American Mineralogist, Volume 74, pages 927-933, 1989

Grandreefite,pseudograndreefite, laurelite, and aravaipaite:Four new from the Grand Reef mineoGraham County, Arizona

AurHoNv R. K,clvrpr Mineralogy Section,Natural History Museum of Los AngelesCounty, 900 Exposition Blvd., Los Angeles,California 90007, U.S.A. Pnrn J. DUNN Department of Sciences,Smithsonian Institution, Washington, D.C. 20560, U.S.A. EucnNB E. Foom U.S. Geological Survey, Mail Stop 905, Denver Federal Center, Lakewood, Colorado 80225, U.S.A.

AssrRAcr Four new fluoride minerals are describedfrom the Grand Reef mine, Laurel Can- yon, Aravaipa mining district, Graham County, Arizona. They occur together in a vug surrounded by layers of quartz, , and galena.The new minerals are interpreted as resulting from the reaction ofsupergene solutions with galenaand fluorite. Grandreefite,Pb2SO4F2, is orthorhombic,a : 4.439(4),b : 13.575(13), c : 4.333,1)L, V : 261.1(4)A', spacegrorry 1222, Z: 2.Il occurs as colorlessprismatic crystals striated parallelto [001], with a densityof 7.0(l) g/cm3(meas.),7 .15 g/crn3(calc.). Grandreefrte is biaxial (+), very small2V, with weak ,r > y, d : 1.872(5),B : 1.873(5),7 : 1.897(5);orientation is X: c, Y : a, Z : b. The compositionis PbO 82.9, SO313.8, F 7.1, sum 103.8,less O = F 3.0, total 100.8wt0/0. Grandreefite is isostructual with IarOrSOo, basedon layers of the B-PbR (fluorite) structure parallel to (010) with SOogroups between layers. Pseudograndreefite,PbuSOoF,o, is orthorhombic, a : 8.5182(5), b : 19.5736(ll), c : 8.4926(5)A, V: 1416.0(l)Ar, spacegrotp F222,2: 4.It occursas colorlesssquare crystalstabular on {010}, with a densityof 7.0(l) g,/cm3(meas.), 7,08 g/cm3(calc.). Pseu- dograndreefiteis biaxial (+),2V: 30(3)', with strongdispersion, r > v, d : 1.864(5),0 : 1.865(5),r : 1.873(5);orientation is X: c, Y : L, Z : b. The composition is PbO 84.9, SO34.7,F 13.1,sum 102.7,less O = F 5.5, total 97.2wto/o.The structureof pseu- dograndreefiteis very similar to that ofgrandreefite. Laurelite,Pb(F,Cl,OH)r, is hexagonal,a: 10.252(9),c : 3.973(l) A, y:36t.1(6) A', spacegroup P6, P6, or P6/m, Z: 6.It occursas colorlessneedles with a densityof 6.2(l) g/cm3(meas.), 6.52 g/cm3(calc.). Laurelite is uniaxial (+), with or: L903(5),e : 1.946(5). The composition is Pb 82.0, F 13.0, Cl 3.6, OH 0.9, total 99.5 wtol0.The structureof laurelite is probably related to that of a-PbFr. Aravaipaite,Pb3AlFe.HrO, is triclinic, with a : 5.842(2),b : 25.20(5),c : 5.652Q)A, a:93.84(4),0:90.14(4),r: 85.28(4)",V:827(2) A', spacegroupPl ot Pl',2:4.Ir occursas colorlessthin plates with perfect micaceous{010i cleavageand a density of 6.37 g/cm3 (calc.). Aravaipaite is biaxial (-), 2V: 70(3)", with strong dispersion, r < v, ot : 1.678(2)'P: 1.690(2),7: 1.69a(2);Euler angles are Q: 67",0: 6Q.,0:76'.The compositionis Pb 73.8, Al 3.6, F 21.0, HrO 3.0, total 101.4wt0/0. The structureof ara- vaipaite may be related to that of p-PbF, with layers of the B-PbF2structure parallel to {010} and Al(F,HrO) octahedrabetween layers.

