THE AMERICAN MINERAI,OGIST, VOL. 49, MARCH-APRIL, 1964

EMPRESSITE AND STUETZITE REDEFINED

Russrrr. M. HoNoa, Department oJ Geology and. Mineralogy,U niv er s i,ty of C olor ad,o, B ould.er, C olor ad,o.

AesrRecrThe name empressite, originally applied to a mineral having the composition AgTe,

has been applied by Thompson et al,. (1951) to material identical with type stuetzite anda synthetic product with the composition AgeTer. New *-ray single crystal, DTA, andchemical analysis data substantiate the original definition. Empressite has the compositionAgTe; is orthorhombic with space group Pmnm or Pmn, a:8.90A, b:20.07, c:4.62,Z:16. Measured and calculated specific gravity is 7.61. Strongest lines of the X-ray pow-der pattern are 2.70(10),2.23(8),3.81(6), and 3.33(6). Empressite decomposes to AgoTe:plus Te at 210'C. The type locality at the Empress Josephine mine, Kerber Creek district,Saguache County, Colorado, remains the only described locality.

The name stuetzite is here applied to the type material which has been shown to beidentical with slnthetic AgrTer and with material from several natural occurrences. Anew analysis of material from the May Day mine, La Plata district, Colorado, confirms theabove composition. Stuetzite is hexagonal, space group C6/mtnm, a:13.38A, c:8.45,Z:7, calc,tlated specific gravity 8.18 (8.00 measured). Strongest lines of the powder pat-tern are 2.16(10),2.55(8), 3.03(7), and2.62(7). New occurrences of stuetzite are describedfrom the analysis locality and the Golden Fleece mine, Lake City, Hinsdale County, Colo-rado.

INrnooucrrox

Stuetzite was described by Schrauf (187S) as a silver telluride with thepossible composition AgaTe, and empressite by Bradley (1914, 1915) ashaving the composition AgTe. Investigations of the synthetic systemAg-Te failed to prove phases with such compositions, but indicated thepresence of a binary phase with the composition of hessite (AgzTe) anda second phase variously assigned the formulae AgTe, AgaTez, AgrzTez,AgzTea, Ag2-*Ter1*, AgsTee, Ags-*Ter. Using a combined study of na-tural and synthetic material Thompson et al. (1951) showed the identityof synthetic material (from run with composition Ag6Te3) with typestuetzite and supposed "type empressite," and applied the name empres-site to this material. X-ray data and a new chemical analysis of the sup-posed type empressite are given in support of the identity, and theformula Agz-*Ter1* is proposed. These authors recognized the presenceof still another silver telluride mineral with a completely different r-raypowder pattern, and designate the mineral as empressite (?), or later asempressite II (Berry and Thompsor', 1962).

Further study by Kracek and Rowland (1955) of the synthetic mate-rial designated empressite Ied to assignment of the composition Ag6Tea.Donnay et al. (1956) modified the formula to Ags-*Tea and proposedomission of silver from the lattice to account for the wide discrepancybetween the measured specific gravity of natural material (7.61) and the

325

RUSSELL M. IIONEA

calculated value (8.07) while maintaining constancv of cell dimenstonswith those of synthetic material. Markham (1960) determined a valuefor r of 0.2 in his study of the s1'nthetic system, while the analysis re-ported by Thompson et al. (1951) yields the formula Ag+ zsTea.

The present study was undertaken to estabish the identity of theempressite (?) of Thompson el al. (1951). Chemical analysis, dif ierentialthermal analysis, and r-ray single crystal data on natural material fromthe type locality show that Bradley's original composition of AgTe wascorrect, and it is proposed that the name empressite be retained for thismaterial. Since type stuetzite has been shown by r-ray methods to beidentical with synthetic Ag5Ter, and since there are several natural occur-rences of identical material, it is proposed that the name stuetzite beapplied to the silver telluride of that composition. While the originaldescription of stuetzite is inadequate in several regards the mineral ashere redefined is fully characterized in the literature and use of the nameeliminates the necessity of introducing sti l l another into the synonomy.

Souncn or Sruov Merpnrar

The nature of this study makes it imperative that the material de-scribed be carefully authenticated for purposes of future reference. Forthis reason a description of the samples used for analysis and r-ray datais given below.

