irregular forms, seems to indicate different periods of development, and it seems further probable 

that a time of disturbance, in which the original .quartz and feldspar 

vein was much fractured, produced the irregular spaces subsequently 

filled by different deposition. The cryolite may have been formed here 

during the time in which fluorite and topaz were deposited in the cavities of the region to the northwest.

The only mineral observed to be undoubtedly contemporaneous with 

the cryolite is columbite, which has been seen in small crystals embedded 

directly in fresh cryolite. At one place as trophyllite blades penetrate 

cryolite, but these are implanted directly upon the granite wall, and are 

probably an earlier formation, as are the zircon crystals at their base, 

and impregnating the granite itself; In the immediate neighborhood 

arfvedsouite and astrophyllite are quite abundant, both occurring most

frequently embedded in white massive quartz. The original locality of

tysonite and bastnasite is not far from Saint Peter's Dome, but little is 

known to us concerning the manner of occurrence of these minerals.

PURELY SCIENTIFIC VALUE OF THE DISCOVERY. As numerous inquiries concerning the probable commercial value of this new cryolite 

locality have been received since the published description, it may be 

well to emphasize the conclusion which is clearly suggested by the description of the occurrence of the mineral. All the cryolite as yet 

known occurs in the form of subordinate masses in the veins of secretion which appear here and there throughout the granitic formation, 

and there is no reason to suppose that masses of econpmic importance 

can occur in the region.

RECENT LITERATURE OF CRYOLITE AND ITS ALTERATION PRODUCTS. The minerals of this group, of which so little was known'a few 

years ago, are now among the best known. As most of the recent pub-

(260)
dices AND HILLBBRAND.] LITERATURE DESCRIPTION OF CRYOLITE. 43

Jications are of direct interest to us in describing the material of the 

new find, a brief mention of the leading articles is in place.

The earliest contribution to be mentioned is that of Prof. P. Groth, 

then in Strassburg, who instituted a careful investigation of cryolite 

and its alteration products, several of which had received names without 

satisfactory proof of their homogeneity, while more or less doubt was 

justifiable in regard to the chemical composition of all of them. Similar rare minerals of other occurrence were also studied. The purely 

mineralogical part of this investigation was conducted by Professor 

Groth personally, while material selected by him was subjected to chemical analysis by Dr. J. Brandl, in Munich. To the papers by Messrs. 

Groth 16 and Brandl 17 we shall refer frequently in the course of the following description. Owing to better material we are able to supplement in some particulars the results of these gentlemen, and in but a 

a single case, namely, in regard to the composition of pachnolite, is there 

any discrepancy between our conclusions and theirs.

Concerning ,the crystallography of the group, Krenner 18 and Des 

Oloizeaux 19 have made important contributions while the laws of twining in massive cryolite have been investigated by Miigge.20

GENERAL DESCRIPTION. The pure cryolite appears in massive aggregates of large individuals, quite like that from Greenland. The three 

prominent cleavage surfaces are often continuous, for two or three inches, 

indicating the size of the individuals present. A delicate pink or even 

decidedly rosy hue is characteristic of the freshest substance found, but 

the greater part is either of a faint greenish tinge or dull white, and none 

so far obtained has the snowy whiteness or the clearness of the Greenland mineral. The color disappears on heating, leaving the cryolite 

pure white.

The three marked cleavage directions.are situated nearly at right angles to each other and one seems slightly more perfect than the other. 

A parting parallel to these planes is by no means so easily effected as 

one would expect from the distinctness with which they are seen, a fact 

explained by the complicated 3 polysynthetic structure to be described.

TWIN STRUCTURE. As.no crystals of cryolite have been found in 

this locality, the study of the complicated twin structure exhibited by 

the massive material is no easy matter. The recent investigations of

16 P. Groth. "Beitriige zur Kenntniss cler natiirlichen Fluorverbiudungen," Zeitsclmft fur Krystallographie, VII, pp. 375-388 and 457-493, 1883.

17 J. Brandl. Sitzungabericht der .konigl-bayr. Akademie der Wissenschaften zu 

Mijnchen, 1882, p. 118, and Annalen der Ckemie, CCXIII, p. 1.

18 J. A. Krenner. "Die gronlandiseheu Minerale der Kryolith Gruppe." Budapest-, 1883.

19 A. Des Cloizeaux. "Nouvelles observations sur le type cristallin anquel doit 

fetre rapporte"e la cryolite." . Bull Soc. Min. d. Fr., 1883.

^O. Mtigge. "Uber die Zwillingsbildung des Kryolith." -Jahrbuch d. wiss. 

Anstalteu zu Hamburg, 1883, p. 67.

(261)
44 MINERALOGY OF THE ROCKY MOUNTAINS. [BULL. 20.

Krenner, and especially those of Mtigge upon the massive mineral 

Greenland, have, however, done much bo make the relations clear.

Dana 21 mentions oo P, Websky 22 OP and o> P co , and Krenner 23 cc P 

and ^ P as twinning planes identified upon crystals of cryolite. Miigge.24 

seems to have identified ± £ P as a twinning plane in the massive material, independently of Krenuer's determination. In all the abovementioned laws the axis of revolution is the normal to the twinning plane, 

which is usually the composition face. The polysynthetic development 

of various laws was briefly alluded to in the first notice of the Colorado 

cryolite, and the descriptions of Miigge show that a similar, although by 

no means equally complicated, structure exists in the Greenland mineral.

The well known pseudo-symmetry of cryolite is illustrated by the following values, taken from Krenner: /5 = 89° 49' ; the prism angles are 

S8° 2' and 91° 58', the angles between OP and opposite prism faces are 

90° 8' and 89° 52'. The axes of elasticity are also situated in peculiar 

agreement with this symmetry, the bisectrix lying in the clinodiagonal 

section, inclined 43° 54' to the vertical axis and 45° 55' to the clino axis. 

It is to be noticed that by all the above-mentioned laws of twinning the 

planes of 0 P and oo P aie brought in so nearly coincident positions that 

the deviations are unnoticeable upon the cleavage surfaces of the massive 

substance.

The examinations of Miigge were conducted upon thin sections lying 

in water, the index of refraction of the 'liquid being almost equal to that 

of cryolite. Our observations were made upon sections prepared in the 

usual manner. As none of them exhibit anything corresponding to the 

results obtained by Miigge on heating to a temperature of'over 400° C., 

it is assumed that no change in the optical properties was produced by 

the temperature necessary in mounting these sections in balsam.

Although we cannot in the cleavage material distinguish with certainty between cc P and 0 P, or between the positive and negative 

quadrants, still, if from a given cube, sections be prepared parallel to 

each of the three cleavage faces, we should be able to observe the relations of all twinning laws seen to each other and to a ground form which 

can be assumed. For a clear distinction of all the individual parts itis 

necessary to examine the thin sections between crossed nicols and with 

an inserted gypsum plate giving the field of vision a red color of the 

higher order. As nearly all the twinned parts are symmetrically related 

to oo P or 0 P, the first position in which their relations can be seen to 

advantage is secured by placing the cleavage lines in each section rt to 

the principal sections of the crossed nicols. This position is hereafter 

designated as position I. It is evident that the extinction in the basal 

section takes place parallel to the diagonals of the prism, as indicated

31 System of Mineralogy, 5th ed., p. 127. 

2Z Neues Jahrbnch fiir Mineralogie, etc., 1867, p. 810. 

23 Loo. cit. 

cit.

(262)
CK088 AND HILLBBBAND.] LAWS OF TWINNING IN CRYOLITE. 45

by the cleavage lines, i. e., about 45° from each. The theoretical extinction parallel to a face of oo P is 31° 15' from the vertical axis (Groth), 

which direction lies parallel to one set of cleavage lines.

The various laws of twinning observed will now be taken up and the 

resulting structure parallel to each of the cleavage faces described.

Laic a. Twinning plane and composition face oo P, axis the normal 

upon it.

One of the three sections shows a fine banded structure parallel to 

one set of cleavage lines; this resembles plagioclase twinned according 

to the albite law, but the boundaries are less clearly defined. In position I alternate bands are blue, the remainder yellow 5 reversed colors 

are produced by a revolution of 90°; extinction occurs at about 31° 

from the twinning plane, right or left according to color. The second 

section shows no such banded structure, but extinction takes place at 

31° from either cleavage system. The third section exhibits a-banded

structure with blue and yellow colors, but with nearly coincident extinction at 45° from the twinning line, which is parallel to one cleavage 

direction.

As experience shows this twinning to be always parallel to one pair 

of prism faces and there is evidently a definite relation between the 

other laws and the present, we will assume the left-hand front prismface as,the twinning plane, oo P (I). .The first section was therefore 

parallel to oo P (r), the second to oo P (1), and the "third to 0 P. This 

assumption is made in all subsequent discussion, so that the relations 

of the different laws may be correctly expressed.

The laminae are sometimes broad, but more frequently narrow, measuring 0.01 to 0.10mm in thickness. It is therefore difficult to prepare a 

section so nearly parallel to oo P (I) that it shall not cut obliquely several of the laminae, producing a broad irregular banding, as represented 

in Fig. 7. The four vertical bands with irregular boundaries are alternately blue or yellow in position I, and extinguish at 31° right or left.

Laic b. Twinning plane and composition face £ P (r), axis the normal upon it.

Sections parallel to oo P (r) usually show in each lamina produced by 

the first law a structure illustrated by the lower left-hand portion of 

Pig. 8. The parts of new orientation are represented by the small rectangular or graphic forms lying parallel to the diagonals of the square, 

right or left as the case may be,' and however zigzag the shape the 

bounding lines are almost always parallel to the diagonals mentioned. 

These forms are apparently identical with those described by Miigge as 

twinned parallel to i ^ P,-and they appear in the other two sections in 

a manner agreeing with this supposition. In Fig. 7 they are represented 

by the smaller horizontal lamellae which do not cross the boundaries of 

the broad bands, and in Fig. 9 by the vertical lamellae included in the 

larger ones. They are therefore cut by the plane oo P (r) nearly or

(263)
46 MINERALOGY OF THE EOCKY MOUNTAINS. [BULL. 20.

quite at right angles, and their inclination is that of the plane ±£ P, 

according to which they are intergrown.

The explanation above given is, however, insufficient, as there are 

particles of three distinct optical orientations among these formally indistinguishable portions. If a lamina cut parallel to oo P (r) be placed 

in position I, and then shows a blue color, the visible included parts of 

the form in question will appear yellow. On revolving the lamina 31°, 

to its position of extinction, it is found that some of those diagonallysituated particles have the same extinction as the lamina containing 

them, while the others become still brighter yellow and are found to extinguish simultaneously with the adjacent yellow lamina. On moving 

the section out of position I diagonal parts of the third orientation appear. These were blue in position I, but do not extinguish with the 

substance surrounding them ; on the contrary, they correspond in this 

particular with the neighboring yellow lamina. It is impossible to definitely determine the laws according to which the substances are twinned, 

but in Fig. 10 the observed relations are explained in one way. The 

larger arrows indicate the normal directions of extinction parallel to 

oo P (r), with reference to the vertical axis. The area x represents the 

position of the corresponding directions of extinction in a lamella twinned 

parallel to tha upper right-hand face of the positive hemipyramid, £ P 

(r). This will extinguish at 31° to the right from the vertical axis, while 

corresponding very nearly in color with tbe inclosing substance in position I. This is considered the equivalent of the law identified by 

Brenner. The lamella y is related to x as if twinned according to law 

a, and thus will exhibit parallel extinction with the inclosing substance 

but the opposite color in position I. The part z corresponds in color 

and extinction to the adjacent lamina, twinned after law a, and intergrown parallel to £ P (r) or ^ P (I).

Careful study of a number of sections has failed to show any method 

of distinguishing between these various parts aside from their optical 

orientation. Now one, now another, seems to predominate, and often 

all three are to be seen in a single lamina.

The sections parallel to oo P (I) and 0 P cut these thm particles at am 

oblique angle, and their proper optical action is thus so obscured that 

they cannot be used to test the accuracy of the relation represented by 

Fig. 10.

Law c. Twinning plane co P <x, axis the normal upon it, composition 

face co P, or an irregular surface near it.

Sections parallel to 0 P never show a twinning plane running parallel 

to.either pinacoid, and yet substance is found whose orientation corresponds to the requirements of the above law. This is shown upon 0 1* 

by polysynthelic twin structure parallel to the second prism plane, 

oo P (r), the Iamina3 extinguishing at 45° and hence presenting 0 P. 

(See Fig. 9.) This might be considered as twinning after the prism 

plane oo P (r) except that a corresponding structure upon oo P (I) does

(264)
CBOBB AND HILU5BBAND.] LAWS OF TWINNING IN CRYOLITE. 47

not appear. There is, it is true, a vertical lamellar twinning sometimes 

seen, but accompanied by the substances iutergrown as described under 

law 6. This is represented in Fig. 7, and is the natural result of law c, 

 which brings oo P (r) with its twinning after laws a and b into parallel 

position with GO P (Z), produces a crossing of the laminae upon 0 P, and, 

lastly, brings oo P (1) parallel to co P (r). This latter position is naturally seldom seen in sections, as the part thus twinned is usually a rather 

thin plate parallel to co P (r), of the chief individual. In one case, however, a section parallel to co P (r) which exhibits the usual complicated 

structure over the- greater part, passes by an irregular indistinct line 

into substance of more simple action, like that represented for co P (I) 

in Fig. 7, as if the slightly oblique section plane had cut into the plate 

twinned after this law c. Websky describes the composition face, in 

the case noticed by him, as irregular, although lying approximately 

parallel to oo P "oo.

Law d. Twinning plane £ P (I), axis the normal upon it, composition 

face co P (£), or an irregular surface hear it.

By this law co P (r) and 0 P are interchanged. It seems required to 

explain the appearance in the section parallel to co P (r) of laminae 

parallel to those of a, but with extinction of 45° (see Fig. 8), and the 

similar laminae on 0 P with extinction of 31°, and including parts twinned 

after the law &. Upon co P (Z), the composition face, this law cannot 

be identified.

Law e. Twinning plane £P (/), axis the normal upon it, composition 

face irregular.

This law seems required to account for certain relations frequently 

seen upon oo P (r) and oo P (I). Upon the former the usual structure 

of this face appears at right angles to its proper position, while upon 

oo P (1) horizontal bands may be seen which are poly synthetic, and give 

extinction at 45° from position I. This would be explained by the law 

above given, and is illustrated by Figs. 7 and 8.

Of the above laws the first seems to be identifiable in all portions not 

parallel to the twinning plane, and the second is nearly as persistent. 

Law d affects substance already twinned alter laws a and 6, while c and 

c produce a twinning of matter showing a, &, and d. Laws c, d, and e 

are thought to be justified, for however irregular their composition face, 

the position of the parts twinned after a and /> is always a very definite 

and regular one. with reference to corresponding parts in the primary 

individual.

Whether the prismatic twinning plane is right or left, it is clear that 

the planes of laws I and e and the composition face of c lie in the zone 

between the prismatic twinning plane and OP, and that the plane of d 

is in the zone of OP to the other prism plane.

No twinning parallel to OP was noticed, unless a horizontal division 

of a few laminae twinned after a be thus interpreted (Fig. 8).

(265)
48 MINERALOGY OF THE ROCKY MOUNTAINS. |BULL. 20.

CHEMICAL COMPOSITION. For all analyses of this and the following 

minerals the greatest care was taken to have the purest of reagents. 

The fluorine was in all cases determined by the Wohler-Fresenius 

method, with the slight modifications introduced by Brandl,25 except 

that the iron plate instead of the oil-bath was used for heating. The 

sulphuric acid was obtained of the highest degree of concentration and 

purity by distillation from a platinum retort. The water was determined by absorption in a chloride of calcium tube, the mineral having 

been heated in a tube with either oxide of lead or carbonate of sodium, 

the results being the same whether one or the other was used.

The cryolite, of which the analysis is here given, possessed the specific 

gravity 2.972 at 24° 0., was faintly pink in color, and contained as a 

visible impurity the oxide of iron represented in the analysis:

Al. 

Ca.

H«0 

F....

<W. F. Hillebrand.)

XXV.

0.40 

«12.81

0.28 

32.40'

0.30 

*53.55

99.74

* Aa the mean of 53.35, 53.46, 53.55, and 53.85.

The presence of a slight amount of water indicates incipient alteration, but although purer and fresher material was 'subsequently obtained, a second analysis seems unnecssary.

ALTERATION OF CRYOLITE. Although pure and fresh cryolite is common, the greater part of masses so near the surface is naturally changed. 

In the Eureka tunnel the surfaces seen upon the walls exhibit plainly the 

three cleavage directions of cryolite, especially when moistened. The 

material is chiefly massive pachnolite, however, as can be distinctly 

seen in thin sections, while fresh cryolite is still visible in small patches. 

Alteration of the cryolite proceeds in two ways, producing the same 

minerals in the end. By one' process the principal cleavage fissures are 

utilized by the solutions which effect the change, and thin walls are 

formed of a white crystalline substance. The next step seems to be the 

bodily removal of the cryolite matter between these walls, leaving a 

network of partitions in the three directions of the chief cleavages of 

the original cryolite. These partitions or walls are lined by minute 

crystals. The second mode of alteration proceeds from the neighboring 

quartz and from the boundaries of the different crystalline individuals 

of the cryolite, the result being a compact crystalline mass of a faint 

bluish tinge. The material at hand illustrates the two processes and 

their products about equally well, and they are often combined.

^Annalen der Chemie und Pharmacie, CCXHI, p. 1.

'"'If Al=27. In this and all subsequent analyses, percentages of aluminium are calculated with the assumption of 27 as its atomic weight.

(266)
CubsR A*:> i:!;...femuxb.j ALTERATION OF CJRVOLITE- PitiliNOLITE. 49

A large part of the material in the Eureka tunnel is a massive mixture of indistinguishable compounds, probably derived from the alteration of pachnolite. Fluorite is one of the further products, but never 

appears prominently.

The small mass of fluorides struck in the incline near the Eureka 

tunnel is remarkable for the purity of a number of further products. 

Nenr the quartz and granite walls decomposition has progressed until a 

pure white substance has been formed, which, when dry, is a kaolinlike powder of extreme fineness. It resembles plaster of Paris when 

wet, as it invariably is in the vein. This is the gearksutite to be described further on. From this same small mass were obtained most of 

the specimens utilized in the determinations of the species whose consideration follows.

PACHNOLITE.

FROM THE THIN WlLLS. The microscopical examination of the walls 

and membranes produced by the first mode of alteration of the cryolite, shows them to be coated by many minute but perfect, colorless, 

and transparent prismatic crystals, which are usually placed at right 

angles to the central plane of the wall, though sometimes in an irregular manner. They reach a maximum length of 2mnj by a thickness of. 

0.2 to 0.4mm. The crystals are occasionally yellow in color while retaining their transparency, the color being doubtless owing to some matter 

derived from the alteration of the astrophyllite which penetrates all 

such specimens. The crystallographical identification of these crystals 

with pachnolite is quite certain, for upon placing them in vertical position under the microscope the prism angles can readily be measured, 

and correspond closely to 81° 24' and 98° 36', the theoretical angles of 

pachnolite (see Groth, 1. c., p. 463). The prism <x> P and base OP are 

in all cases the chief faces, accompanied frequently by a hemi-orthodome and very rarely by a clinodome, both very slightly developed. 

The former is considered to be P » , from data given below. Pyramid 

faces have not been seen upon crystals of this growth. Although all 

detached crystals show, when examined in polarized light as lying upon 

a prism face, an oblique twinning plane in the prismatic zone,27 still a 

projecting angle upon the base can but rarely be seen. The reflecting 

surfaces of the thinnest walls are composed of innumerable small facets 

of rhombic outline, the basal planes of the very low prisms. In fragments from some of the thinnest walls, placed horizontally under" the 

microscope and observed in polarized light, twinning parallel to the 

shorter (ortho-) diagonal can easily be seen. The crystals are usually 

quite equally bisected by the twinning line. The central portion of 

tbese walls is rather dull white, and probably represents the alteration 

product on cleavage planes of the original cryolite, while the crystals .

2~ Groth, Z. c.,p. 464. 

Bull. 20 4 (267)
50 MINERALOGY OF THE ROCKY MOUNTAINS. [BULL. 20.

themselves were formed during or after the removal of the intermediate 

cryolite substance. Material from a network of thin walls covered by 

pachnolite crystals was subjected to chemical analysis, yielding the 

result under XXVII, p. 54.

FROM THE BLUISH MASSIVE ALTERATION PRODUCT. The pale 

bluish mass formed by the second mode of decomposition has, in great 

part, a regular crystalline structure produced by a more or less perfect 

intergrowth of pachnolite individuals in three directions approximately 

at right angles to each other. Nearly simultaneous reflection over the 

greater part of certain irregular surfaces make this relation plain. By 

the examination of such a surface with a lens one can usually identify 

a number of rhombic facets which are nearly or quite coincident in 

position with striated planes, the two corresponding to OP and cc P 

of different individuals. Such a structure is also illustrated by the 

crystals in the numerous small cavities occurring in the massive material.