IurnonucrroN ing the past 25 years, the mine has become well known among mineral collectors for a variety of rare minerals. The Grand Reef mine is situated in Laurel Canyon, The most notable of these is , which has been about 6 km northeast of Klondyke, in the Aravaipa min- found in well-formed crystalsup to 5 cm in length. Jones ing district of Graham County, Aizona. The mine ex- (1980) provided an overview ofthe history, geology,and ploits a small epithermallead-copper-silver deposit, which mineralogy of this deposit. is hosted by a silicified breccia. The breccia is highly re- During the course of a detailed mineralogic and para- sistant, forming a precipitous clifl locally known as the geneticstudy of the Grand Reef mine, Mr. William Besse "reef," from which the name of the mine is derived. Dur- (Besse,l98l) obtained an unusual specimen,which had 0003404x/89/0708-0927$02.00 927 928 KAMPF ET AL.: FOUR NEW MINERALS FROM GRAND REEF MINE, ARIZONA

subsequently provided for examination by its current owner, Mr. ks Presmyk of Mesa, Arizona. The two spec- imens were discovered to be portions of the same vug. To date these are the only specimensknown to contain any of these new minerals. Fragments of rock trimmed from the second specimen were also provided. A block of matrix measuring27 x 25 x I 5 cm was reconstructed from thesefragments and the two vug sections. The matrix is typical of the mineralization found in the bench area of the Grand Reef mine. Veins of galena fol- low irregular fracturesin the breccia,and minor amounts of copper sulfides associatedwith the galena are altered principally to linarite and caledonite. The galena shows lesseralteration to .The vug containing the new Fig. l. Crystaldrawing of grandreefite. minerals occupiesthe center of what was evidently once an interstice between breccia blocks. Although a portion been recoveredin 1980 by Mr. Wayne Thompson under of the rock surrounding the vug is missing, it is clear that the auspices of Southwestern Mineral Associates. Mr. the vug was completely surrounded by galena.An irreg- Bessebrought the specimento the attention of one of us ular and incomplete layer of fluorite is found inside the (A.R.K.) with the observation that it might contain two galena,followed by a complete layer of quartz surround- minerals new to science.In the course of the present in- ing the quartz-lined vug. Anglesite fills fractures in the vestigation, these two minerals, as well as two others on quarlz. A completely filled pocket surrounded by galena the same specimen,were determined to be new. The four and containing only massive fluorite occurs a few centi- new minerals are named grandreefite,pseudograndreefite, meters away from the vug. laurelite, and aravaipaite. Grandreefite is named for the Isolated pocketsin galena,sometimes containing vugs, Grand Reef mine. Pseudograndreefiteis named for its are typical of the bench areaof the Grand Reef mine, and close similarity to grandreefite in physical properties, the mineralization in thesepockets is often quite distinct composition, and structure. Laurelite is named for Laurel from that in the adjacent portions ofthe oxidation zone. Canyon in which the Grand Reef mine is situated. Ara- Mr. Wayne Thompson (personal communication, 1988) vaipaite (iir d vt' pi It) is named for the Aravaipa mining has consideredthe vug containing the four new minerals district in which the mine is located. to be an example of such an occuffence. The speciesand the nameswere approved by the Com- (PbrSOlFr) mission on New Minerals and Mineral Names, IMA, prior Gn-q.NonnnrrrE to publication. The type specimen containing all four Appearanceand physical properties speciesis deposited at the Natural History Museum of The only crystal of grandreefiteon the type specimen Los AngelesCounty (cat. no. 25414). measwes 1.5 x 3 x 4 mm parallel to the F001, [010], and [001] cell directions, respectively. The characleiza- Gnor,ocrc AND MrNERALocrc sETTTNG tion of the mineral used fragments removed from this The at the Grand Reef mine was emplaced in a crystal, which is prismatic and striated parallel to [001]. heavily brecciated,nearly vertical fault zone. The breccia, The forms {120}, {130}, {2931,{293}, and {l0l} were consistingof rhyolite and schist fragments,has been silic- observed and are depicted in Figure l. Two bladelike ified and contains specular hematite and fluorite as the crystals of grandreefiteon the second specimen reach 7 principal gangueminerals. The most prevalent primary mm in length. ore mineral is galena, with chalcopyrite, argentite, and Grandreefite is colorless and has a white . It is pyrite being present in lesser amounts. Chalcocite, co- transparentwith a subadamantineluster. No fluorescence vellite, silver, and copper were products ofsupergeneen- in ultraviolet light was detected. The Mohs hardnessis richment. In addition to the four new minerals described approximately 2Yz.The mineral is brittle with a conchoi- here,Besse (1981) listed 25 other minerals,most of which dal , and no cleavagewas detected.The density, have resulted from oxidation. measuredon a Berman balanceusing 3.43 mg of sample, In 1969a benchwas blastednear the top ofthe "reef' is 7.0(l) g/cm3;the calculateddensity is 7.15 g/cm3. just south ofa vertical stope known as the "glory hole." The area of this bench has produced most of the mine's Opticat properties well-crystallized oxidation minerals, predominantly sul- The optical properties of grandreefitewere determined fates. The type specimen of the four new minerals was by immersion using a Supper spindle stage. Over the found in this area. courseof a few minutes, the crystal surfacesbecame frost- The type specimenmeasures l0 x 7 x 4 cm, and the ed becauseof reaction with the high-index immersion vug containing the new minerals is about 2 x 1.5 x 0.5 liquids. This required that observationsbe made rapidly cm. A second specimenwith a 5 x 2 x 1.5 cm vug was and may have contributed to experimental error. KAMPF ET AL.: FOUR NEW MINERALS FROM GRAND REEF MINE, ARIZONA 929