Empressite. Type material could not be located in the collections of YaleUniversity (A. N. Winchell, personal communication, 1962). A fewfragments of the material described by Thompson et al. (1951) as typematerial (USNM, F.7243) was provided by P. E. Desautels of the U. S.National Museum. This material is described by Desautels (personal

communication, 1962) as having been supplied to Colonel Roebling byMr. Frank Leavitt, who removed the material from the Empress Jose-phine mine, Kerber Creek district, Colorado, and who supplied Prof.R. D. George with the material sent to Bradley for analysis and descrip-tion. This specimen is described in some detail by Thompson et al. (1951)

as their Material 1. A second specimen of empressite from the type local-ity is from the collections of the University of Colorado (UC1649) andwas donated by Professor George as part of the material sent to Bradley.The specimen consists of a massive aggregate of empressite with a smallamount of galena, altaite, and stuetzite on one corner. Much of the sur-face is covered by a fine grained aggregate of sericite containing smallpyrite euhedrons. Except for color, which in this specimen is pale bronzewith a darker bronze tarnish, the above description is the same as thatgiven by Thompson et al. (1951) for Material 1. This sample (UC 1649)

EMPRESSITE AND STAETZITE 327

is the source of the Material 4 of Thompson et al. (1951) which is desig-nated empressite (?). Additional samples of empressite were furnished by

Dr. J. R. Hayes of the Colorado School of Mines and by Mr' H. E. Miller,

a private collector. Both samples proved to be portions of UC1649.

Stu,etzite. Specimens of this mineral were identif ied from the May Day

mine, La Plata district,LaPlata County, Colorado (UC 4128)' and from

the Golden Fleece mine, Lake Citl ' , Hinsdale County, Colorado(UC4l29). A small amount of stuetzite (less than one per cent of the

samples studied) is associated with empressite in both UC1649 and

USNM, R7243.

Pnvsrcer PnopBnrrns

Empressite has a metaliic luster and on fresh surfaces a pale bronze

color which tarnishes to a somewhat darker bronze on exposure. Themineral is brittle, has no cleavage, and breaks with an uneven to sub-

conchoidal fracture. The hardness of empressite is 3+, and the specificgravity as measured for both IJC|649 and USNM, R7243 with the

Berman balance is 7.61+0.01 (7.61 calculated). This value compares

well with the determination of 7.51 by Bradley (1914) and of 7.6I by

Thompson et al. (1951) on USNM, F.7243, but is higher than the value

of 7.30+0.04 reported by Thompson et al. on Material 4. Crystals of

empressite have not been observed, and the material in the specimens

studied is present in compact, granular masses. In polished section

empressite is seen to be present in a coarse granular mosaic aggregate

which takes a good polish. The mineral shows very strong bireflectance,

with the color varying from gray to creamy white depending on orienta-

tion. Anisotropism is very strong, with polarization colors of gray-yel-

lowish white graf ish blue. Etch reactions are as follow: HNO3-slight

effervescence and quickly stains dark gray to black, HCl-negative,

KCN-negative, FeCl3-quickly stains iridescent, KOH negative,

HgCI2-stains brown. The Talmadge hardness is C' Care must be taken

in preparing polished sections so that the low decomposition temperature

ot2l0o C is not exceeded. The decomposition products show an abundant

host material with the properties of stuetzite enclosing irregularly dis-

tributed small grains of tellurium.Stuetzite has a metall ic luster, and on fresh surfaces a dark lead gray

color. Exposed surfaces rapidly develop a dark bronze to iridescent

tarnish. The mineral is britt le, has no cleavage, and breaks with a sub-

conchoidal to uneven fracture. The hardness is 3], and the specific

gravity as measured with a Berman balance on fragments from the May

Dav mine (UC4128) is 8.00*0.02 (8.18 calculated) . This value is con-

328 RUSSELL M. HONEA

siderably higher than the 7.61 reported for the "empressite" of Thomp-son et al. (1951), but as indicated above their measurement is believedby this writer to have been made on empressite proper. The oniy naturalcrystal described (Schrauf , 1878; Thompson et a|.,1951) is hexagonal, hasan equant habit, and is highly modified. Synthetic crystals obtained bythe writer are short prismatic and have well developed pyramidal term-inations. Natural material observed in this study is present in massive,compact, granular aggregates. Polished sections of stuetzite are verysimilar in appearance to hessite, except that the inversion twinning so

Terr,n 1. X-Rlv Srxcre Cnvsrel Dlra ron Elrpnnssrrn elll Srunrzrrr

Empressite

I

Pmnm orPmn8 .e0 A

20.074 .62

16/ . o r

StuetziteSpaceGroup

a

b

ZSG

2

8 . 4 2 9 L

8.45083

1 3 . 4 k X

8 . 5

C6/mmm

13.46 kX

8 . 578 . 0 3

13.49 A

8 .4778 .07

P6/mmm

B . 4 e A

8.487

1 3 3 8 4

at .4J

78 . 1 8

Empressite (UC1649), Empress Josephine mine, Kerber Creek district, Colorado."AgDTe?" or synthetic stuetzite, Koern (1939).Stuetzite (type), probably from Nagyag, Transylvania. M. A. Peacock in Thompsonet ol. (1951).

