CONTRIBUTIONS TO CRYSTALLOGRAPHY:CLAUDETITE; MINASRAGRITE; SAMSONITE; NATIVE

SELENIUM; INDIUM

Cuenros PalacHn, H araard Uni,ttersity.

CLAUDETITE

Our knowledge of the crystal form of the oxide of arsenic, claude-

tite, rests chiefly on the study by Schmidtl of crystals formed as

the result of a mine fire at Szomolnok, Hungary' The crystals

measured by Schmidt were mostly paper thin and striated so that

the values recorded are not altogether reliable.

Crystals of claudetite from two sources have recently come into

the hand.s of the author and proved to give such constant and con-

sonant measurements that new elements have been based upon

them. I am indebted to Mr. wilke of Palo Alto for this material.

(o) Cr-auonurE FRoM lupBnral Co., Car,rnonNra:-The hand

and up to 4 mm. long. With the claudetite are crystals of sulphur'

Two crvstals were detached from the wall of a cavity without

distorting them, the extraordinary softness and ease of cleavage

of the mineral making this a matter of great difficulty.

Two excellent crystals were measured, and the angles obtained

from these crystals are shown in the following table.

(D) CrauonurE lRoM Jnnolrn, AnrzoNe:-A small cavity 3 cm'

across lined with beautiful silky crystals of claudetite comes from

the United Verde Mine and is undoubtedly a product of the mine

fire.2 The crystals are plates or laths, terminated only at the free

ends and measuring at maximum 3 by 10 mm. with thickness less

than .5 mm. Both prism and terminal faces give excellent measure-

ment. Four crystals were measured, one of which was a twin on

(100). Table I presents the angles obtained from the claudetite

crystals of both localities.

I Zeit. I?ist., voi. 14, p. 575, 1888.2 See Lausen, C., Hydrous Sulphates formed under Fumarolic conditions at

the United Verde Mine: Am. Mineral', vol. 13, p. 2O3' 1928'

t94

TOURNAL MINERALOGICAL SOCIETV OF AMERICA 195

Tnsrn I

A-Crystals from Imperial Co., California

No. ofForm faces 6

110 5 67"38'101 2 90 00T11 I -66 01111 4 69 24

B-Crystals from Jerome, Arizona

1300 1 1101r01T111 1 1121

p

90'00'37 5140 334449

90 0020 0443 00.t / .).t

40 2944 4846 15

38 4s+12 0089 43

-90 14-65 52

69 2s-48 24

Range <|

67'29',-67"53',89 49 -90 01

69 24-69 25

37 t2 -39 10

89 35 -89 5089 04 -90 3064 43-67 0269 09 -69 3248 00-48 49

Range p

37"47',-37"5s',

M 44-M 53

37 38 -38 0640 17 -40 45u 4045 0346 13 46 18

1022i

1062

The projection elements were calculatedof each locality with the following results:

separately for crystals

Po'qo'

e '

lL

Imperial Co.

.8547

.3487

.075385'41',

Jerome

.8572

.3499

.076185"38',

Mean

.85595

.3493

.07s895040'

From these mean values the following elements are calculated,with which in adjoining column are the elements of Schmidt.

Er,rurNrs op Cr,Lunttrtn

Palache

a:0 .4092 1o :0 .8535c:0 .3493 qo :0 .34839:94"20' p:85"40'

Table II gives the calculated position and interfacial angles ofall known forms of claudetite together with some of the observedangles oI Palache and Schmidt" The table is based on Palache'selements.

Schmidt

a :0 .4040 Po:0 .8527c:0 .3445 qo :0 .34379:93"57' p:86"03'

THE AMERICAN MINERALOGIST

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JOURNAL MINERALOGICAL SOCIETY OF AMERICA

It will be noted in this table that the aqreement of calculatedposition and interfacial angles with observld angles is for almostall forms excellent. Reference to Schmidt's article will show fur-ther that for interfacial angles his measurements agree better inall cases with the calculated values from the new elements thanwith his own calculated values. There seems no doubt that the newelements are established.

The habits of the claudetite crystals from the two new localitiesare shown in figures I and 2.

Frc. 1

Claudetite, Imperial Valley, Calif .

F rc .2

Claudetite, Jerome, Ariz.

