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Home , Hemihedrite, Phoenicochroite, Vauquelinite, Wulfenite

THE AMERICAN MINERAIOGIST, VOL. 55,JULY-AUGUST, I9?O

HEMIHEDRITE, A NEW FROM ARIZONA SrnwBy A. Wrrlraus, WesternErploration, Ofice, Phelps DodgeCorporation, Douglas, Arizona 85607;

JouN W. ANtttoNv, Department oJ Geology,Unilersity o.f Arizona, Tucson. Arizona 85721.

AssrRacr is a new species discovered at the Florence - mine in Pinal County, Arizona. A second locality is the Rat Tail claim near Wickenburg, Maricopa County, Arizona. Hemihedrite is named in allusion to its morphology. Crystals exhibit tdcliidc hemi 'Ihree hedral slrnmetry with a:120"01', B:91o49', T:55o55', a:b:c:0.8345:l:0.9360. twin laws have been found. The refringence is a:2.105, F:2.32, t:2.65(25'C); optically (*) with 2V(calc.) :88'. is strong and unsymmetric. Crystals are orange to almost black and have a safiron yellow . Hardness on the Mohs scale is 3. Unit-cell data at 22"C are as follows: PI; a:9.497+.001A, 6:11.443+.002 A, c: 10.841+.002 A; a:120o30', A:92"06', z:55o50'. The Delaunay cell is a': 9.954 A, b':10.841 i:', c':9.497 L; at:92006', 9:107o58', tt:123"16'. The most intense X-ray Iinesare:4.872 (90) (t20).4364 (80) (220),3.301(100) (r22),3146 (80) (320),3.102(80) (103, 102), 2.924 (55) (253), 2.849 (45) (%:2).2.182 (45b) (411, 340). t':123o16'. Trans- formation (morphology to Delaunay cell) is T10/001/100. Chemical analyses combined with structural information lead to the composition ZnFz[Pbs(CrOr)sSiOa]:(with Z:l), although chemical compositional variation is indicated. Specific gravity is 6.42 (meas. at24.2oC) and the density (calc.) is 6.50 g/cm3. Hemihedrite forms in the oxide zone of lead-bearing veins. Associated may include the following: , , , , and . INrnooucrroN Specimensof the new mineral were first collected and submitted to us by R. W. Thomssen.The specimenswere found at the FlorenceLead- Silver mine in the Tortilla mountains, Pinal County, Lrizona. Subse- quent trips to the locality yielded ample material for this investigation. During the study a secondlocality was discoveredon the Rat Tail claim (formerly the Pack Rat claim) near Wickenburg, Maricopa County, Arizona. Material from the type locality in Pinal County was used as a basis for this investigation. At both localities the speciesis rather abun- dant. The speciesis named in allusion to its distinctive morphology.r

GBor-ocv At the Florence Lead-Silver mine an adit has been driven along a strong fault zone striking N 70' E and dipping 70" to 77" to the southeast.

r The mineral and name have been approved by the Commission of New Minerals and Mineral Names, IMA. 1088 IIEMIIIEDRITE 1089

Lead minerals including hemihedrite and wulfenite are concentrated in a shoot of small horizontal dimensions localized within the sheared and mineralized rubble and gougein the hanging wall of the fault. Where the Iead minerals occur, a crosscut has been driven exposing the fault zone and hanging wall rocks. The zone consistsof nine feet of calcite and as- sociated oxides cementing partly altered and replaced fragments of quartzite, , and latite porphl'ry. Remnant occurs as replacementsof siliceousfragments adjacent to the fault plane near the footwall side of the zone. Supergenealteration of the calcite and galenahas been most intense on the north side of the fault zone in a narrow selvagewhich consists of a loose aggregate of finely crushed and highly altered rock fragments and iron oxides.Secondary lead minerals occur as oxidation products in cavi- tites left by the leaching of galena, on fractures traversing the fault-zone rubble, and in the aforementioned highly'altered selvage. Strongly brecciated Mississippian Escabrosa Limestone, intruded by altered latite porphyry, comprisesthe south wall of the mineralized zone. Large displacement on the northeast fault has brought these hanging wall .rocks against a footwall section composed of vertically-dipping Precambrian Troy Quartzite and underlying units of the Mescal Lime- stone. A dike of altered diabase separates the Troy Quartzite and the uppermost chertstone unit of the Mescal Limestone on the surface over the adit. Underground the diabase has been displaced by a small fault and is not visible.