4. Synthetic stuetzite. J. F. Rowland in Thompson et al. (1951).5. Synthetic stuetzite. Donnay et aI. (1956).

6. "Empressite I" or stuetzite as here redefined (USNM, R7243), Empress Josephinemine, Kerber Creek district, Colorado. Berry and Thompson (1962).

7. Stuetzite (UC4128), May Day mine, La Plata district, Colorado.

commonly seen in hessite was not observed in stuetzite. The Talmadgehardness is B, and the color is l ight gray. Anisotropism is moderate, withpolarization colors of gray-reddish brown-blue. Etch reactions are:HNO3-quickly stains grayish brown to iridescent, HCI-very slowlystains l ight brown, most of which rubs off, KCN-negative, FeCla-quickly stains iridescent with development of a parallel etch pattern,KOH-negative, HgCl2-stains brown.

X-nay pera

X-ray single crystal data for empressite was obtained from an an-hedral single crvstal fragment oriented through use of the precession

EMPRESSITE AND STUETZITE 329

method. Zero, first, and second level photographs were obtained for the(hkO) and (Okl) orientations, and cone axis photographs with the r-ray

beam parallel to the a and c axes. Empressite is orthorhombic, and hascell dimensions and contents as shown in Table 1. Systematic omissionsshow the space group to be either Pmnm or Pmn. Ln r-ray powder

diffraction pattern was indexed using these dimensions, and calculatedand measured values oI d. are given in Table 2. Identical patterns were

obtained for both samples UCl649 and the principal material making up

USNM, R7243. The pattern is the same as that given by Berry andThompson (1962) Ior empressite II.

Single crystal *-ray measurements are reported for stuetzite by severalinvestigators. The mineral is hexagonal and has cell constants as shownin Table 1. A measured powder pattern is compared with the published

data for empressite I (stuetzite) of Berry and Thomps on (1962) in Table

3. It is apparent that the measured values are similar, but a number ofadditional lines were measured by the writer. Several of these are doub-Iets that are better resolved using a larger diameter camera, and severalare lines of low intensity. The smaller cell dimensions obtained by thewriter are perhaps attributable to correction of the film measurementsfor film shrinkage.

It would appear that the pattern cited by Thompson et al. (1951) andBerry and Thompson (1962) was obtained from the stuetzite associatedwith empressite in the U. S. National Museum specimen.

Cneurcer Couposrrrox

A new analysis of empressite, presented in Column D of Table 4,

reaffirms the originally proposed composition of AgTe based on twoanalyses by Bradley (1914) and two by Dittus reported by Bradley(1915). The analysis of Thompson et al. (1951) on material having thesame measured specific gravity as determined in the present study is pre-

sented in Column E. As mentioned previously, this material was found by

the present writer to consist predominantly of empressite. This is perhaps

to be expected in view of the specific gravity determinations. While thereis no means of satisfactorily resolving the differences between this analy-sis and the others, it is worthy of note that were the analytical results in-

verted and the value reported for Ag given for Te and vice versa, theanalysis would be in almost perfect agreement. Is it possible that the

analyst inverted the determinations in his report? An error in the analy-

sis is further suggested by the atomic ratios determined from the analysis.The analysis yields the formula Aga.rsTea, departing considerably fromthe maximum value of x:0.2 reported by Markham (1960) for theformula Agr-*Tea in his study of the synthetic system. While some de-

330 RUSSELL M. HONEA

Tssrn 2. X-R.lv Pownon DrlnnlcrroN Dara lor Eupnnssrrn (UC1649), Eupness

JosrrnrNe MrNa, Knnsrn Cnnsr Dtsrnrcr, CoLoRADo. Slncn Gnour Pmnm onPmn, a:8.9O it, b:ZO.OZ, c:4.62; Cu Reorerror, Ni Frr-rnn, Wevnr-nrcrn