Tlele 1. X-ray powder-diffractiondata for grandreefite

d 10 6.73 6.78 020 10 1.581 1 581 260 JU 4.20 4.21 110 25 1.545 1.545 202 z3 4.10 4.11 011 <5 1.508 1.506 222 10 3.382 3.389 040 5 1.468 1.467 310 100 3.159 3.162 130 1 426 190 20 1.424 90 3.116 3 120 031 1.422 091 80 3.084 3 090 101 1.403 330 30b 1.401 <5 2.810 2.811 121 1.396 301 RN 2.281 2.283 141 10 1.377 1.381 271 2254 2.259 060 1.370 033 30 2209 2213 200 50b 1.370 1.370 172 30 2 158 2157 002 1.368 103 5 2 101 2104 220 10 1.291 1.291 341 2.058 2.056 022 1.275 zoz 25b 1.274 Fig. 2. Crystaldrawing of pseudograndreefite. 15 1.949 1.949 211 1.268 143 10 1 922 1.920 112 5 1.242 1.241 110.1 't 1.854 1.853 240 <5 215 1.213 312 50 1 824 1.824 161 <5 1.194 1.196 291 diation was employed, and the intensities were visually 60 1.806 1.805 231 1.190 192 20 1 188 1.782 132 1.188 361 estimated. These data along with the calculatedd values 35b 1.780 1.774 170 15 1.176 1.176 332 are given in Table l. 1.767 071 1.170 163 10 1 168 1.165 233 Cornmentson the structure Note: 114.6-mmGandolfi camera, CuKa radiation,visually estimated Grandreefiteis apparently isostructural with LarOrSOo intensitibs,indexed with the aid ol the structure-factordata: b : broad line and may briefly be describedas consistingof layers of the B-PbF, (fluorite) structure parallel to (010), with SOo groups betweenlayers. The layer sequencecorresponding ro one unit cell is [SO.-PL2F-Pb-SO4-PL2F-Pb]. The Grandreefiteis optically biaxial (+). The indices of re- LarOrSOnstructure was determined by Fahey (1976) us- powder-diffraction data, but the positional parame- fraction measured in white light are a : 1.872(5), B : ing 1.873(5),and ^7: 1.897(5).The observed2V was very ters that he assignedto the sulfate oxygen site must be large temperature fac- small; the calculated 2V is 23'. Weak dispersion, r < 4 consideredsuspect because ofthe was observed.The optical orientation is X: c, Y : t, Z tor (15) for this atom. An attempt to solve the structure : b. Coarse polysynthetic twinning was observed under of grandreefite using single-crystal data failed to locate crossedpolarizers, but no twin law could be determined the oxygen site(s)and has resulted in an R value of 0. I l. and no morphological or X-ray diffraction evidence for It is likely that absorption-colrectionproblems are largely twinning was found. to blame, but it is possiblethat either rotational disorder or twinning has obscuredthe site. Efforts are still under Chemical data way to completely solve the structure. Grandreefitewas analyzedwith an electron microprobe PsnuoocnaNDREEFITE (Pb6SO4Fro) utilizing synthetic PbO, celestite, and synthetic CaF, as standards for Pb, S, and F, respectively. The analysis Appearanceand physical properties yieldedPbO 82.9,SO3 13.8, F 7.1,sum 103.8,less O = Pseudograndreefiteoccurs as sqrulre(pseudotetragonal) F 3.0, total 100.8 wt0/0.Single-crystal infrared spectros- crystals tabular on {010}. The tablets form a single sub- copy indicated that no water was present in the mineral parallel ag1;regateon the type specimen measuring4 x I (<0.001 wto/o).The empirical formula based upon O + x 4 mm parallelto the u001, [010], and [001] cell direc- F : 6 is PbrorSonuOrnrFror.The simplified formula, tions, respectively.The pseudograndreefiteaggregate is in Pb,SOoFr,requires PbO 81.39, SO. 14.60,F 6.93, sum contact with the grandreefitecrystal and appearsto have 102.92,lessO = F 2.92, total 100.00wt0/0. Grandreefite partially overgrown the grandreefite. The forms {010}, decomposesin cold water. {100}, t00l}, {210}, and {012} wereobserved on pseu- dograndreefitecrystals, as depicted in Figure 2. No twin- Crystallography ning was detected. Precessionphotographs showed grandreefiteto be or- The physical properties ofpseudograndreefiteare near- thorhombic, with the spacegroup 1222, I2r22r, Imm2, ly identical to those ofgrandreefite. It is transparent and or Immm. The structure determination showedthe space colorlesswith a subadamantineluster and a white streak. group to be 1222. The cell parameterswere refined using It exhibits no fluorescencein ultraviolet light and has a four-circle difractometer data, yielding a: 4.439(4),b : Mohs hardnessof approximately 2t/2.It is brittle with a 13.575(13),and c : 4.333(4) A. l]tre cell volume is conchoidal fracture and no discerniblecleavage. The den- 261.1(4)A' and Z: 2. sity, measured on a Berman balance using 4.41 mg of The X-ray powder-difraction pattern was recorded us- sample, is 7.0(l) g/cm3; the calculateddensity is 7.08 ing a Gandolfi cameraof 114.6-mmdiameter. ClKa ra- {cm'- 930 KAMPF ET AL.: FOUR NEW MINERALS FROM GRAND REEF MINE, ARIZONA