These cavities are wholly of irregular shape and reach a maximum 

observed diameter of 3 to 4cm . The crystals lining them are often very 

perfect, and are occasionally 2 to 3mm in length, with a thickness of 

lnnn or iess< rpne study of these crystals proves that, as in the preceding case, most of them must be referred to pachnolite, although thomsenolite is sparingly present. These pachnolite crystals differ in habit 

from those already described in that the pyramid is usually prominent, 

being, however, in nearly every case truncated by the basal plane; in 

fact, crystals without 0 P are very rare. The rhombic section of the prism 

is everywhere plain. Although every prism on being optically tested 

shows a twinning plane in the prismatic zone, the low projecting angle 

of 179° 20' upon 0 P can seldom be distinctly seen. Many crystals are 

somewhat extended parallel to one pair of prism faces. A bemi-orthodome of the same order as the pyramid is sometimes developed, aud 

probably corresponds to that noticed upon the crystals of the foregoing 

type. Most of the crystals of these cavities, while very perfect aud distinctly recognizable as pachnolite, are too small and their surfaces are too 

frequently covered by minute crystals of a later growth to be available 

for measurements with the goniometer. Two specimens, however, of the 

bluish massive material, when carefully examined, proved to contain 

pachnolite in a form allowing of more exact crystallographical, optical,, 

and chemical investigation.

CRYSTALLOGRAPHICAL DETERMINATIONS. The first of the specimens above mentioned, which we will designate specimen A, is about 

8x5x2cm in.size, is somewhat more coarsely granular than the variety 

just described, and possesses in an eminent degree the regular structure 

there observed. While compact in the greater part of the specimen, 

there are portions in which the grains are more loosely aggregated together, and parts of individuals have perfectly developed crystal faces. 

In some minute cavities a few crystals with quite perfect terminations

(268)
CROSS AXD HILLKBRAND.] CRYSTAL FORM OF PACHNOLITE. 51

were found, and upon these some faces were sufficiently large and polished to admit of measurements with a Fuess reflection goniometer. 

These crystals are about lmm long and nearly the same in thickness. 

They show oo P, 0 P, with subordinate P, and a negative pyramid 

determined, as 3 P 3. They are all twinned parallel to oo P w, and 

the low projecting angle upon OP is sometimes distinctly visible.

The angles given in the following table are all means of numerous 

closely agreeing measurements and demonstrate the crystallographical 

identity of the mineral under discussion with pachnolite:

. Angle.

eo P A OP .................

--P A OP ..:..............

-3P3A-3P3...... ...... ....

-3P3A ocP .................

OP A OP (twin) ..........

Crystal a.

o / 

81 19

138 45

149 03

Crystal 6.

o / 

81 22

90 21

116 39

179 21

Other crystals.

o / 

81 18

90 21

116 30

138 45

Calculated.

O ' //

81 24

90 20

110 30

138 52 14

149 07 19

179 20

The face 3P3 was observed on a number of distinct twin crystals, 

with projecting angle on OP, and in several cases on both of the negative angles.

Upon one side of specimen A are a few thomsenolite crystals, distinguishable by their prism angle of nearly 90°. They lie irregularly, and 

seem to be later in formation than the pachuolite. Upon them are deposited minute prosopite crystals and indistinct alteration products. In 

the mass of this specimen no thomsenolite can be detected, while all individuals with partially free development are plainly pachnolite. Analysis XXVIII of the table (p. 54) was made upon material obtained from 

the clear loosely granular portions of specimen A, and although it was 

necessary to include many transparent grains of irregular shape, in order 

to obtain a desirable amount of substance, there is no doubt in our own 

minds that thomsenolite was wholly absent from the material analyzed.

The second specimen, B. from which especially good material was obtained, had a seam 2cm thick of coarse granular structure running through 

it, and upon splitting it open along this seam two surfaces of waterclear loosely adhering crystalline grains of pachuolite were exposed 

with the regular arrangement described. Actual development of cry.st al 

faces other than the prism is rarer than in specimen A, but the size of 

the grains, reaching 5mm in length by 1 3mm in thickness, is such as to 

admit of the preparation of thin sections for optical examination, and 

also gave absolutely pure material for chemical analysis. None of the 

crystals upon which the taces were well formed were superior to thos«'. 

of specimen A, and only measurements of the prism angles were made. 

The face 3P3 was not observed at all.

The optical properties of these pachnolite crystals are such as to 

leave no doubt concerning their crystallographical identity with the

(269)
52 MINERALOGY OP THE ROCKY MOUNTAINS. [BULL. 20.

mineral described by Professor Groth as pachnolite. Several sections 

were prepared as nearly parallel to the clinopinacoid as possible. These 

exhibit in all cases a twin structure, and this is frequently poly synthetic. 

The twinning lines are straight and lie parallel to the vertical axis. 

Extinction takes place at 21° 30' to 22°, or 68° to 68° 30' from the twin 

ning line, in opposed directions in alternate larninse. According to 

Groth the bisectrix is in the plane of symmetry, and inclined 08° 5' forward from the vertical axis. Sections parallel to the base also show 

the twinning structure, the line lying parallel to the orthodiagonal. 

- A large part of the purest crystals and fragments from this specimen 

were used for chemical analysis and repeated water determinations, the 

results of which are given below (XXIX, p. 54).

CHEMICAL INVESTIGATION. Previous to the analysis by Brandl 2" of 

pachnolite carefully selected by Groth, pachnolite and thomsenolite 

were considered to possess the same chemical composition. The results 

of all earlier analyses, excluding such as referred to manifestly very 

impure material, while frequently deviating materially from the figures 

required by theory for the formula NaF, CaF2 , A1F3 , H2O, still agree on 

the whole very well, as shown in the accompanying table, and fully 

justified the belief in the chemical identity of the two species.

AI '....:'.. .......

Ca. .............

Na.... ..........

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

F...... ........

. ' > 

Thomsenolite.

"Wohler.*9

13 43 

17.84 

10. 75 

8.20 

49. 78

100. 00

 Konig.so

13.74 

16. 79 

10.10 

9.00 

50.37

100. 00

Pjichnolite.

Knop. 31

13.14 

17. 25. 

*12. 16 

9. CO 

50.79

102. 94

Konig.30

12.50 

. 18. 17 

10. 23 

8.19 

51.54

100. 63

Vom Rath. 82 .

13. 46 

18.10 

10.fi3

12.93 

17.09 

12.06

Hagemann.33

10.37 

17.44 

12.04 

 8.63 

51.15

99.63

Calculated 

forNnF, 

-CaP«, AlFs, 

H',0

' 12.32 

17. 98 

10.34 

H. 10 

51.26

100.00

*Alao, 10;80 and 10.81.

Wohler's analysis was entirely confirmed some years subsequently by 

JannaschjH in Gottingen^ who analyzed pure thomsenolite selected by

-In^view of the above, the analysis o^f pachnolite by Brandl, showing 

results agreeing well with 'those required by the formula NaF, CaF2 , 

'AiF3 , was calculated.to cause no little surprise. Groth accepts without 

question the anhydrous nature of pachnolite, and endeavors to explain

- ; ^.Annalen der Chemie und Pharmacie, CCXIII, p 6. 

39 N.eues jahrbucb fur Mineralogio, etc., 1876, p. 851. 

^Proceedings Acad. Sci. of Phila., 1876, p. 42. 

3v Annaleu der Chemie und Phammcie, CXXVII, p. 61. 

" Sitzungsbericht d. niederrheiii. Ges. fur Natur.- und Heilkunde, 1860, XX, p. 141.

-3 Am. Jour. Sci., 1866, II, XLI, p. 119.

^Neues Jahrbucb. fur Miueralogie, etc., 1877, p. 808.

(270)
cnoss AND MLtEBBAND.l CHEMICAL COMPOSITION OF PACHNOLITE. 53

away the opposing evidence, shown in the foregoing table, by assuming 

that the supposed homogeneous material analyzed was contaminated 

largely with thoinsenolite. As in no published analysis does the percentage of water fall below 7 per cent., this assumption necessitates a 

most improbable admixture of thorn sen olite. In those cases where the 

percentage of water equals or exceeds that required for thomsenolite 

the presence of gearksutite is suggested by Groth as a possible explanation. Even on this supposition the percentage of foreign admixture 

could not fall below 50 per cent., in which extreme case the whole of the 

impurity must be gearksutite, an amount which it is difficult to conceive 

should have escaped the notice of such observers as Konig, vom Bath, 

and Knop, the latter of whom expressly says that his analysis was 

made upon material identified as pachnolite.35 Notwithstanding the 

difficulty of explaining the agreement between the previous analyses of 

pachnolite and thouisenolite, on the assumption of the anhydrous nature 

of the former, the correctness of Brandl's analysis was not at first questioned by us.

In the course of the present investigation the compact bluish mate-' 

rial (see page 50), having the specific gravity 2.980 at 22° C., was first 

analyzed, the crystalline pachuolite not having yet been observed. The 

results of analysis as given under XXVI, below, agree in the main so 

well with the figures required for the formula NaF, CaF2 , Al F3, H2O, that 

no hesitation was felt in considering the mineral to be thomsenolite, 

probably slightly contaminated with fluorite. Later, the crystalline 

coating on the thin walls produced by the first mode of alteration of the 

cryolite, the crystals forming which had not yet been identified crystallographically as pachnolite, were subjected to analysis with the results 

given under XXVIT. Here again the identity with tbomsenolite seemed 

clear. It was not until the analysis of perfectly transparent fresh crystals and crystal fragments, all taken from specimen A, above described, 

gave the results shown under XXVIII, that the possibility of the first 

analyses having been also made upon pachnolite was suggested. That 

this was, however, .so in the case of No. XXVII, subsequent careful examination fully revealed, though the crystals analyzed were not entirely 

free from foreign admixture. / It seems certain, also, that the compact 

bluish portions (XXVI) consist almost entirely of pachuolite, although 

it cannot be positively asserted that some thomsenolite may not be intergrown with it. That no possible doubt might exist in the mind of 

any one as to the homogeneity of the material used for analysis XXVIII, 

a further analysis was made upon crystals from specimen B, above described, particular care being taken to identify each as pachnolite by 

the rhombic section. The results of this analysis appear under. XXIX.

35Neues Jahrbuch fiir Mineralogie, etc., 1876, p. 850. 

(271)
MINERALOGY OF THE ROCKY MOUNTAINS. [BULL. 20.

Al

Ca...... .......... 

Ms ...............

Na...... .......... 

K ...............

HsO

 p 0

Hillebrand.

XXVI.

11.94

19.32 

0.13

10.43

7:87 7.95

XXVII

12. 93 

15.27 

v vt

10.28

0 1Q

8.64

12.92 

15.17

8.79

......

XXVIII.

12.14 

18.06

10.23

8.10 

51. 33

99.88

8.11 

51. 28

XXIX.

12.27 

18.04

10.25

8.05 

*5l. 39

100.00

Brandl.86

13.51 

18.83

11.73

55.69

99.76

Calculated 

for NaF, 

Cal\ Airgl

n.o.

12. 10 

18.02

10.36

8.11 

51.35

100. 00

*By difference.

Further determinations of water, on material from specimen B, gave 

7.95, 7.99, 8.14, aud 8.15 per cent. Still other determinations, some on 

material every fragment of which showed the rhombic section, others 

on material taken at random from the crystalline mass, gave results between 7.90 and 8.20 per cent. The specific gravity at 17°0. of the perfectly pure material, as the mean of four determinations varying between 2.963 and 2.968, was 2.965. A single determination on another 

portion, equally pure, at 22°0. gave 2.962. The transparent crystals, 

as well as all the other portions analyzed decrepitated violently on heating in a test tube, the walls became lined with the white deposit so 

characteristic of thomsenolite and pachnolite, and much water was 

given off. Hence it appears that the pachuolite from Pike's Peak and 

thomsenolite are identical in composition, unless the fact of all analyses of thomsenolite showing slightly more water than required for the 

formula NaF, CaF2 , A1F3 , H2O may indicate, as suggested by Groth, a 

partial replacement of fluorine by hydroxyl in that mineral. Should 

this prove to be the case, a plausible explanation of the difference in 

crystallization of the two minerals is offered without recourse to the 

theory of dimorphism.

A satisfactory explanation of Brandl's results, so oppo.sed to those 

presented by all earlier analyses and the ones above given, is impossible, but it may be well to call attention to the fact that Braudl \\AS 

obliged to make his determinations of fluorine and the metals upon 

quantities of 0.1106 gr. and 0.1430 gr. weight respectively, whereas material was not wanting for the present analyses, the determinations having 

been made upon weights of from 0.3 gr. to 0.75 gr. It nowhere appears 

that a direct test for water was made upon the material furnished by 

Groth. The latter, it is true, remarks (/. c. p. 461): "Ausserdem bildet 

sich bei letzterem (Thomsenolite) in den Mlteren Theilen des Rohrea ein 

Wasserbeschlag, welcher beim Erhitzen rtincn Pachnolith&s naturlich 

ausUeibV The absence of water does not, however, seem to be 

hereby p'roveo, but simply to be assumed from the close approximation to 100 of Brandl's results, exclusive of water. Brandl himself says 

water is wanting, but does not mention whether this was ascertained

36 Annalen der Chemie und Pharmacie, CCXIII, -p. 6. The percentage of Al is calculated to correspond with the other analyses (Al=27).

(272)
PACHNOLITE THOMSENOLITE. .55

by direct experiment. The small amount of material at his disposal 

renders it not improbable that no direct test was made.

Since the conclusion of the above investigations, through the kindness of Mr. Albert F. Damon, president of the Pennsylvania Salt Manufacturing Company, we have obtained specimens of Greenland cryolite 

and its alteration products. From one of these specimens was removed 

a large number of small, needle-like, pyramidally terminated, twinned 

crystals with a rhombic prismatic section, showing in fact precisely the 

common occurrence37 and ordinary habit of pachnolite38 as described 

by Groth. These crystals, slightly yellowish in color, but quite transparent, were individually examined under the microscope, all such as 

did not show beyond a doubt the above described habit being excluded. 

They were then tested in a small glass tube for water. Decrepitation 

ensued on heating and the walls of the tube became lined with a white 

powder, and also with a deposit of water, in such quantity as to preclude 

the possibility of its having been derived from, but a small portion of the 

material experimented upon.

OTHER FORMS OP PACHNOLITE. In some very cellular specimens, 

whose walls run irregularly and seemingly without reference to the 

cleavage of the original cryolite, are crystals of pachnolite of different 

habit from that so far described.

One or two of these cavities show crystals corresponding in size to 

those upon the thin walls, but exhibiting each and every one a re-entering angle on the free termination. In such little crystals the basal planes 

are prominent, and they are bounded on the inside by a pyramid and 

dome, doubtless P and P<*. 'Outward there sometimes appears 

another pyramid (+P?), though the prismatic faces themselves usually 

form a sharp edge with OP. All these crystals are too small for measurement, but as the appearance described is such as would be'normal for 

the termination by which the twin crystals are commonly attached, it 

seems admissible to consider the faces as OP, P, P 55 and probably 

-f P. On many twins of this kind the outer or positive angles between 

co P and OP are replaced by two faces greatly resembling those of 3P 3, 

and although entirely too minute for measurement it is probable that 

this form 3P3 is here represented. The crystals of Greenland pachnolite are always attached by the end with the re-entering angle, according to Groth.

THOMSENOLITE.

OCCURRENCE AND DESCRIPTION. While it is quite certain that thomsenolite is present in small quantity with the pachnolite, it has been impossible to obtain any quantity of it for examination. The microscopical study of the minute crystals lining the thin walls described, shows 

a few of nearly square section with sharp pyramidal form and destitute

8T p. Grotb, I o., p. 461. . is P. Groth, I c., p. 462,

(273)
56 MINERALOGY OF THE ROCKY MOUNTAINS. IIHJM..:O.

of a twin structure. These are usually deposited with corresponding 

ones of pachnolite in a wholly irregular manner upon the low crystals 

of pachnolite forming the main portion of the walls. The reflecting 

surfaces of the massive product show under the lens distinctly rhombic 

facets or striated planes; and thin sections, which reveal the characteristic twinning of pachnolite, afford no reason for suspecting the presence of thoinsenolite here in any considerable quantity.

The statement already made for a single case (p. 51) is probably true 

for all cases where thomsenolite has been noticed, viz., that it is later 

in formation than the greater part of the pachnolite, although the latter 

mineral is usually present in a second generation, as contemporary with 

the thomsenolite. No chemical identification has been possible, but the 

nearly square section, perfect basal cleavage, and absence of twinning 

are under the circumstances quite sufficient proofs.

In many cavities, arising from both modes of decomposition of the 

cryolite, a second series of minerals has been deposited, chiefly as a 

whitish, easily crumbling aggregate of minute crystalline grains, which 

are recognizable under the microscope as thomsenolite, pachnolite, and 

a mineral of the isometric system. Th§ difference in habit of the former 

two species is here quite plain, for some of the little crystals of thomsenolite are doubly terminated and show distinct monoclinic symmetry 

in spite of the square section, through the more prominent development of the negative pyramid, while pachnolite seems perfectly rhombic 

in form, through its twinning. 

EALSTOSTITE.

PROBABLE IDENTIFICATION. This rare species, originally described 

by Brush,39 from microscopic crystals, has been more definitely determined by Groth and Brandl. Its chemical composition is, according to 

Brandl, expressed by the formula 3NaF, 4A1F3 , H2O, a small part of 

the sodium being replaced by calcium. The crystals are of the isometric

system, and represent the cube modified by the octahedron.

Groth's description of the occurrence of the mineral agrees very 

closely with that of the isometric mineral mentioned above as appearing 

with a recent generation of thomsenolite and pachnolite. The crystals 

here found are transparent cubes whose corners are replaced by small 

octahedron faces and seldom reach a diameter of lmm, while sinking to 

microscopic size. Some crystals of pachnolite seem by a low magnifying power to be coated by a crystalline dust whose particles are found, 

by applying a high power, to be most perfect little crystals of the form 

just mentioned. These sometimes unite to form a crust. No material 

for a chemical test could be secured, but the analogy in form and occurrence is so complete that scarcely a doubt can exist of the identity of 

these beautiful little crystals with the species ralstonite, although another mineral of the same crystal system is now.to be described.

39 G. J. B^sh, Am. Jour. Sci., Ill, II, 30,1871. 

(274)
CIJOSS AND I1ILLEBRAND.J ELPASOLITE. 57

ELPASOLITE, A NEW MINERAL,.

Jtist at the close of our investigations a mineral was found, occurring 

sparingly in a few specimens, which seems to be very different from any 

known species. It was found in small cavities in the massive pachuolite as a compact irregular mass, colorless but not perfectly clear,'and 

exhibiting but seldom traces of crystalline form. In one specimen, however, the mass of the mineral was covered by small rounded crystal-like 

projections, which seemed like crystals of the isometric system. An examination with a loupe showed the absence of recognizable faces, but 

such particles when broken off and tested under the microscope proved 

to be fully isotropic. A few faces found on one crystal seemed to belong 

to cube and octahedron, and particles detached from the same are isotropic in action in polarized light. Supposing that this substance must 

be ralstonite in exceptional development, enough material for the following partial chemical analysis was selected, being carefully freed from 

attached particles of pachnolite and other anisotropic minerals by microscopical examination. The Al, Ca, and Mg were accurately determined, the K and Na, owing to an unfortunate mishap, only approximately. No water could be detected by "direct test upon a small portion. 

Fluorine was present in quantity, and the percentage given below is 

calculated on the assumption that the metals are fully combined with it:

Al...... ...................

Ca. ........................

Mg...... ..................

K...... ....................

Na...... ...................

F..... .....................

(W.F.Hillebrand.)

X3CX.

11.32

0.72

0.22

28.94

9.90

46.98

9&08

From this analysis may be derived a formula analogous to that of 

cryolite, in which about two-thirds of the sodium is replaced by potassium.

The imperfections of the above analysis do not allow of definite conclusions as to the composition of the mineral, but it is nevertheless 

widely different from any known mineral species, while the purity of 

the substance is shown by its isotropic action in polarized light. Since 

the original description of the mineral 40 the locality has been revisited 

in the hope of obtaining more material, but the spot was at the time 

inaccessible, so that we can offer no further data concerning this iuieresting new species. We wish to propose the name elpasolite for it, from 

the county El Paso, which embraces the greater part of the Pike's Peak 

region. Further investigations as to the properties of the mineral will 

be made as soon as material can be procured.

-»°Ain. Jour. Sci., Ill, XXVI, 283,1883. 

(275)
58 MINERALOGY OF THE ROCKY MOUNTAINS.

GEARKSTTTITE.

[BULL. 20.

