American Mineralogist, Volume 75, pages 1421-1425, 1990

Francisite, CurBi(SeO3)2O2Cl,a new mineral from Iron Monarch, South Australia: Description and crystal structure Ar-r,,q.NPnrxc Department of , South Australian Museum, North Terrace,Adelaide, South Australia 5000, Australia Bny,c.lrM. Garnrrousn Department of Chemistry, Monash University, Clayton, Victoria 3168, Australia Wrr,r,raivrD. Brncn Department of Mineralogy and Petrology,Museum of Victoria, 285 Russell Street,Melbourne, Victoria 3000, Australia

Ansrntcr Francisite is a new copper bismuth oxy-chloro selenitefrom Iron Monarch, South Aus- tralia. The new mineral occurs as radiating clusters of bright green bladed crystals up to 0.25 mm in length. The crystals are elongated along [010], and the principal forms are {100}, {0ll}, and {l0l}. Associatedwith francisiteare barite, chlorargyrite,muscovite, native bismuth, naumannite, djurleite, and a number of poorly characterizedselenides of Bi, Ag, and Cu. Francisite appearsto have formed as a result of hydrothermal alteration of the selenideand sulfide minerals. Electronmicroprobe analysis yielded CuO 32.62,Bi,O3 35.75, SeOr27.23, Cl 4.1l, less O : Cl, 0.93, total 98.78 wo/o; the simplified formula is close to CurBi(SeOr)rOrCl.The mineral is transparent and has a pale green . The estimated Mohs hardnessis 34, and D*. : 5.42 gm/cm3.Single-crystal studies gave an orthorhombic cell with a: 6.354(l), D : 9.630(l), c : 7.220(2)A, V : 441.80(2)A,, spacegroup Pmmn andZ :2. The crystal structure was solved by Pattersonmethods and refined to R : 0.0443 and wR : 0.0395, using a set of 734 reflections, of which 434 were consideredto be observed [I > 3o(I)]. The structure consistsof an infinite three-dimensionalframework of cations and O, con- taining eight-coordinate Bi3r, square-planarCu2*, and three-coordinateSeo*. The Cl ions and the Se lone pair electronsoccupy tunnels parallel to [001]. The strongestlines in the X-ray powder pattern are (doo",I"b- hkl) 5.31 (60) (l l0); 3.39 (r00)(r2r)2.866 (80) (r30);2.652 (70) (220);2.4er (60) (22r); r.695 (35) (2a2); 1.588 (60) (332). The name is for Glyn Francis of Iron Knob, South Australia.

INrnorucrroN OccunnnNcn In May 1987 Glyn Francis, Quality Control Officer at The new mineral was found in cavities at the core of the Iron Monarch iron deposit, submitted a group of an isolated lens of barite within massivehematite ore on specimensfrom the mine to one of us (A.P.) for identi- the 138-m level at the southern end of the open cut. The fication. One specimencontained small bright apple green barite lens was at the lower end of an open channel run- crystals that were unfamiliar. Energy-dispersiveX-ray ning along the hinge of a major anticline within the ore analysesshowed that the mineral contained Cu, Bi, Se, body. In addition to barite, the minerals associatedwith and Cl, an unusual combination of elements. Electron francisite include chlorargyrite, which occurs as hexago- microprobe and powder X-ray diffraction analysesindi- nal prisms (pseudomorphsafter apatite?)and fine-grained cated that the mineral was an undescribedspecies but left white muscovite. Also present are naumannite, native aspectsof the mineral's chemistry unclear. A single-crys- bismuth, djurleite, and severalpoorly defined copper, sil- tal structure determination was undertaken in order to ver, and bismuth selenides,all of which occur as small fully resolve the composition and stoichiometry of the blebs within the barite. Francisite occurs as radiating mineral. Francisite is a copper bismuth oxy-chloro sele- clustersand groups of bladelike crystalson barite crystals nite and has been named in recognition of Glyn Francis's and in hollows in the fine-grained muscovite that fills contribution to the understandingand preservationof the many of the cavities within the barite. Approximately minerals of the Iron Monarch ore body. The mineral and 100 small specimensbearing the new mineral were re- the name were approved by the Commission on New covered; the total mass of francisite on all known speci- Minerals and Mineral Names in 1989. Type specimens mens is

Fig. 2. Schematicdiagram showingthe principal forms of francisite:a, {100};m, Il0ll; andz, {0ll}.

