CanadianMin*alogist Vol.23,pp. 233-20 (1985)

ABHURITE, A NEW HYDROXYCHLORIDE , AND A COMPARATIVE STUDY WITH A SYNTHETIC BASIC TIN CHLORIDE*

JOHN J. MATZKO, HOWARD T. EVANS JR., MARY E. MROSE AND PHILIP ARUSCAVAGE U.S. GeologicalSurve!, Reston,Virginia 22092, U.S.A.

ABSTRACT longueur d'onde de l'ultraviolet. Le min6ral sedissout rapi- dement dans I'acide nitrique et lentement dans l'acide r6v&le73.490 (en poids) Abhurite Sn3O(OH)2C12is a new mineral speciesfound chlorhydrique. L'analyse chimique 1.090O et 0.4a/oH, et correspondd la for- in blister-like protuberanceson the surfaceof tin ingots sub- Sn, l5.7YoCl, I L'analyse thermique diff6rentielle mergedin a shipwreckabout l00years ago. The recovery mule Sn3O(OH)2C12. que d6gaged235"C et SnCl2,d 525'C. En site, at a depth of about 35 m, in an arm of the Red Sea montre l'eau se de pr6cessionr6vdlent descristaux known as Sharm Abhur, is located 30 km north of Jiddah, diffraction X, les clichds de gxoupespatial iR3m, R3m ou R32, Saudi Arabia. Abhurite forms tlin, platy, colorless,fragile, rhombo6driques, (0@l). Les donndesde poudre six-sidedcrystals averaging 1.5 mm in diameter. The plates g6n6ralementmaclds selon pour arriver ir une maille 616- show no , the uniaxial figure is positive, and Guinier-Hiigg furent affindes les parametressont d 10.0175(3)' or is 2.06. No fluorescencefor either shortwaveor long- mentaire heryrgonaledont c/a 4.3937.Les raiesprincipales du clichd wave ultraviolet light was detected.Density Dx4.34, Dm c 44.01\2) L; (m6thode des poudres) en A(Ixrttl)l sont: 4.29 g/mt, The mineral dissolvesrapidly in nitric acid and de diffraction Id 3.634(35X0.1.11),3.404(50X208), slowly in hydrochloric acid. Chemical analysis gives 73.4 4.139(50Xll6), 3.244(3s)(r22), 3.r42(3s)(2r4), wt.Vo Sn, 15.7 Cl, ll.0 O and 0.4 H, which corresponds 3.27r(3s)(zrr\, 2.89 I 5(70)(300), 2. 838 I (25X303), to the formula Sn3O(OH)2C12.Differential thermal anal- 2.9074(3 5)(217), 2.5313(l00xl.l. l5)' Descristaux svnth6- ysisshows release of H2O al 235oC and of SnCl2at 525'C. 2.8175(50X128), pr6par€spar Howie de l'Universit€ d'Aberdeen' X-ray-precessionpatternlshow that the crystals are rhom- tiquq R,A. prdsententen plaquetteshexagonales minces, bohedral, spacegroup R3m, R3m or R32, and commonly en ilcosse, se uniaxes positives. Cette phase twinned on (ffiI). Guinier-Hiigg powder data were refingd incolores, unir6fringentes, possbde diffraction presque identique iL celui to give hexagonalparameters a 10.0175(3),c 44.014Q\A; un clichd de phasessont dfunorphes,I'abhurite c/a 4.3937. The pri"ncipal lines in the powder-diffraction de I'abhurite. Les deux 6tant rhombo6drique et les cristaux synth€tiques, hexa- pattern [d in A (l)(hkl)l are: 4.139(50)(tl6), gonarD(. 3.634(35X0.l. l 1), 3.404(50)(208),3.27 | (35X2I l), 3.244(35)(122), 3.r42(3s)(2r4), 2.9074(3s)(2r7), par la R€daction) 2.8915(70X300),2.8381(25)(303), 2.8175(50X128), Clraduit 2.53l3(lmxl.l.l5). Syntietic crystalsprepared by Dr. R.A. d'6tain, Arabie Howie of the University of Aberdeen, Scotland are thin, Mots-clds: abhurite, hydroxychlorure colorless, hexagonalplates that show no birefringence, are S6oudite, uniaxial positive and produce an X-ray pattern nearly iden- tical to that of abhurite, The two phasesare dimorphous: abhurite is rhombohedral, the synthetic crystals are hex- agonal. INtnooucloN