GENERAL DESCRIPTION. This mineral, first observed by Hageman 41 on compact thornsenolite, and described as earthy and kaolinlike in aspect, dull white, opaque, and of hardness 2, seems to be so rare 

in cdnnection with the Greenland fluorides-that no one has had material for further examination. Groth 42 found it in very small quantity 

among the minerals at his disposal, but could not obtain enough for 

analysis. He found, however, that it consisted of very minute microscopic needles, with oblique extinction, and considers it as undoubtedly 

a definite species.

Among the mineral's from St. Peter's Dome gearksutite is quite 

abundant. It is not formed from other minerals by molecular replacement, but is deposited from solution in cavities upon fresh crystals of 

pachnolite, etc. The smaller cavities are sometimes filled by it, and on 

the contact with the quartz it is specially developed.

In appearance it corresponds closely to the description of the Greenland mineral as given by Dana, the resemblance to the purest, finest 

kaolin being especially remarkable. Examined microscopically, gearksutite is seen to consist, as stated" by Groth, of, exceedingly minute 

colorless needles, the average length of which is less than 0.02mm and 

the thickness less than 0.002mm, and apparently possessing oblique 

extinction.

CHEMICAL INVESTIGATION. Gearksutite was found by Hagemann 

(I. c.) to possess the following composition:

Al

Ca.... .....................

Na...... ...................

^0.. ........ ..............

F....... ......... ..........

15.52

19.25

2.46

2G.22

41.18

98.63

An examination of the above results shows that the atomic ratio of 

Al:Ca+Na2 :F is 1:1:4, instead of 1:1:5, which would represent complete saturation and require about 12 per cent, more fluorine than \VJIH 

found. On the assumption that the missing fluorine is replaced in the 

mineral by oxygen or hydroxyl, there should appear a much greater 

loss than the analysis indicates. An error is therefore evident, probably in connection with the determination of the fluorine or of the 

water, or both, in consequence of which the construction of a satisfactory formula has heretofore been impossible.

The material for the following analyses was first partially crushed, 

then freed from admixed heavier particles of foreign matter by triturating in a beaker with water, the impurities falling to the bottom of the 

vessel, while the light gearksutite remained suspended fn the liquid

41 Dana, System of Mineralogy, 5th ed., p. 130. 

« Groth. /. c., pp. 460,481.

(276)
CHEMICAL COMPOSITION OF GEABKSUTITE. 59

and was removed by decantation. By repeating this operation a great 

many times a product was finally obtained entirely free from all foreign 

admixture. It was allowed to settle completely, the supernatant liquid 

poured off and the residue dried first on the water bath, then at 100° 

C. Thorough pulverization of this residue is a difficult matter, as it 

flattens out under the pestle, forming flakes which strongly resist the 

pulverizing action. This is of little moment, however, since the flakes 

are so spongy as to offer no hindrance to attack by sulphuric acid. Two 

analyses were made from the same sample, with the results tabulated 

below. In 6 sodium and potassium were not determined:

Al

Ca. ......................

Na....... ................

K... .....................

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

F. .......................

Loss as 0. ................

(W.F.Hillebrand.)

a.

15.22

22.29

0.04

15.54

42.14

95.33 

4.67

100. 00

XXXI.

6.

15.19

22.32

15.39

42.01

......

Mean.

15.20

22.30

. 0.10

0.04

15.46

42.07

95.17 

4.83

100. 00

Taking the figures in the third column and combining the fluorine 

with the calcium, sodium, potassium, and, as far as possible, with the 

aluminium, there remains of the latter 5.35 per cent., requiring 4.76 

per cent, of oxygen, an amount agreeing very well with that obtained 

above by difference and making the sum total almost exactly 100:

22.30 Ca 

0.10 Na 

0.04K 

9. 85 Al

10.11 A12O3

15. 46 H2O

42. 07 F

requires 21.18 F. 

requires 0. 08 F. 

requires 0. 02 F. 

requires 20. 79 F.

42.07

99.93

The agreement of the above analysis with that of Hagemann, after 

substituting in the latter for the sodium its equivalent in calcium, is 

very close, with the single exception of the water. As -his analysis was 

manifestly erroneous in some particular, the assumption of the identity 

of gearksutite with the mineral here discussed is fully justified, supported as it is by the'similarity in occurrence, appearance, and physical 

characteristics. His error would then consist in having obtained from 

4 to 5 per cent, too much water, a result not difl&cult of explanation, in

(277)*
60 MINERALOGY OF THE ROCKY MOUNTAINS. [BULL.20.

the case of a hydrated fluoride, if no precaution was taken to prevent 

the escape of fluorine.

Substituting in the mean of analyses a and 6 for sodium and potassium their equivalent of calcium, and dividing the percentages by the 

atomic weights, the atomic ratio is found to be as given-below:

Al...... 15.20

Ca ...... 22.41

H2O ... 15.46 

O....... 4.76

F....... 42.07

 27=0.563

 40=0.560 

.18=0.859

 16=0.297

 19=2.214

The ratio of Al: Ca : F is here nearly as 1:1: 4, the same as found by 

Hagemann. Subtracting from the atomic value for water an amount 

0.297 equal to that for oxygen, in order to form with the latter hydroxyl, 

the result is as given in the-first column below, while in the second appears the ratio referred to calcium as unity.

Al........ 0.563 1.005

Ca........ 0.560 1.000

H2O ...... 0.562 1.004

HO....... 0.594 1.061) KMK

F......... 2.214 3.954 I 5'015

It will be seen that by combining hydroxyl and fluorine the ratio 

Al: Ca: H2O: (F,OH) is 1:1:1:5, and the formula for the mineral becomes 

CaF2 , A1(F, OH)3 , H2O, in which the fluorine and hydroxyl combined 

with the aluminium, stand nearly as 2:1. Were the latter proportion 

exactly fulfilled, the formula might be written 3CaF2 , 2A1F3 , A1(OH)3 , 

3H2O, requiring the percentages: Al 15.17, Ca 22.47, F 42.69, O 4.50, 

H2O 15.17=100.00.

Of the 15.46 per cent, of water found by analysis, 5,35 per cent, has 

been considered in the foregoing as basic. While this amount may, on 

theoretical grounds alone, enter into the inner constitution of the mineral as basic water, the remainder cannot, but must be water of crystallization. That a portion of the water is basic is rendered more than 

probable by the fact that at 300° C. some is still-retained. In this connection the following experiments were made: 0.5677 gram of the mineral, not, however, from the same sample as that used for analysis, dried 

first at 100° C. and contained in a platinum crucible, was exposed in an 

air bath during 145 hours to temperatures ranging from 100° C. to 300° 

C., the weight being taken at intervals averaging 10 hours each. The 

results in brief showed that at 145° C. the loss was but 0.35 per cent., at 

230° C. only 0.92 per cent., at 250° C. 7.02 per cent., after prolonged heating at 265°-27Uo C. 9.49 per cent., and at 295? C. 13.92 per cent, As no 

further loss occurred after six hours heating at 295°-300° C., a portion 

of the residue which still retained its original appearance was subjected 

to a quantitative test for water, of which 1.76 per cent, was found.

(278)
ci:o*8 A.NO HILLEBRAXD.] GEAUKSUTlTK EV1GTOK1T13. 61

This added to the 13.92 per cent, driven off below 300° C. made the 

' total 15.08 per cent. Since this is slightly higher than the mean of the 

previous results, it seemed possible that some fluorine might have escaped. The remainder of the residue was therefore tested quantitatively for fluorine, of which was found 40.60 per cent., thus apparently 

proving the correctness of the surmise. A similar experiment with the 

same general results was made upon a smaller portion of another sample. 

A comparison of the full results of both experiments showed that by 

sufficiently prolonged heating at approximately 270° 0. all the water of 

"crystallization could be driven off; also that by still further heating at 

little if any higher temperature the basic water began to escape, but 

was not entirely expelled even after many hours exposure to a temperature of 295°-300° C.

While these experiments cannot be considered as affording any conclusive proof that the water in this mineral is to beTeckoned as water 

of crystallization and basic water in the above given proportions, since 

at the "point when the last of the former is driven off by heat some of 

the latter appears also to escape, still the belief that this should be done 

is a natural one and is supported by the fact (which may possibly, however, be merely the result of accident) that by so doing the ratio of calcium to water of crystallization is exactly 1:1, while if all the water is 

assumed to be water of crystallization the ratio is 1:1.534 or 2:3.068.

EviGrTOKiTE. In the Journal of the Chemical Society for 1883, p. 

140, Walter Flight describes a mineral obtained from the cryolite bed 

of Greenland. "It is made up of a congeries of minute white transparent crystals, mostly broken up and lying entangled among each other 

in every sort of direction, which gives the mass an appearance of opacity 

much resembling that of kaolin or chalk."

Chemical analysis showed it to consist of 

Al....

Ca....

Na

... 16. 23 with F 33. 64 49. 87

...22. 39 with F 21. 27 43.66

.... 0.43withF 0.33=* 0.76

94. 29

100. 00

Equivalents.

0.59

1.12

0.63

The fluorine seems to have been calculated for the metals, and the 

water was found by difference.

From the above data the author obtains the formula 2CaF2 , A12FG , 

'2H2O,43 and, considering the mineral new, names it evigtokite.

Mr. Flight seems to have overlooked the description of gearksutite in 

Dana's Systeui of Mineralogy and Professor Groth's remarks upon the 

same (1. c., pp. 481 and 493), else the very fair agreement of his analytical 

data for the metals with those of Hagemann, and the similarity of oo43 Probably a printer's error. It should read 2CaF2 , A! S F8, H2 0.

(279)
62 MINERALOGY OF THE ROCKY MOUNTAINS. [BULL.20.

currence, appearance, and physical characteristics of the two minerals, 

must have led to at least a suspicion of their identity. There can hardly 

exist a doubt that Flight has analyzed gearksutite and that the name 

evigtokite is therefore to be dropped.

PBOSOPITE.

OCCURRENCE. This rare species, hitherto unobserved in association 

with the cryolite minerals and known only in connection with the tinbearing veins of Altenberg in Saxony, has been identified at St. Peter's 

Dome.

Both of the coarsely crystalline specimens of pachnolite, above described as A and B, have prosopite upon them. Specimen B is in parts 

in process of alteration to a dull white substance with little cavities iu 

which are minute crystals of prosopite. These are colorless, transparent, tabular in shape, agreeing exactly in form and optical behavior 

with those determined as prosopite by chemical analysis. In two other 

specimens of pachnolite prosopito tablets may be seen upon (jertain 

granular surfaces when decomposition of the pachnolite has already 

begun. The crystals are usually attached by the prismatic edges, 

although free and perfect terminations are to be found. Gearksutite 

was noticed upon them in one specimen and the position of prosopite 

in the series of hydrous fluorides is doubtless between thomsenolite 

and gearksutite. No material for chemical tests could be procured from 

the specimens described.

The penetration of the fluoride mass by astrophyllite blades springing from the side of the vein has been mentioned (p. 42). Here the 

cryolite has been altered to cellular pachnolite, according to the first 

mode described, and this has for the greater part given way to other 

products and been dissolved and carried away, leaving the astrophyllite, blades more or less free or imbedded in gearksutite and other 

soft, crumbling material, The free blades usually have a coating com

posed of a little purplish fluorite, and over this a nearly colorless or 

slightly yellowish substance. At and toward the base-of the astrophyllite blades the latter is present in roundish aggregates made up, as 

shown by the lens, of clear tablets, in more or less radiate arrangement 

The crystal form is here quite ojjscure, but the general appearance was 

so suggestive of prosopite that by sacrificing the best specimen enough 

material was obtained for determination of the bases and of fluorine, 

with the result given below, XXXVI, p. 64.

Adjoining the quartz in the Eureka mine is usually an irregular zone 

of purplish or greenish fluorite, and next to this a rather coarsely granular mass of a colorless mineral, with two distinct cleavage planes, 

which passes gradually into the compact white substance beyond. This 

zonal arrangement is not without exceptions, for both granular and. 

compact masses come directly in contact with the quartz in some specimens, and fluorite is more or less abundantly sprinkled through the
CH08S AND HILLEBRAND.] PR080PITE. 63

other substances; in fact, the relation of the minerals to each other is 

such as to indicate that they are but different phases of alteration from 

a common source. The granular mineral occurs in sufficient purity to 

afford material for chemical analysis, and its individuals are large 

enough to admit of the preparation of thin sections, with definite relations to the cleavage planes. The analysis first proved the identity of 

this mineral with prosopite, the optical properties shown by the thin 

section confirmed this determination, and a few minute crystals were 

found in one specimen, which agree with the published data on the 

Saxon mineral. As the identification of this rare species, particularly 

in its present association, is a matter of considerable interest, we will 

describe it somewhat in detail.

CRYSTALLINE FORM AND PHYSICAL PROPERTIES. The minute crystals observed are all of the habit shown in Fig. 11 of the plate. This is 

from a camera lucida drawing of a crystal measuring 0.5mm normal to 

the edge of the prism, and can therefore make no pretensions to crystallographic accuracy. The crystals are colorless and transparent, have 

uniformly a tabular form through the development of co P So, and show 

painty the prism and two pyramids, which may be considered as P and

 2 P 2, for extinction takes place nearly or quite parallel to the edge of

 2 P 2, which is, according to Des Cloizeaux44 and Groth,45 the position 

of the bisectrix.

Thin sections prepared as nearly as possible perpendicular to the 

edge of the two cleavage faces in the irregular granular individuals, 

show that the angle of the cleavage planes is very nearly 135°, and 

that extinction takes place parallel to the direction bisecting that angle. 

This behavior agrees perfectly with the statements concerning prosopite, according to which the chief cleavage is parallel to 2 P 2", the 

angle of which is about 134°. The present material does not allow of 

a definite settlement of the question of the crystalline form of prosopite, but nothing observed is in conflict with the reference to the monoclinic system.

CHEMICAL INVESTIGATION. The formula deduced by Brandl48 for 

prosopite, from the results of his analysis as here given 

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

Al...... ...................

Ca...... ..................

Mg........................

Na.... .....................

H80 .......................

35.01

23.37

16.19

0.11

0.33

12.41

12.58

100. 00

Atomic

values.

1.842

0.853

0.405

0..004

0.014

0.689

0.786

44 Bull. Soc. Min. de Fr., V, 317. 

*» 1. c., p. 290.

der Chemie und Pharmacie, CCXIII, p. 13.

(281)
MINERALOGY OF THE ROCKY MOUNTAINS. (BULL. 20.

is Oa F2, 2A1 (F,OH)3 . The whole of the water is assumed to be basic, 

entering with oxygen into the constitution of the mineral as hydroxyl, 

the latter replacing an equivalent amount of fluorine. In support of this 

assumption Brandl mentions that no loss is perceptible below 260° C.

In an earlier partial analysis Scheerer (Pogg. Ann., CI, p. 361) found 

Al 22.77, Ca 16.41, H2O 15.50.

Of the analyses tabulated below, those under XXXII, XXXIII, 

XXXIV, and XXXV were made upon material from vein B. That analyzed under XXXII, a and &, was composed of comparatively large 

irregular crystalline pieces showing no visible impurity whatever, having 

a specific gravity at 23° C. of 2.880 and a hardness of about 4.5. As 

the ratio Al: Oa differed materially from that of 2:1, required by Brandl's 

formula, it appeared that some foreign matter must be present, consequently no further determinations were made, as it was hoped better material might be obtained.

Analysis XXXIII was made upon material separated from quartz, 

zircon, fluorite, and other accompanying minerals, by a solution of iodide 

of mercury in iodide of potassium. The result was a slight improvement, and'the analysis was completed. The material for XXXIV was 

picked out carefully by hand with the aid of a leas, but as the result 

was still unsatisfactory, a further portion (XXXV), aggregating, however, only 0.1022 gram, was selected with the greatest possible care, 

every particle being distinctly crystalline, and showing under the mi-- 

croscope no trace of impurity. Here a slight improvement becomes evident in the ratio, but as the amount taken for analysis was so extremely 

small, it cannot be asserted that the better results may not be due to 

unavoidable errors of analysis. The material for analysis XXXVI was 

derived from the crystals occurring on astrophyllite. This material was, 

however, evidently not quite pure, being opaque and very slightly colored in part by oxide of iron. The analysis was made merely to prove 

its identity with the prosopite of the other occurrence.

Al

Mg...... .......................

K. ..............................

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

F. ..............................

^

(W. F. HUlebrand.)

XX"!

a21.94

17.67

6.

21.68

17.87

21.88

16.92

0.20

0.-48

*13. 54

33.14

86. 16

13.84

100. 00

22. 13

17.14

,

33.22

22.49

16.80

0.15

0.48

21.64

16.84

0.35

0 70

0.11

32.30

' And 13.37.

(282)
'cnoss ASb ttiLLfefcRAfcb.l FORMULA FOR PROSOftTE. 

The mean of analyses XXXI1-XXXV is as follows

Al.... .........................

Ca. ............................

Mg....... .....................

Na.... ........................

HiO.... ............... .......

F ... .........................

22.02

17.28

0.17

0.48

13.46

33.18

86.59 

13.41

100. 00

After subtracting from the fluorine an equivalent for the calcium, 

magnesium, and sodium, and combining the remainder with aluminium, 

there remains of the latter 14.39 .per cent., requiring 12.79 per cent, of 

oxygen, instead of 13.41 per cent, found by difference. The atomic 

\Talues appear as follows, after substituting for magnesium and sodium

an equivalent of calcium:

Al ...... 22. 02

Ca......17.98-

F.......33.18

H2() .... 13. 46

O.......12. 79

-27=0. 815 

40=0. 449

 19=1.746 

18=0. 748 

16=0.799 1.547 3.293

The result is unsatisfactory, the ratio of Ca: Al being 1:1.81 instead 

of 1: 2. In none of the material analyzed was the slightest trace of kaoliniza-tion to be observed, nor any other foreign matter. It therefore 

becomes impossible to explain with any degree of certainty the. above 

abnormal results.

The general agreement of "all the analyses, the aluminium being 

found too low and the calcium too high in each cas*>, shows pretty conclusively that an explanation cannot be sought for in analytical errors.

As fluorite occurs here always in most intimate 'association with 

prosopite, and the possibility suggested itself that some of this might be 

so intergrown with the latter as to escape the closest scrutiny, it became desirable to ascertain what change would be effected in the ratio 

above given by subtracting enough calcium to make the ratio Ca: Al as 

1:2, and an equivalent amount of fluorine. The atomic values then become:

Al ..... 0. 815 2. (JO

Ca...... 0.408 1.00

F.......1.664 » s -7. 87

H0.....1.547r' w

which agree nearly as well for the formula Ca, A1 2 (F, OH)8 as those 

obtained by Brandl. 

If, instead of the mean of all the analyses, the figures of XXXIII alone

Bull. 20 5 (283)
66 MINERALOGY OF THE ROCKY MOUNTAINS.

are taken for calculations similar to the above> the result is the same, 

even a little more closely approximating to the ratio 2:1:8.

The prosopite is much less readily attacked by sulphuric acid than 

the' other fliiorides described, and unless the pulverization is very 

thorough a small portion is generally left undecomposed even by boiling acid. To this fact may possibly be due the deficit of nearly 2 per 

cent, iu fluorine, as compared with Brandl's results. On the assumption, 

that 35 represents more nearly than 33.18 the true percentage of fluorine in the mineral analyzed, the ratio ot water tcr required oxygen after 

combining all fluorine is I : 1.005, instead of 1.068. Allowing, then, for 

possible admixture of fiuorite as above, the ratio Al:Ca:F+OH is 

2.00 :1.00.: 7.99, almost exactly 2°: 1: 8.

The observation made by Brandl that below 200° C. 110 loss in weight 

occurs, was found to apply here, provided the exposure to this degree 

of temperature is short. If continued for many hours a slight but sensible loss is observed.

ZIRCON.

GENERAL OCCURRENCE. Zircon is one of the most widely distributed minerals of the region, occurring as an associate of nearly all other 

species in veins and druses and also impregnating the granite itself. 

Eonig 47 has described it as an associate of astrophyllite and as inter 

.grown with rnicrocline. In its usual form it is brown or nearly black 

in color, and has only the ground pyramid and corresponding prism, 

the latter quite subordinate. Kb'nig identified the basal plane 01', 

and it seems to appear in very minute form upon crystals of all modes 

of occurrence though on comparatively few from each place. Some. 

times the zircon crystals are more than an inch in diameter, sacrificing

perfection to Mzeyas there is commonly more or less distortion of angles

and unevenne^s of surfaces in such individuals.

ZIRCON FIIOM THE EUREKA TUNNEL. Reference has already been 

made in describing the occurrence of cryolite to the mutual relations of 

the different parts of the irregular vein into which the Eureka tunnel 

 has been driven. The part containing zircon is but small, comparatively, 

and is sharply defined. It evidently represents a contemporaneous 

formation, of quartz, zircon, and microcline. Zircon crystals varying in 

size from less than l"'m to lcm are very plentifully and uniformly scattered throughout, while small patches of reddish microcline were also 

included in the more abundant quartz and themselves inclosed nnmer 

small zircons. The occurrence is noteworthy from the perfection in 

form and the transparency of the zircon.