OccunneNce Hemihedrite occurs in an oxide assemblageindicative of alkaline solu- tions of relatively low Eh (Williams, 1966).Primary minerals from which the oxide assemblageis derived consisted of galena, , , and minor . occursvery sparingly as blebs in the sphalerite. Chromates occur where the oxide are near an altered diabase dike; one sample of this dike showed a CrOs content of 0.14 weight percent by X-ray fluorescenceanalysis. Oxidation of the sulfide ores has been almost complete so that only minor amounts of galena remain in an oxide assemblageconsisting largely of hemihedrite, wulfenite, willemite, and cerussite. Other speciesnoted are vauquelinite, , and . The paragenesisin the oxide asemblageis as follows: cerussite (first) followed by hemihedrite and wulfenite, with wulfenite continuing to crystallize after hemihedrite, and vauquelinite (last). Willemite is evi- dently earlier and mimetite is later than most wulfenite. Wulfenite con- temporaneous with hemihedrite is orange and chrome-free. Wulfenite 1090 S. A. WILLIAMS, AND J. W. ANTHONY which has replaced hemihedrite is brilliant red and contains, in one ana- lyzed specimen,0.83 weight percent CrOa. Continued crystallization of Iater wulfenite was marked by continuously decreasingchrome contentl Iate wulfenite is yellow and chrome-free. At the Rat Tail claim hemihedrite occursin a similar assemblagewhich consists largely of hemihedrite, willemite, cerussite, and phoenico- chroite, with minor amounts of mimetite and vauquelinite. These minerals have formed by oxidation of galena, sphalerite, and pyrite in quarlz veins which cut an andesite agglomerate.

Pnvsrcer. PnopBnrrrs Crystals of hemihedrite range in color from bright orange to henna brown to almost black. Crystals vary in length from 0.2 to 10 mm, and average 0.5 mm. The streak is saffron yellow (Munsell 5Y 8/10). Hard- nesson the Mohs scaleis 3. The specificgravity measuredon the Berman density balance is6.42 (24.2"C).

CnBlrtcar- Couposrrrou The initial qualitative spectrographic examination of hemihedrite showedmajorPb, Cr, and Zn;traces of Ca, Si, Mg, Cu, Ni, Ag, andAl; and failed to show F. Several quantitative analyseswere made by differ- ent methods for Pb, Cr, and Zn. One of theseanalyses showed significant Ca and a second showed significant Si. The infrared spectrum failed to reveal either water or hydroxyl, but did confirm chromate ion. A thermo- gravimetric balance tracing showed no weight loss to 313oC, then a gradual loss amounting to 10.7 percent of the initial weight between 313oCand 967"C.The crystal-structureanalysis (McLean and Anthony, 1970) indicated two sites that would be most logically filled by Si in the one instance and F in the other, based on scattering power, charge, and atom size. Subsequent chemical work verified their presence.Electron- microprobe examination of hemihedrite established that the silicon is uniformly distributed throughout the mineral and not present in a sepa- rate phase. Table 1 presents the analytical results. The empirical composition derived from the average analysis (column 14, Table 1) by assuming six CrOgper unit cell as indicated by the struc- ture and the consistencyof the Cr analysesis:

Znr.rTFs.2rlpb 1.36(CrO.r) 3(SiOq) o.ar]r. The ideal formula deducedfrom the crvstal structure is: znF,[Pb6(cron) rsio,l,. The excessZn and defrciency of Pb in the analysesare presumably due HEMIHEDRITE 1091

?\q.: N oO\Oi or e b\

r HO\C4 ro\oN iF O'GJd

\od\or o. *r NC)4N sNc)N

ao

oo'd; E :>.