Keywords: abhtrite, tin chloride hydroxide, Saudi Arabia. Abhurite, a new mineral speciesof composition Sn3O(OH)2C12,was found as a corrosion product on ingots of tin recoveredfrom the cargo of a sunken SoMMAIRE ship, wrecked possibly 100years ago, lying in a cove of the Red Sea known as Sharm Abhur. The site L'abhurite Sn3O(OH)2C12est une nouvelle espdcemin6- (Lat,2l"4'N, Long. 39"07'E) is about 30 km by rale qui se trouve dans des protub6rances en forme air north of Jiddah, Saudi Arabia. The shorelinenear d'ampoulesA la surfacede lingots d'6tain submergdsdepuis the coveis borderedby coral reefs, and the arearecei- environ cent ans d la suite d'un naufrage. Le site de la ves water runoff only intermittently. The tin ingot ddcouverteest ir environ 35 m de profondeur, dans un bras was located inside the cove on a sandy bottom at a 30 km de la Mer Rouge appeld Sharm Abhur, i environ depth of about 35 m in water of about 21'C. en Arabie S€oudite. L'abhurite forme au nord de Jiddah, geographic des cristaux en plaquettes incolores i six c0t6s, minces et An attempt to identify the source of fragiles,d'un diambtremoyen d'environ 1.5mm. Les pla- the ingot was made by comparing trace elements quettes sont unir6fringentes; la figure uniaxe est positive, reported for ores and the corresponding et

Few descriptions have been made of alteration crusts that contain somewhat less Cl than the ma- products of tin ingots exposedto marine waters for rine sample. Smythe consideredthat the chloride so- long periods. Encrustedtin ingots recoveredfrom lutions were active in an initial electrochemicalreac- a tidal river in the Kampar area, westernMalaysia, tion in the corrosion proce$s.Tin artifacts recovered have been describedby Hosking (1970). In these from the Winnipeg River, Ontario carry incru$tations crusts, investigators at the British Museum (Natur- of the new romarchite SnO (Organ & Man- al History) tentatively identified two phasesof tin darino 1971) and hydroromarchite 3SnO.H2O oxychloride. Hosking suggestedthat the tin oxychlo- (Howie & Moser 1973). ride was formed by reaction with salt accidentally Fragile, colorless crystals of high index of refrac- spilled on the ingot just after it had been poured. tion were found in blisters that formed on the ingot Ariother instanceof saline corrosion was noted by from Saudi Arabia. Semiquantitativespectrographic Smythe (1946). He found that light greyish brown and energy-dispersion analysis (EDX) in the material occurring on a lead-containing tin ingot scanning-electronmicroscope (SEM) showedthat tin recoveredfrom the seaat Falmouth Harbor, U.K., is the only metallisssmpeaenf of the crystals.These containsas much as 1.6 wt.qo Cl. Five other sam- crystals, named abhurite after the locality, and a ples from ingots that had been buried in soil have closely similar syntheticpolymorph, are described

Ftc. l. (a) Abhurite crystals within a fractured pod (mm scaleis shown); O) abhurite crystals with massivecream