Fig. l. SEMphotomicrograph showing a groupoffrancisite found to sink in Clerici's solution; the calculateddensity crystals,with a baritecrystal O) and flakesof muscovite(m). is 5.42g/cm3. Crrnvrrsrnv Middleback Rangesof South Australia, approximately400 Francisite was analyzed using a JEOL electron micro- km northwest of Adelaide. Iron Monarch and the adjoin- probe operatingat l5 kV with a specimencurrent of 0.020 ing deposit, Iron Knob, have been worked since the turn pA. The standardsused were pure metals (Cu, Bi), ber- of the century by Broken Hill Proprietary Limited, first zelianite (Se),and NaCl (Cl). No other elementswith an as a source of flux for the lead smelting works at Port atomic number greaterthan eight were detectedby wave- Pirie and later as a source of iron ore for steel making. length spectroscopy,and HrO was not determined, as the The principal ore mineral is hematite, which gradesinto infrared spectrumindicated that neither H'O nor OH was siliceous banded iron formation (Milnes, 1954).The up- present. A total of seven analyseswere obtained, for which per part ofthe deposit also contains large lensesofman- the averageis given in Table l. The empirical formula, ganeseoxides, principally hausmannite. Small amounts calculated on the basis of nine anions, is Cu, roBi,,u- of other unusual secondaryminerals, mainly phosphates, Se,ruO,,rClo.rr, with the simplified formula being Cur- have also beenfound in isolatedareas within the ore body Bi(SeO.)rOrCl.This formula was confirmed by the crystal (Segnitand Francis, 1983; Pring et al., 1989;Pilkington structure determination. eIal.,1979). The occurrenceof francisite,native bismuth, and the associatedselenide minerals is the first record of Powonn X-RAY DrFFRAcrroN Se- and Bi-bearing minerals from Iron Monarch. The powder X-ray diffraction pattern was recorded us- ing a 100-mm diameter Guinier-Hiigg camera with Prrysrclt AND oPTrcAL PRoPERTTES monochromated CuKa, radiation and with Si employed Francisite occurs as bladed crystals up to 0.25 mm in as an internal standard. Line intensities were estimated length that are elongatedparallel to [010]. The principal visually by comparison with a set of standard reflections. forms observedare {100}, {0ll}, and {101} (Figs.1 and The powder pattern (Table 2) was indexed on an ortho- 2). Contacttwinning on {100} is sometimespresent. The rhombic cell and, least-squaresrefinement was under- crystalsdo not have a cleavageand when broken display taken using 34 reflections with2? <80'. The final param- a conchoidal fracture. Francisite is bright apple green in eters obtained were a : 6.356(l), b : 9.633(2), c : color (no. l40A on the Royal Horticultural Society of 7.224Q)4.. London chart) and the streak is a paler shade of apple green.The optical properties offrancisite were not deter- INrn-r,nno sPECTRUM mined in detail, as the mineral was found to react with The infrared spectrum of francisite was recorded on a oils of high refractive index; all refractive indices were Mattson Instruments Cygnus 25B Fourier transform in- found to be greaterthan 1.79. The high refractive indices frared spectrophotometer.The spectrum contains three are in accord with the adamantine luster of the mineral. absorption bands. Weak bands are presentat 1000 cm-' The crystals are length slow and exhibit a distinct ple- and 820 cm-r, and a strong band is evident between 680 ochroism that varies in color from pale green to bright and 740 cm-'. The strong band is characteristicof Se-O green,with the brighter shadebeing parallel to the length stretching in selenites,whereas in selenatesthe strong Se-O of the crystals.Neither the hardnessnor the density could stretching absorption is around 895 cm ' (Sathianandan be accuratelymeasured because of the small crystal size. et al., 1964). The infrared spectrum of francisite con- The hardnessis estimated at 34. and the crvstals were tained no absorption bands attributable to HrO or OH. PRING ET AL.: FRANCISITE, Cu,Bi(SeO,).O,Cl 1423