Ni9N $N 90 NOo14 4N r) o rN vt o

:N Ni n !r ltl fl I FE: ^o:: E =N6 r ii<'idLN ,i aeh

a N

Fl z N q

(.)

U N

N tsl a F N

rN q':\9 NiNC) NN

s a aq N r No.

O\ NO a 1q q No rN r .. k ! -. >i>>J2d !s cd d tr-

^--/{ 6' 55853," F TO92 S. A. WILLIAMS AND T. W. ANTHONY to substitution of Zn for Pb in some samples. Fluorine in the amount indicated by the colorimetric analyses is inconsistent with the evidence from the structure and with the charge requirements of the remainder of the compound. The addition of both SiOzand F in the amounts indicated by the analysesmade subsequent to the analyses 2-4 ol Table 1 would result in totals consistently greater than 100 percent (average 103.6)' while addition of fluorine in the amount indicated by the structure analysis would give totals much closer to 100 percent (average 101.2) in all cases.Therefore, we believe the fluorine analysesto be too high. The results of the refined X-ray structure analysis (R:4 percent) (Mcl-ean and Anthony, 1970) lead us to the ideal composition ZnFz[Pbr(CrOa)3SiOa]2,but the variability in the analysesindicates that some compositional variation does exist. There is, however, insufficient chemical evidence to justify proposing a specificformula to expressthe compositional variation for the species. Reactions of hemihedrite to certain reagents are as follows: in 1:1 HNOa, white powdery Pb(NOe)zis formed; in 1:1HCI, a coating of PbClz slowly develops. Hemihedrite is slowly decomposedin 20 percent KOH, but is unaffected by 20 percent NHTOH.

Monpnolocv Hemihed.rite crystals of great perfection and ideal size for goniometry were easily obtained. About 40 crystals were measured on a Stoe two- circle goniometer. Many of these were doubly terminated. About a dozen twins were also examined. The morphological study shows that the crystals are triclinic hemihedral. Goniometric data for a single crystal and three twins are given in Table 2. similar results for many crystals were averaged (using only faces regarded as good or excellent) to calcu- late the crystallographic elements from which the angle table (Table 3) is derived. The angle table is for a right-handed crystal; left-handed crystals show all the complementary_forms.A complete list of forms is given here: verti,cal:a1oro1, a{oro}, o{100}, d[100], {1?0} ,rn{Il}l, {31-0}, {120}, {x0}, {34d;,nlttol, lA0l, nlTlol, 1sto1,MIrrol, {tzo},and MITToI upper:c{001} , dl\l2l, plolrl, L0321,ql02t },_{102}, {-203} ,h|Lgrl, rt Tdft, 14tis 1,' lrri\, i lt'ttl, ulrl2l,Jl 1T1_1,{1 14 L' {1 1_!, s {!!1 }, 35s Is1 6t+ 1sSz 1, 15ss 1, itzzl,'"\trzl, iIlri, t t, { }, 1 1,1s2zy, lT42l, HEMIHEDMTE 1093

Tenr.r 2. Typrcu, Go*rolrnrmc Dnrl"

Single Crystal Twin on (0T2) V V

010 349"10', 90"00' 010 16"76', 90000' T00 40 06 90 00 010 16 18 9t 07 ITO 103 00 90 00 110 83 07 90 00 010 169 08 90 00 210 83 08 93 02 100 220 08 90 00 100 r45 26 90 00 111 25 14 63 25 100 14528 92 0l o2I 350 09 64 43 212 35054 69 1l 111 247 06 48 44 021 19525 64 59 017 35151 34 36 111 60 30 59 30 t12 42 57 36 45 001 1833 35M 00I 166 36 JJ J/ 212 350 15 1r0 46 o12 t12 33 206 021 19528 rt4 54 111 ffi 2t 12318