OCcURRENCE AND MINERALOCY

The tin ingot on which the abhurite crystals are found is 18 cm long, 9 cm wide at one end and 8 cm at the other, and 3 cm thick. The ingot is prin- cipally tin, alloyed with minor amountsof Cu, Pb, Bi, Zn and Sb. The larger crystals of abhurite form within blisters or pods that contain a viscous mass of liquid and solids. Within a few months after removal from seawater, the blistershad dried out. The fluid has an acidity (pH) of 1, as determined by indicator paper. The pods, which cover all the surfacesof the ingot, rise as much as 7 mm above the ingot surface and penetrate as much as 5 mrir below the surface.Their basedimensions range from about I to 10 mm. Thesepodlike chamberspermit- ted the formation of large, transparent crystals of abhurite (Fig. l). Abhurite crystals that are unprotected by the blisters formed on the surface of the ingot to a depth of about 2 mm, and wereinter- rupted in their developmentby a covering of romar- chite and a subsequenl precipitation (about 2 mm Frc. 2. (a) Abhurite crystalsin multiplelayers, with typi- thick) of kutnohorite, aragoniteand coral. This coat- cal anglesof 120";(b) abhuritecrystal with stepangles ing apparently protected the tin ingot from further of 60'. Bar equalsI mm in both views. reaction with the seawater, and also coatedthe pods. Most of the abhurite contains fragments of the tin alloy and other crystallites. Apparently, not all of Some crystal habits of abhurite are shown in the tin is completely dissolved in the corrosion Figures2 and3a. The hexagonalplates are bounded process,and the remaining fragments were incorpo- by rhombohedral facesthat give poor optical gonio- rated into the abhurite orystalsand masses.The white metric signalsal p - 43". For the negativerhombo- metallic-appearing spherical inclusions have been hedron {0115}, g is equal to 4.6o . Figures2b and identified by X-ray diffraction as B-tin, $imilar to 3a show the common twin habit of abhurite, in which the ingot metal. one individual twinned on (0001) coalesceson the The liquid core containing the abhurite crystals is basal face of the other, felming beveled triangular encasedby a shell of milky white to tan cryptocrystal- elevations. In crossedpolarized light the crystals are line material, which in turn is rimmed by a black to bluish grey to colorlessand show a positive uniaxial bluish black material containing romarchite (Fig. 1b), interference-figure. The physical and chemical and may be followed again on the outer surface by properties of abhurite are summarized in Table 1. more tan to white cryptocrystalline material. The As describedin a later section,various attempts abundant cryptocrystalline material has been iden- reported in the literature to synthesizea homogene- tified by X-ray diffraction as abhurite. The black- ous basic stannouschloride have had diverseresults. ish mineralized areas handpicked for X-ray tests One conforming most closelywith abhurite in com- show mainly abhurite, probably mixed with romar- position and properties was very kindly preparedfor chite. An X-ray powder-diffraction pattern of single us by R.A. Howie of the University of Aberdeen, black grains showsthe presenceof romarchite, but Scotland. Using the method of Donaldson el a/. another pattern of a similar sample sho"wsonly (1963) (summarizedbelow), Howie obtained hex- abhurite. Examination of thesedark grains by SEM agonal crystals that evidently are not the same as reveals a complex mixture of abhurite, tin oxides, those of Donaldsone/ al., bttt appearto be identi- and sulfates or sulfides of other metals such as lead cal with abhurite in composition, X-ray crystallog- and bismuth. raphy and morphology. As shown in Figure 3b, 236 THE CANADIAN MINERALOGIST

Howie's hexagonalplates have very steeprounded the ingot to determine the composition of the alloy edgesthat give no optical signaland showno rhom- (Table 2). bohedral aspect. The synthetic phase will be Crystallization of abhurite removed only tin from describedin detail in the following sections. the ingot, although the ingot also containedminor but appreciableamount of Cu, Pb, Bi, Zn and Sb. CHEMICAL ANALYSIS AND COMPOSITIoN SEM-EDX analysesof selectedabhurite crystalscon- firm the presenceof Sn and Cl only; Br was looked Crystals of abhurite, handpicked under the for but not detected. Differential-thermal analyses binocular microscopeto be free of obvious inclu- (DTA) and thermogravimetric analyses of the sions, were analyzedby wet-chemicalmethods (Iable abhurite crystalsin a helium atmospherewere done 2). Semiquantitative spectrographic analyses were on a Mettler apparatus.Peaks were produced in the run on the separated crystals of abhurite and also DTA at 235oand 525oC.At the latter temperature SnCl2is probably evolved, as the residuewas shown by an X-ray powder pattern to be SnO2(SnCl, sub- limes at 652"C). Thoresidue produced at 235"C was not examined,but this point probably marks the evo- lution of rather tightly bound water. Resultsof the chemicalanalysis Clable 2) conform well with the formula SnClr.2SnO.H2O or Sn3O(OH)2C12.The DTA experiment indicates that the water is probably presentas OH groups, as wou$ be expectedin a product of hydrolysis. Laboratory experimentsshow that NaCl-saturated solutions attack tin shot over a period of about a year, to form very small crystals of abhurite and blackish rims of romarchite. A 1090 solution of hydrochloric acid attacksthe tin shot more rapidly, and in a year's exposuresomewhat larger crystalsof abhurite form. Globulesof remobilizedvery fragile abhurite form on the crystalsover a period of 4 years in the humid environment of the laboratory in Jiddah. X-RAY Cnysrarrocnaprry