TABLE1. Electronmicroprobe analyses of francisite TABLE3. Crystaldata and results of crystal-structurerefinement for francisite 1' 3t x x Atom Crystalsize 0.113 0.021 0.013mm proportions Unit-celldimensions (A) CuO 32.62 33.10 3.10 a 6.354(1) (32.25J2.96) b (A) 9.630(1) (A) 7.220(2) Biros 35.75 32.31 1.16 c (34.98-36.99) v(A*) 441.8O(2) 2 SeO, 27.23 30.78 1.86 z (26.9U27.751 4 (g cm*) 5.42 p ') 4.11 4.92 0.88 (cm 354.36 (4.054.22) RadiationMoKa 0.7107A limit 2d(MoKa) 60" Less O = Cl 0.93 1.11 Collection 734 Total 98.78 100.00 Unique reflections Reflections| > 3o(l) 434 ' Francisite,lron Monarch, South Australia.Average of sevenanalyses, R 0.0443 ranges given in parentheses. 0.0395 -. Cu"Bi(SeO.),O,Cl. a residual(e A-3) t Francisite, lron Monarch, South Australia. Atomic proportions cal- + 3.92 culated such that O + Cl : 9. 3.38

The infrared spectrum is in full accord with the crystal On the basis of systematic extinctions (hkI, h + k : chemistry revealedby the structure determination. 2n + l), spacegroups Pmmn and Pm2,n are permitted; Pmmn was confinned by refinement. The Bi atom was Cnysr.q.L srRUcruRE located using the Patterson method, and subsequentdif- Experimental ference-Fouriersyntheses revealed the remaining atoms. Crystal data were obtained using a Philips PW ll00 Weighted least-squaresrefinement was undertaken using four-circle diffractometer. Lattice parameters (Table 3) neutral-atom scattering factors with corrections for were refined using angles obtained from 24 reflections anomalous dispersion (Cromer and Weber, 1974).Table with 30' < 20 < 34. 3 reports details of data measurementand structure re- finement. TrsLe2, PowderX-ray diffraction data for francisite The final list of observed and calculatedstructure fac- tor amplitudes is given in Table 4.' The final atomic pa- nh d*" (A) d* (A) rametersand their estimated standard deviations are giv- 20 5.81 5.78 011 en in Table 5. 60 5.31 5.31 110 100 3.39 3.39 121 30 3.18 3.18 200 I A copy of Table 4 may be ordered as Document Am-90-442 3.11 3.14 102 from the BusinessOffice, Mineralogical Society of America, I130 15 2.988 2.986 112 DC 20036, 15 2.911 2.909 201 Seventeenth Street NW, Suite 330, Washington, 15 2.888 2.890 022 U.S.A. Pleaseremit $5.00 in advancefor the microfiche. 80 2.866 2.866 130 5 2.786 2.785 211 70 2.652 2.653 220 60 2.49'l 2.490 221 TABLE5. Final atomic coordinates and thermal parameters for 25 2.408 2.408 040 francisite 5 2.386 2.386 202 3 2.285 2.285 041 Atomic coordinatesand equivalentisotropic thermal parameters(4'z) 10 2.244 2.245 132 x y z leql c 2.155 2.156 231 10 2.150 2.150 141 Bi V4 V4 0.2416(21 0.0071(3)- 10 2.136 2.138 222 Cu(l) 0 0 0 0.0131(7)' 30 2.069 2.069 310 Cu(2) V4 V4 o.7922(51 0.0137(12r 10 1.872 1.873 321 Se Y4 0.s570(2) 0.6096(3) 0.0076(6)' 10 1.863 1.862 051 Cf V4 t4 0.1488(1 4) 0.0330(33)- 10 1.795 1.796 312 O(1) r/c 0.11 13(14) 0.9941(21) 0.0074(29) 25 1.768 1.768 330 o(2) 0.040s(16) 0.583600) 0.75s2(16) 0.o157(21) 35 1.695 1.695 242 O(3) 1/t 0.11 73(1 7) 0.5872(231 0.0169(37) 15 1.605 1.606 060 60 1.588 1.588 332 20 1.433 1.433 260 Anisotropicthermal parameters1[z x 10a) 15 1.391 1.392 422 u, U"" us u4 ur" ur" 15 1.335 1.336 063 20 1.325 1.325 432 Bi 66(5) 64(5) 82(6) 000 -87(11) J 1.259 1.260 361 cu(1) 116(3) 5s(12) 123(13)-69(12) 41(13) 5 1.211 1.212 521 Cu(2) 322(251 61(16) 27(211 000 5 1.208 1.209 451 Se 72(10) 64(10) 92(11) 8(8) 0 0 cl 474(68) 345(s4) 172(461 000 Note.'Cell parametersrefined from the data above: a: 6.356(1)A, b: 9.633(2)A, c : 7.224(2)A. volume : 442.4e) N. ' U(eq) : V3>2,(UtjaiEat. at) t424 PRING ET AL.: FRANCISITE, Cu'Bi(SeOJ'O'Cl