1.5413 A. Connncroo loR FrLM Snnrwr.tcr. C,lunne 114.6 ruu Dta.unrnn

Idcatc dca lc hkl d c a t c

422 1 583r92 1 .579J 4 l | 5 l l

+90 1 5750 12 .1 1 573

481 1 5662 . 1 2 0 1 . 5 6 63 . 1 0 1 1 5 6 4

4 3 2 1 . 5 5 81 . 1 3 0 1 . 5 2 1

1 0 3 1 . 5 1 7o 1 2 . 2 1 . 5 1 5

1 t 3 1 . 5 1 3570 | 5r2

1 . 1 0 . 2 | + 9 4491 | 491

4 . 1 0 0 1 . 4 9 0452 1 .488561 1 488382 1 .474

3 . 1 1 1 1 4 7 3043 1 472620 t.+67223 t .440053 1 4385 7 | 1 . 4 3 1

0 . 1 4 0 1 . 4 3 42 1 2 2 t 4 3 40 . 1 1 . 2 r . 8 2

640 | 4222 3 3 r . 4 2 2153 1 419

4 1 0 . 1 1 . 4 1 8512 1 406472 1 .39962t 1 .399243 1 .398

0 1 4 . 1 1 3 6 9253 1 368303 1 367073 1 357

t0 044 3 74 0 2

2 . 0 4

2 . O t

1 962

| 920

1 .864

1 833

1. .796

1 7 7 1

| 7 s 7

1.669

2021422t2440

0 1 0 0091222o52361421232

1 1 0 0431062380441162

2 10 .0291252072

3 1 2 13224 5 15 1 03 8 1332470520

o . 1 2 . 01822 7 2

1 . 1 1 . 14805 1 1

t 1 2 0471092402362

2 0 52 0 42 0 42 . O 32 0 12 . O 12 . 0 12 . O O2 0 01,.9661.9601 9581.9201 917| 9161.8621 8591 . 8 3 01 .830| 8261 7991 7931 7931 . 7 9 31 7 7 31 7701 7591 7581 753L 6721.6691 6681 . 6 6 7

1 . 6 5 51 . 6 4 4I 6431 6041 6021 .600

414

6

6

51

o20 10 041 4 0 4 . 3 71 1 1 + 0 2050 4 01031 3 8012r 3 80060 3 34240 3 331 4 1 3 . 1 82 2 1 3 0 5051 3 03250 2 .98l s l 2 9 0231 2 89320 2 840 6 1 2 . 7 13 3 0 2 . 7 1241 2 701 6 1 2 5 9340 2 52080 2 51301 2 502 5 1 2 . 5 0071 2 44321 2 42261 2 3 lo l2 2 29400 2 .23090 2 23341 2 23360 2 221 1 2 2 . 2 2280 2 .1 ,9o 3 2 2 . 1 8122 2 184 2 0 2 . 1 71 8 1 2 1 42 7 1 2 t 4tsz 2 123 s 1 2 . 1 24 3 0 2 . 1 r

1b

3 . 3 3

3 1 83 0 4

2 9 72 . 8 9

2 8 52 7 0

2 . 6 02 5 1

I L r

2 3 22 2 92 . 2 3

3l 0

1 490

1 .436

I

1

2b

2 1 8

2 1 4

2 . 1 2

r .650

l .6045

4

1 b

I D

d-.u" I d -uu"

0 952o.9290 9 1 80 . 9 0 50 896

1 333| 3 1 2| 296

1 245

1 . 1 3 41. .1121 . 0 9 91 .0891 . O 7 4

122t)1 D

1

1vb1

1 bl v D

1 0 s 9 +t .o32 lb1 007 1vbO 974 1vb0 9 7 0 i

1

+b+b1

+b

* b:broad.

Taetr 3. X-Rey Pomrn DrlrnecrroN D.qrl r.on srurrzrtn (uc4128), M'qv De'v

MrNr, Le Plltl Drsrnrcr, Cor,oneoo, Coupanno wrTn Dere tnou Bnnnv lxo

TnoupsoN (1962) ron E rpnnssrtn I (Sruerzrrr es Rrnnlrxal)' Spacr

Gxovr C6f mmm, a:13,38 A, c:8.45; Cu R,lrrarroN, Ni Frr'rnn, Wevn-

LENGTH 1.5418 A Connrcrro ron Frr,n SnnrNr<ace

Cnuene Dt.qneren 114.6 uu

Stuetzite Empressite I Stuetzite Empressite I

d c a i cu, I hk i l

1 1 5 9 54 7 7 r4 . 3 7 43 8 8 33 . 5 6 63 5 2 63 . 3 5 53 . 2 1 23 . 1 1 53 . 0 3 72 . 8 2 32 6 2 72 55 8b*