Crystals of abhurite were studied by X-ray diffrac- tion using Debye-Scherrer and Guinier-Hiigg

TABLE1. PHYSICAIAND CHENICAL PROPERTIES OF A9IIURITE

PhJslc.l PrcFrtles

Optlc.llJ unldxlal posltlvei 3tr!lned plrtes shol blrefringence and sdll 2V rlth tsoores that @ln seFrated on rctitlon. Indlc6 of refraailonl: o 2.06, e >2.05, -2.1I (Cargllle llquld n 2.11 slorly 'b ottacks crysuls). lsotrcplc nonortlngilshlng blue on centEd unld't.l flgum, to hlgh blrefrlnqence on off{entre flSEi. Colorloss, trin3tsrent rlth op.lesc€nt lustrei rhlte streati no pleochrcls. llo fluorescencs dr absorptlon llth shodmvs or longnYo ul-trqvlolqt'llght. Hlblt platy or hhillar on her. (000I)i rh@bohedral foms l01I5]' l000ll' Tdnnlng cd@n or (0001)i step groshs InteE4tlng at 60" or 120o. FracluE ltrcllyi no cloavag€ obseiled. thrdn€ss 2i fuslblllty 1. knslt*:4.29 q/@3. Frrn2 lsodynMla concontr.tlon not clean. Mt b€st In I'5 noMgnetlc. Avelage crrsul 3lz€: 1.5 @,

Ch@lcal PrcPedlos

lnsolubl€ ln dlstl'llod hter ot Red S€. ftteri hrdtatlon to ! cttstllllno dusb rtthln 60 drys ovor ntor ln a dE!3l6tot. Ihon helbd on n hot plal€ tums bm$lsh tlth @ttlllc tln @amllng fM lho abhurlt€ at ?30o !o 260"C (as Indlcoted by t@p€rEture Fnclls). lnqot @lts bhoon 230" rnd 320"c (Nre sn nelB at 2326C)' Ih€n h€;t€d ln closed tub€ ylelds a rhlts subllEft (Prchbly sncl2). Dlssolr€s ilorly ln HCI (10t or 6nc.) rlthout effenescenc€. bss not dlssolis ln Hrsoa (10X), but surface etched to helagonal outllnesi crFhlllnlty destrcied In conc. acld. Dlssolros ln tllto3 tlth efforvescence, sllght ln 10, acld' lttung ln coac. acld. lb relctlon ln ilH!011. Ftc. 3, Scanning-electronmicrographs of crystals of (a) llnterfemnce Dlcroscopy detomlnttlon by E. C. T. Ch.o lnd Jean Hlnkln abhurite (natural), and (b) Howie's synthetic tin oxy- (cho 1976). zlbnsltJ d€tomlned bJ John l{lrlnanlo uslng tetrachlorc- chloride. Photographsby E.J. Dwornik. €thtl€e ln a dlcfpJcnodstor. h for Horlo's smthetlc crystals $s Bar in lower d€kdlnEd !s 4.25 s/@5 bJ th€ sea mthod. right corner equals0.1 mm in a), 0.01 mm in b). ABHURITE, A NEW TIN HYDROXYCHLORIDE MINERAL 237 powder methods and Buerger-precessionsingle- confirmed by the upper-levelimages, one of which crystal methods. Abhurite is rhombohedral, with is shown in Figure 4b. A Guinier-Hngg focusing spacegroup R3m, R3m or R32.Precession patterns powderpatterqmade al25oC with CuKel radiation of upper levelsnormal to c* in the hexagonallat- O: 1.540162A) and BaF, as an internal standard tice, although not compleGly separated,clearly show (a 6.1970A) gave 157 measuredlines. Thesewere the 3m symmetry.The &0/ net, shownin Figure 4a, indexed with the aid of intensities observed on the is complicated by twinning on (@1), and shows single-crystal patterns, and the 2d values were used strong deviations from expectedmm symmetry. A in a least-squaresrefinement of the unit-cell dimen- study of the intensity relationshipsshows that the sions(hexagonal cell) (Appleman & Evans t93). The paired arrangement of spots on rows parallel to c* unit-cell dimensions and powder data are given in wrth h+3n is consistentwith two rhombohedrallar- Table 3, along with correspondingdata for Howie's tices superposedby twinning. This interpretation is synthetic polymorph of abhurite. If we assumethat