Tlsr-e 6. Bond distances (A) and angles (") in francisite

Bondsat Bi a Bi\o(1)"(x2) 2.23(2) -O(2)o ( x 4) 2.45(11 -o(3)" ( x 2) 2.8o(2) Mean 2.48 Bia... cu(2)s 3.245(41 Angle at Bi o(1)B-o(1)c 2.67(31 73.5(7) O(1)^-912;o1"0, 3.92(2) 113.6(3) O(1)A-O(2)E( x 4) 2.60(2) 67.4(3) o(1f-O(3)A(x2) 4.28(2) 116.1(5) o(1f-O(3)H(x2) 5.02(21 170.4(5) a O(2)A-O(2)E( x 2) 4.89(2) 178.9(5) o(2)n-612;r1"' 3.70(2) e8.1(s) o(2)r-912;c1"r' 3.21(21 81.e(s) O(2)A-O(3)A( x a) 4.22(2) 106.9(3) O(2)^-O(3)"(xa) 3.10(2) 72.1(3) o(3r-o(3r 2.56(3) 54.2(7) Bonds at Cu(1) Cu(1)a-O(1)B(x2) 1.917(8) Fig. 3. A diagramof francisiteviewed along Unique -O(2)c( x 2) 1.96(1) [001]. 1.939 labeled in Table5. drawnusing SHELXTL Mean atomsare as [Diagram Cu(1)A... CIJ(x2) 3.078(4) PLUS(Sheldrick, 1988)1. Angleat Cu o(1)+9111 3.83(2) 180.0(-) -o(z;c 2.87(2) 9s.7(5) Structure description -O1e1n 2.60(2) 84.3(s) Bonds at Cu(2) The structure of francisite is depicted in Figure 3; the Cu(2)A-O(3)H(x2) 1.96(2) atomic arrangementconsists of an infinite, three-dimen- -O(1)H(x2) 1.s8(2) sional cation and O framework containing eight-coordi- Mean 1.97 Cu(2)A...Clo(x2) 3.206(1) nate Bi3*, four-coordinate Cu2*and three-coordinateSe4* Angleat Cu ions. The coordination ofeach ion is illustrated in Figure o(3r-o(3)- 2.56(3) 81.6(s) 2.e4(2) 96.7(6) pair of Se oc- o(3r-o(1r 't78.3(7) 4. Chlorine ions and the lone of electrons o(3)A-O(1)" 3.93(2) cupy tunnels within the framework parallel to [001]. Bonds at Se The Bi ion coordination polyhedron is best described Seo-o(3)" 1.6e(2) -O(2)M( x 2) 1.71(2) as an 8,14,8-Drnpolyhedron, using the method of King Mean 1.70 (1970), in which the three numbers refer to the number se^.. cu(2r 3.237(3) Angleat Se of vertices, edges,and faces of the polyhedron, respec- o(3)r-o12y1, '' 2.64(2) 102.0(5) tively. King also refers to the polyhedron in terms of 2, o(2r-o(2)M 2.66(2) 101.7(71 4, and 2 stackedparallel planes ofanions, in this caseO A/ote; (A) x, y, z; (Bl x, y, z - 1 ; (C) x, lz - y, z - 1 ; (ol - x, 1 - y, 1 ions. The Bi-O distances(Table 6) range ftom 2.23-2.80 - z;(E)Vz+x,y-V2,1 - z;(ny2+ x,1 - y,1 - z;(Gl-x,y-Vz, - -x,1 - A, witn a mean distance of 2.48 A. ttre eight O ions of 1 - z; (H)x,y2 - y, z(D -x,-y,1 - z;(Jlx, y 1,z,(K) y, -z; (L)1 - x,1 - y,1 - zi (M)lz - x, z. the Bi polyhedron bridge to four Cu(l) atoms, to two Y,