TABLE2. X-ray powder-diffractiondata for pseudograndreefite The X-ray powder-diffraction pattern was recordedus- ing a Gandolfi camera of I14.6-mm diameter and Cu/(a intensities were visually estimated. These 10 9.75 9.82 020 1.782 0.10.2 radiation. The <5 4.90 4.91 040 1.781 2.10.0 data and the calculatedd values are given in Table 2. 70b 1.779 't.771 <5 4.23 4.25 o02 244 4.23 200 1.767 442 Commentson the structure 3.90 022 1.694 193 20 3.89 5 1.694 3.89 220 1.691 391 As for grandreefite, the pseudograndreefitestructure has <5 3.262 3.272 060 1.607 084 10 1.606 as yet resisted complete solution. All Pb and S atoms 100 3.204 3.213 o42 1.602 480 3.205 240 1.527 012-2 have been located, as have most F atoms; but the oxygen 1.527 30 2.999 2.999 202 5 1.526 2 12 0 atoms in the presumedsulfate group and the "interlayer" 5 2.447 2.454 080 5 1.503 1.499 404 F atoms have not been located. The resulting R value is 25 2.212 2.211 262 <5 1.465 1.465 1 13.1 2.125 <5 1.404 1.402 0.1 l. The structure of pseudograndreefiteis very similar 20 2.123 004 014.0 2.'t16 400 1.365 2 10.4 to that of grandreefiteand may briefly be described as 5 2.051 2.050 191 1.363 4.10.2 p-PbF, (fluorite) par- 20 1.900 1.899 282 25b 1.364 1.363 464 consisting of layers of the structure (010) F between layers. The layer 5 1.865 1.865 224 1.361 046 allel to with SOoand 1.860 422 1.357 640 sequencecorresponding to one unit cell is 1.344 206 [(2SO.,4FF 5 1.346 1.339 602 4Pb-8F-4Pb-8F-4PH2SO4, 4D-4Pb-8F-4PL8F-4Pb]. Efforts are still under way to completely solve the struc- Note.'114.6-mm Gandolfi camera, CuKa radiation,visually estimated intensities,indexed with the aid of the structure-factor data; b : broad ture. line.