g 1 t: ; :; :#

F $ { ? * $, :; : l; T. ; f fi g 'r'li * t ; il

q3 d *i :;;:; v

$ : ': - r, ;, ,,$,, o j i i, t,;

,r,,*]j :ti: ffi 238 THE CANADIAN MINERALOGIST

TABLE2. CHS,IICALCONPOSIIION OF AEHURITEAND II{GOI FROI,ISAUDI ARASIA Keller derived the formula SnCl2.SnO.Keller sug- gestedthat the saline solution had accessto the A. ndjor ele@nts (rt.t) interior of the tin mass through openings at the Found Theoretlcal surface. sn(r) 73.4 71.6 cl (r) 15.7 14.9 0(3) ll.0 x0.1 H(q) -Tdfj50.4 0.4 TABLE3. POTDERDATA FOR SHURITE AXO HOIIT'S SYflTIETICPOLYTORPHI 106.7

B. lilnor eleoents (pp!)5 Abhurlte2 Horie's smthetlc cry3hlss Abhurlte Ingot d(calc) d(obs) I(rel ) h I r d(calc) d(obs) I(re]) Fo 2000 3000 1 0 r 8.512 8.505 4 101 8.509 8.504 9 t{9 2000 500 0 0 6 7.336 1.337 13 006 7.337 b0 I I I 0 4 6.813 6.828 18 10{ 6.81? 5.824 6 Bl nd 300 0 I 5 6.179 6.179 13 t05 6.179 6.186 6 Co nd 1 0 7 5.091 5.096 13 107 5.087 6 Cu1 1000 0 o 9 4.892 4.892 9 009 4.892 1.899 9 Nt 10 50 I I 3 4,740 4,744 9 ll3 4.739 4.735 13 Pb nd 1500 0 2 I 4.317 4.322 2 201 4.316 Sb nd 200 203 4.159 4,165 2 116 4.136 4.133 50 Zn 200 300 I I 6 4.136 4.139 50 0 2 q 4.0i5 4.043 4 204 4.035 4.030 2 0 0 12 3.668 0012 3.669 3.668 3 0 1 u 3.633 3.634 35 1011 3.634 3.635 ]Averago of detemlnatlons b.y P. Aruscavage, IJSGS. 201 3.570 zAveroge o 2 7 3.570 3.571 I of tro an6lysles by speclflc-lon electrcde I I 9 3.499 1.498 18 3.499 3.499 18 uslng pemanganate and hydrofluorlc acld lr4, b, 2 0 I 3.406 3.404 50 208 3,406 3.407 18 E. Caopbell, USGS. 0n the synthetlc tln orrchloflde 2 1 1 3,270 3.27L 35 3.269 3.268 35 16.91 Cl ras detemlned by the sade nethod. r 2 2 3.243 4.2q4 35 2t2 3.242 3.241 35 3Total oxygen detemlned on 3 saEples. one of the 2tx 3.199 3.195 13 suples drled 0t 105"C shored 2t less orygen. Analyses 2r4 r,M2 3.142 35 2t4 3.142 3.142 2010 3,089 3.089 by l. D. Ehoann. Unlv. of kntucky, by fast-neutron 0210 3.089 3.091 l3 t 112 2.9592\ 1112 2.9594 actlvatlon for total orygen. 2.9564 3 qH 0114 2.9557) 1014 2.9562 detemlned uslng CllH lnstrunentatlon by 2 0ll 2.9411 2.9411, 2 2011 2.941I -P. Aruscavage. 