Cu(2) atoms, and to two Se atoms. The anglessubtended by pairs of O ions at Bi and the O-O distancesare listed in Table 6. The two independent Cu ions are both square-planar in their coordination; Cu( I )-O distancesrange from | .9 l7 - 1.96A (mean 1.939A) and Cu(2) 1.9G1.98A (mean 1.97 L); anglessubtended at Cu by pairs of O ions and the O-O distancesare given in Table 6. It is evident from Figure 3 that the Cu(l) squareplanes have one O in com- mon, O(l), that links them into a zig-zag chain parallel to [00]. The angle between successivesquare planes is I17.8'. Thesechains are reflectedin the mirror plane at | : t/c,on which the Bi, Cu(2), and Cl ions are located. The Cu(2) ions link the Bi coordination polyhedra along 0(1b) In Cu,SerOrCl,(Galy et al., 1979) Cu occurs in Fig. 4. A diagram showing the O and Cl coordination ofthe [001]. the square-planar arrangement of one Bi, Cu(1), Cu(2), and Se atoms. Small letters in parenthesescor- three coordinations; with a respond to the symmetry transformations indicated in capital Cu in this structure is similar to that in francisite, A with the mean lettersat the bottom of Table 6. [Diagram drawn usingSHELXTL mean Cu-O distanceof 1.961 compared PLUS (Sheldrick, 1988).1 Cu-O distancein francisite of 1.955 A. However, the Cu- PRING ET AL.: FRANCISITE, Cu,Bi(SeOJ,O,CI t425