2 3 92 3 72 3 22 2 72 2 4

2 16 10b

2 1 1 6

2 0 3 4

1 9 3 1 5

1 . 9 0 0 3

1 8 6 5 3

1 8 1 6 +1 7 9 O +

1 7s7 *b

1 6 9 9 +

1 6 7 4 2

1 6 5 7 2

1 5 7 9 1

1 547 1b

101002212130213111220331224031+O224121320003224213+23251o44221335050033332520.551336041523361224s426113430004055251610443325360603470213451624371527052710553221431440662o414s272516.344800 1 1 5707053803254628143732 13552730335

dca lc

1 8

1 1 . 5 94 . 7 84 3 83 8 93 . 5 73 5 23 3 53 21.3 1 13 . 0 42 . 8 22 6 22 5 62 5 42 . 3 92 3 72 3 22 2 82 2 52 2 42 2 32 1 72 1 62 1 52 1 22 1 22 1 12 0 32 0 22 . O 2t

II1

4 1 13 9 83 9 23 5 93 5 43 4 33 3 73 . 2 43 0 63 . 0 32 8 32 . 6 42 5 5Z J J

2 5 42 . 2 5

t . 5 3 6 1 b

r 4 8 4 1

r 4 6 + 2

r . 44 r +

1 .424 4

r 2 9 3 +

1 2 8 1 +

18915.5 10 0

12362465459344841565

3 7 1 0 0099008831316268409910665

1 3501 3491 3461 3451 3221 . 3 2 01 . 3 1 9| 3141. 2981 2 9 71 - 2 9 61 2871 283| 278

4 4 03 9 7

3 5 6

3 4 0

336454905 1645491

12310r12123111220331022222401340123213110003224223511450o223055133601452 2 183361 2 l72243 2 16

0 7 7 2 1 . 535a2 1 5

+ 0664 1 434

5 . 3 8 2 1 5 4 10772 1 5415382 1 547180 1 53

1 s 3 4 1 1 . 3 1 8

2 8 32 6 42 5 5

I

z2

I

1

J

6390 10445 11182 16391 14483 1 .0881 1 4

.538332550664

8192 1 291

0773 11 41 4

3365 1 3477292 1 3422156 | 341

24 1

r 7 1 02 2 5 | 346 6 7183 1 .

t2 2 2461 2.14 1 3r4 2 6 4 1 0 1 1 3 1

1343 2 130004 2 12

2 0 4 1 0 5 5 2 2 0 5

I 931 3470 I

31,46 1.0883 1

7 3 , 1 0 1 19090 1

5 5 1 O 2 1 2 7 60991 | 273066-5 1 .272

+t6a | 2

rs61 2 04 11 2eo044.3 2 03ll24 2 02

r 933 1 0660 1 947xE3 1 914

1 7651 1L 707

I

1 8 1I

1 . 7

l 6

l 6

1 e 1 0 +r 8 7 3 +

1 .664 +

1 s 4 6 +

1 4 6 3 +

1 4 4 s +

3256 1 247184 1 24

+ 0992 1,.23

r 2 4 6 + 8 2 1 0 1 1 .5275 I

73 10.2 1

| 674

1 5 5 1 0 3 10007 10.556 1

6 4 t O 3 1 2 0 26394 1 2010 1 1 7 1 . 2 0 1

2355 1 .4s2790 1 423474 1 .42

t ua

1I

t

1 5 7

" I hki l d"n;" d*sa. I hki l dcalc

* b:broad-

2792 1

332 RUSSELL M. HONEA

parture of natural material from synthetic is to be expected, it is unlikelythat the discrepancy would be this great.

In Columns G and H is reported an analysis for stuetzite. Unfor-tunately the analysis sample contained approximately 20 per cent of

T,tsl,n 4. Cnnurc.Ar CouposrrroN ol Elrpnrssrrn .luo Srunrztre.

B r-

AgPbCuZnFefeSRem.

A

4 5 . 8 1

54. 19

+5 17

0 . 2 254.75

0 3 9

0 . 3 5

0 .205 3 60 . 100. 70

45.26

58.49

G

47 .39 . 1 80 .030 . 78| . 7 0

3 3 . 63 .473 . 5 0

5 8 5

4 l . . )

