Tsn AUERTcAN M rxERA LocIST

JOURNAL OF THE MINERALOGICAL SOCIETY OF AMERICA

Vol. 53 SEPTEMBER-OCTOBER, 1968 Nos. 9 and 10

WICKENBURGITE, A NEW MINERAL FROM ARIZONA SroNBv A. Wnrrnrus, Phelps Dod.geCorporation, Western E*ploralion Ofi,ce,Douglos, Arizona.

ABSTRACT Wickenburgite, PbsAlzCaSiroOzr(OH)e,is a new mineral lound in abundance at several prospects near Wickenburg, Arizona. It is an oxide zone mineral derived from lead ores and occurs with phoenicochroite, mimetite, cerussite, and willemite. The mineral is well crystallized to granular; white, colorless, or rarely pink, and has a vitreous luster. The hardness is 5, G:3.85 (meas); 3.88 (calc.). FluorescesduII orange in short wave a.o. Crystals show dihexagonal dipyramidal symmetry, are tabular, and dominated by [0001] and {1011}. The axial ratio is a:c:l:2.354 (morph.) and.a:c:1:2.363 with o:8.53 A and c:20.16 A derived from the refined powder data. Z:2. Morphological and Weissenberg data establish the space group as P6zf mmc. The strongest Iines are 10.085 A (10),5.e62 (3);5.043 (3),3.392 (6),3.3ss (4),3.2s7 (8),2.79r (3), and 2.6s9 (4). Crystalsare uniaxial(-) with eo:1.6480,oo:1.6918. Dispersion of the indices (z>1) is moderate. No previously established species are likely to be confused with wickenburgite with the exccption of belmontite (?). INrnonucrrow The new mineral has been found in abundanceat several Iocalities south of Wickenburg, Maricopa County, Arizona. The speciesis named for the locality. The type locality is the Potter-Cramer property which is near the sectioncorner common to sections13,14,23, and 24,T4N, R7W Belmont Mountains 15' quadrangle.Wickenburgite is abundant here as veins in outcrop near the collar of a steeply inclined shaft. It is also very abundant at another prospect 18 miles to the north along a power line road, at the nearby Moon Anchor mine, and at severalother nearbypros- pects. OccunnpNcn At the type locality wickenburgite occurs as an oxide zone mineral in a vein which originally carried galena and sphalerite in a gangue consisting iargely of quartz and fluorite. The vein cuts steeply acrossa nearly hori- zontal fault contact between granodiorite and overlying rhyolite breccia. An intensely altered purple andesiteoccurs as irregular lensesalong the fault zone. Only relics of galena remain in a remarkable oxide suite which consists 1433 1434 SIDNEY A, WILLIAMS largely of wickenburgite, phoenicochroite,and mimetite with lesser amounts of cerussite,willemite, crocoite,B duftite, hemihedrit.e,ajoite, vauquelinite,descloizite, laumontite, and shattuckite. Wickenburgite is by far the most abundant of theseminerals and was among the last to crystallize.

Pnysrc,u PnopBnrrBs Wickenburgite is perfectly transparent and colorless,or rarely salmon pink, when well-crystallized.Massive or granular material is dull white. Crystalsvary from 0.2 mm to 1.5mm in diameter and averageabout 0.5 mm. Cleavageon the base (0001)is indistinct. Crystals often occur as spongy aggregatesof small, highly perfect in- dividuals.Larger crystalstend to build subparallelaggregates or rosettes on (0001). The crystals are tough and brittle with a Mohs' hardnessof 5. The specificgravity is 3.85 (Berman balance)and 3.88 (calc.). In short-wave ultraviolet light wickenburgite fluorescesdull orange. Specimens with willemite are particularly handsome for the willemite fluorescesand phosphorescesyellow-green.