L.q,uREr-rrn(Pb(F,Cl,OH)r) Optical properties Appearanceand physical properties The optical properties of pseudograndreefitewere de- Laurelite occursas needlesup to l0 mm long and 0.05 termined by immersion using a Supper spindle stage. mm in diameter, but most needlesare much thinner and Pseudograndreefiteexhibited the same surface deterio- are typically groupedin parallel bundles.Laurelite needles ration in high-index immersion liquids noted for grand- in loosejackstraw-fashion fill the interior ofthe vug sur- reefite. rounding and atop the crystals of grandreefiteand pseu- Pseudograndreefiteis optically biaxial (+). The indices dograndreefite.Laurelite needlesare also found included of refractionmeasured in white light are a: 1.864(5),B in plates of aravaipaite and, to a lesserextent, in crystals : 1.865(5),and,y: 1.873(5).The observed2Vis30(3); of pseudograndreefite. the calculated 2V is 39'. Strong dispersion, r > v, was The needlesare prismatic parallel to [001] and have observed.The optical orientation is X: c, Y : s, Z : b. basal {001} terminations. Becauseof a combination of The lower indices of refraction, larger 2V, and stronger twinning, parallel growth, and narrowness,no distinct go- dispersion are useful in distinguishing pseudograndreefite niometer signalscould be obtained from the prism faces. from grandreefite. The crystalsare twinned by rotation around [001]' Laurelite is colorlessand has a white streak.It is trans- Chemical data parent with a silky luster. No fluorescencein ultraviolet Pseudograndreefite was analyzed with an electron mi- light was detected.The Mohs hardnessis approximately croprobe utilizing the same standardsas for grandreefite. 2. The tenacity can best be describedas brittle, although The analysisyielded PbO 84.9, SO34.7, F 13.1, sum the needlesare slightly flexible. The fracture is conchoidal 102.7,less O = F 5.5, total 97.2 wta/o.Single-crystal in- and an imperfect {001} cleavagewas observed. A pyc- frared spectroscopyindicated that no water was present nometer wasused for the density determination. The mea- (<0.01 wto/o).The empirical formula basedupon O + F surement on a 9-mg sample yielded 6.2(l) g1cn3. The : 14 is Pb5ersoero32nF,or,.The simplified formula, calculateddensity is 6.52 g/cm3.The discrepancymay be Pb6SOoFro,requires PbO 87.57, SO35.24, F 12.42,sum attributable to the difficulty in handling the needlesand l05.23,lessO = F 5.23,total 100.00wt0/0. Pseudogrand- to small sample size. reefite decomposesin cold water. Optical properties Crystallography The optical properties of laurelite were determined by Precessionphotographs showed pseudograndreefiteto immersion. No crystals suitable for conoscopicobserva- be orthorhombic with the spacegroup F222, Fmm2, or tion were found, but the mineral is assumedto be uniaxial Fmmm. The structure determination showed the space becauseof its hexagonalsymmetry. The optic sign is pos- group to be F222. The cell parameterswere refined using itive, and the indices of refraction measuredin white light four-circle diffractometer data yieldine a : 8,5182(5), b aree: 1.903(5)and e : 1.946(5).Laurelite was stablein : 19.5736(ll), and c -- 8.4926(il A. fne cell volume is high-index immersion liquids during the courseof optical 1416.0(l)Ar andZ: 4. study. KAMPF ET AL.: FOUR NEW MINERALS FROM GRAND REEF MINE, ARZONA 931

TABLE3. X-ray powder-diffractiondata for laurelite

d- d^ <5 5 07 5.13 110 <5 1.651 1.650 302 <5 4.40 4.44 200 5- 1.595 1.595 510 <5 4.01 3.97 001 1.570 222 1.570 Fig. 3. Crystaldrawing of aravaipaite. 25 3.61 3.63 101 5. 1.570 331 100 3 33 3.36 210 <5 1.546 312 40 3.125 3.140 '111 1.542 1.546 421 t aAl 40 2.s4s 201 10' 1.481 1.480 402 estimated.These data, along with the calculateddvalues, ;.ilo 300 10' 1.422 1.422 520 are given in Table 3. 30 z'ccv 2.564 211 35. 1.388 1.387 601 2.s63 220 5. 1.371 1.370 431 <5 2.457 2.463 310 15- 1.339 1.339 521 Commentson the structure 10 2.369 2.374 301 1.282 113 Laurelite has not yielded crystalsadequate for structure J 2.213 2.220 400 1.282 422 40 1.282 <5 2.'t47 2.154 221 1.282 611 determination. However, a structural relationshp with 2.090 2.093 311 1.282 440 a-PbF, (as well as the minerals cotunnite, laurionite, 2.434 2.037 320 1.269 203 15' 1.268 t( 1.986 1.987 002 1.268 700 , and fiedlerite) is indicated. The intense 1.939 102 <5 1.246 1.244 512 reflections 210, 140, and 420 onthe hk} precessionpho- 60 1.934 1.938 401 1.232 213 <5 1.234 't,231 tograph of laurelite are consistentwith an orthorhombic 1.937 410 620 : .t 1.913 202 1.209 303 pseudocellhaving a : 6.73,b : 7.79, and c 3.97 A. aR* Al) 15' 1.209 1.813 321 1.208 701 This is analogousto the orthorhombic (pseudohexagonal) 10. 1.740 1 741 411 1.177 223 c: 40- 1.709 1.710 212 1 176 432 a-PbF,cell, which hasa: 6.440,b:7.651, and 10 1.178 20- 1.676 1.678 420 1.176 621 3.899.The slightly larger dimensionsofthe laurelite pseu- 1.176 710 docell are consistentwith the partial replacementof F by Note.'114.6-mm Gandolfi camera, CuKq radiation,visually estimated Cl. In the a-PbF, structure, Pb is 9-coordinated in tri- intensities,indexed with the aid of the precession-filmdata. capped trigonal prisms. These prisms form face-sharing t Reflectionsthat were used in the least-souaresrefinement of the cell parameters. columns parallel to c, which are joined by sharing edges.