The zircon crystals imbedded in quartz are sometimes perfect, but in 

most cases the formal development has been hindered by the surround 

ing mineral, producing- striated or distorted faces. These crystals,

 "G. A. K6ni£, Zeitschnft fiir Krystallographie, I, 423, 1877. 

(284)
CROSS A&D ttlLLftBRAKD.] ZIRCON KAOLINITE, 6?

too, are much shattered by the jars of the blasting and the blows necessary in breaking up the larger pieces. Those smaller crystals deposited 

in the microcline were able to develop freely and they are now found 

imbedded in pure white kaolinite or a compact yellowish mica the 

alteration products of the original microcline, some of which is yet visible. The nature of the surrounding material has protected these crystals from jars and also makes it possible to isolate siugle ones, absolutely unharmed, for examination. The color varies from a rich reddish 

brown to a light wine or honey yellow shade. A few minute crystals 

are of a deep emerald green and spots of similar color were noticed in 

some pinkish crystals. While a few are really gems in clearness and 

color, they are usually of the smallest size, and are those found in the 

kaolinite or mica.

The common habit of all crystals is pyramidal, the prisms being al

ways subordinate when they appear. The forms determined with certainty are P, 3P, OP, 3P3, oo P and <x> Pco . The rare face OP is. much 

less frequently developed than any of the others, but it was observed 

distinctly on at least twenty-five crystals. Eepeated measurements on 

different crystals of the angle OP/\P give results varying less I ban 3' 

from the calculated value (137°50'). Between bP and P is a low pyramid, appearing quite constantly with OP, which forms an angle of 

164° 46' with P. This corresponds very nearly to £f-P. The angle be 

tween this form and P is replaced by a curved surface giving an almost. 

continuous reflection, but the angle with OP is distinct. OP is often 

visible on but one termination, but it is by no means rare to find it upon 

both.

Chemical analysis shows this zircon to be exceedingly pure and the 

specific gravity of transparent crystals is 4.709 at 21° 0.

KAOLIXITE.

The chief alteration product of microcline in the Eureka vein proves 

to be a very pure kaolinite. Some of the large individuals are changed 

into a compact white foliate kaolinite in the mass of which the cleavage 

planes of the mierocliue are still indicated.' In other cases a more 

coarsely foliate aggregate is formed, the single leaves of which are beautiful transparent crystals.

The smaller patches of microcline deposited in the zircon-bearing 

quartz are also changed into kaolinite or a yellow micaceous mineral 

whose analysis accompanies that of the kaolinite below. Sometimes 

small cavities in the quartz contain single projecting crystals. These 

are exceedingly thin, colorless, transparent, rhombic leaves, the acute angle being usually evenly truncated, producing sometimes an almost perfect hexagon. The result of many measurements under the microscope 

seems to indicate that the obtuse angle of the rhomb is slightly less than

(285)
MINERALOGY OF THE ROCKY [fiULL. 2"d.

1200, the best results varying from 118° 30' to 119° 30'. The thinnest 

leaves show distinct action on polarized light and extinguish parallel 

to tbe diagonals of the rhomb. The thicker crystals are made up of 

many tablets which are usually not perfectly coincident in position and 

sometimes form more or less perfect rosettes. The kaolinite possesses 

the composition XXXVII, and the mica XXXVIII, as given below. 

The kaolinite contained a small amount of fluorite in almost microscopic crystals, the quantity being calculated from the Ca found.

SiOs...... ...................

AbOs .......................

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

CaF2 ...... .................

<\y.F.Hmebrand.)

2

a.

45.91

39. 65

13.77 

0.68

100.01

CXXVIJ

6.

46.22

39. 62

Mean.

46.06

39.63

13.77 

0.68

100. 14

i

Si02 ........................

AhOs. ......................

FwOs. ........ .............. 

CaO .................:......

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

K20 ........................

NajO. .............'.........

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

("W. F. Hillebrand )

XXXVIII.

52.59

29. 72

1.40 

0.26

2.12

8.33

0. f,0

4.39

*99. 31

* The presence or absence of fluorine was not ascertained.

Oxygen ratio of XXXVII: * 

A12O3 : SiO*: H2O. 

3.05 : 4.01: 2.02.

Tbe kaolinite has nearly the theoretical composition, while tbe mica 

is probably a variety of muscovite.

PHENACITE.

FROM CRYSTAL PARK. This mineral was first identified from two

crystals found in association with topaz in Crystal Park, near Manitou. 

Subsequent search revealed a number of others at the same place, but 

as they are inferior to those originally described48 no new data can 

be given of this occurrence. The crystals found are but fragments, 

representing in each case.somewhat less than half of the complete crystal. Fig. 12 of the plate represents one, crystal in about the natural 

 size; another measures nearly 7cm in longest diameter, and has the 

same faces developed in similar manner. In no crystal do any faces of 

the vertical zone appear, thus producing a flat lenticular habitus. Tbe 

forms appearing have been identified as E, £R, R and §P2, and although the faces are too rough to admit of exact measurements with 

the reflection-goniometer, tbe size of the faces and their simple devel4 «Am. Jour. Sci., Ill, XXIV, p. 282. October, 1882, 

(286).
CBOS8 AND HILU5UBAND.J PHENACITE.

opment render sufficiently accurate results with the hand instrument 

possible. The angles obtained as means of several measurements are:

E A-iR(overfP2) .... 

R A$P2. ................

R A-R.. ...............

-JR A -JR.. .............

-JR A-R.................

JP2A-4R ...........O..1 .

fP2A$P2. ................

Crystal a (Fig.)

o /

148 30 

15945

.74 30

143-144 00

168 H

150 40

Crystal b.

0 /

116 20

63 00

148 50 

159 58

74 40

163 43

168 50

156 00

Authorities.

o / // 

116 36 (D)

63 24 (S)

148 18 (D) 

159 56 (D&S)

74 42 45 (S)

144 1 26

.103 32 2

168 22 (S)

156 44 (D&S)

The figures of the third column are the calculated angles given for 

pheuacite by Dana49 or Seligmanu,50 or else our own calculations based 

on the theoretical values given by them. The agreement between the 

angles measured on these crystals and the theoretical ones is sufficiently 

close to justify the signs given to the faces of the figures. In the development of the different forms E and $E are always prominent, 

while the faces of §P2 are variable. One face of § P2 on crystal b is 

2.5cm broad, although usually each face of %R is broader than both 

adjoining faces of f P2; E is subordinate and the faces are quite rough; 

$ P 2 appears with its full complement of faces. The roughness of 

the faces is in part caused by striae, which on \ E and f P2 run parallel to the terminal edge of B replaced by those faces. On E the markings are less distinct. These strise and partially regular depressions 

seem like natural etching figures, and bring out the rhombohedral symmetry of the mineral very plainty.

The crystallographical determination of these minerals as phenacite is 

confirmed by all the physical characteristics as far as observed and by 

the chemical composition. There is an imperfect cleavage parallel to 

.00 P2. Both crystals are clear and colorless, resembling quartz, and 

the hardness is nearly or quite 8. The specific gravity of the crystal 

figured, though containing some impurities, is 2.967 at 23° 0.

PHENACITE FROM NEAR FLORISSANT. Another occurrence of phenacite was discovered during the summer of 1884, near Florissant, in 

association with the topaz crystals described later on. The crystals, 

here are small, colorless, of lenticular form, and are deposited upon or 

slightly embedded in amazon stone crystals, in the same manner as the 

topaz, which is often present side by side with the pheuacite. None 

seen exceed 5mm in diameter, arid crystals of this size in one case form 

an almost continuous crust upon the surface of a feldspar crystal. More 

commonly they are attached by an edge, although occasionally in all 

other positions. '

49 Dana, System of Mineralogy, 5th ed., p. 263.

60 Cr. Seligmann, in Neues Jahrbuch fiir Miueralogie, etc., 1880, I, 129.

(287) '
70 MINERALOGY OF THE ROCKY MOUNTAINS. [BULL. 20.

These small crystals, while preserving the lenticular form of those 

from the first locality, exhibit a development of several new faces. These 

can be determined with considerable certainty by a reference to the article by Sieligmann, reviewing the crystallography of the species.51 All 

the present forms are mentioned by him as occurring with very nearly 

the same relative development upon the phenacite from the Ilmen 

Mountains, in the Urals. The zonal relations are almost sufficient to 

determine the new faces, although measurements were made to insure 

accuracy.

The new forms observed are: 2R, seen in a few crystals in good development; £R3, which appears prominently with six nearly equal 

faces; R3, of which only three faces were found on any crystal, and 

which is often not developed at all; <# E and co PL', appearing as very 

narrow faces, which do not produce a prismatic habit in any case and 

are often wanting. A narrow face sometimes seen between R and ^E3 

is probably f P2.62

TOPAZ.

Within the past two years topaz has been found in several places 

within the Pike's Peak region, and we can supplement our original notice53 of the mineral quite materially.

Topaz has been found in Crystal Park, south of Manitou, in a cavity 

containing feldspars, smoky quartz, zircon, and phenacite; at the main 

amazon stone locality near Florissant, about 12 miles northwest from 

Pike's Peak; and, more plentifully and in better form than elsewhere, 

on Devil's Head Mountain (Platte Mountain), north of Pike's Peak 

about 30 miles.

CRYSTAL PARK. Of the few crystals found in this locality the most 

perfect one measures 2.5cm. parallel to the vertical axis, 3.3cm. parallel to 

the brachy axis, and 2.8cra. parallel to the macro axis. It is colorless and 

some parts of the crystal are very clear. The prisms oo P and <» P2 

are well developed. The terminations are drusy, although many of the 

prominences are large enough to admit of the determination of some of 

the faces which bound them. The pyramid 2P has been recognized 

with certainty, while a form between f P and P, which is probably £P, 

and another pyramid near 2P4 are also present. Measurements of sufficient accuracy for the calculation of these latter forms could not be obtained. The lateral edges'of these pyramidal prominences lie in a plane 

corresponding to the brachydome 2 P oo , and although that form does 

not actually appear, the crystal has a domatic habit. A rough face of 

4f* oo is present quite distinctly. WJiile one termination is more perfect

51 G. Seligmann. " Krystallographische Notizen, I," Neues Jahrbuch fiir Mineralogie, etc., 1830, I, 129. .

MAn announcement of this locality was made by W. E. Hidden, Am. Jour. Sci:, 

March, 1885, received after this article was written.

w Am. Jour. Sci., Ill, XXIV, p. 282,1882. X

(288)
CROSS AND HILLKBRAND.J

than the other, both are alike. Not more than a dozen crystals have 

been found in this locality.

FLORISSANT. The first specimen identified from Florissant is mainly 

noteworthy on account of the enormous size of the original crystal from 

which it came. This specimen is but a corner of a large crystal, the 

forms appearing being two faces of cc P2, one of co P, and one each .of 

2f* <x> and 4f*co . The fragment is about 9cm (3£ in.) in its longest dianir 

eter, and if the other faces were developed to correspond to those here 

seen, the complete crystal must have been nearly or quite one foot in 

diameter parallel to the brachy diagonal. It is clear in parts and has a 

decided greenish tinge. It was supposed to be fluor spar by the original collectors, and the other pieces of the crystal are undoubtedly lost.

The specific gravity of this fragment is 3.578 at 22° 0. and it has the 

following composition: i

SiOs ........................

AWfe.... .................. ..

V.... ........ ...............

OforF. ...... ...............

(W. 1'. Hillebrand.)

XXXIX.

33.15

57.01

106. 20 

6.75

99.45

Atomic ratio:

Si : A12. 

1.025: l.T)00.

Within a few months a further discovery of topaz has been made near 

Florissant. In this case the crystals were found deposited upon or 

partially imbedded in amazon stone, albite, or limonite (pseudomorph 

after siderite). The crystals seen by us are deposited upon different 

faces of the microcline and. so seldom with any parallelism in position 

that any such coincidence must be considered accidental. In size the 

crystals vary from a length of nearly two inches to those which are almost microscopic. . They are deposited singly or in groups and are attached in all positions, so that many of them are quite well terminated 

at both ends. The forms observed are as follows : oo P and co £*2, both 

polished and striated ; 4J?co , 2Pco , and fPco ; OP ; 2Pco j P and f P ;

CO

Quite characteristic is the prominent development of the brachydomes 

4lr>co and 2f> co , the former in particular, the faces of opposite terminations often meeting. 4Pco is almost uniformly dull, like ground glass, 

while 2P\» is smooth and brilliant, passing into f£co or OP by a roughened line. ffco and OP are usually rough through minute irregularities bounded by crystal planes. The base is usually very narrow through 

the predominance of the brachydomes, the pyramidal planes and the 

rnacrodome are quite insignificant when present at all, and co £ co is occasionally present .as a small, smooth face. No indications of herni-

(289)
72 MINERALOGY OF THE ROCKY MOUNTAINS. [BUM.. 20.

morphism are noticeable, although the faces of opposite ends are seldom 

symmetrically developed.

Some of the crystals have a decided greenish tinge, although many 

are colorless.

TOPAZ FROM DEVIL'S HEAD MOUNTAIN. The country embracing 

Devil's Head Mountain is composed chiefly of the same granite which 

has been described in its occurrence near Pike's Peak, and it contains 

similar druses of microcliue, smoky quart/, and other minerals. Tintopaz found here is the most noteworthy crystallized species, some of 

the specimens found being probably thebestyet discovered in the United 

States. The discoverer, / Mr. W. B. Smith, ' ** ' now assistant in the liockv

Mountain division of the Survey, has given us a few notes on the manner of occurrence and associations of the topaz, which are appended to 

this description, p. 73.

In the American Journal of Science for December, 1883, Kev. E. T. 

Cross, of Denver, published a note announcing the discovery of this 

locality by Mr. Smith. The specimens obtained since that time are 

much superior to those first found, though comparatively few in number.

Specimens from Devil's Head have found their way into various mineral collections of the country, and as the most noteworthy crystals 

passed through our hands we are able to give some details. All are 

colorless or-faintly wine-colored and very clear within, though marred 

by more or less roughened surfaces, often stained by oxide of iron which 

penetrates fissures. Many fragments are sufficiently clear for cutting.

Three especially fine crystals have been obtained. Of these the one 

with the most polished surfaces, and hence the clearest, weighs 3.5 

ounces, measuring S:b: c=4.4: 4.9: 3cm. The faces x> P, GO P"2, 4? oo, 

£f* oo, OP, f P oo, P, and 2P are quite well developed, while oc f*3, oo £<» , 

2 Poo, and |P are less'prominent or not present in full quota. But 

one termination has definite faces.

The Second crystal weighs 5.5 ounces, and measures &: b: c=3.7: 5.5: 

4,6cm. Clear with dull surfaces. One termination has large OP, with 

a very symetrical development of the faces mentioned above and 2P oo. 

A second termination is formed by one large undulating face, corresponding to §P, with OP and single faces of 4? oo and 2P.

A third crystal weighs Cf ounces and measures 9, :b : c = 4.2 : 5.3 : 

4.5 cm. It has rather dull surfaces but is clear within, and has a distinct 

wine color. One termination is quite symmetrical, showing the planes 

named.

A number of the smaller crystals are very clear and transparent, 

with beautifully polished surfaces, although it is seldom that all are 

smooth.

Nearly all crystals from Devil's Head, Crystal Park, and many from 

Florissant, have been found detached, some being badly broken. The 

same is true of a large portion of the crystals of the accompanying

(290)
CROSS AND HILLEBBAND.1 APPENDIX, BY W. B SMITH. 73

minerals. Movements of the whole mountain mass, as in folding or 

faulting, have probably caused this detachment and fracture of the 

crystals. Particularly noticeable with the topaz, though also observed 

on smoky quartz, is the fact that all these old fracture planes are 

healed over, so to speak, and are now covered by drusy surfaces caused 

by little prominences which are bounded by glistening crystal faces. 

An examination shows that pyramidal planes of both orders are the 

most common, tbe little elevations resembling those upon 2lr*co above 

described. JWhen the fractured plane is parallel OP there are usually 

a great number of the pits or etching figures also previously noticed.

APPENDIX.

NOTES UPON THE OCCURRENCE OF TOPAZ AT DEVIL'S HEAD MOUNTAIN, BY W. B. SMITH.

The name " Devil's Head " was applied many years since to a jagged 

and precipitous mass of granite, rising to a height of 9,348 feet, in the 

Colorado range, some 30 miles north of Pike's Peak. This is the name 

by which it is still known locally, though upon Haydeu's Atlas it is 

called. " Platte Mountain."

The granite forming the mountain is similar to that near Pike's Peak, 

and the minerals found occur in cavities or pockets as in the latter region. No extensive pockets of amazon stone, smoky quartz, etc., have 

been found, but a few smaller ones contain a noteworthy association of 

species.

TOPAZ. The pocket in which the topaz was found is of irregular 

shape, being about 50 feet long, from 2 to 15 feet wide, and averaging 

4 feet in depth. Owing to the disintegration of the rock at the surface many of the crystals had been carried in the dSbris to a considerable distance down the mountain side, and were badly worn and 

broken.

The topaz occurs in isolated and usually loose crystals, surrounded 

by distorted quartz crystals, of smoky and reddish shades frequently 

the exact color of the topaz light green microcline, mamellary radiations of albite, cleavage masses and compact nodules of mica probably muscovite, although sometimes much altered from the original substance. Also, more rarely, cassiterite, goethite, orthite?, fluorite and 

kaolinite occur. Much of the topaz is reddish, though wine-yellow, 

milky blue, and colorless crystals were found. '

All the crystals attached to the gangue were more or less decomposed, a kaolin-like substance being the result. Frequently the terminal planes and a part of the prism would be found protruding from 

the rock unaltered,*while the remainder of the crystal, running into the

(291)
74 MINERALOGY OF THE ROCKY MOUNTAINS. [BULL. 20.

albite, would be composed of alternate layers of topaz and kaolin. More 

frequently, however, the kaolin, instead of being parallel to the cleavage 

planes, occupied curved fissures running irregularly through the topaz.

MICROCLINE. This mineral in simple crystals was the common species 

in the pocket. Some were very large, measuring 18 inches across. They 

were usually badly fractured and fell in pieces on being removed. The 

base, 0 P, of each crystal has a curious appearance, owing to the angular 

elevations and depressions that compose the surface, looking not unlike 

oriental characters cut in relief.

CASSITERITE. Twenty-five or thirty small, irregularly-shaped masses 

of this mineral were found embedded in massive albite or quartz. A 

few rude crystals were obtained, one being a little less than an inch in 

diameter. Only the pyramid is developed. No cassiterite was found 

outside of the topaz-bearing cavity.

FLUORITIS. In the adjacent region a number of interesting crystals 

of the chlorophane variety of fluorite were found in a small pocket of 

inicrocline and smoky quartz. -The most perfect crystal is a cubo-octahedrou, with every face well developed. It was found lying loose in the 

cavity and the surface is rough. The color is of a greenish tinge outwardly, with an included cube of dark purple.

(292)
III.-ON THE LUSTRE EXHIBITED BY SANIDINE IN CERTAIN RHYOLITES.

, By WHITMAN CROSS.

The sanidines of two rhyolites in Colorado, examined by the writer, 

possess a remarkable lustre which is, as far as he can ascertain, unlike 

anything previously described by any other observer. One of these 

cases has already been briefly noticed in the American Journal of Science for February, 1884. The discovery of a second iugtance of this 

same lustre, and the results of a comparison with earlier descriptions 

of lustre and color in feldspar, render a fuller treatment in this place 

desirable.

SANIDINE IN RHYOLITE FROM CHALK MOUNTAIN.- The rh jolite containing the*lustrous sauidine occurs in a massive body forming the 

greater part of Chalk Mountain, situated upon the continental divide 

at the headwaters of the Arkansas, Ten Mile, and Eagle Rivers, in central Colorado. It is of the type recently defined as nevadite by Messrs. 

Hague and Iddings,54 and may be characterized as a porphyritic rock, 

showing large glassy sanidine and many smoky quartz crystals embedded 

in a grayish ground mass, which appears under the lens to be evenly grauular,aud is really so, with the exception of isolated glass particles revealed 

by the microscope. Biotite is but sparingly present. This nevadite is 

one of the most beautiful of rocks, owing to its abundant smoky quartz 

crystals and to the .lustrous sanidines about to be described. Chalk 

Mountain lies upon the boundary between the geological maps of the 

Mosquito range and of the Ten-Mile mining district, which are soon to 

be published, with monographic reports, by the U. S. Geological Survey. 

In both of these works the manner of occurrence and the characteristics 

of the rock will be fully given.

Many crystals of sauidiue in the nevadite exhibit in certain positions 

a delicate or brilliant satin-like lustre. If examined with the aid of a 

lens a faint play of very delicate colors is seen, while the crystal seems 

white and opaque when looking down upon the lustrous surface in such 

a direction that the lustre itself does not appear. The position of the 

lustrous plane is readily seen to be near that of the orthopinacoid, and 

the extent of the deviation from it is plain when a crystal twinned acM Am. Jour. Sci., Ill, XXVII, 461, 1384.