Twin on (223) Twin on (0f0) 110 232"39' 90000' 010 92"29' 90000 2to 045 90 00 100 13330 90 00 100 23 30 90 00 100 21t 32 90 00 010 75 3l 90 00 010 26230 90 00 100 204 t8 90 00 212 57 08 69 09 010 255 02 88 07 2t2 287 50 69 08 021 252 37 65 12 o2l 261 50 64 59 021 25237 65 12 021 83 17 65 03 010 279 3l 58 39 111 12643 59 30 011 223 50 78 50 001 84 45 35 43 012 r94 02 97 32 00r 260 t2 35 50 001 16157 11355 012 164r0 t 4r 111 2r8 07 65 03 012 18050 1 40 111 JJ/ 56 46 12 001 81 21 36 t2 012 148 16 443 010 100 30 12120 100 253 55 1148

" Italicized indices are underlined in Figures 3-6.

The major forms are c, e, a, d, b, rt,, f , g, Q, t, tl, ar'd,f . Various habits are illustrated in Figure 1. The morphological setting makes the best zone the c axis. This zone, dominated by a, d.,m,fu, and 6, is one of moderate elongation. Another strong zone, used for the d axis, includes c and.q; c is the brightest and most persistent face close to a polar position. Other orientations were tried but none gave as low a sum of indices as that adopted. Evidence for hemihedrism is excellent. Many crystals show a large bright c and a small etched f; a large, snlooth 6 and small. etched, or 1094 S. A. WILLIAMS AND J. W. ANTHONY

Tnlrs 3. Cer-cur,etnoANor.rs lon HrMrntnntrB. aibic:0 .8345.1:0 .9630 a: l2Dool' A:91"40' v:729"O6' ry:55o55' tr : 54o14l P: 110'30' ro': 0292 ys': .72O8 Po':1.4876 qo': l .43tl

liorms

Lower Upper & Vertical

d 001 2018' 35'48', I 10030' 54014' 0000' r 001 -r77 42 tM t2 69 30 125 +6 180 00 90 00 t29 06 000 5414 -bb 010 000 010 180 00 90 00 50 54 180 00 125 46 o 100 t29 06 90 00 000 129 06 110 30 d 100 -50 54 90 00 180 00 50 54 69 30 m ll0 66 48 90 00 62 t8 66 48 75 24 M 110 15402 90 00 24 56 154 02 12r Or F 0rr -2 20 lM 3r rtz 35 54 33 108 46 q O2t r79 14 65 00 5428 155 00 100 46 q 02r o46 11500 12532 25 00 79 14 h tol 100 24 50 16 47 34 97 59 62 56 f rlr lM 22 63 47 30 04 13648 93 12

Direct and reciDrocalmatrices of Bond (1946) and Evans (1948): il 8341s .54608 0 M:l o .67142 0 il ll .02427 .50025 . e6301|

-.97503 ll 1.1e88 0 M-': lL0 1.4894 0 ll-.03022 - .74347 1.0384

absent 6;large and deeply etched M while 7Z is small, vicinal, and un- etched. Etching in 10 percent FeClg was especially successfulo\ rll ^nd m, m etched deeply while fr. was but slightly affected; etch patterns for these two forms are quite different. Both right- and left-handed crystals show preferential etching of m.In 1:5 HCl, nxcorrodes very rapidly and becomes coated with powdery PbCb while m is notabll' less afiected. Similar preferential corrosion was noted in dilute HNOe. Commonl-v the crystals have a large blunt positive end and a small tapered negative end. Choice of the blunt end as positive obeys conven- tion for polar species. Visual examinationof many crystals indicatesthat about 75 percent are right-handed and that the negative ends of crystals of both hands point away from the matrix about 90 percent of the time. Overall devel- HEMIIIEDRIT'L