Anrvup.trrn (PbrAlF'HtO) Appearanceand physical properties Chemical data Aravaipaite occursas thin plates,0.001 to 0.1 mm thick, Laurelite was analyzed with an electron microprobe and up to 3 mm across.The platesare lamellaron {010}, utilizing synthetic PbF, for Pb and F and synthetic PbCl, the only prominently developedface. The {041} face was for Cl. Water was determined on a Mitsubishi moisture also detected,but plate edgesare usually rounded when titrator using a 3.35-mg sample.The water determination not forming contacts with other crystals. A perfect mi- indicated that the water is tightly bound, probably in the caceous{0 I 0} cleavagewas observed,as weregood { I 00}, form of OH. Theseanalyses yielded Pb 82.0, F 13.0,Cl {001}, {101}, and {101} cleavages.Figure 3 depictsa 3.6, OH 0.9 (HrO 0.5), total 99.5 vtto/o.The empirical single-crystalbounded by the observed faces and cleav- formula based upon F + Cl + OH 2 is ages.Polysynthetic twinning on {010} is always present. Pboe4[F,63Cl024OHo,.]rroo. The simplified formula is Aravaipaite is colorless and has a white streak. It is Pb(F,CI,OH),,which (with F: Cl : OH : 1.63:0.24:0.13)transparent with a vitreous to pearly luster. No fluores- requiresPb 83.25,F 12.44,CL3.42,OH0.89, total 100.00 cencein ultraviolet light was detected.The Mohs hardness wto/0.Laurelite decomposesrapidly in cold 1:l HCI and is about 2. Thin plates are flexible, although not as much dissolvesvery slowly in cold water. so as muscovite. The fracture is irregular. The density could not be measured,as the mineral sinks Crystallography rapidly in Clerici solution (p: 4.2 g/cm3),and the amount No single crystals large enough for X-ray diffraction of material available is insufrcient for density determi- studiescould be found. Becauseofthe growth ofneedles nation by other means. A cell content of four formula -- in parallel bundles and the pervasive twinning on [001], weights (Z 4) was chosenbecause it provides a reason- most samplesexamined by the precessionmethod yielded able packing efficiency of 620/o,compared with 54010for diffuse streaked reflections about the c axis. The crystal B-PbF, and 660/ofor the compound PbAlFs. This yields a used in the cell determination was nearly single, having calculateddensity of 6.37 g/crn3. only one smaller twin crystal attached. Laurelite is hex- agonal with possible spacegroups P6, P-6,or P6/m. The Optical properties cell parameters refined from the powder data are a : The optical properties of aravaipaite were determined 10.252(9),c : 3.973(l) A. ttre cell volume is 361.7(6)A3 by immersion using a Supperspindle stage.The polysyn- andZ: 6. thetic twinning on {010} is obvious under crossedpolar- The X-ray powder-diffraction pattern was recorded us- izers and considerablycomplicated the determination of ing a Gandolfi camera of I14.6-mm diameter. CuKa ra- optical properties. Utilizing the perfect {010} ,a diation was employed and the intensities were visually nearly single crystal with a very small attached twin was 932 KAMPF ET AL.: FOUR NEW MINERALS FROM GRAND REEF MINE, ARIZONA