H

TotalSG

100.00

2 1 653 .84

0. 34

100 04 99 .90, / . o l

100. 53/ . J I

100 03/ . o r

9 9 . 5 68 0 0

100.0

A. Theoretical weight percentages for empressite, AgTe.B. Empressite, Empress Josephine mine, Kerber creek district, colorado Average of

two analyses. Remainder is insoluble 0.39. Analyst Bradley (1914).c. Empressite, type locality Average of two analyses. Remainder is insoluble-0.34,

trace CaO present. Analyst Dittus in tsradley (1915).D. Empressite, type locality. Remainder includes SiOr-040, AlrO3 0.3. Contains

very minor pyrite, chalcopyrite, and sericite. Analyst Jun Ito.E. Empressite, "type materiai,,, USNM, R7243 Analyst R. N. Williams in Thompson

et al. 0951\.F. Theoretical weight percentages for stuetzite, Ag5Te:.G. stuetzite, May Day mine, La Plata district, colorado (uc412g). Remainder in-

cludes Au-0.1; As--{.10; SiOz-2.19; AbOa 0.60; TiOr-001; VzOs-0.3; NISO*MnO 0.2; Ca, Sr, Ba trace. Contains known impurities of galena (major), silicates(major), and minor amounts of tetraheclrite-tennantite, pyrite, and sphalerite.Analyst Jun Ito.

H. Stuetzite, analysis G recalculated after deductins imnrrrities.

intimately intergrown impurit ies that could not be separated by physicalmeans, and it was necessarv to identify the impurit ies and deduct themfrom the total. The recalculated analysis yields precisely the formulaAg5Te3, and supports Markham's (1960) conclusion that there is onlyslight deviation from this ratio. Perfect agreement of the recalculatedanalysis with the theoretical weight percentages is somewhat fortuitoussince a small but undetermined amount of silver is probabry present inthe galena and tetrahedrite-tennantite known to be present as impurities.

EIIIPRESSITE AN D STU ETZITE

SvNrHBsrs

The synthesis of a silver telluride with higher tellurium content than

hessite (AgrTe) has been reported by several investigators (Pelabon,

1906; Pell ini and Quercigh, 1910; Chickashige and Saito, 1916; Koern,

1939; Kracek and Ksand a, 1940; Thompson et al., l95I; and Markham,

1960). Various formulae have been assigned to the phase, but that most

recently shown to apply is AgsTea or Agr-,Tea. This material, correspond-

ing to stuetzite as here redefined, is readily prepared from fusions of the

elements and by reaction in the solid state between the elements in

either dry or hydrothermal runs.Attempts by the writer to synthesize the phase AgTe were not success-

ful. The low temperature range of stability of empressite makes prepara-

tion from fusions impossible. Both dry and hydrothermal runs containing

stoichiometric amounts of Ag and Te gave as products hessite plus tel-

Iurium, stuetzite plus tellurium, or hessite plus stuetzite plus tellurium.

Silver apparently reacts early to form hessite and is thus depleted. Reac-

tion with the remaining tellurium metal is slow, and the hessite may be-

come armored with stuetzite.A third phase, having the composition Agr eTe, is reported by Kiuk-

kula and Wagner (1957), who determined free energies of formation for

hessite (AgzTe), Agr sTe, and stuetzite (Agr.orTe) at temperatures of

250' C. and 300o C. This phase was not encountered in the present study.

Tnonn.q.r BBnevron

A differential thermal analysis curve was obtained for empressite from

the type Iocality (UC1649) using a Deltatherm unit with a constant heat-

ing rate of 10o C. per minute. The curve is reproduced below as Fig. 1 and

shows a series of endothermic reactions, all but one of which is readily ac-

counted for by referring to the phase diagram for the system Ag-Te

(Fig. 2). X-ray powder diffraction photographs were prepared from ma-

terial heated in stages in evacuated silica tubes and quenched in water to

aid in interpretation of the reactions.The first endothermic peak at 210' C. marks the thermal decomposition

of empressite to stuetzite plus tellurium. This decomposition is not re-

versible on the down-temperature gradient, at least at the experimental

cooling rate used. The rather broad endothermic peak at 294" C. marks

the inversion of the low temperature or alpha polymorph of stuetzite to

the beta form (see Koern, 1939; and Kracek and Rowland, 1955). The

peak present at 335o C. could not be accounted for by either the phase

diagram or fi-ray photographs, and may represent a reaction of the

thermocouple. This conclusion is supported by the greater variance in

334 RUSSqLL M. HONEA

temperature recorded for the higher temperature reactions as comparedwith those shown in Figure 2. The major endothermic reaction at 356o c.results from the beginning of melting at the eutectic between beta steut-zite and tellurium. The sharp endothermic peak at 433. C. has a temper-ature somewhat higher than would be indicated from the phase diagram(419' C.), and marks the temperature of the peritectic reaction by whichbeta stuetzite plus l iquid is converted to gamma stuetzite plus l iquid.The endothermic trough culminating at 456o c. results from the peritec-

,oo 200 300 400 500

T , 'C

Frc. 1 Difierential thermal analysis curve for empressite

t ic reaction of gamma stuetzite plus l iquid to form the cubic (beta)modification of hessite plus l iquid. The final reaction, beginning at558" C., results from total melting to form one homogeneous liquid, andis somewhat higher in temperature than is indicated by the solidus curveof the phase study.