(293) 75
76 MINERALOGY OP THE ROCKY MOUNTAINS. [BULLED.

cording to the Carlsbad law is observed. By facing the light and revolving such a crystal about its orthoaxis it is found that the lustrous 

planes of the two halves are not coincident, but are inclined at approximately 20° to each other, while evidently lying in or very near the orthodiagonal zone.

On examining the larger crystals a cleavage parallel to the plane of 

lustre is evident, and if an isolated fragment be fractured by a sharp 

blow upon the predominant brachypinacoid many flakes are produced, 

some of which are parallel to OP, while others are parallel to the lustrous surface. Those parallel to OP exhibit under the microscope a very 

fine striation at right angles to the trace of oo P So, while optical action 

is normal. The flakes parallel to the plane of lustre are fouud to be 

made up of extremely thin plates, usually rectangular through the development of cleavages parallel to OP and GO P So If but a few of 

these plates overlie each other, delicate variegated colors appear in 

ordinary light. By increase in the number of plates the flake becomes 

dull white and opaque.. The phenomena are very plainly the familiar 

ones produced by polarization and interference of light in traversing a 

series of thin plates. Transmitted light is soon wholly extinguished by 

a sufficient increase in the number of plates, and reflected light produces the lustre seen.

A parting parallel to this plane can be easily produced with a knifeblade in those crystals having a very bright lustre. The separation is 

as sharp and perfect as that parallel to any cleavage plane of the crystal. By sections parallel to o> P 3b the position of the plane with reference to the axes a and c is readily determined with approximate correctness ; but the most satisfactory, and probably the most accurate, 

measurements were obtained in the following manner:

At one point in the mountain the nevadite, here unusually coarsegrained, was found to contain many small round or irregular drusec. 

lined by minute but perfect transparent crysfals, chiefly of sanidine 

and quartz. The quartz crystals are for the most part simple dihexahedrons; the sanidines thin tablets, which are almost invariably Callsbad twins, with prominent development of the clinopinacoid. Such 

crystals examined under the microscope, as they lie upon the predominant pinacoidal face, afford a means of determining approximately the 

position of the plane parallel to which the parting referred to takes, 

place.

Fig. 13 of the plate represents one of these crystals, a normal Carlsbad twin, with a third and smaller plate, also in twin position. The 

faces shown in profile are co P, OP, PCC , and 2 Poo From all the outlines and from basal cleavage or irregular fissures run very fine dark lines, 

in uniform direction for each individual of the twin, and penetrating 

varying distances into the crystal. This undoubtedly represents an incipient stage of that parting which, in some crystals of the rock, occn 

sions the brilliant lustre, for these dark lines do not represent needles o

(294)
lnLLBBRAHD.1 LUSTtlE IN SANID1NB. 7 7

any mineral substance, but air films, upon the fissures', showing the extent to which actual parting has taken place in the direction indicated 

in the remainder of the crystal by the fine, clear striation. As seen from 

the figure, the position of the surface is that of a positive hemi-orthodome, for the cleavage plates of large crystals show the plane to be at 

right angles to the clinopinacoid. The mean of a number of measurements in different parts of the crystal places the inclination of the plane 

thus indicated to the vertical axis at 8° 40'. Assuming the axial ratio 

a: 6: 6 = 0.653:1:0.552 and j3 = 64.

-as determined by Striiver55 , for free crystals of sanidine, the face corresponds closely to -^ P oo~. This would require an angle of 72° 40' with 

the basa.1 plane, while that measured in the crystal figured was 72° 53'. 

Of course this cannot be regarded, under the circumstances, as anything more than an approximate determination.

The lustre as'thus far described is found chiefly in the sanidines of 

the coarser-grained modifications of the rock. Some of the crystals do 

not exhibit the phenomenon distinctly, and in those of the finer-grained 

portions of the mass it is commonly not visible at all. Yet, thin sections of such varieties do sometimes show a pale, delicate, bluish color 

in the sanidines, which is like that often seen in labradorite. By close 

examination of sections parallel to the plane of the satiny lustre it is 

frequently found that there are clear and transparent portions which 

do not exhibit the bright lustre, but if the light be properly guarded a 

faint bluish color is seen in these clear portions simultaneously with the 

satin-like lustre in the remainder. After the connection has thus been 

established it becomes easy to see, in most cases, that the blue color, 

seen only in clear and transparent crystals, appears upon the same 

plane which in other cases shows the satiny lustre.

SANIDINE IN BH YOLITE FROM BAGGED MOUNTAIN. Since the appearance of the article describing the lustre of the Chalk Mountain sanidine, 

another and even more striking instance has been brought to the notice 

of the writer, through his friend Mr. B. C. Hills, of Denver, who presented him with a sanidine crystal from the rhyolite of Bagged Mountain, Guunison County, Colorado, in which the satiny lustre is very 

marked. The crystal in question was several inches in length parallel 

to the clinoaxis, and has a square prismatic form in that direction, 

through the predominant and equal development of GO Pob and OP. 

The brilliant, satiny lustre is exhibited in all its beauty when these 

elongated crystals are fractured transversely, and in the crystal seen 

the fracture is parallel to the lustrous plane itself. According to Mr. 

Hills, this is commonly the case, and large masses of the rock often 

show numerous square sections, reaching 2-3 inches in diameter, each 

possessing the lustre very distinctly. .

65 Cited by Tschennak, Lehrbuch der Mineralogie, 1883, p. 455. 

(295)
78 MINERALOGY OF THE KOCfcY MOUNTAINS. {BULL 20.

From the crystal mentioned thin sections were prepared parallel to 

OP, co P ob and the plane of the lustre. That parallel to OP shows 

under the microscope uniform extinction ± to the edge of oTP 5b. The 

lustrous plane is indicated in the pure and transparent portions by a 

very fine clear striation lying, so far as determmable, exactly at right 

angles to the trace of GO P So . This striation is exceedingly delicate, 

and appears most distinctly \vhen directed from the observer toward 

the source of light. Through a large part of the section, however, the 

clear striation is replaced by dark lines, easily seen to be sections of 

parallel planes, upon which are many dark bodies like gas cavities or 

empty spaces. These are zigzag in shape, but bounded chiefly by lines 

seemingly parallel to OP and co P <3b . The plane holding these bodies 

is steeply inclined to OP.

The section parallel to cc P 5^ shows a clear striation where parting 

has not taken place, and dark lines representing the sections of planes 

containing air or empty cavities where the separation has begun. The 

situation of the lustrous plane with reference to the axes a and c is here 

plain. The angle susceptible of most accurate measurement is that 

between the basal cleavage fracture (a) and the clear striation. Bepeated determinations show this angle to be between 72° 30' and 73°. 

This corresponds closely to the results obtained from the crystal in the 

Chalk Mountain rock, and shows conclusively that the lustrous planes 

in the two cases may be considered identical.

The thin section parallel to the lustrous plane brings out still more 

distinctly a zonal structure which was visible in the crystal. The outer 

zone has a much more brilliant lustre than the interior, and certain 

parts of the latter are quite transparent. In these portions, when the 

satiny lustre of the outer zone is at its maximum of brightness, a delicate pale blue color is visible, like that noticed in the Chalk Mountain 

sanidiue. Under the microscope the appearance is similar to that 

already described for cleavage flakes. Where the lustre is brightest 

the parting is apparently complete, with continuous air films between 

plates. Where the sanidine exhibits the blue color there is either no indication of the laminated structure, or the beginnings ot the parting 

are represented by the same dark zigzag cavities or air pores seen in 

the basal section. These are now clearly seen to be bounded for the 

most part by lines parallel to OP and oo P 56 .

Although no alteration in the ordinary sense is visible, the section is 

opaque where the number of plates overlying each other is great.

PREVIOUS DESCRIPTIONS OF LUSTRE IN FELDSPAR. The bluish 

color sometimes seen in adularia, albite, or oligoclase and the play of 

colors so beautifully exhibited by la.bradorite have been the subjects of 

studyon the part of various mineralogists. Sir David Brewster ascribed 

the phenomenon to the action of certain flat rectangular bodies observed with the microscope, and which he considered as filled by air, or,

(296)
cnoss AND HILLBBRAND.J INVESTIGATIONS OF REUSCH. 79

at least, by some matter of much lower refractive power than the feldspar.

The first satisfactory investigation of this subject was, however, by 

E. Beusch,56 who made (18G2-'63), a careful study of the bright lustres 

and chatoyant colors exhibited by various minerals.

The results of Eeusch's study of the feldspars are of particular interest in connection with the foregoing, and although the original has been 

consulted, the writer wishes to quote the concise r&umt given by Dana 

in his System of Mineralogy, 5th edition, p. 336: " The play of colors, 

especially remarkable in much labradorite, and occurring also in some 

adularia, albite, and oligoclase, indicates, according to Eeusch, the 

existence of a cleavage structure of extreme delicacy transverse to 

the median* or brachydiagonal section. In adularia the plane of this 

cleavage is perpendicular to this section (or that of the clino-cliagonal);

in labradorite it is in general more or less inclined, and differently in 

different specimens. The play of colors, Eeusch observes, appears therefore to be that of thin plates; yet the lining of what he regards as a 

cleavage system appears to be of indistinguishable minuteness; and although the existence of thin plates can hardly be established by the 

microscope, it is proved by their effects in the play of colors, nebulous 

images within, and the phenomena of inflection or diffraction which result from their regular grouping." By preparing a polished surface parallel to the orthopinacoid, Eeusch determined, for adularia, the inclination of the plane producing the nebulous images to the vertical axis, at 

11° 38', as a mean of many careful observations. The angle with the 

clinoaxis is given at 74° 18'. The corresponding measurements of the 

cleavage inclinations in the Chalk Mountain sanidiue given above are 

8° 40' and 72° 53'. If we assume /?=63° 53' for adularia, as is commonly given, the latter measurement of Eeusch would require the 

former angle to be 10° 25', and as the value 11° 38' was obtained from 

an artificially-prepared surface we may perhaps be justified in considering the measurement 74° 18' the more correct, in view of the nearer 

agreement thus shown with the results on sanidine where the direction 

of the new cleavage plane is more distinctly indicated.

It seems almost unnecessary to point out any more clearly that the 

actual parting observed in thesauidines of these ihyolites is a beautiful 

natural proof of the correctness of the conclusion drawn by Eeusch from 

his admirable investigation. The satiny lustre is caused by the fuller 

development of that internal lamellar structure which produces the 

beautiful delicate blue color in clear adularia or sanidine in the manner 

explained by Eeusch.

Vogelsang, who ma'cle a study of the play of color in labradorite,57 exW1E. Eeusch, " UVber das Scbillern gowisser Krystalle," in Pogg. Ann.. CXVI, 392; 

CXVIir, 250; CXX, 9:..

"Cited by Nuuiiuum-Zirkel. Mineralogio, p. 158, llth Ed.,Original in "Archives 

N^orlaudaises," Tome III, 1868.

(297) ,
80 MINERALOGY OF THE ROCKY MOUNTAINS. lnutt.20.

\ 

plained the blue color as clue to x>olarization from thin plates, the yellow

and red as caused by numerous included lamellse and ruicrolites of 

mineral substances, while the green and violet shades are thought to be 

the result of a combination of the blue with the yellow or the red. 

lleusch states, as mentioned above, that the undeveloped cleavage. in 

labradorite does not correspond in position to that in adularia, being 

near the brachypinacoid and variable in different specimens.

From the above it seems quite possible that the rectangular bodies 

thought by Brewster to be the cause of the bluish color may have been 

the equivalent of those seen in the sanidiue, which indicate the beginning of the actual parting in the direction of the latent cleavage.

LUSTRE UPON OTHER SANIDINES. In the Microscopical Petrography 

of the Fortieth Parallel (p. 83), Professor Zirkel mentions a "superb blue 

c lor" as characteristic of the small sanidines in a rhyolite from Chataya 

Peak, Pah Ute Mountains, Nevada. It is also visible in various rhy elites 

east of the point named. The cause of the color is thought unexplainable, for "no strange particles can be detected, neither needles, nor 

plates, nor grains, nor a dust-like powder, nor glass or fluid inclusions."

An examination of these rhyelites by th'e writer indicates clearly that 

this phenomenon is simply another instance of that which has been described. The intensity or brilliancy of the color exhibited in some of 

these rocks is quite striking.

CONCLUSION. The phenomenon which has been described does not 

seem comparable with any hitherto recognized property of crystals. It 

seem incorrect to speak of it as "cleavage," for that internal structure 

manifested by the fine basal cleavage of this same species is accompanied 

by no such optical action ; nor can the writer recall any such combination in any other mineral. This lamellar structure is to be considered 

as another of those physical characteristics of minerals, such as cleavage, fracture-figures, " gleilflachen," etching-figures, twinning produced 

by pressure, etc., which will doubtless remain unexplained until the 

molecular constitution of crystallized bodies is made clear.

(298)
IV. AN UNUSUAL OCCURRENCE OF TOPAZ.

By WHITMAN CROSS.

The nevadite of Chalk Mountain, which was described in the preceding section, contains in its small drusy cavities another mineral of 

decided interest besides the sanidine. Accompanying the quartz and

sairidine in the cavities are minute leaflets of biotite, a few ore grains, 

and, in a few druses only, very perfect crystals of colorless transparent 

topaz. Usually but a single crystal of topaz is present in one of the 

druses,' and that is larger and more perfect in development than any 

other. The topaz is attached directly to the walls of the cavity and 

often bears small tablets of sanidine upon it. The crystals which can 

be recognized as topaz vary from 0.5ram to 3mm in length, but it seems 

quite probable that there are some smaller ones indistinguishable from 

quartz.

The determination as topaz rests upon the crystalline form which is 

very distinct and is that of common topaz. One crystal measuring 

3mm in length and lnim in thickness was removed from the rock and its 

angles measured with a Fuess reflection goniometer. This crystal 

presents op P, oo 1*2, and 2t3 oo as the dominant forms ; OP is a narrow 

face and 4£ oo, 2P oo, 2P? and P are minute, but very distinct. The 

angles measured are as follows:

o /

ooPAooP........................ 124 10

oof 2 over oof oo................. 93 7

OPAafcoD........................ 136 30

OPAP........................... 134 11

OPA2P.......................... 115 55

2P QO appears as a very narrow face in the zone of 2P to 2P. This 

is the usual habit, with the occasional addition of oo P oo and a more 

prominent development of OP. This crystal is also imperfectly terminated at the attached end, showing 2f* GO most prominently, with 4P oo 

and 2P also recognizable, and there are no signs of hemimorphism.

In some druses all crystals are thinly coated by a black incrustation 

which seems to be pyrolusite.

So far as I can ascertain, all previously known and described occurBull. 20 6 (299) 81
82 MINERALOGY OF THE ROCKY MOUNTAINS. [BULL.20.

rences of topaz are in granite, gneiss, or some other member of the 

series of metamorphic or crystalline schists. In the present case topaz 

is found in an eruptive rock, probably of early tertiary age, while the 

appearance of the associated minerals certainly suggests that they may 

all be sublimation products, though it is not capable of direct proof. 

The sanidine crystals from the druses, examined microscopically, contain gas inclusions, while neither fluid nor glass inclusions were seen.

(300)
V. ASSOCIATED BARE MINERALS FROM UTAH.

BY W. F. HlLLEBRAND.

In the American Eagle mine, Tin tic mining district, Utah, occur, in 

intimate association, several minerals, the majority of which, it is believed, are ne\v to the American continent. All the specimens examined were obtained from an ore-heap at the works of the Boston 

and Colorado Smelting Company, near Denver, where they were tirst 

observed and their probable identity established by Mr. Eichard Pearce, 

metallurgist to the above company. More detailed examinations were 

made in the laboratory of the Survey at Denver, as opportunity ottered, 

in compliance with a desire expressed by Mr. Pearce.

OLIVENITE.

Recognizable by its dark olive-green and wood-brown color, and by 

its crystal form, is olivenite, occurring in a mixture of various brown 

and yellow oxygen salts of iron, copper and calcium. The only planes 

observed, according to Mr. Whitman Cross, belong to the prism and 

brachydome. While fine crystals are not of infrequent occurrence, the 

major part of the mineral appears in that characteristic brown, compact, 

fibrous state to which it owes its old name of wood-copper. The amount 

of crystallized material available sufficiently pure for a satisfactory 

analysis was very limited on account of the firm adherence of small 

green hemispheres of conichalcite on many of the crystals. Analysis 

gave the following results:

CuO.... . = .... ..............

AssOs.... ...................

PtOs. ................ ......

HS0 ........................

FetOa...... .................

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

ZnO...... ..................

XL.

55.40

40.05

0.06

3.39

0.25

0.16

0.40

99.71

The ferric oxide of the analysis was derived from a little adhering 

hydrated cupri-ferric arseniate and the calcium and zinc oxides from attached conichalcite. The oxygen ratio for CuO : As2O5 (P2O5 ) : H2O is

(301) 83
84 MINERALOGY OF THE ROCKY MOUNTAINS. [BULL. 20.

4.00 : 5.00 : 1.08, instead of 4 : 5 : 1 required by the formula Cu3As2O8 + 

H2CuO2 .

CONICHALCltf^E.

Covering the surface of often large pieces of more or less soft and 

friable-mixed arseuiates, sometimes uniting°to form a complete coating, 

are innum rable beautiful emerald-green semi-translucent globules, 

averaging three-fourths of a millimeter in diameter and showing distinct radiate structure when broken. Notwithstanding the considerable 

amount of material from which to select, the obtaining of perfectly 

pure material iu sufficient quantity for analysis was impossible without 

devoting several days to the work, in consequence of the firm adherence 

of gangue to the flattened base of the globules and of the fact that the 

nucleus of each globule usually consisted of some of the same soft 

gangue matter. The material analyzed was so small in quantity, therefore, that the analytical results can lay no claim to the highest degree 

of accuracy, especially as all estimations had to be made upon the same 

portion. No specific gravity determination was attempted for this 

reason, and also because there were no means of determining the corrections to be made for small amounts of impurities other than quartz.

CuO ........................

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

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

ZnO ................:.......

Ag ..... ................

Asi05 .... ...................

PsOs...... .............. ...

V20s.... ....................

HzO. ........................

Fe^Os.-- ...................

CO*. ........................

XLI.

28.68

1 0 7Q

0.54

2.86

0.30

39.94

0.14

1 f»9

0.36 ' 0. 97

0.90

100. 00

Conichalcite 

from Spain.

31.76

91 nfi

30.68

8.81

1 7fl

5.61

100.00

* By difference.

The ferric oxide was derived from attached gangue. The carbon 

dioxide was probably combined with lime, since a temperature was required for its expulsion higher than that at which all the water escaped, 

the latter having been estimated by direct weight. Part of the water 

seemed to escape at a much lower temperature than the remainder. 

The silver is not a constituent of the gangue, since none could be found 

 in the latter underlying the green coating. It is not present as chloride, 

for nitric acid readily takes it all into solution ; nor could any native 

silver or sulphide be detected. The only conclusion to be drawn is that 

it exists in the mineral in an oxidized state, presumably as silver arseniate.

In appearance and composition this mineral resembles no other than 

conichalcite, found hitherto only in Andalusia, Spain, and represented by 

a single analysis in Dana's System of Mineralogy, p. 563 (quoted above

(302)
CROSS AND HILLKBRAND.J CONICHALCITE CHENEVIXITE. 85

for the sake of comparison). It will be noticed that vanadium is wanting (it was specially looked for) in the mineral from Utah, and phosphorus nearly so; while zinc, which was not a constituent of the Spanish mineral, here replaces apparently some copper.

Allowing for the CO2 its equivalent of CaO, the oxygen ratio is as 

follows:

KO : As2 05 (P205 ):H20.

1.00 : 1.18 : 0.41. or 

4.00 : 4.72 : 1.64.

instead of 4:5:1.5 required by the supposed formula (Cu, Ca) 3 As2O8 + 

H2CuO2 + £H2O.

Heated in any manner before the blow-pipe most violent decrepitation ensues, the entire fragment flying into fine powder. In a closed! 

tube, after decrepitation has ceased, the particles by gentle tapping majbe made to collect at the bottom as a brown-black spongy mass of great

volume. This collected ou a loop of platinum wire fuses before the 

blow-pipe, at first with a pale bluish coloration of the flame. This behavior accords in a measure with that mentioned in Daua's System of 

Mineralogy (loc. cit.).

CHEiNTSVIXITE.

Thickly scattered in irregular patches throughout some portions of 

such ore as occurs in hard lumps, giving to a broken surface a mottled 

appearance, is a compact greenish opaque body, with little or no lustre, 

which corresponds in composition very well with cheuevixite from Cornwall, as represented by one of the two analyses in Dana's System of 

Mineralogy, p. 583. The hardness, however, is lower, being 3.5 instead 

of 4.5, as there given. The color is an olive-green, sometimes shading 

away into a greenish yellow after exposure. The fracture is subconchoidal.

CnO... 

CaO ... 