CnBltsrtv The chemicalanalysis was planned on the basis of results of qualita- tive tests by spectrographic, X-ray fluorescence, and microchemical means. These tests showed major Pb and Si, and minor Al and Ca. Traces of Mg and P were also noted. X-ray analvsiseliminated all ele- ments other than Pb with Z)20; lor the lighter elementsspecial efforts were made to prove the absenceof B, N, S, COe,and the halogens. The chemical analysisshown in Table 1 is based on three separate samples.All of thesesamples were obtainedfrom one hand specimenand

Taere 1. Cntlrrclr, AN.lr,ysrs or WrcxeNeuxcrrr

\\t.Ta Ratio To ideal

Pbo M.0" o.r97 45.16 SiOr 42.\b .70r 40.53 AhOs 7 .6b .0715 688 CaO 3.8@ .0678 3.78 H:O* 3.77" .209 3.65

100.00

Analysts: (a) Rocky Mountain Geochemical Corp., Salt Lake City, Utah. Pb and Ca by colorimetry on 80 mg sample. (b) E. C. Thompson, Jr., Phelps Dodge Corp., Si and Al gravimetrically on 72 mg sample. (c) by author, gravimetrically on 34 mg sample. WICKENBARGITE 1435

were free of any visible impurities. The analysis gives, in terms o{ unit 'Ihis cell contents,6PbO, 2AlzOa,2CaO,20SiOz, 6HzO. may bc written PbrAlzCaSiroOx'(OH)0. Wickenburgite is not visibly affected by hot or cold acids or alkalis (HCl, HNO3, KOH, NH4OH). Solution must be affectedby prior fusion as with borax or sodium bicarbonate. Fusion of the pure mineral occurs at red heat and the resulting glasshas an index of refraction of 1.64n'

Monpuorocv Because of an unfortunate tendency for wickenburgite to build sub- parallel aggregateson {OOOt} , only the smallest(0.2 to 0.4 mm) crystals were suited for the determination of angular constants' Larger crystals tend to be more complex, however, so these were used to discoverthe rarer forms. A varied batch of 20 crystals was examined. No evidence contrary to dihexagonal dipyramidal symmetry was discovered. Other than the forms siven in Table 2 are the uncommon forms

Tneln 2. Cnvst,lllocnapnrc D,q.te ron WtcruNsurcrre

Dihexagonal dipyramidal, 6/ mmm ; o: c : | : 2.354, p;i r o: 2.778' 1

Form A!

c 0001 0'00' 90"00' 90'00' m 1010 solool 90 00 60 00 90 00 1014 30 00 3+12 /J +t 90 00 r. 1011 30 00 69 48 62 1 90 00 z 3032 30 00 76 13 60 57 90 00 p 112+ 000 49 39 90 00 67 36 6 | 7.12 2224 .)o J 7134 8342

andr {toTz},lst4+}, and {4150}.Mostcrystalsexhibitonlyc {0001}, {tOtt} with traces of m | 1010}. A typical crystal and an unusually complexone are shown in Fig. 1. No twinning was observed. The larger crystals and the most complex ones were found onl-v with willemite. These crystals fluoresce more strongly than small or simple crystals.

Frc. 1. A typical crystal on the Ieft and an unusually complex crystal on the right. 1436 SIDNEY A. WILLIAMS

Cnvsrar, Dara If the s1'mmetry is taken as 6/mmm on the basis of morphological study, Weissenberglevel photographs of single crystals establish the spacegroup as Pfif mmc. Cell data found by various methods are pre- .ented in Table 3.

Tasln 3. UNrr Cnr,r, CoxsraNrs Fon WrcrrNsuRcrrr

Morph. Powder Rotation Weissenberg

a:c l:2 354 l:2.363 7i2.365 1:2.358 a 8.53A+.007 8.53A+.01 8.53A+.01 c 20.16L+.02 10.16A+.04 20.12L+.02

The powder data given in Table 4 were obtained with both CrK" and CuK. radiation; CuK" radiation was used only for lines with very small d spacings.The pattern was indexed and then used to refine the cell constantswith programscreated by F. B. Millett on an Epic 3000calcu- lator. The cell volume determinedfrom the refined constantsis 1271 A3 which gives a calculatedspecific gravity of 3.88 il Z:2.