I c

l"ig. 1. A, left-handed crystal. f end up; B and C, right-handed crystals, f ends up. opment of the crvstalsand especiallythe appearanceof c and Dwere used to determine the handednessand sign of the c axis. The precedingdiscussion applies to material from the type locality. Crystals from the Rat Tail claim show almost identical habit and forms. No twins were observed in the Rat Tail material but several laws are recognizedin the type material. The most common type of twinning is twinning by reflection in (223). Thesecrystals occur as penetrations of individuals of oppositehand which form an X, V, or I with their c axesinclined at about 102o.The faces (021) are exactly parallel in the two individuals and often are abnormally large.About 50 of thesetwins wereobserved. They tend to be commonin certain vugs rather than systematically distributed throughout the material.These twins are shownin Figure 2, C and D. A less common type of twinning is twinning by reflection in (010). Normally the compositionsurface is (010) (Figure 2-B), but on occasion it may follow the base of terminal forms. Some of these twins which show no reentrant simulate monoclinic classm symmetry. A third law (Figure 2-A) involves two individuals twinned by reflec- tion in (012) which is a pseudo-monoclinic b face. A number of these twins werefound on one specimen. Stereographicprojections of a single crystal and examplesof measured twins are shownin Figures3 through 6.

X-nay Drnln,r.crroN Sruny The morphological orientation was retained in selecting the unit cell of hemihedrite. Rotation and Weissenberg photographs were made around each of the three morphological axes. Evidences of the point- group symmetry consideredunder the discussionon morphology show the spacegroup to be P1. Unit-cell constants were derived independently from data collected by WILLIAMS, ANTHONY AND THOMSSEN

Fig. 2. A, twin on (012); B and E, twin on (0T0) ; C and D, twin on (X23). the Weissenbergmethod and with a Picker single crystal diffractometer.l In both casesreflections were measured from spheresabout 0.05 mm in diameter ground from single, untwinned crystals, Wiessenberg_-film calibration was made with sodium chloride powder (ao:5.6402 L) aL 22"C. 20 angles from 108 reflections were used to calculate and refine the cell constants through a least squaresroutine with a program written for the IBM 1620computer. Exdellent agreementwas obtainedbetween these parameters and those derived from the diffractometer measure- ments of 29 reflections similarly processed.Table 4 gives the cell con-

r The refined cell constants were determined by Dr. W. John Mclean at the Crystallog- raphy Laboratory, University of Pittsburgh. Fig. 3. Stereographic projection of a single crystal (see Table 2) and optic orientation at two wavelengths (see Table 7).

----- ' \ _t 'i't'u-'-

Fig. 4. Stereographic projection of twin on (D3) from data in Table 2. Fig. 5. Stereographicprojection of trvin on (0T2)from data in Table 2.

Fig. 6. Stergographic projection of twin on (0T0) from data in Table 2. IIEMIHEDRI'TE twg

Tarln 4. UNrt-Cnr.r-CoNs:raNrs ol Hrulrpnnrtn

X-Ray Cell Morphology Delaunay Cellb

o':111il: U' lVeissenbergDiffracrometer OneCrl'stal.

o 9.a97Q) fr" 9.495Q)A o' 9.954A b lr.Ms(2) rr.Mr(7) b' 10.841 c r0.Mr(2) 10.841(6) c' 9.497 a 120o30(1), 120031(3)/ l20"ol' 720016' a' 92o06' p 92.06(1)', 92004(2)' 91054', 91"54' p',107"58', 7 55'50(1)' 55053(1)' 55051', 55o52' 7'123o16' a:b:c .830:.1:.9.17 830:1:.948 .834.5:1 : 9630 .824:l:.947 Volume787 .29 Az Density (calc.):6. 50 g/cm3

' From which the angle table, Table 3, was calculated. b Derived from Weissenberg data. Transformation matrix morphology to Delaunay celi is I 10/001/100 " Precisions stated are one standard deviation