MgO... 

FezOs . .

AlArAssOs.. 

PaOs...

HsO ... 

Quartz

a.

26.41 

0.44 

0.10 

27.37

0.66 

35.08

9.41 

0.40

99.03

XLII.

6.

26.21

"'35.' 20"

9.25

. M ean.

26.31 

0.44 

0.16 

27.37

0. 06 

35.14

9.33 

0.40

99.81

ChenevixCornwall.

31.70 

0.34

'""25."i6"

""32."26" 

2.30

8.66

100.30

The analysis was made upon air-dried powder, since the latter loses 

about 0.75 per cent, of water even over sulphuric acid, which loss be-

(303)
00 MINERALOGY OF THE ROCKY MOUNTAINS. [BULL. 20.

eomes slightly greater at 100° C., and continually increases as the temperature rises. The oxygen ratio is 

EO + E2O3 : As2O5 : H2O. 

6.00 :5.23 :3.55.,

while that of the above-quoted analysis of the Cornwall mineral is 

6:5.35:3.30 instead of 6:5: 3, as assumed most probable. The material 

now analyzed cannot with any certainty be regarded as pure, hence the 

deviation from this theoretical ratio is not of great importance.

Before the blow-pipe the mineral from Utah differs from that from 

Cornwall, in that it does not usually decrepitate, while in other respects 

the behavior is identical; it fuses readily, gives off arsenical fumes, and 

leaves a black magnetic scoria.

Both cheuevixite and conichalcite appear to be generally regarded 

as doubtful species, for their names do not figure at all in some of the 

best miheralogical works, but it can hardly be questioned now that they 

represent definite species whose precise nature, however, is yet a matter for further investigation to reveal.

A HYDROUS CTJPRI-CALCITJM ARSEOTATE.

In rare instances, fine silky white needles have been observed, chiefly 

on conichalcite, but in such small quantity that the only data as to their 

composition are the following determinations made by Mr. Pearce on 

less than a centigram of material:

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

AssOs ...... ................

CnOandHsO*....; ..........

31.5

38.6

29.9

100. 0

* By difference.

The copper estimation was a failure, but the percentage of CuO was 

judged to be fully 20 per cent. The composition would then seem to 

be near that of conichalcite with the proportions of CuO and CaO reversed, but in view of the wide limits to be allowed for possible error in 

the analysis, further comment is useless.

JAROSITE.

Jarosite in fine transparent brown crystals was observed by Mr. 

Fearce on a few specimens of ore. The identification rests upon partial 

chemical analysis, and more fully upon angle measurements by Mr. 

"Whitman Cross.

THE MASSIVE ORE.

With jarosite is completed the list of probably distinct species, as far 

as observed, with the exception of one or two others present in too small 

quantity for even qualitative'identification. There are, however, cer-

(304)
CROSS AND HILLEBRAND.] MASSIVE ARSENIATES AND SULPHATES. 87

tain characteristic components of the ore which seemed to merit examination.

A portion of the ore is a brown substance, showing nodular forms and 

a granular surface when broken and of considerable hardness owing to 

disseminated quartz. Analysis furnished the following results:

Fe203.... ...'................

AliOa....... ................

CuO...... ..................

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

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

K20 ........................

NaiiO ...... .........:.......

AssOs...... .................

 SOs...... ...................

HuO. .........................

XLIII.

44.22

0.48

1.30

1.33

0.10

1.72

0.40

20.01

0.66

11. 02

J2.00

99.30

These figures probably represent a mixture of a hydrated ferric-alkali 

sulphate (perhaps jarosite), and one or more hydrated arseuiates.

In places it passes gradually into a brilliant black substance, closely 

resembling jet, and possessing conchoidal fracture, difficult to extract 

even in very small quantity, but having, according to Mr. Pearce, tnV 

following composition:

Fe203.. ............... ......

CuO ........................

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

A8206 ...... .................

41.47

4.88

7.27

27.155

18.49

99. 76

It was subsequently ascertained that the loss on ignition represents 

SO3 as well as H2O, hence it is useless to attempt the construction of 

a formula. 

Filling interstices7 between the nodular forms of the brown mixture 

above described and occurring as an irregular coating on much of the 

ore, there is a soft powder of a bright straw color of which the average 

composition is as follows:

FezOs. ....... ..............

PbO!..... ..................

CuO........................

KsO ) NaaOl - - - 

AszOs...... .................

P*0. ........................

SOs...... ...................

HzO ........................

XLIV.

37.84

13.74

2.33

*3.93

12.22

0.40

16.85

9.39

3.30

100. 00

* By difference.

(305)
88 MINERALOGY OF THE ROCKY MOtNTAINS. [BULL. 20.

The resemblance to certain alteration products of galena and pyrite 

found in several of the Leadville mines is striking, and, like some of 

these, it seems to be a mixture of lead sulphate, jarosite, and hydrated 

ferric arseniate.

All of the above-described minerals and mixtures, with exception of 

crystallized jarosite, may sometimes be observed on one and the same 

piece of ore* It is not improbable that further investigation at the mine 

itself might bring to light still other minerals belonging to the group 

of hydrous arseniates.

In this connection it may be mentioned that Mr. Pearce has identified pseudomalachite occurring with hiibnerite (see p. 96) from near Phillipsburg, Montana Territory. According to Mr. Pearce's analysis it 

contains OuO 62.56, P2O5 20.10,H2O 17.34 (by difference).

(306)
VI.-MISCELLANEOTJS MINERAL NOTES.

By W. F. HlLLEBRAND.

LOLLINGITE,

OCCURRENCE. The cobaltiferous and nickeliferous variety of 1611- 

ingite which is to be described occurs at the head of Brush Creek, Gunnison County, Colorado, It has been found in the Luona mine at the

western base of Teocalli Mountain, and in the American Eagle and 

Horace Porter mines on White Rock Mountain. The peculiar ore bodies 

of which the lollingite forms a part are irregular masses, the relations 

of which are not yet understood. The investigations of the United 

States Geological Survey, now in progress iu Gunnison County, include 

the area of Brush Creek, and these interesting bodies will be carefully 

studied.

At the Luona mine, according to Mr. J. G. Ridgley, of Denver, the 

lollingite is associated with native silver, proustite, argentite, pyrargyrite, chalcopyrite, galena, siderite, barite, and calcite, the last three 

composing the gaugue. Much of it is decomposed, forming secondary 

oxidized products, most conspicuous among which is erythrite. At the 

other localities sinaltite is a common associate. The smaltite analyzed 

by Dr. W. M. lies (Am. Jour, of Sci., Ill, XXIII, 380, 1882) was probably from one of tbe mines on White Rock Mountain.

DESCRIPTION. The lollingite occurs in compact, massive form, and 

also embedded in barite or siderite, and presents a very striking appearance on fresh or newly fractured surfaces. There are seen embedded in 

the siderite and barite gangue, steely white forms, about one-eighth of 

an, inch in diameter, of pronounced radiate structure, the longer radii 

protruding from the mass and giving the whole a beautiful stellate appearance. The star forms occur sometimes single, but more frequently 

joined together in greater or less number without losing in any marked 

degree the peculiar character of the individual. In some specimens the 

appearance approaches that of a dense, homogeneous mass, several inches 

in diameter, but even in the densest portions the radiate structure is 

generally distinctly discernible.

In order to discover, if possible, a clue to the crystallographic structure, and also to obtain material for analysis, specimens were treated 

with hydrochloric acid without previous crushing, whereby the siderite

(307) 89
90 MINERALOGY OF THE ROCKY MOUNTAINS. [BULL.20.

and the arseniates of iron, cobalt, and nickel were entirely dissolved. 

The lolliugite remained quite black on all parts where the gangue had 

been eaten away,' but surfaces of previous fracture retained their white 

color. The star like forms were then seen to be composed of a considerable number of long flattened ellipsoids, interpenetrating at a common centre in every direction. When one of these clusters was broken 

through, the star form appeared on the surface of fracture. The aggregates were joined together loosely, now that the cementing material had 

been removed, though frequently in large clusters of many hundreds of 

all sizes, from those visible only with the aid of a microscope to others 

.an eighth of an inch or more in diameter.

A microscopical study of the finer part of the material liberated from 

its imprisonment in the gangue, and broken off from the larger pieces 

during the treatment with acid and subsequent washing, furnished 

the solution to the question as to what was the crystallographic 

form of the flattened ellipsoids composing the aggregates, and the law 

of the twinning. The fundamental form is that of lollingite, showing 

only the prism and macrodome, as in Fig. 14.58 Frequently these two 

forms are equally developed, producing a resemblance to a low pyramid of the tetragonal system. Very few even of the most minute 

crystals are perfect in form, and possessed of sufficiently smooth surfaces to allow of even approximate measurement under the microscope. 

Eepeated attempts were made to get these in proper position under 

the instrument, but in only one case with comparative success, owing 

to their microscopic size. The angle of the prism was then found to be 

very nearly 122°, that given for lollingite being 122° 26'.

Parallel to the combination edge of the prism and macrodome there 

is almost always on the prism a striation (more coarsely marked the 

larger the crystal), caused by the alternate reproduction of the prismatic and domatic faces. Approaching the combination edge the reproduced dome face becomes relatively larger than that of the prism, the

 consequence of which is a gradual roundiug of the corners and a contraction, and eventual disappearance of a distinct terminal dome, the 

result being, as represented in Fig. 15, an elipsoidal form with a slight 

ridge through the center representing a prism edge. Frequently the

 corners of a crystal, occupying the position of Fig. 14, appear as if 

modified by a brachydome, but no such form has been observed, the replacement being a straight serrated edge, caused by the same alternation of faces as in the case of rounded corners. Even where the macrodome is well developed it generally shows a continuation in some degree 

of the prismatic striation parallel to the same combination edge. 

The first step toward the complex twin structure is the formation of

68 All the accompanying figures, with the exception of Fig. 14, were drawn by the 

aid of a camera lucida, and therefore make no pretensions to cryetallographic accuracy. Fig. 17 is magnified about 15 diameters, the others from 40 to 150 diameters.

(308)
CB088 AND UILLEBBAND.] LOLLINGITE AND ASSOCIATES. 91

a single twin, or, rather, trilling, by interpenetration of three single 

crystals having the basal section in common, and a face of the prism as 

composition face (Fig. 16). A basal section shows a six-rayed star, with 

angles of very nearly 60°, by microscopical measurement, between the 

iixes of the rays. In the microscopic trillings one individual frequently 

predominates greatly in size over the other two, these appearing often as 

thin leaves, projecting but a short way out of the larger crystal. These 

trillings are finally found again interpenetrating, not according to any 

recognizable law, but seemingly in every direction, and in indefinite 

numbers, forming thus the complex aggregates first spoken of. All these 

stages of changes in form may be observed with great ease under the 

microscope, the very smallest crystals alone showing crystallographic 

faces well defined. As the crystals, single or twin, increase in size, the 

faces gradually grow more and more indistinct, and finally disappear 

entirely in consequence of increasing striation.

ISotwithstandiug repeated attempts, the basal cleavage mentioned in 

text-books as characteristic of lollingite could rarely be produced, and 

no cleavage in any other direction except in the case of the trillings. Here an individual frequently broke off at the line of union of 

the three; that is, in a plane parallel to the brachypinacoid.

Aside from the forms distinctly recognizable as lollingite are, however, 

others belonging apparently to two different minerals. The first of 

these became visible on dissolving the gaugue, when there came to the 

surface of the acid and the water used for washing out the latter a 

great number of minute but brilliant metallic particles, which resolved 

themselves, under the loupe, but still better under the microscope, into 

thin leaves or blades, of which Fig. 17 represents one of the more perfect examples. Its forms appear to consist of two pinacoids of the 

rhombic system, one very broad, the other very narrow, and a terminal 

dome having an angle of almost exactly 90° by microscopical measurement. The faces are most brilliantly reflecting. Distinct cleavage was 

not observable. The second mineral, which is almost always microscopic in size, is represented in Figs. 18, 19, and 20. The prominent 

form is that of a lengthened prism with an angle of very nearly if not 

quite 90°. Repeated measurements gave values fluctuating between 

88° and 92° as the extremes. It is terminated at right angles by a 

basal plane, the four corners of which are frequently replaced by faces 

which may be those of a pyramid or two .domes, according as the habit 

:is pinacoidal or prismatic. The cleavage is parallel to the base. Single 

crystals are rave, two or more being generally seen interpenetrating, as 

in Figs. 18 and 19, generally at an angle of 90°, or united, as in Fig. 20. 

In the latter figure only the outlines, not the faces, of the different horizontal individuals are shown; nor do the numerous vertical attachments present appear. Occasional instances of three prisms crossing 

at right angles like the axes of a rectangular system were observed, 

and also a single instance of the form represented in Fig. 21, where

(309)
92 MINERALOGY O'F THE ROCKY MOUNTAINS. [BULL. 20.

each of the arms showed a domatic face. The most striking feature of 

all but the last of these different forms is the invariable widening at 

the point of union or intersection, as shown in the figures.

CHEMICAL COMPOSITION. Even an approximate separation of the 

last two minerals described, from each other and from the smallest 

lollingite crystals, was impossible, hence no conclusion could be reached 

as to their quantitative composition. Qualitative tests proved them 

both to be arseniates of cobalt, the square prismatic forms containing 

also iron and nickel. An incomplete quantitative test upon a mixture 

of these three minerals showed a much higher percentage of cobalt 

and nickel than the analysis of the pure lollingite.

Before the blow-pipe the lollingite furnished the reactions mentioned 

in the text-books, the residue after treatment with charcoal being infusible, strongly magnetic, and, furthermore, giving the characteristic reaction for cobalt with fluxes; soluble in nitric acid, giving a pink solution.

Of the analyses given below, XLV was made upon clusters of lollingite trillings, free, so far as could be determined by the loupe, from 

attached or penetrating blades or prisms of the other two minerals 

described. As a check a small quantity of the single crystals and trillings was picked out with the utmost care under the microscope and subjected to partial analysis (XLVI), no trace of foreign adherent matter 

being visible. The specific gravity of the material used for the first 

analysis was 7.335 at 14£° .0. Correcting for one half per cent, of siliceous gangue of assumed specific gravity 2.65, the true specific gravity 

of the mineral becomes 7.400.

A a f~\

a ::::::" :: $:::::::::

Bi...... ....................

Cu .................

Fe. ...........

Co..........................

Ni...... ....................

XLV

71.18

0.56

0.08

0.39

A Q7

0.21

99.75

XLVI

99 OQ

4. '-!<)

0.19

The first of these analyses leads closely to the formula Fe (Co, Ni) As 

(S)2, while XLVI shows beyond a doubt that both cobalt and nickel are 

constituents of the lollingite and not derived from attached crystals of 

either of the other minerals. The presence of cobalt recalls the glaucopyrite of Sandberger, though the antimony found in that mineral is 

here wanting. The peculiar comb-like excrescences described by him, 

indicating rhombic twinning by interpenetration, may be analogous in 

some degree to the twinned structure of the present mineral.

Some varieties of rhombic CoAs2 , all of which, according to Leroy 

W. McCay,59 should be united under the name safflorite, present features

S9lnaugural Dissertation, Freiberg, 1883. 

(310)
CKOSS AND HILLEBRAND.] LOLLINGITE ZINCKENITE 93

remaikably like some of those herein described, notably as regards the 

tendency to form twins of interpenetration; and from the presence of cobalt it might be suspected that this mineral was rather to be considered 

as safflorite than lollingite. Its exceedingly high percentage of iron 

and high specific gravity, both greater than that of any safflorite yet 

examined, are not unimportant objections to this conclusion.

In the description of this mineral in the American Journal of Science, 

Vol XXVII, p. 354, through a misapprehension not to be explained in 

fi few words, Saudberger is wrongly quoted as authority for the statement that the brachydome is characteristic of rhombic Co As2. Attention was called to this error by Mr. Leroy W. McCay, who is inclined 

to consider the above described mineral as safflorite. While acknowledging that through the elimination of the statement referred to, the 

main point there brought forward in favor of identity with lollingite 

was taken away, the evidence is by no means conclusive that the mineral should be classed with safflorite. Further examination, especially

of a crystallographical nature, on both lollingite and safflorite, are necessary in order to settle this question. The mineral having been 

already described as lollingite, this name is here retained.

ZLffCKENTTE.

In the Brobdignag mine, Eed Mountain, San Juan County, Colorado, 

occurs a massive gray mineral showing greasy metallic lustre, without 

apparent crystalline structure, but to all appearances of complete homogeneity; of specific gravity 5.21 at 18° C. and hardness 3-3.5, which upon 

analysis was found to be an- arseniferous zinckenite, this being, it is 

believed, the first observed occurrence of the mineral in the United 

States. . Besides the usual blow-pipe reactions for zinckenite, including 

violent decrepitation, there appear those for arsenic, preceded in the 

olosed tube by a light sublimate of sulphur. .The results of analysis 

are:

' 

Sb. .........................

Pb. .........................

Cu. .........................

Ag. ........... .............

Fe. ......... ................

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

KsO ? NaaO* " - - 

s.... ..:....................

Ganguo .....................

XLVII.

a.

35. 00

5.04 

32.77 

1.20

0.23

0.02

0.31

0.45

22.50 

0.59

98.71

b.

5.59 

32.79

22.50

"The atomic ratio is, for

(PbCu2Ag2 ) : (Sb2 As2 ) : S 

1.00 : 1.09 :4.11.

(311)
94 MINERALOGY OF THE ROCKY MOUNTAINS. [BULL. 2ft

While this is close enough to the theoretical ratio 1:1:4 to establish theprobable formula PbS,Sb2S3 , the result was not such as the care expended on the analysis warranted, supposing that no impurities were 

present. Calculation shows that while the antimony and arsenic taken 

together are in excess of the amount required for lead, copper, and silver, the sulphur falls short by half of one per cent. The aciual deficit 

in the latter amounts, however, to about one per cent., for it was found 

that about half of one per cent, existed in the free state and could beextracted by carbon-disulphide. The only explanation of these contradictory circumstances was to be sought in the presence of oxygen salts, 

which would at the same time account for the difference between thesum total of the analysis and 100.

Ammonium acetate failed to extract any lead sulphate, but nevertheless pure water extracted a not inconsiderable quantity of soluble matter, even when the digestion was carried on in an atmosphere of carbonic acid. The filtrate showed neither acid nor alkaline reaction 

toward litmus paper. Silver nitrate produced no precipitate whatever, 

thus showing the absence of soluble chlorides or sulphides; but hydrogen sulphide threw down a copious orange colored precipitate of antimony trisulphide and the corresponding arsenic compound, entirely free 

from lead. Barium chloride produced a slight precipitate of barium 

sulphate. The antimony consequently existed in solution in an oxidized state that of trioxide as shown by evaporating some of the 

original solution with hydrochloric acid and adding potassium iodide* 

The manner of combination was not ascertained, but from the presence 

of alkalies this seems pretty certainly indicated. The salts, whatever 

they may be, are not very readily solub'e, for six digestions with warm 

water in an atmosphere of carbonic acid were iusufficent to complete 

the extraction. The sulphur trioxide found was probably combined 

with lime.

These experiments show that a large part of the apparent loss in the 

analysis is to be made up by oxygen, which, by requiring a considerable proportion of antimony, arsenic, and sulphur for combination, 

brings the ratio of the elements actually constituting the zinckenite 

very near that required by theory. They also show that the specific 

gravity given above, even were it corrected for quartz, is too low. 

Suitable corrections for quartz, free sulphur, and soluble salts would 

undoubtedly increase the specific gravity to the figure given in textbooks, i. 0., 5.3-5.35.

The above method of examination and its results have been dwelt upon 

somewhat in detail, because they show so clearly that apparent homogeneity in the case of non-crystallized metallic sulphides is no criterion of 

their purity, and also because thereby is indicated a possible way of reconciling with some definite formula the results of many analyses, especially of massive uncrystallized metallic sulphides, like the one here de-

(312)
CROSS AND HILLEBBAND.] COSALITE. 95

scribed, whose position in a system of classification might otherwise be 

impossible of precise determination. (See also Guitermanite, p. 106.)

COSALITE.

In the collection of the Colorado Scientific Society are a few specimensof a mineral from the Comstock mine, near Parrott City, La Plata 

County, Colorado, presented by Mr.'E. C. Hills, according to whom it 

occurs in a quartz vein associated with pyrite, sphalerite, a telluride of 

unknown composition, though probably sylvanite, and native gold. In 

the specimens examined it appears in irregular masses of small size,. 

rarely an inch in length, and generally much smaller, without cleavage 

or recognizable crystalline structure except for an occasional faint indication of fibrous texture on fractured surface. The fracture is irregular j. 

color, grayish white, but pale yellow on exposed surfaces j hardness,, 

about 3.5; specific gravity undetermined.