2.9074 2r7 2.9069 2.9@3 13 sSslquantltatlye 217 2.9074 spectrographlc analyses of saoples 300 2.8918 2.8915 70 300 2.8910 2.9925 100 b, l. tloh'd Naqvl, US0Sand Dlrectorate Ceneral of 303 2.A372 2.8381 25 303 2.8365 2.8360 50 I'llneral Resources, squdl Arabla. Syrbol nd . not deter- 128 2.8161 2.4V5 50 218 2.8161 2,8165 25 olned. Looled lor but not found: As, I, Ba, Cd, La, 2.7231 2.1204 1 lln, Io. Found ln lngot but not ln abhurlte rere 20 ppn 306 2.6903 2.6901 13 306 2.6891 2.6592 l3 2.6218 Cr. Sc, Sr, nnd V. 2110 2.6295 2.6304 2110 2.6292 l016 2.6222 2.6210 1016 2.6221 2014 2.5456 2.5457 I 2014 2.5451 1115 2.5318 2.5313 100 2.5321 2.5329 70 220 2.5044 2.5061 220 2.5037 2.5047 4 309 2.4A92 2.qa91 309 2.4888 2.4889 18 0117 2.4809 2.4800 1017 2.4A14 2.4816 the unit cell contains 21 formula units (a multiple 223 2.4687 2.4694 223 2.4580 2.4680 131 2.4025 2.4039 311 2.4019 2.4011 of 3 as required by the rhombohedral symmetry), the 2.3919 2.3918 312 2.3912 2.3909 226 2.3701 2.3709 226 2.3695 2.3696 calculateddensity D, is 4.35 g/cm3. 2113 2.3554 2.3568 2113 2.3553 2.3556 134 2.3506 2.3507 314 2.3500 2.3494 315 2.X2!0 2.3206 2.3204 3012 2.2709 2.2696 3012 2.2701 2.2703 25 COMPARISON OF ABHURITE wITH PREvIoUSLY 1019 2.2W1 2,2379 6 l0 t9 2.23€5 229 2,2291 2.2291 229 2.22A7 2.2286 25 Dnscntsso Bastc Srnmsous CHLoRIDES 1110 2.1973 2.1968 ir18 2.1976 2.1990 -.+0r 2.t662 2.1665 401 2.1656 2.1649 042 2.1584 2.1596 402 2.1578 2.157e 404 2.t219 2.l?8l 404 2.1274 ?.t269 Severalstannous chloride-oxide-hydroxide phases 1310 2.1t12 2.1093 3110 2.t109 2.L092 2116 2.L074 2116 2.t015 have been previously described, none of which 045 2.1059 405 2.1059 22t2 2.0682 2.0674 2212 2.06A0 2.0681 appear to be identical to abhurite. In terms of the 3l11 2.0620 2.0615 3111 2.0611 ?.0622 t217 2.0320 2.0317 2117 2.032L general formula rSnClr7SnO.4,H2Ol phaseswith 048 2.OL17 2.0165 408 2.0173 2.0174 321 1.9882 1.9891 32t 1.9877 1.9885 various (x,,y,e)values have beenreported as follows: 232 1.9822 322 1.9816 1.9819 (1,4,O, 323 1.9717 1.9730 (1,1,4)and Q,3,6)by Ditte (1882);(1,1,0) 2020 . 