785 The Carudian Min eralogist Vol. 35, pp.785-786(1997) A NOTEON THECRYSTAL STRUCTURE OF MARSHITE MARK A. COOPERIAND FRANK C. HAWTHORNE Department d Geological Scierces, University of Manitoba Winnipeg, Manitoba R3T 2N2 ABsrRAcr The crystal structurcof untwinnedmarshite, CuI, a 6.6063(D L, V 222,9(L)A3, spacegrotp F43m,Z = 2,has beenrefined to an ft inclex of 2.07o on the basis of 98 observedreflections measuredwith MoKa X-radiation. Untwinned marshite is isosfiuctural with sphaleriteand with y-CuI, and must have crystallized below 367"C, the temperatureof the p-CuI + CUI transition. Keywords: marshite,crystal structure,sphalerite. Sotulaene |.a sfiucture d'un cristal non macl6 de marshite,CuI, a 6.6063(1)i," V 222.9(l) A', gtoup" spattalF43m, Z = 2, a &E afme jusqu'd un r6siduR de 2.0Voen utilisant 98 r6flexions observ6es,mesur6qs avec rayonnement MoKa. La marshitenon macl6ea hmeme stucturequela sphaldriteetlaformeyde CuI, etdoitdonc avoircristallis6imoins de 367'C, tempdraturedelatransition p-CuI+ CuI. Clraduit par la R6daction) Mots-cl4s: marshite,structwe cristalline,sphal6rite. INTRoDuc"iloN Eprnnrmlrer Marshite, CuI, occurs as pale pink to brownish red The materialused in this work is from Broken Hill, tetrahedra.Where fresh, it is colorlessto pale shadesof New SouthWales, Australia andwas obtainedfrom ftre yellow, but becomespink to red on exposure.It is found Royal Ontario Museum,sample number M12531. It is at Broken Hill" New SouthWales, Ausralia" whereit is associaledwith spessartinenanother pale pink cubic associatedwith'\ilad", cerussite,cuprite, native copper mineral.Most of themarshiteis moderatepink-to'orang9, and limonite, and at Chuquicamata"Chile, where it is and appearstwinned (on {111}); a small fraction of associatedwitl atacamite, leightonite and gypsum. marsbiteis translucentyellow-to-P-ink and is not twinned" Marshite was originally repor0edas being teffagonal, A cleavageplate [indexedas (011)] was usedto collect but was later recognizedas cubic. the X-ray intensity data on a Nicolet R3n instrument (1985). The temperature-dependentphase transitions in CUI accordingto theprocedure of Hawthome& Groar havebeen investigated extensively, and eadier work is A psi-scanabsorption correction reduced R(azimuthal) summarizedby Yude et aL (1990).At room tem1teranre, from 18.4to 3.3Eo.Atotil of 98 reflectionswas collected CuI is isostuctural with sphalerite (ZnS, F43m). At over two asymmglris units, and all reflections were 367' C, CuI becomeshexagon aI (P6m2), artd at N7 "C, it observedat the 5o level. The strucflre refined to an R becomescubic again lFmjm, althoughF43ra was sug- index of 2.07ofor 47 unique observed(5o) reflections gested by Btihrer & Hiilg (1977)1.As the synthetic and four variable parameters.Cell dimensions and systemis very well characterized,we thoughtit worth- information pertinentto data collection and refinement while to test the low-temperatureorigin of marshite. are given in Table 1, and final atom parametersand 1 E-mail address: [email protected] 786 TIIE CANADIAN MINERALOGIST TABLE1. SINGLE.CRYSTALX-RAY DIFFRACTTON DATA. COLLECTIONAND FEFINEMENT INFORMATION FOR MARSHITE the correspondingU* values(Table 2) to B-values(via multiplicationby 8zr2)gives 2.65(4) and 1.53(2)4'z, a (A) 6.06s(1) (mm) Crysialsizs 0.22x 0.38x 0.09 respectively. Thus the X-ray values are somewhat v(4") 222.9(1) Fadlallon/Mono. MoKa higher than tle neutron values, as expected:neutron Toralno. lFl 98 scatleringoccurs effectively from a point source,and Spacegroup F43n No.lF"l 47 the displacement parametersrepresent true thermal F(azlmuthal)% 18.4- 3.S and zero-point motion (presumingthat no positional Csll contont 4[CuU A(observsd)% 2.0 disorder is present),whereas X-ray scatteringoccurs rF(observed)% 2.0 from the much larger volume of the electron density. F-:(|Fol-l4|)/:| Fonwn -lzw(lFol-lFar2rzF11",w- 1 Moreoverothe relative sizes of the two displacement factors are similar in each shucture, suggestingthat thereis no Cu-I disorderat thetwo sites.Thus untqrinned marshite must crystallize below the p-CuI -+ y-CuI TABLE 2. FINALATOM PARAMETERS,SELECTED INTERATOMIGDISTANCES (A, ' ' fransitiontemperature of. 367' C. AND ANGLES (.) FOR MAR8HNE x Y z 'u,, lL u- L u,^ u.- tt. ACKT,IOWLEDGETVENrIS Cu 1t4 114 114 3{t6(8) 3s6(8)sr}6(8) O o 0 936(5) r 0 o 0 194(5)104(5)rs4(6) 0 0 0 1s4(3) Cu-l x4 2.625(11 l-Cu-l r09.s(1) Maferial for this work was supplied by the Deparhent l-cu x4 2.626(l) Cu-l-C! 109. of Mineralogy, Royal Ontario Museum; we thank the 'Ux I0" stafffor their cooperation in this matter. This work was supported by Natural Sciencesand Engineedng Research Council of Canada Operating, Infrastuctue, andMajor Equipment Grants to FCH. selectedbond-lengths and anglesare given in Table 2. Structurefactors may be obtainedfrom The Depository Rmsnnqcgs of UnpublishedData, CISTI, NationalResearch Council, Ottawa.Ontario KlA 0S2. BfrnER, W. & IlAIc, W, (1977): Crystal structure of high temperaturecuprous iodide andcuprous bromide. Electro- DIscUssIoN chim.Acta22,70l:7M. HAwu{oRNE,F.C. & GRoAr,L.A. (1985):The crystalstructure The resultsof the currentrefinement show marshite of wroewolfeite, a mineral with [Cua(SOaXOtI)o(HzO)] to have the space groupF43m and to be isostructural sheets.Am Mineral.70, 105G1055. with sphalerite.Marshite is thuslCuI in the nomencla- ture ofYude et al. (1990).There is no evidencefor any YIIDE,Y., BovsuN,H. & Sqrure, H. (1990): Neutronpowder disorder of the Cu and I atoms, as occurs for high- investigationof CuI. Z Kristallo8r, l9l, 7 9-91. temperafurecubic o-CuI. The powderneutron-difuction sffucture-refinementof Yude et aI. (L990) gives the , isotropic-displacementfactors for the Cz and f sitesas ReceivedNovember 15, 1996, revised mantscript accepted 2.20(8) and 1.41(1)A2, respectively.Conversions of February 2, 1997..