Telrr 4. PownBn Dare ror lVrcrBNluncnB

I kit

t0 10 08 10 08 0002 (t ttt 2134 t.764 | 761 3038 2 146 7 39.1 7 388 1010 r+.s 3031 2r39 \2. 1 750 It.t+t 6 961 6 937 loil 2 391 2 .392 3032 Ir.zso 3146 5 962 5 9.59 tO72 2 3t4 2 312 3033 I 735 r.731 4044 5 043 5.040 0004 2 277 2.271 2027 1.696 l 695 3250 4.267 4 266 1120 2 215 2.213 3034 3117 1.673 [1.67o ,1.158 1 161 1014 2.t71 2 170 I 128 \r .672 3252 3 932 3.928 1122 |2.114 1019 642 2.O2-11 2 114 1.646 Jt .3 700 2 694 2020 ),2 t+t 2136 lr are 3253 3.51I 3.s39 1015 2.088 2 087 2242 osa 1.07 12 I .636 fr 3 47.5 3 ,168 2022 [r nro 3140 oss 2.t.3.10 2 01t \r 3.355 .3 360 0006 I 2.039 3t4l 1.620 1 619 4046 3 257 3 256 1121 2.016 0.0.0 10 (r aot 3251 2.0r2 ) 3 0.58 3 oss 1016 \z ooa 3112 1 610 I t .arz 4150 2 980 2 980 2021 | 987 1 986 .3036 lr.oor 4t5l 2.i91 2 792 2130 e64 2211 1.590 1.590 3148 I 963 Ir 2 767 2 766 zt\r \r ooo 3143 (r.sas 1.1.2t2 2-726 2 724 2025 1.900 1.898 3114 1.563 .{r soo 30310 2 691 2 691 2t32 t 2138 l. JoJ JZOJ | 872 It.u I 2 639 2 639 1126 l1.sz2 3037 t .539 1.536 4154 2.520 2 520 0008 1.848 1.847 4040 f r stc 3149 1.514 2.466 2 163 3030 | 822 1.823 1.12.10 )r

a I

Oprrcs In Lhin section wickenburgilecxhiltits a poor basal cleavagcwhit:h is enhancedby grinding. Extinction is parallel to this cleavagewhich is the length slow direction. When fine grained,wickenburgite could easih' be confusedwith sericite. Most of the crystalsare perfectly uniaxial (-) but someof the aggre- gate crystals show a small separationof isogyres.Dispersion of the in- dicesis moderateand normal (tDr). The refractiveindices are given in Table 5.

T.c.nln 5. RetnActrvn lxorcrs or WrcrnNsunclrn

Line

|.7043 1.7006 1 6918 1.683.5 e 1.6603 1.6556 1.6480 1.6418 biref. (calc) 0 0440 0.0450 0.0438 0.0417 biref. (meas) .0439 .0447 .0441 .0425

The indiceswere measured on a heating stageusing interferencefilters for monochromatic light. Liquids and filter bandpass characteristics were checkedon a divided circle spectrometer.The measuredbirefrin- gencewas determined in monochromaticlight usinga Berek compensator specially calibrated for the interference filters used. Values of refringence and birefringenceare probably within 0.0005although no correctionfor dn/dt of the mineral was applied.

Srrrrrnn SpBcrBs Wickenburgiteis unlikely to be confusedwith any well definedspecies. It is most similar to an unnamed artificial lead silicate describedb1' Dana and Penfield (1835) and Wheeler (1886) The artificial material has a much higher Pb: Si ratio and is morphologicallydistinct. The mineral belmontite (?) was not available for comparison.It is said to be a yellow lead silicateoccurring with stetefelditeat the High- bridge mine, Belmont, Nevada. Several days' examination of these dumps produced considerableamounts of stetefelditeand many other species.Some of the stetefeldite occurs with bright yellow mimetite crystalson quartz, and I suspectthat this is belmontite (?). No wicken- burgite was found at this locality. Type specimensof wickenburgitewill be depositedat the U. S Na- tional Museum. 1438 SIDNEY A. WILLIAMS

AcKNowLEDGIdENTS

I am especially grateful to F. B. Millett for creating programs for indexing and refining the cell. E. V. Ciancanelli and A. E. Nevin furnished a number of specimens from the type locality. Paul E. Desautels provided stetefeldite from the Highbridge mine. The Phelps Dodge Corporation provided financial assistance for the analytical work. I am grateful to my wife and daughter lor patiently helping comb the dumps at the Highbridge mine and the type locality. Dr. A. Pabst critically reviewed the manuscript. The mineral and the name have been approved by the IMA.

RnrBnaNcns

D.r.Na,E. S. alrn S. L. PrNlrcm (1885) An artificial crystallized lead silicate.Am.er.f .Sci.., 30, 136-139. Wunnmn, H. A. (1886) Further notes on the artificial iead siiicate from Bonne Terre, Mo. Amer. J. Sci., 32, pp. 272-273.

Manuscriptreceited., April 3, 1968; acceptedJorpublicotion, June 21, 1968.