stants with morphologicalconstants for comparison.The Delaunay re- duction yields the cell given in Table 4 for which ctlatlb' with inter- axial angles non-acute. The transformation matrix morphological to Delaunay cell is 110/00I/l00.In addition to the argument presentedfor the morphological orientation, the retention of the cell indicated on morphological grounds is strongly supported by structural evidence.The complete structure determination (Mcl,ean and Anthony, 1970) singles out the morphological D direction as fundamental in the structure. Pro- jections along it greatly facilitate direct comparison with other related mineral structures. An X-ray powder pattern was prepared with Ni-filtered radia- tion (1.5418A) in a 114.59mm Debye-Scherrercamera. The Straumanis mounting was used to correct for film shrinkage. The pattern yielded more than 100 measurable lines, the low theta orders of which were indexed using the cell parametersderived from Weissenbergphotographs. Interplanar spacings, intensities, visually estimated with the use of a calibrated film strip, and indices are given in Table 5. Opucs In thin sectionhemihedrite shows feeble pleochroism with ZIY> X. A poor cleavageon (110)is enhancedby grinding and its trace may show extinctions of up to 30o to a in prismatic sections.Relief is extreme. Re- fringence data are given in Table 6. Dispersion is noticeablein interferencefi.gures and resembleshorizontal I 100 S. A. WILLIAMS AND T. W. ANTHONV

Telr,n 5. X-Rev Powonn D,lre ron llrurnsonrrE.' CuKa:1.5418 A.

d(obs.),A d(calc.), A d(obs.),A

4 6. /O5 8.755 001 o4o 7 1.912 It.ort 3 7.481 7.366 100 fr.orr 22s 9 5.5t2 5 508 111 1.90s 722 20 1 904 J 3 5 384 5.416 ot2 56-3 20 r.876 I1.eo3 90 4 872 4.880 120 r.876 054 30 4.675 4 691 122 4oo 3 1.841 It.e+t 80 4.364 4.363 220 \1.838 014 4 136 4.156 110 .82s 2_31 5 1.E23 11 20 3 909 3.917 201 \1.822 221 4 3.820 3 826 o20 .sos s-5s 5 1.808 1r -frt 20 3.676 3 683 200 \r.sos 3 3 584 3.590 222 23s 9 1.779 l1.77e 30 3.478 3 477 202 s42 3 1.754 I1.7zs 20 3. 399 3 404 723 1.753 126 100 3 301 3.301 122 9 1.7s7 10 3.234 3 218 133 80 3. 164 3 t63 320 8 1.716 too 103 80 3.102 10. ot2 2 3 033 t3.09s 8 1.686 3.038 201 211 t0 3.019 [s.oze 3 t.663 t3.012 113 20 2.933 3 001 123 20 1.647 55 2.924 2.922 n3 2.849 2.855 242 10 1.621 30 2.774 2.777 30 2.708 2.708 024 11 1.613 z.aao 243 10 I .598 2 2 672 I 143 LL 1.579 20 2.607 12.663 2.608 342 5 1 566 20 2 558 2 556 lI4 9 1.548 30 2 514 2.5r9 322 2 1.51E I12 1.505 2.450 !2.++t 10 1.494 10 2.420 12.4s4 2.421 340 1.479 20 2.354 2 356 430 r.464 30 2.324 2.326 M2 1.460 (z. soz 131 t.425 20 2.299 lz.soz l0 1.415 lr roo 421 r.394 10 2.244 2.245 SB2 J 1.391 rzs 4lL 10 1.373 45bc 2 .182 [2. 12.r81 440 1.i49 rz+ 34r 10 1.338 10 [z rzo 410 8 L.324 20 2.O77 \2. 2.O78 220 6 1.316 20 2.O42 130 9 1.305 045 E 1.295 20 2 009 135 11 1.285 10 1 994 432 10 10 1.956 47r 11 1.260 1+4 9 1.236 10 1.940 215 10 1.230

e Iudexing on basis of the morphological cell and Weissenbergdata b Intensity visually estimated with calibrated film strip o b:brcadline Plus 28 add.itional Iines to 0.729 i HEMIHEDRITE I l0r

TaerE 6. Oprrcer, ConsreNrs or Hnuurnonur.

a:2 105*0.005ye11ow p:2.32 *0.02 yellow t:2.65 *0.02 orange : 0 . 545 2V"(meas.):92'(-) 2V"(calc.):88"(+)

dispersion.The optical orientation (Table 7) was determined by universal stage methods using a goniometrically oriented, right-handed crystal. The crystal is assumed to be oriented so as to give @and p angles as shown in Table 2. A stereographicprojection of the optical orientation is shownin Figure 3. Optical activitv could not be demonstratedin interf erencefigures taken from thin sections.Attempts to see such effects in thick sectionsfailed owing to strong scattering and absorption of incident light.