MINASRAGRITE

Minasragrite is a highly hydrous sulphate of vanadium first de-scribed and named by Schaller.s As the name implies, the mineral

3 Schaller, W. T., Minasragrite, a hydrous sulphate of vanadium: Wash. Acad,.Sci . Jour. , vol .7, p.501, 1917.

198 THE AtrIEMCAN MIN ERALOGIST

was found at the vanadium mine at Minasragra, Peru, where it

occurs as a blue incrustation on patronite. Schaller described the

physical properties of the new mineral and assigned to it the form-

ula VzOa.3SOB.16H2O. He found no measureable crystals but de-

termined from its optical properties that it was monoclinic or

triclinic.Specimens of patronite in the Harvard mineral collection, which

in the course of many years have become coated with various al-

Frc. 3. Minasragrite

teration products, showed in places a vivid blue incrustation

which proved to be minasragrite. The crust is composed of minute

but very perfect crystals forming an open net work which falls

to pieces at a touch. Some of the tiny crystals are quite complete

anJ pro.red to be measureable. The two best which were completely

measured, have an average diameter of .2 mm' and a maximum

dimension of .25 mm. Notwithstanding their minute size the crys-

tals gave excellent reflections and proved to be monoclinic' The

habit of the crystals is shown in fi.gure 3. The measured and cal-

culated angles of the forms are contained in Table I. Table II

contains calculated interfacial angles.No close relation in form to any previously described sulphate is

apparent from these angles.Efiorts to prove the presence of any distinct cleavage were not

successful. The crystals were so minute that the handling of them

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JOURNAL MINERALOGICAL SOCIETY OF AMERICA

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2OO THE AMEKICAN MINERALOGIST

was difficult. There seems to be a tendency to break in the general

direction of the side sinacoid but with no true cleavage parallel to

that plane as Larsen suspected on optical ground.

SAMSONITE

The crystal form of samsonite has been described by three

authors whose measurements yield closely agreeing results. W'

Bruhnsa calculated elements from three angles between two forms'

His position differs from that adopted by later observers and

here used. Calculating his measurements to the new position, we

obtain the elements:-

a : 1 . 2 7 8 7 , c :0 .8204, F:92"42'

F. Slaviks gave a fuller description based on the measurement of

many crystals. His elements, derived from three angles between

three forms, are:-

a : 1 . 2 7 7 6 , c : 0 . 8 1 8 0 , F:92"46'

The third description is by F. Kolbeck and V' Goldschmidt,G who

measured. six crystals on the two-circle goniometer. The elements

calculated from their two best crystals are:-

a : 1 . 2 7 7 7 , c --0.8192, A:92"42'

The author measured. five crystals, also by the two-circle method

and his calculation yielded the elements:-

a : 1 . 2 7 8 6 , c : 0 . 8 2 1 7 , B:92"3+'

Since these four independent values for the elements are in such

close agreement, it was felt that the mean of all of them was better

than any one. This mean value is as follows:-

a : 1 . 2 7 8 2 ,Ps :0 '6414,

c :0 .8198 ,qs :0.8189,

B:92"4I 'y ' :87" 19'

An angle table was calculated from these elements and has been

published elsewhere.T Table I contains the position-angles for all

a Kristallform des Samsonit von St. Andreasberg, Itrl Jahresb' il. Niedersdchs'

geol,. V ereines, E annoaer, l9ll.5 Morphologie des Samsonits, Bull. internat. iJe l'ocad" des sciences de Bohame,

1911, p. 16.s Ueber Samsonit von Andreasberg, Zeit. Jiir Krist-, vol,50, p. 455, 1912'7 Crystallographic Angle-Tables, 1933. Dept. of Mineralogy, Harvard univer-

sity, privately printed.

,TOURNAL MINERALOGICAL SOCIETY OF AMERICA

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TH E AM ERICAN MI NERALOGIST

the forms hitherto observed and, for the forms observed by the

author, the measured angles.In Table II there are shown the forms found by the various

observers.

Tasr,n II

Bruhn'ss1'rnbol Slavik Kol. & Cold. Palache

b

aq

IkT

010100140

xx x

?

s t J ( ,

n 120tn 110

?

x

x

203T01001

?

xx

2ro0120 1 1

)

x

3015011 1 1

1 1 12 1 2T2T

47s

xx

x

It is somewhat remarkable that the forms observed by the four

observers are so difierent, for the mineral samsonite seems to have

been found in only two vugs in the Samson shaft at the St' Andreas-

berg mine and one would. expect more uniformity in the habit of

the crystals. The total absence of the orthodome forms on the

crystals of Kolbeck and Goldschmidt is in strong contrast to their

strong development in all others measured. The author's study

103101I01

Jd

hp

Forms of Samsonite by various observers

JOURNAL MINER.4LOGICAI, SOCIETY OF AMERICA 203

establishes (130) as a well-developed member of the form seriesand adds the two f orms fr(O12) and x(l2l), both weakly developed.