1.9626] 1.9617 2020 1.96?8 1.9630 1313 1.9613J !.9611 1.9630 byKeller(1917); (3,5,O andQ,7,1)by Carson (1919); 324 1.9585 324 1.9s80 1.9598 235 1.9413 1.9419 325 1.9408 (1,1,2)by Randall& Murakami (1930);(l,l,l) by 0411 1.9068 1.9064 40ll 1.9064 r.9055 327 1.8975 1.8992 327 1.8970 Hayek (1933); (1,3,3) by Donaldson et al. (1963)i 410 1.8931 1.8928 410 1.8926 1.8924 50 143 L4776 t.8781 2 4t3 1.8771 L.4774 (1,2,1), abhurite and Howie's syntheticphase (this 238 1.8716 1.8718 328 1.8712 1.8714 0024 1,8339 1.8332 0024 1.8343 L.8327 work). 146 1.8331 416 Ltrl26 1.8327 4013 1.8253 1.8261 13 4013 1.8260 t..9267 Keller (1917)described a new oxychloride of tin 3?10 1.8135 1.8136 3210 1.8131 1.8131 2311 L.7820 1.7817 9 3211 1.7817 1.7823 as brilliant crystalsin a cavitywithin a lenticular mass 149 1.7655 1.7655 3 419 1,7651 1.7644 3tt7 t.7625 1.7622 9 3117 t.7624 1.7615 of tin found in an aboriginal cemetery in Florida. 22t8 1.7496 1.7501 2218 1.7495 1.7498 Lr24 1.122L t.7220 I r124 1.7224 t.7232 Someof the crystalswere readily separatedfrom the 3?13 1.7158 1.7157 32t3 1,7155 1.7078 L,7073 3 2122 1.7@0 tin, whereasothers were found to be disseminated 40!6 1.70?2 1.7029 4016 1,.7030 1.7025 0321 t.6970 1.6971 3021 1.6971 1.6978 throughout the mass. The crystals occur as "thin 1412 1.68rt 4112 1.6820 1.6816 plates"; a few are "distinctly acicular". A closed- 330 1.6696 1.6695 330 1.6691 1.6686 tube test did not yield any water. Solubility in dilute lcnlnler-Heggd€thod uslng cukr r.dlatlon (r"1.540562I). Intensltles estlm.t€d br cmpailson rlth 3 callbrated fllE. Cmpleto acidswithout effervescenceand other qualitative tests dah for abhurlte (to d l.ll A) depslted rlth the Jolnt c@ltt€ ror the PorderDlffractlon tlle. showedstannous tin and chlorine as principal con- 2Rhombohedral,spoco qroup n-4, nlu, o. R3i a lo.0l75(3), c 14.014(2)t. 3flexagonal,space group P6l@. P-6@2,P6@, or P522ia f0.0U7(4)' stituentsof the compound.Analyses showed 70.9 to c 44.024({) A. 73.1 wt.Vo Sn and 21.7 to 22.0s/oCl. from which ABHURITE, A NEW TIN HYDROXYCHLORIDE MINERAL 239