The outer zone of the small bodies Spoken of is found on close examination to be a mixture of two or more minerals, amoug which minute 

grains of pyrite were alone recognizable. Sufficient material was, however, obtained for analysis, free from all impurity, except a little pyrite 

and 1.29 per cent, of insoluble gangue. This afforded the following reactions: In closed tube, sublimate of sulphur; in open tube, formation 

of sulphur dioxide; on charcoal, fusible, giving reactions for lead, bismuth, silver, and copper; soluble in chlorhydric and nitric acids, in theformer with precipitation of silver chloride.

The analysis, after deduction of the gangue. gave these results:

Bi. ........... ..............

Ag .........................

Cu...... ....................

Pb..... ................. ....

Fe...... ....................

Zn... ....... ................

s...... .....................

XLVIII.*

42.93

8.43

7.50

22.49

0.70

17.11

99.16

* The following atomic weights are used: Bi. 208, Ag. 108, Cu. 63.4, Pb. 207, Fe. 56, S. 32.

Allowing for the iron and a proportionate amount of sulphur as pyrite,. 

the atomic ratio deduced from the above is:

E : Bi2 

2.00 :' 1.00

S 

4.94

showing the general formula for the mineral to be 2 ES+Bi2S3 , wherein 

E represents Pb and the double atoms Ag2 and Cu2. The ratio of 

Ag2+Cu2 : Pb is 1: 1.11.

Although copper was absent, and but 2 per cent, of silver present in 

the mineral originally described by Genth as cosalite, it does not appear

(313)
MINERALOGY OF THE EOCKY MOUNTAINS. [BULL 20.

advisable, in the absence of any data as to the crystallographic form, 

to consider this a distinct species, but to class it, as has been done with 

fojelkite, under cosalite.

HUBNERITE.

In the collection of the Colorado Scientific Society are specimens of 

ihiibnerite from the Royal Albert vein, Uncompahgre district, Ouray 

Oounty, Colorado.

The mineral occurs in long flattened crystals vertically striated, imbedded in quartz, but none sufficiently well formed for measurement 

 could be extracted; in fact, definite faces are rarely visible, though two 

prisms and the orthopinacoid have been observed. The lustre is subvitreous to resinous, and the color brownish black to pale yellow in very 

thin crystals. ID transmitted light the color is ruby red to yellow, 

slightly tinged with greeu when the thickness is not too great. Extinction takes place parallel to the vertical axis in a plate parallel to 

the orthopinacoid, and at an angle of 19° to 20° to the same axis in a 

cleavage section parallel to the clinopinacoid, as observed by Des Cloizeaux for wolframite. In the plates parallel to the orthopinacoid a 

tendency to cleave at right angles to the clinopinacoid and also at 

angles approximating 61° and 68° to the same face was observed. The 

specific gravity at 24° 0. is 7.177, and the composition as follows:

SiO» ........................

Nb206 (1).... ..............

W03 . ............ ..........

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

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

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

XLIX.

0.62

0.05

75.58

23.40

0.24

0.13

100. 02

Which agrees very closely with that required by theory for the formula 

MnWO4.

This mineral is also found in a mine near Phillipsburg, Montana, 

according to Mr. Richard Pearce. The specimens in the collection of 

the Colorado Scientific Society show large flattened crystals of imperfect 

form in quartz. Mr. A. H. Low, chemist at the Boston and Colorado 

 Smelting Works, has analyzed the mineral approximately and found:

WOs.... ....................

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

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

74.82

25.00

0.06

99.88

Other localities of occurrence in Colorado are James town, in Boulder 

Oounty, and near Silverton, in San Juan County.

(314)
 CBOSS AND HILLEBBAND.] BINDHEIMITE KAOLINITE. 97

BINDHEIMITE.

A specimen of bindbeimite from a claim near the Bertrand mine, 

 Secret Canon, Nevada, came into possession of tbe Colorado Scientific 

Society, and was analyzed in .tbe laboratory of tbe Survey. The specimen was compact and devoid of crystal for in, except for a few minute 

crystals impossible of identification. The color, in general a yellowish, 

.green, was in places lemon yellow. Tbe specific gravity at 19° C. was 

.5.01, after allowing for 4.59 per cent, of quartz of 2.65 specific gravity, 

and 20.33 per cent, of cerussite of specific gravity 6.5. The following 

.are the results of analysis :

PbO.........................

CuO. ................... .....

ZnO ..........................

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

MffO. ...... ................... K-,0 ..........................

NazO... ......... .............

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

SbaOs .........................

FezOs.. .......................

Ag...... ...... ....... ........ 

COi....... ....................

a.

49.68

0 *\ti

0.17

0.66

0.03

0.14

0 91

5.86

35.18

0.09

0.29 

3.35

4.59

100. 83

L.

6.

49.32

0.59 0 19

5.87

35.21

"3.36

Mean.

49.50

0.58

n is

0.66

0.03

0.14

0 91

5.86

35.20

0.09

0.29 

3.35

4.59

100. 68

Of the water 1.95 per cent, escaped over sulphuric acid, and a further 

0.70 per cent, at 100° C. Tbe oxygen ratio derived from tbe above, excluding PbCO3 , Ag, and Fe2O3, is:

EO: Sb2O5 : H2O 

3.14: 10.00: 5.92

If that water which escapes over sulphuric acid be considered true 

hygroscopic water, the ratio becomes 3.14:10.00:3.98. The first of 

these ratios corresponds to the formula 3 PbO, 2 Sb2O5 , 6 H2O, while 

-the second is represented by 3 PbO, 2 Sb2O5,4 H2O.

KAOLINITE.

In the American Journal of Science, Vol. XXVII, 1884, p. 472, Mr. 

U. C. Hills gave a short description of the material whose chemical composition is discussed below. The mineral appears as'a white or strawcolored powder, composed of minute scales, and occurs in certain vuggs 

or cavities in a quartz vein material, inclosed in a large mass of eruptive rock, of which it is an alteration product. Barite, galena, and occasionally other ore minerals are associated with the kaoliuite. The 

National Belle mine, on Bed Mountain, near Silverton, San Juan 

County. Colorado, is the original and principal locality for this mineral. 

Bull. 20 7 (315)
MINERALOGY OF THE ROCKY MOUNTAINS.

Under the microscope the powder resolves into a multitude of most 

perfect transparent crystals of hexagonal form, but evidently of the 

rhombic system, as shown by the optical action. They present a predominant basal plane, but also very distinctly a rhombic pyramid and 

a brachydome of very similar development, thus maintaining the resemblance to a hexagonal form. Figures illustrating these crystals 

accompanied Mr. Hill's description.

CHEMICAL COMPOSITION. The material examined contained a number of black grains as an impurity, and was of a very faint straw-yellow color, from a thin coating oi? limonite. The latter was mostly removed by hydrochloric acid and the former by stirring up with water 

in a beaker, allowing the glass to stand for a moment and then pouring 

off what had not yet settled. The residue was again treated in a similar 

manner. From the decanted portion a very pure product was obtained,, 

of brilliant whiteness.

The fine flakes, when suspended in quantity in water, impart to the 

latter a most beautiful satiny appearance.

At 18£° C. the specific gravity of the purified substance is 2.611. Before the blow-pipe intumescence takes place, but no fusion whatever. 

Strong boiling hydrochloric and sulphuric acids exercise little solvent 

action. The following are the results of analysis:

Si02 ........................

AlsOs. ......................

FesOs...- ...................

HzO ........................

F. ..........................

LI.

46.35

39.59

0.11

13.93 *0. 15

100. 13 

.06

100. 07

*As mean of 0.17, 0.14, and 0.14.

The Fe2O3 comes undoubtedly from limonite which had not been entirely removed by hydrochloric acid.

None of the water escapes at a temperature of 330° C.; it is therefore probably all basic water. The text-books mention half the water 

of kaolinite as probably basic. If this is true, a marked distinction,, 

aside from that occasioned by the presence of fluorine, exists between 

this mineral and kaolinite. Frenzel has described a variety of kaolin 

(myelin),60 which loses none of its water until a very high temperature 

is reached.

This point should be carefully observed in future examinations of 

similar minerals, for upon the confirmation of such a difference as that 

mentioned, coupled, perhaps, with the presence of fluorine, there would

^Naumann-Zirkel, Mineralogie, llth ed., p. 676. 

(316)
ciioss AND IIILLKBBAND.] PSEUDOMORPH NATIVE LEAD.

be necessitated the separation of such minerals as the present one and 

myelin from kaolinite.

A CHBOMTFEBOCTS PSETTDOMOBPH.

From the Eochelle mine, on Running Water River, Wyoming Ter 

ritory, there was obtained a single fragment of a dark green mineral, 

apparently a pseudomorph. Although crystal planes were visible, as 

well as more than one direction of cleavage, the identity of the original 

mineral could not be ascertained, partly owing to the cutting of artificial 

faces. In one direction, parallel to one of pronounced cleavage, a distinct lamination was observable. Edges and thin<> flakes were translucent. The lustre was greasy, and the color of the powder apple-green. 

Specific gravity at 12£° 0., 2.831. Hardness about 3. Analysis gave:

SiOs ........................

AlsOa. ......................

Cn08 .. .....................

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

K20 ........................

H20 ........................

LIT.

45.54

37. 15 I

0.795

0.38

10.70

0.90

4.80

100. 26

45.24

38.07

0.34

It is evident from the analysis that the product of alteration is allied 

to muscovite. With substitution of Fe203 for Cr2O3 the composition 

agrees almost exactly with that of the pseudomorph liebenerite.

NATIVE LEAD.

W. P. Blake describes in the American Journal of Science, Vol. 

XXV, p. 161, native lead occurring on galena, from the Jay Gould 

mine, Wood River district, Idaho Territory. A specimen of this occurrence in the collection of the Survey shows metallic lead, without any 

galena, running through a mass of quartz rock (the latter stained reddish, perhaps from minium). The quartz is somewhat cracked, and 

the several pieces are held in place by filaments of lead. A white coating of lead carbonate appears in a few small cavities. The lead is 

argentiferous.

(317)
MINERAL SPECIES FROM COLORADO.

By W. F. HlLLEBRAND.

ZTTNYITE.

The Zuiii mine on Anvil Mountain, near Silverton, San Juan County, 

Colorado, has furnished to science two new minerals, one of them being 

of a remarkably interesting nature.

A portion of the ore from this mine, as represented by two specimens, 

for the use of which I am indebted to Mr. Franklin Guiterman, consists, 

when unaltered, of an uncrystallized sulphide of lead and arsenic, upon 

broken surfaces of which appear numberless projecting glassy faces of 

tetrahedra of the regular system. On destroying the sulphide by nitric 

or nitro-hydrochloric acid, washing thoroughly by decantation, and 

finally employing a solution of high specific gravity to effect separation 

from a very small amount of barite and whatever other lighter or heavier impurities may be present, a product is obtained consisting of fine

crystals on which the predominant form is r., generally modified by

Li

TJ, and frequently also by oc 0 cc and ^ (Whitman Cross). While

goniometric measurements of the tetrahedral angles by Mr. Cross varied frequently within a degree from the normal, this must have been 

owing to surface irregularities, for generally the crystals are entirely 

without action on polarized light, and can therefore belong to none but 

the regular system, although a few show very faint polarization due to 

interior tension (Cross).

Their, size varies from that of extreme minuteness to a diameter, in 

rare instances, of 6 millimeters. The smallest of the crystals are generally quite clear and transparent, but the vast majority carry more or 

less uncrystallized, unmagnetic, black inclusions, the nature of which 

the microscope does not reveal. .Repeated preliminary tests showed 

that these were in no respect similar to the sulphide in which the crystals had been imbedded, being practically insoluble in the strongest 

acids, with the exception of hydrofluoric acid. The tetrahedra themselves, even in fine powder, are also unaffected by any acids other than 

hydrofluoric, and even with this acid the action is very slow. Fusion 

with potassium hydrosulphate effects decomposition in time, and with 

alkaline carbonates quite readily.

The lustre is glassy, cleavage octahedral, hardness about 7, and the

specific gravity in the case of two different lots, carrying in so far as

could be judged the same amount of inclusions, was 2.906 and 2.894, at

18£° C. and 20° C., respectively. By diluting a portion of the Thoulet

e 100 (318)
ZUNYITE, A NEW MINERAL. 101

solution until a few minute crystals free from black specks remained 

suspended in the liquid, and then taking the density of the latter by a 

Mohr balance, the specific gravity of the pure mineral was found to be 

2.875 at 150 C.

The influence of the inclusions upon the specific gravity was not 

sufficient to allow of effecting anything like a complete separation, by 

the employment of a solution of high density, of pure matter from that 

carrying inclusions, even when finely powdered. For although the portions first falling consisted of the largest and blackest crystals or fragments, and each succeeding precipitate was of a slightly lighter shade,, 

the last was still noticeably dark and by no means pure. The difficulty 

of separation in this manner was further enhanced by the fact that 

much of the material from which the portions taken for final analysis 

were obtained was more or less altered and consequently of lower 

specific gravity, the result being that the pure crystals and slightly altered Ones Containing many inclusions fell together. After very great 

labor, however, enough material for final tests was obtained by handpicking under the loupe. This showed no signs of alteration and but 

here and there a minute black speck.

Qualitative analysis of less pure material showed the presence of 

silica, titanic oxide, alumina, ferric oxide, soda, potassa, lithia, fluorine, 

chlorine, phosphorus peutoxide, and water. When heated in a tube 

acid water which attacked glass was given off. Whole crystals when 

heated sometimes decrepitated, and always became opaque and ptjrcelain-like, but showed no sign of fusion in the hottest blow-pipe flame.

On account of the hardness, which rendered grinding in an agate 

mortar uuadvisable, the sample was crushed in a steel mortar, the metal 

from the latter extracted by hydrochloric acid, and, after washing thoroughly by filtration, the finest portions were separated from the coarse 

by levigating with water. The most impalpable powder was reserved 

for alkali tests.

In these, decomposition was effected by igniting with three parts of 

bismuth oxide for half an hour at a dull red heat. Treatment with hydrofluoric acid would have required several days for the decomposition 

alone, and it is improbable that the Lawrence Smith method would have 

succeeded well. Lithia could not be quantitatively estimated, although 

the spectroscopic evidence of its presence was strong.

Silica, alumina, ferric oxide, titanic oxide, and fluorine were generally 

estimated in the same portion, and, in one instance, also chlorine and 

phosphorus pentoxide. Fusion was made with potassium carbonate. 

After separation of silica, alumina, etc., in the usual manner, the phosphoric acid remaining in solution was removed by silver nitrate. The 

fluorine was not calculated from the weight of calcium fluoride obtained, 

but from the difference between this weight and that after conversion 

into sulphate. In one instance (analysis LV, below) a considerable 

amount of pure silica was added before fusion with alkaline carbonate,

(319)
102 MINEEALOGY OF THE EOCKY MOUNTAINS. [BULL. 20.

and here somewhat more fluorine was found than when no silica was 

added. Silica was always examined for phosphoric as well as for titanic 

acid when the latter was known to be present.

The solution containing ferric (titanic) and phosphoric oxides and 

alumina was divided into two parts, in the one of which the phosphorus was determined, in the other the weight of the combined oxidesThe latter were brought into solution by fusion with potassium hydrosulphate; the titanic oxide if present was then thrown down by boiling 

in presence of sulphurous acid, and the iron was precipitated as sulphide 

from a tartaric acid solution and subsequently weighed as oxide. The 

alumina was found by difference.

Beryllia was carefully tested for by digesting the alumina and ferric 

oxide (introduced as chlorides) for several days with ammonium carbonate in excess. The very slight amount of matter found then in solution proved to be alumina.

Chlorine was estimated in a separate portion by precipitating as silver chloride in a platinum dish, after leaching the alkaline carbonate 

fusion and acidifying the filtrate with nitric acid. As a precautionary 

measure the chloride was then dissolved on the filter with ammonia and 

reprecipitated by nitric acid, after which it was collected and weighed 

in a Gooch crucible. In one instance the silver chloride thrown down 

before precipitating the fluorine as calcium fluoride was weighed and 

found to tally very closely with the results obtained on separate portions.

Water was estimated by heating the mineral with dry sodium carbonate in a glass tube and collecting in a weighed calcium chloride tube.

The results upon the purest material were as follows:

LIIL 0.9055 gram gave 0.2200 SiOa, 0.0018 FesOs, 0.5230 AhOs, and 0.0466 F. 

LIV 1.1568 gram gave 0.2817 SiUs, 0.0022 FesOa, O.C710 AhOs and 0.0613 F. 

LV. 0.843C gram gave 0.4882 Als03 , 0.0018 Fe2 03, 0.0054 PaOs, 0.0244 Cl and 0.0473 F. 

LVI. 0.6512 gram jjave 0.0058 Mpul^Or, hence 0.0037 P2 0s. 

LVII. 1.0039 gram gave 0. 0060 KC1, NaCl and trace LiCl, 0.0052 KjPtClc, whence 0.0016 KC1 and

0.0044 Nad, LiCl, or 0.0010 K20 and 0.0023 Na*0, LisO. 

LVIII. 1.0042 gram gave 0.0064 KC1, NaCl, LiCl, 0.0052 KsPtCle, whence 0.0016 KC1 and 0.0048

NaCl, LiCl, or 0.0010 K2 0 and 0.0025 NasO, LisO. . LIX. 0.7022 gram gave 0.0824 AgCl, whence 0.0204 Cl. 

LX. 0.7505 grain gave 0.0891 AgCl, whence 0.0220 Cl. 

LXL 0.5073 gram gave 0.0552 HzO. 

LXII. 0.4021 grain gave 0.0439 H20. 

LXIII. 0.3502 gram gave 0.0381 EbO.

SiOz .....

AhOs..-.- 

KsO.... ..

"Wo^n

LhO......

HsO......

PaOfi......

F. ........

Cl

LHI.

24.30

0.20

57.76

5 11

LIV.

24.36

0.20

58.00

5.30

Less O for F and Cl

LV.

0.21

57.87

0.64

5.61

2.89

LVI.

0.57

LVII.

o.io

0.23

LVIII

0.10

0.25

LIX.

2.90.

LX.

2.93

LXL

10.88

LXTI.

10.92

LXIII.

10.88

Mean.

24.33 

0.20 

57.88 

0.10 

0.24 

trace. 

10.89 

0.60 

*5.61 

2.91

102. 76 

3.02

99.74

* The highest figure for fluorine is here taken as probably nearer correct than the others, because of a possible analytical error in the latter having in this case been lessened by the addition of 

silica before making the alkaline fusion.

(320)
CKOSS AND HILLEBRAND.] FORMULA OF ZUNYITE. 1 03

In deducing a formula from these data the Fe203 and P2O5 may for 

reasons subsequently mentioned be neglected. Since none of the water 

escapes at 270°0, it may be assumed that it exists as water of constitution, or basic water, and it is perhaps to be reckoned with the small 

quantities of alkalies. The atomic ratio is then found to be: 

(H,K,Na) : Si : (A12) : (O,F2 ,C12 )

1.2208 :0.4055 :0.5674 : 3.1232 

or

18.06 : 6.00 : 8. L'9 : 46.21 

which is not far from

18.00 : 6.00 : 8.00 : 45.00

giving the formula E18Si6 (Al2)8(O,F2Cl2 )45 or 9 K2O, 6 SiO2, 8 A12O3 , with 

part of the oxygen replaced by fluorine and chlorine.

The Fe2O3 of the above analyses came undoubtedly from a thin film 

of ferric oxide on the tetrahedral crystals which had not been entirely

removed by the various treatments with acids to which thty had been

subjected.

The P2O5 cannot well be a constituent of the tetrahedra and is probably derived from a small proportion of an admixed aluminium phosphate. The excess of alumina constantly found over that required for 

the above formula renders this the more likely. Evidence of the presence of an admixed phosphate was also obtained by direct experiment. 

In material not specially purified there were observed a few irregular 

.and generally dull grains which at first were supposed to be fragments 

of tetrahedra, perhaps slightly altered. Half a dozen of these, weighing in all less than 1 milligram, were picked out, crushed, fused with 

sodium carbonate, the fusion dissolved in nitric acid, and a few drops

 of molybdate solution added. A distinct yellow precipitate formed in a

 short time. Yet while the presence of an aluminium phosphate would, 

by lowering the aluminium of the above analyses, make the ratio Si:Al2 

nearer 6:8 than it has been shown to be, I am not at all certain that the 

discrepancy is hereby entirely to be explained. For the given amount 

of SiO2 only 55.19 per cent, of A12O3 is required, leaving 2.69 per cent, 

for combination with only 0.60 per cent, of P2O5. Moreover, the above 

.given ratio between SiO2 and A12O3 has been found by repeated careful 

.analyses not included in the above, made on entirely different samples, 

to be practically constant. It is therefore possible that the true formula 

is more complex than that given above, or that some source of contamination exists which has as yet escaped detection.61

61 After the above was ready for the press Mr. Cross communicated to me the following facts as the results of further microscopical examination:

" The zunyite has a polarizing inclusion, quite plentiful in a, few crystals, but lacking entirely in most of them. When mounted in balsam the dark impurities stand 

out very plainly, causing the crystals to seem much more impure than they really are. 