ConctusroNs Hemihedrite has been carefully compared to , phoenicochrotie (Temple, 1956)and (Bariand and Herpin, 1963).Powd'er patterns of these chromates show certain similarities (Table 8) so that confusion could arise. A specimenof "jossaite" (Breithaupt, 1858), provided by the U.S. National Museum (cat. no. R6032) was examined and proved to be crocoite. The crystals on this specimen fit the description given by Breithaupt. Type specimensof hemihedritewill be depositedat the U.S. National Museum and the University of Arizona.

AcKNowLEDGMENTS

We are grateful to Mr. R. W. Thomssen for bringing the problem to our attention a.nd providing specimens of the type material. Mr. Thomssen kindly wrote the section on the geology of the type locality. Mr. Richard A. Bideaux has provided help in many of the computations. The morpho- Iogical angle table was computed by him.

t^"* ?.O"""^".o-T-t

tt*@

a -90.1" 25.70 - 90.lo 25.7" B 163,7 82.3 175.3 88.0 t 70.0 6s. 1 84.2 64.2 1102 S A. WILLIAMS AND T. W'. ANTLIONY

Teer,r 8. Str.oNc Poworn Du'ructroN LrNrs or !'oun Cnroulros.

Crocoite Phoenicochroite Iranite Henihedrite USNM R-9618 (Beresov) (Iran) (ty'pe locality)

d(A) d(A) r d(L)

4.87 4.36 359 3.60 10 3 .48 3.49 10 3 .48 3.39 328 328 10 330 10 3.18 10 3.16 8 3.08 10 3.10 8 2.99

Mr' Pau Mr. John Jago provided a specimen of phoenicochroite for comparison; Desautels of the U.S. National Museum provided crocoite and "jossaite." Dr. A. K' Temple provided information on phoenicochroite from Leadhills-wanlockhead. Dr. Clifford Frondel provided a specimen of Beresov phoenicochroite. Mr. Robert B. Laughon kindly made the electron-probe examination of hemihedrite. we are pleased to acknowledge the many assistances of Dr. w. John Mclean who determined the precise unit-cell parameters and who maintained a continuing intelest throughout the study. We are grateful to Dr. A. Pabst who criticized an early version of the manuscript. Dr. the J. D. H. Donnay has spent an inordinate amount of time reviewing and correcting manuscript, and the quality of the paper owes much to his efiorts.

RrI.annr.rcns

BARTAND,P., el{o P. Hrrprx (1963) Une nouvelie espbce minerale: Iranite, chromate hydratd de plomb. Bull. Soc.Fr. Mineral. Cristallogr. 36' 133-135. BoNo, W. L. (1946) Computation of interfacial angies, interzonal angles, a.nd clinographic projection by matrix methods. Amer. Mineral' 31,3142 Bnnttururt, A. (1858) Jossaite. Berg HutrtenmannischeZ' 17' 51t-55. (1963) Dorxav, J. D. H., G. Donnay, E. G. Cox, O. Kennard, and M' V. King Crystol Data. Amer Crystallogr.Ass. Monogr.5r63. 33, EvaNs, H. T., Jn. (19aS) Relations among crystallographic elements. Amer. Minerol' 60-63. Amer. McLraN, W. J., eno J. W. Amrnonv (1970) The of hemihedrite. M ineral.ss, 1103-l I 14. Trrrrrr, A. K. (1956) The Leadhills-Wanlockhead lead and deposits. Trans. Roy. Soc-, Ed:inbargh63,7. Wrrlr.mrs, S. A. (1966) The significance of habit and morphology of wultenite Amer. Mineral' 51,1212-1217

Monuscript recei'oeit,April T, 1969; accepteil'for publication, April 8, 1970.