TABLE4. X-ray powder-diffractiondata for aravaipaite

o* 80 12.5 12.5 020 10 2.304 2.301 260 <5 5.78 5.78 110 10 2.263 2.26s 162 <5 5.64 5.64 001 10 2.226 2.226 280 10 5.27 5.28 021 25 2.172 2.169 082 25 4.98 497 130 2.050 280 10 2.045 5 4.34 4.34 041 2.039 281 a nn 4.01 111 2.030 222 c 4.00 111 2.029 082 40 2.028 3.66 131 2.029 202 0 70 3.65 3.65 150 2.022 2o2 4ooo looo 3.64 131 1.981 2 100 15 1.979 ,::::,',0""= ,.'ilt 60 3.50 3.50 131 1.978 f .ii 1 60 3.33 3.32 i51 5 1.946 1.948 310 3.240 3.245 141 1.901 i.11.1 Fig. 4. Single-crystalinfrared spectrumof aravaipaite. 10 1.900 100 3.134 3.132 080 1.899 281 1.816 911 5 3.000 2.997 151 10 1.816 2.920 210 1.816 i i3 1 40 , olA obtained for determination of optical properties. Aravai- 2.912 200 5 1.790 1.790 341 1.774 331 40 5 1.772 paite was determined to be biaxial (-). The indices of 2822?Z?3 31l. 1.771 1i3 refraction measuredin white light are a : 1.678(2),0 : 2588 1.760 143 1.690(2),and ^y: 1.694(2).The observed2V is 70(3)'; SZZ|?31 5 1758 1.757 351 1.755 the calculated 2V is 66". Strong dispersion, r < L was 5 2.561 2.558 221 331 10 2.505 2.505 0 10 0 1.739 143 observed.The optical orientation is specifiedby the Euler 20 1.737 ) A1a 2.41s igl 1.737 133 anglesf : 67", {) : 60,0 : 76o. Aravaipaite was stable 2.414 132 10 1.702 1.702 571 in the immersion liquids during the period of optical study. 2.3s4 2.354 152 15 1.671 1.673 1.13 1 Note: 114 6-mm Gandolfi camera, CUK@radiation, visually estimated Chemical data intensities,indexed with the aid of the precession-filmdata. All reflections Aravaipaite was analyzedwith an electron microprobe were used in the least-squaresrefinement of the cell parameters. utilizing synthetic PbO, hornblende, and synthetic CaF, for Pb, Al, and F respectively. The analysis yielded Pb 73.8, Al 3.6,F 21.0, total 98.4 wt0/0.The amount of ar- avaipaite available was insufrcient for water determina- 93.84(4),0:90.14(4), and 7 : 85.28(4)".The cell volume tion by conventional methods, so recoursewas made to is 827(2)A' and Z: 4. single-crystalinfrared spectroscopythat required only a The X-ray powder-diffraction pattern was recorded us- single small plate of the mineral. The spectrum (Fig. a) ing a Gandolfi camera of 114.6-mm diameter. CuKa ra- indicated about 3 wto/owater. The uncertainty in this value diation was employed and the intensities were visually is judged to be about I wto/0,principally becauseof the estimated. These data along with the calculatedd values uncertainty in the molar absorptivity. The intensity of the are given in Table 4. 1650cm-'band, correspondingtothe HrO bendingmode, is consistentwith all water being in the form of molecular Commentson the structure HrO. Anisotropic absorbancein the 3400 cm-' region Aravaipaite crystals adequate for structure determina- suggeststhat the HrO is structurally bound. tion were not found. However, a structural relationship The empirical formula based upon F : 9 is with p-PbF, is indicated. The formula, cell dimensions, Pb2eoAlronFnoo. l.36HrO. The simplified formula is and perfect cleavage suggest that the structure may be Pb3AlFr.HrOrequiring Pb 74.21,Al3.22,F 20.42,HrO basedupon layersofthe B-PbR (fluorite) structureparallel 2.15, total 100.00 wt0/0.Aravaipaite decomposesrapidly to {010} with Al(F,HrO)u octahedrabetween layers. Note in cold l: I HCI and dissolvesverv slowlv in cold water. that the a and c cell dimensions are 5.842 and 5.652 A, respectively,and B is very closeto 90". (The lOlprecession Crystallography photograph is pseudotetragonal.)The unit cell ofp-PbF, Becauseofthe pervasive {010} polysynthetic twinning, is cubic with a : 5.940A. no completely singlecrystal suitable for X-ray difraction study could be found. The crystal chosen for the X-ray Gr,lnsroNn-Dn r,n coMPATrBrLrrY (and optical) study was nearly single, having only one The Gladstone-Dale compatibility indices, | - (KJKJ, smaller twin lamella attached.The two intersecting twin for grandreefite, pseudograndreefite,laurelite, and ara- lattices were readily apparent on the precessionphoto- vaipaiteare -0.061, -0.017, -0. 136, and 0.100, re- graphs.Aravaipaite is triclinic with possiblespace groups spectively(Mandarino, I 98 1).These suggest that the com- Pl or Pl. The cell parametersrefined from the powder patibility among the density, averageindex of refraction, daraarc a: 5.842(2),b : 25.20(5),c : 5.652(2)A, o: and composition is adequateonly for pseudograndreefite. KAMPF ET AL.: FOUR NEW MINERALS FROM GRAND REEF MINE, ARIZONA 933