The polarizing substance cannot be identified, but it is too brilliant for apatite. It 

lias no good crystal form." This polarization, he further says, is distinct from that 

mentioned on p. 100, as occasionally shown by the zunyite itself. Hereby the opinion

 expressed above, that some foreign admixture was present, is confirmed.

(321)
104 MINEEALOGY OF THE ROCKY MOUNTAINS. [BULL. 20..

As a name for the mineral, Zunyite is proposed, after the mine from 

which it was obtained.

The black inclusions in the zunyite were shown to contain titanic 

oxide by the following partial analyses of dark crystals:

SiOz .................... ......

Ti02 ...... ............... ....

Ak08 - ........ ................

23.93

0.75

*58. 30

23.86

0.84

*58. 45

*Not freed from FezOs and PzOs.

In order to ascertain whether they consisted only of titanic oxide or of 

some titanate, an attempt was made to separate from the zunyite a quantity sufficient for analysis. It was soon found that this could be but 

very imperfectly accomplished and only by reducing large quantities of 

zunyite crystals to fine powder and then effecting the separation by 

means of the Thoulet solution. In this manner a mixture of barite, black 

particles, and attached zunyite was obtained, weighing, after thorough 

washing, but 0.5528 gram, which furnished the following results on; 

analysis:

SiOz .......................

TiOs.-.. .............. ....

AlzOs- .....................

FejOs -.-.-- ...............

PsOs.-.. ...................

HS0,F,C1, and loss. ........

LXIV.

83.90

1.50

8.60

3.33

0.20

2.47

100. 00

Since the silica and alumina bear to each other nearly the same ratio* 

as in zunyite, and since both fluorine and water were found to be present 

in small quantity, it is probable that all these were derived from 

attached zunyite, the perfect separation of which from the inclusionsis practically impossible even with the comparatively large amounts 

Operated upon. There remains then only titanic and a little ferric 

oxide, showing that the inclusions consist, in all probability, of titanicoxide alone.

By far the greater part of the zunyite-bearing ore seems to be in an 

advanced stage of decomposition. Through the kindness of Mr. J. A.. 

Porter, of Durango, Colorado, the Colorado Scientific Society is the possessor of about fifty pounds of this altered ore completely filled with 

zunyite. The original double sulphide has almost disappeared, being, 

changed into lead sulphate and other less well-defined compounds. 

While the zunyite is here in great measure still perfectly fresh, a considerable portion has been more or less altered, incipient change being 

indicated by a faint cloudiness through the crystals which, beginning, 

apparently at the centre, spreads outward and increases in degree 

until, as a final product, there ensues a dull white opaque substance 

retaining in a measure the outlines of the original crystal and showing: 

here and there a black grain of titanic oxide.

(322)
CBOSS AND HILLBBBAND.] GUITERMANITE, A NEW MINERAL. 105

It was from this partially-altered ore that the material for the complete analysis above given and for the investigation of the inclusions 

was obtained, as the specimens of unaltered sulphide were two small to 

afford sufficient material by hand-picking.

A knowledge of the composition of the result of alteration of zunyite 

seemed desirable; hence the lightest of all portions separated by the 

Thoulet solution, of specific gravity 2.45, was partially analyzed. The 

result was unsatisfactory, indicating a mixture of probably several substances, of which a little undeeornposed zunyite is known to be one, but 

the general character of the chemical change is in a measure shown.

SiOs .......................

AbOs. ............. ........

FezOs.. ....................

CaO(SrO»)......... ........

ZnO. ......................

KaO...... .................

MazO(LisO). ...............

P20s.. ...................

AssOs. .....................

SO,. .......................

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

Cl...... ....................

LXV.

58.47

22.03

0.27

1.70

0.20

0.53

2.21

0.40

4.52

0.91

9.32

100. 00

Some of the constituents, as the As2O5 and ZnO, have evidently been 

derived from the sulphide ore in which the mineral was imbedded.

GUITEBM ANITE.

The metallic sulphide forming the matrix of the zunyite, of which in 

a fresh state, as before observed, but two specimens were at disposal, 

is of a bluish-gray color, possesses light metallic lustre, and a hardness 

of about 3 011 places free from included zunyite. A small amount of 

pyrite is visible in spots.

Heated in the closed tube it fuses readily and there appears a slight 

sublimate of sulphur followed by a heavy one of arsenic sulphide; while 

on charcoal the usual reactions for sulphur, arsenic, and lead may be observed.

The following analyses were made:

A Q

Pb... ...............................................

Cu ................................................. AR ................................................. i^. .................................................

s.. .................................................

0...... ...... .................... . r ..... .......... ..

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

a.

1.77

13.50

63.40

0.17

0.02

0.42

19.65

LXVI.

b.

13.30

63.80

0.18

0.43

19.70

Mean.

1.77

13.40

63.60

0.17

0.02

0.43

19. 67

a.

3.81

13.00

61.65

0.17

0.02

0.87

19.67

O KK

LXVTE

6.

3.82

61.62

0.17

0.89

19. 45

Mean.

3.82

13.00

61.63

0.17

0.02

0.88

19.58

0.55

99.63

(323)
106 MINEEALOGY OF THE ROCKY MOUNTAINS. [BULL. 20.

Analyses LXVI a and & were first made, on material which had a 

specific gravity of 5.828 at 17£° 0. Corrected for admixed zunyite of 

specific gravity 2.9, this becomes 5.94. As the total could hardly be 

brought above 99 per cent., in spite of great care in analyzing, the cause 

of this was sought for and found as will be subsequently explained.

In the experiments (not of a quantitative nature) having this end in 

view the sample was exhausted, therefore fresh material was used for 

two subsequent analyses, LXVII a and &.

In both these and the previous ones the sulphur was found in excess of 

that required for the metals, on the assumption that all the arsenic was 

present as trisulphide and the iron as disulphide. TJhis was due to the 

presence of free sulphur, which was estimated quantitatively by extracting with carbon disulphide and carefully evaporating the filtrate to dryness in a weighed crucible. After three extractions no more sulphur 

was dissolved. The amount thus obtained represented 0.59 per cent, of 

the material used for analyses, LXVII, a and &.

While accounting completely and satisfactorily for the excess of 

sulphur, this did not explain the low vsummation shown in the first 

analyses. It was found, however, that notwithstanding the apparent 

purity of the mineral, lead sulphate was present in some quantity.

The sulphur trioxide of this was estimated by extracting the sulphate 

from the mineral by digestion with warm dilute hydrochloric acid in an 

atmosphere of carbonic acid, three or four digestions being sufficient 

for complete extraction, and, after partial neutralization of the filtrate, 

precipitating as barium sulphate. The result was 0.69 per cent. SO3 . 

The lead oxide of the sulphate could not be estimated in this extract, 

because even the dilute acid slightly decomposed the sulphide, taking 

lead but no arsenic into solution. Under the conditions of the experiment practically no hydrogen-sulphide could be oxidized in the short 

time required for making tlie extraction,

As a check, the lead oxide of the sulphate was estimated quantitatively by extracting the sulphate with neutral ammonium acetate in a 

closed flask, three or four digestions with fresh solution being sufficient, 

throwing down the lead as sulphide, and converting into sulphate before 

weighing. The percentage of lead oxide thus found was 2.70, instead 

2.61 required by the 0.69 of SO3 found. 2.61 of PbSO4 contains 1.78 of 

lead, 0.28 of sulphur, and 0.55 of oxygen. Thus the sum total was 

brought much nearer to 100.

Excluding now the lead sulphate, free sulphur, and pyrite, the following atomic values are obtained:

Pb.......... 59.854-207. =0.2891) n OQn , o o* nft AK Cu2 ......... 0.174-126.8=0.0013 [ 0'2904 3'35 10'05

As2 ......... 13.004-150. =0.0866 1100 3.00

S .......... 17.684- 32. =0.5525 6.38 19.14

These lead to the formula 10 PbS, 3 As2S3 . A simpler formula, and 

one not far removed from the above, is 3PbS, As2S3 . If a small quan-

(324)
CROSS AND HILLBBBAND.] . A PROBABLY NEW MINERAL. 107

tity of galena was present, of which, however, there was no evidence, 

other than that afforded by the decomposition of some lead sulphide by 

dilute hydrochloric acid without simultaneous solution of arsenic, the 

latter formula is probably the correct one. But this evidence is of little 

value, for any arsenic dissolved from the double sulphide would probably be immediately thrown down again by the hydrogen sulphide 

evolved. Whichever formula may be the true one, the mineral appears 

to be new to science, and a name, Guitermanite, is proposed, in honor of 

Mr. Franklin Guiterinan, who first called attention to this and the 

associated zunyite.

In conclusion, a few words will be in place respecting the occurrence 

of these two new minerals. According to Mr. Guiterman there appears 

to be no decided indication of a fissure vein in the Zuni mine, but the 

minerals occur in what seem to be pipe veins enlarged in places, the 

surrounding rock being probably andesite. In this and other mines of 

the region kaolinization of the country rock is a marked feature.

A PROBABLY ]STEW MESTERAL.

A portion of the ore from the Missouri mine, Hall's Valley, Park 

County, Colorado, is composed largely of a sulpho-bisrnuthide of copper 

and silver. It occurs in a quartz gangue associated with chalcopyrite 

and wolframite, and although the latter is only visible on close examination, it comprises from 1 to 2 per cent, of the whole, as found by special 

tests. A considerable quantity was extracted by chemical and mechanical means, free from all foreign matter except a little attached quartz, 

and was proven to be wolframite by qualitative chemical tests and by 

a determination of the specific gravity.

The mass of the sulpho-bismuthide appears throughout the quartz as 

a dark, bluish-gray substance without distinct forms of crystallization. 

In numerous cavities appear small slender crystals, generally bronzed 

by oxidation and so deeply striated as sometimes to present the appearance under the loupe of bunches of needles. Occasionally they seem 

to be joined together laterally forming thin corrugated plates. Owing 

to this deep striation no crystal faces can be detected either on the 

sides or the free terminations. The habit is strikingly like that of bismuthinite, for which the crystals were, indeed, at first taken.

After several days labor enough material was removed from the cavities for the determination of the metals. It could not, however, be 

freed altogether from quartz and chalcopyrite. The specific gravity at 

17° 0. was 5.75. Making correction for 4.43 per cent, of quartz and 

6.98 per cent, of chalcopyrite of assumed specific gravities 2.65 and 

4.2, this becomes 6.31. The analysis appears under LXVIII below.

The more compact material, excluding as far as possible the needles, 

gave, after deducting 59.75 per cent, of gangue, the results under LXIX.

(325)
108 MINERALOGY OF THE EOCKY MOUNTAINS. [BULL. 20,

LXX is the analysis of a mineral presented by Mr. William McCree 

as coming probably from the Missouri mine. In appearance it differs in no respect from the compact material already described, except 

that no chalcopyrite is distinctly visible in the small specimens at my 

disposal, and the quartz grains are less firmly cemented together. It 

contains, however, some lead, which is entirely wanting in the other 

specimens analyzed, although the general formula is the same; hence I 

am led to believe that it came from some other portion of the workings 

or from an adjacent mine where ore like that from the Missouri mine 

is reported to occur. The specific gravity was 3,869 at 15° C., which 

becomes 6.680 on making correction for 47.57 per cent, of gangue of 

ascertained specific gravity 2.643.

The most marked blow-pipe reactions for LXVIII, LXIX, and LXX, 

were entirely similar, a sublimate of sulphur appearing in the closed 

tube, sulphur dioxide escaping in the open tube, and the fused fragment 

or powder on charcoal affording the bismuth reactions with great intensity. All were soluble in nitric and hydrochloric acids, in the latter 

with precipitation of silver chloride.

Bi .........................

Ag. ........................

Cn. .........................

Pb. .........................

Pe.... .....................

Zn. ............ .............

s...:......... ..............

LXVI1L

60.74

0 80

15.96

2.13

0.10

*19. 94

99.76

LXIX.

63.36 i no

12.65

0.59

0.07

*18. 83

99.59

LXX.

62.45

9.89

6.68

2.74

0.10

0.07

17.90

99.83

*Calculated.

After subtracting from LXVIII 6.97 per cent.; from LXIX, 1.91 per

cent, and from LXX, 0.33 per cent, of chalcopyrite, with the proportions of sphalerite represented by the zinc, the atomic ratios become:

E

LXVIII. 3.00 

LXIX. 3.00 

LXX. 3.00

Bi 2 

3.95 

4.03 

4.10

S.

14.75. 

14.98. 

15.15.

where li represents Pb and the double atoms Ag2 and Ou2. In each 

case the ratio is nearly 3 : 4:15? which leads to the general formula 

3ES + 4Bi2S3.

It seems probable that the needle-like crystals are a pure sulphobismuthide of copper, and that in the more compact portions silver replaces a part of the copper, and in some cases a further replacement of 

copper by lead takes place.

(326)
CROSS AND HILUSBBAND.] A PROBABLY NEW MINERAL. 109

This ore from the Missouri mine is auriferous. The material used for 

analysis LXIX, gangue and sulphide together, assayed 1.85 ounces gold 

to the ton. According to Mr. Pearce, of the Boston and Colorado Smelting Works, it was frequently much richer, running as high as 40 ounces 

to the ton.

Before conferring a name upon this mineral, or even definitely claiming it as a new species, further investigation is advisable. A personal 

visit to the Missouri and other neighboring mines in October, 1884, in 

the hope of obtaining better material, was not rewarded with success.

(327)

INDEX.

Page.

Analcite .................................................................. 27

Apophyllite ........... ...... ............................................ 29

Aragonite...........1................:.................................... 39

Basalt of Table Mountain ................................................. 13

Bindheimite .............................................................. 97

Bole...................................................................... 38

Brandl, J., Analysis of pachnolite by; quoted .............................. 54

Analysis of prosopite by; quoted............................... 63

on chemical composition of minerals of the cryolite group....... 43

Calcite.................................................................... 39

Casaiterite................................................................ 74

Chabazite ................................................................ 23

Chalk Mountain, Colorado, Nevadite of..................................... 75

Chenevixite .............................................................. 85

Chlorine in zunyite ........................................................ 102

Chromiferous pseudomorph, A............................................. 99

Colorado Scientific Society, -Specimens from collections of................... 94,95,96

Conichalcite ......................................................... .... 64

Cosalite ...... ...... ....................................................... 95

Cross, Rev. R. T., Note on Topaz from Devil's Head Mountain by .......... 72

Cryolite .................................................................. 41

Crystal Park, Phenacite from.............................................. 68

Topaz from ..................... ............................ 70

Desmin .... ...... ......................................................... 19

Devil's Head Mountain, Occurrence of minerals from; W. B. Smith......... 73

Topaz from........................................ 72

Elpasolite, a new mineral.................................................. 57

Erythrite from Gunnison County, Colorado ................................ 89

Evigtokite (= Gearksutite) ............................................... 61

Flight, W., Description and analysis of evigtokite, by...................... 61

Florissant, Phenacite from near .......................................... 69

Topaz from near............................................... 71

Fluorine in kaolinite .......................... ...... ...................... 98

in zunyite........................:............................... 102

Fluorite .................................................................. 74

Gearksutite .......... .................................................... 58

Granite of Pike's Peak region.............................................. 41

Groth, P., on cryolite groiip............. .................................. 43

Guitermau, F., Mineral specimens from .................................... 100

Guitermauite. a new mineral .............i..........^..................... 105

Hagemann, Analysis of gearksutite by, quoted............................. 58

Analysis of pachnolite by, quoted ............................. 52

Hills, R. C., Description of kaolinite by.................................... 97

Hubnerite ...................:............................................ 96

(329) 111
112 INDEX.

 I'age.

Jarosite........................................... ..................... 86

Kaolinite from National Belle mine........................................ 97

from Saiut Peter's Dome ......................................... 67

Klein, C.,on analcite from Table Mountain, Colorado...................... 28

ou apophyllite from Table Mountain............................. 29

Knop, Analysis of pachnolite by, quoted ................................... 52

Konig, Analyses of pachnolite and thomsenolite by, quoted................. 52

Lasaulx, A. von, on stilbite................................................ 20

Laumontite............................................................... 16

Lead, Native.............................................................. . 99

Levynite .......... .................1..................................... 37

Liebenerite, A pseudomorph allied to ....................................... 99

Lollingite..----..-.....---................................................ 89

Low, A., Analysis of hiibnerite by .......................................... 96

Lustre, On the, exhibited by sanidine in certainrhyolites.................... 75

Massive ore consisting of mixed arseniates ................................. 86

Mesole, Kelatiou of thomsonite to... .......... ............................. 26

Mesolite .................................................................. 35

Microcline (Amazonstone) ................................................ 74

Miigge, O.,on twin structure of cryolite.................................... 43

Muscovite, Analysis of mica allied to ...................................... 68

Natrolite.................................................................. 36

Nevadite of Chalk Mountain, Colorado........................... i ......... 75

New minerals from Colorado............................................... 100

A probably new mineral-.............................................. 107

Guitermanite ....................................j..................... 105

Elpasolite ............................................................ 57

'Zunyite.'............................................................... 100

Olivenite ................................................................. 83

Optical anomalies of analcite............................ ....<.............. 27

apophyllite .......................................... 29

Oxygen salts mixed with metallic sulphides a source of error in analysis.... 93,106

Pachnolite................................................................ 49

Pearce, R., Specimens from ................................................ 83

Analyses by................I...................................86,87,88

Phenacite from Crystal Park ..............................,.:............. 68

from Florissant ................................................... 69

Pike's Peak, Minerals from the neighborhood of............................ 40

Prosopite ................................................................. 62

Pseudomalachite, identified in Montana by R. Pearee....................... 88

Pseudomorph, A chromiferous.............................................. 99

Eagged Mountain, Lustrous sanidine from.................................. 77

Ralstonite ................................................................ 56

Rath, G. vom, Analysis of pachnolite by, quoted............................. 52

Reusch, E.,0n the cause of chatoyant colors in feldspars.................... 79

Safflorite,Possible relation of lollingite to ................................. 93

Saint Peter's Dome, Occurrence of fl uorides near ........................... 41

Sanidine, On the lustre exhibited by....................................... 75

Scolecite............................... r .................................. 36

Smaltite ....................°.............................................. 89

Smith, W. B., on occurrence of minerals at Devil's Head Mountain.......... 73

Stilbite ...................... ............................*................... 19

Sulphur found in massive sulphides, Native ................................ 93,106

Table Mountain, Description of............................................ 13

Thomsenolite .... .... ......... . ... - .................. 55

(330)
INDEX. 113

	Page. 

Thomsonite............................................................... 18,24

Titanic oxide in zunyite.................................................... 104

Topaz from neighborhood of Pike's Peak ...........................:....... 70

from Devil's Head Mountain (W. B. Smith).......................... 73

in nevadite of Chalk Mountain...................................... 81

Trippke.P., on crystal form of phillipsite.................................. 22

Twin structure of cryolite................................................. 43

stilbite..........................................:...... 19

Utah,On associated rare minerals from .................................... 83

Wohler, Analysis of thomsenolite by, quoted................................ 52

Xeno time............................................ _.................. 40

Yttrotantalite............................................................. 40

Zeolites, Manner of occurrence in Table Mountain.......................... 14

Order of deposition in Table Mountain............................ 15

Zinckenite................................................................ 93

Zircon.................................................................... 66

Zunyite; anew mineral.............................___.......____ 100

(331)
EXPLANATION OF PLATE.

Fig. 1 illustrates the twin structure and optical properties of stilbite, seen in clinopinacoiclal section, as described by von Lasaulx. See text, p. 20.

Fig. 2 illustrates the twin structure and optical properties of stilbite from Table Mountain, in corresponding position to that of Fig. 1. See text,'p. 21.

Fig. 3 illustrates the twin structure and optical properties of phillipsite, as described 

by Trippke. See text, p. 23. ' x

Figs. 4,5, and G show the optical anomalies observed in the apophyllite of Table Mountain, by C. Klein. See text, p. 30.

Figs. 7,8,9, and 10 illustrate the polysynthetic twin structure observed in'the cryo- 

 lite of Saint Peter's Dome. See text, pp. 43-47.

Fig. 11 represents the crystal form of prosopite from Saint Peter's Dome. See text, 

p. 63. '

Fig. 12 represents a crystal of phenacite from Crystal Park, natural size. See text, 

p. 68.

Fig. 13 shows the position of the parting which produces the lustre of the sanidine 

in the nevadite of Chalk Mountain. See text, p. 76.

Fig. 14 the fundamental form of lollingite. See text, p. 90.

Figs. 15 and 16, forms of lollingite, observed in the material from Gunnison County, 

Colorado. See text, p. 90-91.

Figs. 17,18,19,20, and 21 represent different forms of a rhombic arsenide of iron, 

cobalt, and nickel, observed iu association with lollingite, Gunnison County, Colorado., See text, p. 91. 

114 (332)
U. 8. GEOLOGICAL SURVEY

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BULLETIN NO. 20 PL. I

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CoP

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COLORADO MINERALS.