The only previous mention of the thermal behavior of empressite isby Thompson et al. (1951) who state that when fused in vacuum theproduct gives powder l ines of "empressite" (stuetzite) and strong linesof clausthalite. There is no elaboration as to a source for selenium to formclausthalite.

OccunnnNco .cNo Assocrarror{s

Empressite has been reported only at the Empress Josephine mine,Kerber Creek district, Saguache County, Colorado. Burbank (1932) andPatton (1915) describe the occurrence of a lens-shaped body of tellurides

EMPRESSITE AND STUETZITE 335

between faces of lead-zinc ore. Telluride minerals include empressite,nlt ive tellurium, sylvanite, petzite, hessite, rickardite and altaite.Telluride mineralization is later than deposition of the enclosing sulfides,

and a reaction rim of altaite often separates other tellurides from the

abundant galena. Hessite is described (Burbank, 1932) as irregular inter-

growths with empressite, suggesting contemporaneity. CoLinear relations

+1---- ,---' Te + t a"

802

oo

200

A g + h s hs\+ \L \

ae<

h s + L \

acrAg + hs ( i so )

4 t 7

25C

t 4 l

B s t

P slz+Te 2er

a slz+Te 2r

a s I z+em

em+Teto:Ag + hs(o t lh I

Ag Atomic Yo Te

Frc. 2. The binary system silver tellurium modified from Kracek and Ksanda (1940)'

Kracek and Rowlancl (1955), and Markham (1960) to show the presence of empressite

(AgTe). Abbreviations used: hs:hessite, stz:stuetzite, em:empressite, Ag:silver,

Te: tellurium, L:liquid.

of hessite, stuetzite and empressite (Fig.3), combined with polished sec-

tion similarit ies between hessite and stuetzite, suggest that the associa-

tion is probably that of empressite stuetzite observed in the present

study. Pelzite and sylvanite were not observed by the writer, but are de-

scribed by Burbank (1932) as present in veinlets in qtartz with sphaler-ite, galena and altaite. Native tellurium and rickardite are closely asso-

ciated with each other but were not observed in contact with empressitein the present study. Bradley (I9I4) mentions native tellurium as pres-

ent with empressite on the type specimen. Thus, both of the described

direct associations empressite-stuetzite and empressite-tellurium lie

on the Ag-Te b inary jo in.

6 0 0

r, tC

400

336 RUSSELL M. HONEA

Stuetzite has been described from several localit ies, and is noted fromtwo new occurrences in the present study. Previously described is theassociation with empressite which led to redefinit ion of the species byThompson et al. (1951) from study of the U. S. National Museum speci-men from the type localit l .. This association was also noted by the presentwriter. Thompson et al. (195r) aiso describe the occurrence of stuetzitewith associated altaite from the Red Cloud mine. Gold Hil l district.

Frc. 3. Observed (--) and inferred (- - -) tie iines in the system Au-Ag-Te basedon associations of empressite and stuetzite from colorado localities. Tie lines to em-pressite valid only to 2 10o C., above rvhich temperature empressite decomposes to stuetziteplus tellurium. (Modified from Markham, 1960).

Boulder County, Colorado. Other tellurides from this mine identified inthe present study include hessite, petzite and sylvanite.

Markham (1960) describes stuetzite associated with sylvanite in asingle specimen from the Kalgoorlie district, Western Australia; andfrom Vatukoula, island of Viti Levu, Fij ian group. For the second localitythe observed associations are listed as stuetzite-sylvanite, stuetzite-tellurium, stuetzite-tellurium-sylvanite, and stuetzite-tellurium-coloradoite

In the present investigation new occurrences of stuetzite were noted atthe May Day mine, La Plata district, La Plata County, Colorado, andthe Golden Fleece mine, Lake City, Hinsdale County, Colorado. In theMay Day ores stuetzite (mislabeled hessite) is an abundant constituentof telluride replacement masses, and was observed in the associations

EMPRESSITE AND STUETZITE

stuetzite-sylvanite, stuetzite-hessite-sylvanite, and stuetzite-al-

taite. sulfide minerals are commonly intergrown with the tellurides and

include galena, sphalerite, tetrahedrite-tennantite. It is believed that

r-ray examination of "hessite" specimens from the May Day mine may

prove stuetzite to be the most common telluride mineral from the de-

posit. More complete data concerning the mineralogy of telluride de-

posits in the La Plata district are given by F. W. Galbraith in Eckel (1949) .