The fust detailed description ofthe hydrous reac- those of abhurite (only 4 lines are presentthat are tions of SnCl2 with water was given by Carson not consistentwith,the R lattice of abhurite), but (1919).His procedureconsisted ofrefluxing solutions there are distinct differences in the details of inten, of SnCl2in water a4d also in KOH solutions in var- sity distribution. The intensity {ifferences are most ious ratios under nitrogen for 6 to 8 hours, followed clearly seenon precessionphotographs of the ,0/ and by analysisof the precipitatesand the mother liquors. hll nets, shown in Figure 5. In abhurite, when Consistent results were obtained for the crystalline h+2k+3n, only reflectionswith /+3n are observed, products formed 6a sosling the filtered boiling solu- corresponding to the R centring with the twin lat- tions. Carson observedthe formation of "hexagonal tice superposed.In tfuesynthetic crystals, reflections rosets made up of thin, transparent, colorless appear in thesegroups for all / (except 0). The latter pletes." Thesecrystalline products were found to patterns always show true mm symmetry, unlike the contain73.5 t 0.5wt.9o Sn and 16.3!.0.60/o Cl; the abhurite patterns. Laue patterns show that the syn- formula 3SnCl2.5SnO.3H2Ooffered by Carson thetic crystals are not of as good quality as the requires73.3V0 Sn and 16.4t/oCl. The product syn- abhurite crystalsand possibly show some disorder thesizedby Carson is interesting in its chemical and along the c axis. The precessionpatterns coulil pos- morphological similarity to Howie's synthetic tin sibly result from finely twinned rhombohedral lat- oxychloride. tices of abhurite plus a superposedhexagonal lattice Donaldson et al. (1963)have also carefully studied with c axis either equal to or tA that of abhurite. On the products of hydrolysis of SnCl, solutions. They the other hand, there is no real evidenceto indicate prepared an acid solution with concentrated HCI that the synthetic crystalsare not a singlehomogene- under nitrogen and adjusted acidity with 2N ammo- ous phase. nium hydroxide so that the hot solution just began Evidently, there are many compounds,each with to precipitate, and allowed the filtered solution to a different proportion of x, y, and a but the par- cool. The crystallized product gaveconsistent values ticular phase that forms is very sensitiveto' the that averaged73.20/o Sn, 10.890Cl and 8.4t70HrO; method of preparation (heatingregime, method of their formula, SnClr.3SnO.3HrO[or Snr(Ott)rCl2], pH adjustment, acids and alkalis used, etc.). requires73.390 Sn, ll.09o Cl and 8.390HrO. T[is Presumably, the overall reaction of Sn metal with compound is obviously different from Carson's arid acid brine containing dissolvedoxygen czmbe gener- also from abhurite. Donaldsone/ a/. obtainedpow- ally representedas follows: der and single+rystalX-ray data for their compound, which permit closer characterization and differenti- (x+y)sn + (x/2+y/2)O2+2rHCl+(z-x)HzQ - ation from abhurite. The compound consistsof "six- xSnCI2TSnO.zH20 sidedcrystals, which show parallel extinctionn'and "high birefringence." Rotation and Weissenberg The product of natural alteration may vary with par- photographs showedan orthorhombic unit-cell in ticular conditions of formation but cannot be spacegrgup Pbcn, with a l0.l8Q), b 17.06(3),c predicted.The sourceof the acid is not clear. The 14.66Q)A, and Z = 8. This pseudohexagonalcell has availability of oxygenmust be restrictedto avoid oxi- dimensions that show an approxinqale relationship dation of Sn2* to SnO2(cassiterite). to those of abhurite (a - ou6,b -.13a6, c - c^6/3), The developmentof abhurite in seawater may take but the disparity of the optical and X-ray powder placein two stages:(l) oxidation of Sn metal by 02 - data showsthat the two phasesare quite distinct. or HrO while OH is dissipatedand SnCl, is con- An associateof Donaldson, Dr. R.A. Howie of centrated; (2) hydrolysis of SnClr with the forma- the University of Aberdeen, has attempted to repeat tion of abhurite, romarchite, and free acid. the preparationof Donaldsonet al. in order to pro- vide us with material to compare with abhurite. Dr. Howie's synthetic crystals are thin, colorless, AcKNowLEDGEMENTS hexagonalplates that show no optical extinction (uni- axial positive) and produce an X-ray powder pattern Specialthanks are due to Dr. R. Alan Howie of that is nearly identical with that of abhurite (Table the University of Aberdeen,Scotland, who advised 3). Closeexamination of the single-crystalpatterns concerning the earlier tin oxychloride synthesesand @igs. 4c, d) and Guinier-Higg powder patterns kindly prepared new material for this study. We are (Iable 3) showsthat in fact the two phasesare differ- grateful to W.D. Edmann, University of Kentucky, ent, but dimorphous. Both have practically identi- who did the analysis for total oxygen. Several col- cal unit-cell dimensions, but whereas abhurite is leaguesat the U.S. GeologicalSurvey contributed rhombohedral, the synthetic crystals are hexagonal significantly to this work: Edward Dwornik and with spacegroupP6/mmm or subgroupthereof. The Richard Larson made scanning-electron micro- spacingsof the powder pattern of Howie's crystals graphs, Priestley Toulmin III ran a differential ther- listed in Table 3 are practically indistinguishablefrom mal analysison abhurite crystals,and Harry J. Rose, 240 THE CANADIAN MINERALOGIST

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