Cl distancesof this Cu in Cu,Se2O8CI2,2.957 4,, are of synthetic francisite have been made by hydrothermal somewhatshorter than the mean Cu-Cl distancereported methods (Berrigan and Gatehouse,unpublished results). herefor francisite(3.142 L). The Se ions are three-coordinatein a triangular pyra- AcrNowr,nncMENTS midal arrangementwith a mean Se-O distanceof 1.70 A; The assistanceof G.D. Fallon in preparation of the figures is gratefully the Se-O bond lengths are typical ofthose in other sele- acknowledged.Thanks are also due to Stuart McClure ofCSIRO Division nites (e.g.,Kohn et al., 1976; Galy et al., 19791-Effenber- of Soils for the SEM photornicrographs and David Tilbrook of the South Australian Conservation Center for the infrared spectrum offrancisite. ger, 1986; Effenbergerand Pertlik, 1986; Hawthorne et al., 1986;Efenberger, 1988). The position ofthe stereo- Rrrnnnucns crrnn chemically active lone pair of electrons of Se was calcu- Cromer, D.T., and Weber, J.T. (1974) International tablesfor X-ray crys- lated as being at the apex ofthe tetrahedron whose base tallography, vol. IV, Kynoch Press, Birmingham, England. is formed by the three O ions coordinated to Se. From Effenberger,H. (1986)Die Ikistallstrukluren von drei Modifikationen des Figure 4 it can be seenthat the lone pair is located in the Cu(SeOJ.Zeitschrift fiir Kristallographte, 175, 6l-7 2. -(1988) tunnel that the Cl ions occupy. The structure of Contribution to the stereochemistryof copper. The tran- pyramidal (Galy sition from a tetragonal to a trigonal bipyramidal Cu(II)O, CurSerOrCl, et al., 1979) is described as having a coordination figure with a structure determination of PbCudSeO,)r. Cl ion, and the lone pair of a Se atom (E) located in an Journal ofSolid StateChemistry, 73, 118-126. O polyhedron with l5 verticesin which the E-Cl distance Effenberger,H., and Pertlik, F. (1986) Die K-ristallstrukturender Kup- is given as -2. l0 A. ttre possibility of some interaction fe(Il)-oxo-selenite CurO(SeO3)ftubisch und monoklin) und Cu.O(SeOr), (monoklin betweenthe lone pair and the large anion was suggested. und triklin). Monatsheftefiir Chemie, I17, 887-896. -2.51 Galy, J., Bonnet, J.-J., and Andersson,S. (1979) The crystal structure of The E-Cl distancein francisite of A, calculated a new oxide chloride ofcopper(I) and selenium(V): Cu,SerOrCl,.Acta using the same Se-E distanceas Galy et al., (1979) of Chemica Scandinavica,A33, 383-389. - 1.3 A, could indicate a further example of such an in- Hawthorne, F.C., Ercit, T.S., and Groat, L.A. (1986) Structuresof zinc teraction. selenite and copper selenite. Acta Crystallographica, C42, 1285-1287. King, R.B. (1970) Chemical applications ofgroup theory IV. Journal of PlRAcnNnsrs the American Chemical Society,92, 646M466. Kohn, K., Inoue, K., Horie, O., and Akimoto, S-L (1976) Crystal chem- Francisite appearsto have formed from the oxidation istry of MSeO, and MTeO, (M = Mg,Mn, Co, Ni, Cu, and Zn). Journal of the primary copper and bismuth selenidesand sulfides of Solid StateChemistry, 18, 27-37. that occur with it, probably through the action of low Milnes, K. R- (1954) The geologyand iron ore resourcesof the Middle- back Range Area. Geological Survey ofSouth Ausralia, Bulletin 33, temperaturehydrothermal fluids. It is known that the Fe- 245 p. Mn ore contains significant amounts of elementssuch as Pilkington, E.S.,Segnit, E.R., and Wans, J. (1979) Kleemanite,a new zinc Cl, Zn, As, and P, which have been sufficiently concen- aluminium phosphate. Mineralogical rnagazine, 43, 9T95. trated to give rise to suites oflocally abundant secondary Pring, A., Francis, G. L., and Birch, W. D. (1989) Pyrobelonite, arsen- minerals such as , pseudomalachite, oklasite, swiuerite and other rec€nt finds at Iron Monarch, South Aus- turquoise, tralia. Australian Mineralogist, 4, 49-55. faustite (Segnit and Francis, 1983), kleemanite (Pilking- Sathianandan,K., McCory, L.D., and Margrave, J.L. (1964) Infrared ab- ton et al., 1979), arsenoklasite,pyrobelonite, and switz- sorption spectra ofinorganic solids-Ill selenites and selenates.Spectro- erite (Pring et al., 1989). The formation of francisite chimica Acta. 20. 957-963. therefore seemslikely to have been a two-stageprocess. Segnit, E.R., and Francis, G.L. (1983) Secondaryphosphate minerals from Iron Monarch South Australia. Australian Mineralogist, l, (43),243- Small amounts of Se, Bi, Ag, and Cu were leachedfrom 250. the Fe-Mg ore body by Ba- and S-rich fluids, possibly Sheldrick, C.M. (1976) SHELX76, Program for crystal structure deter- during a low grade metamorphic event associatedwith mination. Cambridge Universiry, Cambridge, United Kingdom. - the folds, and their constituents were redepositedas in- (1988) SHELXTL PLUS, Revision 3.4, SiemensAnalytical X-Ray Instruments, Inc., Madison, Wisconsin, clusionswithin massivebarite. This assemblagewas later U.S.A. subjectedto oxidation, possiblyby Cl-rich ground waters, M.tluscnrrr REcETvEDJaxumv 2, 1990 precipitating francisite and chlorargyrite. Small crystals M,r.Nuscnrp.rAccEprED Ser.rernrnen 28. 1990