NATIVE SELENIUM

The element selenium has never been certainly identified as aminerall nor have crystals of the metallic gamma-selenium everbeen made artif icially which were accurately measureable. Muth-mann8 has, it is true, f igured a combination of prism and rhombo-hedron of this substance, but the figure is based on approximatemeasurements on the microscope stage of the edges of minutecrystals, and these measurements by no means justify his assertionthat selenium is completelv isomorphous with tellurium.

Much interest, therefore, attaches to specimens of seleniumfound in the fire-zone of the United Verde Mine which, like theclaudetite already described, were secured through Mr. Wilke.

There are several hand specimens of quartzite and of fire-frittedsandstone partly encrusted with needles of selenium. The needlesmay reach a length of 2 cm. with a diameter not over 1 mm. Some-times they are clustered in flattened sheets parallel to a prismface so that patches up to 5 mm. across reflect together. On onespecimen the selenium is in melted films or in droplets of dark redglass. Loose crystals up to 2 mm. long were also present and whileclearly of hexagonal form were generally bent and twisted so thatthey could not be measured. Many of the crystals were hollowand tube-like with facets on the edges. A few tiny crystals about.5 mm. in Iength proved to be undistorted and gave excellent re-flections on the goniometer. They always showed the prism of lhefirst order, m, and a rhombohedron. On the best crystal faces ofother forms were found. The table shows the observations madeon this crystal.

No' of Measured Calculatedf a c e s 4 R a n g e p R a n g e Q p

ln 1010 5 30'02' + 11' 90"00' 0 30'00' 90'00'a l l20 2 0004 + 1 u 0 000h 2130 4 1922 +15 u 0 1906r l0l l 3 -30 07 111 52 40 +4' -30 00 52 28

e ol12 | 29 17 34 20 30 00 33 13

J 1123 1 o 06 37 33 0 oo 37 0.5+

8 Zeit J. Krist., vol. 17, p 357, 1889.

204 TH E AMERIC.IN M IN ERALOGIST

The mean angle p of the unit rhombohedron from the seven bestreadings on four crystals is 52o38' with a range of 52"36'-52"43'.Calculating from this angle, we obtain the axial ratio and angles

shown below in comparison with those of tellurium.

Se

Te

c

1 . t34I .330

2o0.75500.8867

c A r

52'38's6 ss+

rAr

86"59;',

93 03

Frc.4. Crystal of Native Selenium showing the forms zz(1010) and r(1011).

Two crystals showed minute faces in the position of the nega-

tive rhombohedron. It was impossible to determine whether these

were due to twinning on the vertical axis with complete penetra-

tion or to the normal development of this form. Figure 4 shows,idealized, the habit of the average crystal.

Cleavage of good quality was occasionally visible but, becauseof the softness and extreme flexibility of the crystals, it was very

difficult to develop it without rendering the crystal unmeasure-able. Approximate measurement showed, however, that it was

JOURNAL MINERALOGICAL SOCIETY OF AMERICA 205

parallel to the negative rhombohedron e(0II2). fn tellurium thecleavage is prismatic and basal, another point of difference betweenthe two elements.

A sample of the very homogeneous crystals was analyzed byF. A. Gonyer and proved to be without a trace of tellurium and tohave but a trace of sulphur.

INDIUM

A sample of crystallized indium, prepared in the Harvard Chem-ical Laboratory by Chester M. Alter in 1932, was studied by Dr.M. A. Peacock. The sample consisted of arborescent groups ofbrilliantly silver-white crystals. Some of the groups were severalcentimeters long, but the individuals composing them were lessthan a millimeter in any dimension. The substance is.so soft andwax-like that only occasionally could a crystal be detached withoutdistortion. The symmetry proved to be tetragonal with close ap-proach to isometric form. The angle cAp, (001)/\(111), is 56o35', the mean of nine measurements with the range 56"10'-57o00'.The value of c calculated from this angle is 1.072. The forms ob-served are c(001), o(100), m(lI}) and p(111). The arborescentgroups were largely developed by elongation of the crystals parallelto an o-axis.