Specimens from the Golden Fleece mine show the associations stuetzite-

petzite and stuetzite-hessite-p etzite.The associations of stuetzite observed in the present study are com-

patible with Markham's (1960) 300' C. isothermal section of the system

Au-Ag-Te and with his equilibrium diagrams assembled from associa-

tions in the Kalgoorlie and Vatukoula deposits. The presence of empres-

site as a lower temperature phase requires modification of the tie l ines on

a lower temperature isothermal section as shown in Fig. 3. This tie i ine

configuration is based on associations observed or inferred from the pres-

ent study. Decomposition of empressite at temperatures exceeding 210o

C. would yield precisely the same configuration as shown by Markham

(1e60).

AcTNowTBoGMENTS

The writer gratefully acknowledges financial assistance from the

George and Anna Garrey Fund for defraying the cost of chemical analy-

ses. Specimens for the study were made available through the courtesy of

Mr. P. E. Desautels of the U. S. National Museuml Prof. J. R. Hayes of

the Colorado School of Mines; Mr. John Murphy of the Denver Museum

of Natural History; and by Mr. H. E. Miller, a Boulder, Colorado, min-

eral collector.

RnlennNcns

Bnntv, L. G. eNo R. M. TnoupsoN (1962) X-ray powder data for ore minerals: The Pea-

cock atlas. Geotr. Soc. Am. Memoir 85.

BunrANr, W. S. (1932) Geology and ore deposits of the Bonanza mining district, Colorado.

U. S. Geol'. Suraey ProJ. PaPer 169.

Bne.or-rv, W. M. (1914) Empressite, a new tellurium mineral from Colorado. Am. f our.

Sci. 38. 163-165.--- (1915) On the mineral empressite. Am. Jour. \ci.39,223.

Cntcxasxrce, M .lNo I. Serro (1916) Metallographische Untersuchung iiber das System

von Silber and Tellur. Mem. Col'\. Sci. Unin. Kyoto, 1,361-368.

DoNltav, G., F. C. Knecrr ar"'n W. R. Rowr-mo (1956). The chemical formula of empres-

site. Am.. Mineral'. 41, 722-723.

Ecrol, E. B. (1949) Geology and ore deposits of the La Plata district, Colorado [/. S.

Geol. Swoey ProJ. Paper 219.

Krurr<ur,e, K. .qNn C. W.lcNnn (1957) Measurements on galvanic cells involving solid

electrolytes. f ow. Electrochem. Soc. 104' 385-386.

337

338 RUSSD,LL M. HONEA

KornN, V. (1939) Das binare Legierungssystem Ag-Te Natuurwi,ssenschaJten,27,432.Knlcnr<, F. C. ,c.No C. J. Kslm,r. (1940) Phase relations in the system silver-tellurium

(abs.) Trans. Am. Geophys. Union, 21, 363.W. R. Rowrlm (1955) The system silver-tellurium. Ann. Rept. Geophls.

Lab., Carnegie Inst. Waskington Yearbooh 54, 135-136.M.r.rrnau, N. L. (1960) Synthetic and natural phases in the system At-Ag-Te. Econ.

Geol, 55, 1148 1178, 1460-1477.PnrroN, H. B (1915) Geology and ore deposits of the Bonanza district, Saguache Countl',

Colorado. CoIo. State Geol Suney Butrl. 15, 105 111.Prr,aroN, M. H. (1906) Sur le sulfre, le seleniure, et le tellure d'argent. Compte Rendus

Acad.. Sci. 143, 294-296.Pnr-trNr, G. er.ro E. Quoncrcrr (1910) I tellururi d'argento. Renil. Acca . Lincei (Roma)

(5) , te ,415-42r .Scuneur, A. (1878) Ueber die Tellurerze Siebenburgens. Zeit. Krist.2,209 252.Tnouesou, R. M. (1949) The telluride minerals and their occurrence in Canada. Am

Mineral,. 34,342-382.- - M A. Pucocr, J. F. Rowr.eNo eNo L. G. Bomv (1951) Empressite and stuetzite.

Am Mi.neral,. 36, 458-470.

Manuscript receioed., August 30, 1963; accepted Jor publicati.on, Notember 4, 1963.