The Gladstone-Dalerelationship should probably not be gation with decreasingtemperature. The decreasein sul- considereda valid measureof compatibility for thesemin- fate and increasein F suggestthat the sulfate was selec- erals becausecurrent knowledge concerning the interac- tively incorporated into the earlier phases.The selective tion of Pb with halogen elementsis incomplete. incorporation ofCl in laurelite is probably attributable to the preferenceof Cl for the a-PbF, (Pbclr) structural ar- P.q.RAcnNnsrs rangement. The Al in aravaipaite was probably present The new minerals are interpreted as resulting from the in the invading supergenesolution and was progressively reaction of supergenesolutions with galena and fluorite. concentratedas the earlier lead fluoride minerals crystal- This is suggestedby their compositions, by their spatial lized. proximity to galena and fluorite, and by the presenceof The combination of conditions that resulted in the for- anglesitefracture-filling in the quartz surrounding the vug. mation of these four new minerals thus far appears to The presenceofPb2* in solution is clearly critical to the have been unique, since only one vug containing these formation of the new minerals. Becauseof the strong ten- minerals has been recognizedduring nearly a century of dency of this ion to combine with sulfate or carbonate, mine operation and a quarter century of intense interest its mobility in systemsdominated by theseanions is very in this mine on the part of mineral collectors. The com- limited. Close proximity of galenato a sourceof fluoride mon associationof galenaand fluorite in this and count- ion is seemingly necessaryfor the formation of the new less other deposits throughout the world further testifies minerals. to the unusual set of conditions that must have existed Of apparent importance as well is the isolation of the for thesefour minerals to form. It should be noted, how- vug from acidic sulfate-rich solutions, which permeated ever, that the new minerals are inconspicuous in com- most of the adjacent oxidation zone. Otherwise either parison to the brightly colored secondarycopper minerals, anglesite would have formed in preference to the lead which are of particular interest to collectors at the Grand fluorides or earlier-formedlead fluorides would have been Reef mine. Specimenswith colorless needlelike crystals destroyedby the later solutions. In this regard, it is pre- consistentin appearancewith laurelite have beenreported sumed that the quartz, fluorite, and galena layers on the by at least two other personswho have collectedminerals specimenformed a continuous envelope around the vug. at the Grand Reef mine, but they discardedthe specimens This view is supportedby observationson other isolated thinking them insignificant. vugs in the bencharea (Wayne Thompson, personalcom- munication, 1988). Acxllowr-rocMENTS The secondarycalcium fluoride minerals gearksutite and creeditewere reported from the mine by both Jones(1980) We acknowledgecontributions to this study by a number ofindividuals. the attention of A.R.K. Wayne and Besse(1981). Besse reported gearksutite to mod- William Bessebroughtthe type specimento be Thompson and Richard A. Bideaux of SouthwesternMineral Associates erately common in the bench area as a very late stage, donatedthe type specimen.Les Presmykloaned the secondspecimen and chalkycavity filling. Besse(personal communication, 1988) matrix fragmentsfor examination.William Besse,Wayne Thompson, and also reported the occurrenceof prosopite in an isolated David Shannon provided information regardingthe geologyand rniner- vug in the bench area.None of theseminerals is found in alogy of the Grand Reef mine. GeorgeRossman of the California Institute ofTechnology conductedthe infrared studies.Larry L. Jacksonofthe U.S. associationwith the new lead fluoride minerals described GeologicalSurvey in Denver conductedthe Karl Fischer moistwe titra- here, although small amounts of gearksutite are present tion. CharlesRoss and CharlesStrouse ofthe University ofCalifornia at in the matrix surrounding the vug. The conditions present Los Angelesassisted A.R.K. in the crystal-structureinvestigations of gran- in this isolated vug must have favored the formation of dreefite and pseudograndreefite. secondary lead fluorides rather than calcium fluorides, since Ca would have been available from the alteration RrrnnnNcns crrnt ofthe fluorite. Besse,W.W. (1981) The mineralogy of the Grand Reef mine, Aravaipa The new minerals probably crystallized from the same mining district, Graham County, Arizona. Master'sthesis, Department supergenesolution as it evolved under approximately ofGeology, California StateUniversity at Los Angeles. (1976) oxysulfate. Proceedings closed system conditions within the vug. Although the Fahey, J.A. Crystal structurc oflanthanum ofthe I 2th Rare Earth ResearchConference (Vail, Colorado),162-77 l. crystallization rangesundoubtedly overlapped consider- Jones, RW (1980) The Grand Reef mine, Graham County, Arizona. ably, growth interrelationships suggestthe following crys- Mineralogical Record, I 1, 219-225. tallization order: grandreefite+ pseudograndreefiter lau- Mandarino, J.A. (1981) The Gladstone-Dalerelationship: Part IV. The relite - aravaipaite. The trend among these minerals is compatibility concept and its application Canadian Mineralogist, 19, toward decreasing amounts of sulfate and increasing 441450. amounts of F and water. The increasein water content Mewuscnrpr RECEIvEDNovpr'rnen 17, 1988 follows the normal tendency toward increasingwater li- Mnxuscnrsr AccEprEDMencn 16, 1989