Canadian Mineralogist Vol.23, pp. 6l-76 (1985) THE RELATIONSHIPBETWEEN CRYSTAL STRUCTURE, BONDING AND CELLDIMENSIONS IN THE GOPPERSULFIDES RONALD J. GOBLE Deportment of Geology, University of Nebrasko-Lincoln, 433 Morrill Holl, Lincoln, Nebrosko 68588-0340,U.S.A, ABSTRACT de cui'ire de structureconnue indiquent que la structure de la yarrowiteet cellede la spionkopiteressembleraient Copper and copper-iron sulfidescan be classifiedinro surplusieurs points i cellede la covelline,mais on doit con- three generalgroups: (1) anilite, digenite, geerite,cubanite, siddrercomme probable une occupation statistique des sites. chalcopyrite, haycockite, talnakhite, mooihoekite and bor- Lestentatives de ddtermination de la structurede la spion- nite with structuresbased upon approximatecubic close- kopiteont 6t€entravdes par I'imperfectiondes cristaux et packing of the sulfur atoms; (2) djurleite and chalcocite le grand nombrede sitesde cuivrevacants. La stru4ure with structures based upon approximate hexagonal close- de la geeriteest rhomboddrique (fi32?), a 15.77A, a packing oftle sulfur atoms; (3) covelline, yarrowite, spion- 13o56', Z = l, et ressembleraiti celle de la digdnite. kopite and idaite with a combination of hexagonalclose- packing and covalent bonding of the sulfur atoms. The (Traduit par la R6daction) average spacing D between layers in all groups can be expressedas D = 2.M3 + 0.654(Cu:S) + l. 183@e:S). The Mots-clds:yarrowite, spionkopite, geerite, sulfurc de cui- ionic radius R of sulfur for group-l mineralsis R, = 2t7 vre, sulfuresde cuivre et fer, covellineblaubleibender, Q'l2A), where D is from the previous expression;for structurecristalline, liaisons. group-2 minerals, Rz = 1.856+ 0.060 (Cu:S)+ 0.023 @e:S);for group-3minerals, R: = 1.857+ 0.039(Cu:S) - 0.020 @e:S). Consideration of bond lengths in co- INTRODUCTIoN ordination polyhedra of known copper sulfide structures indicatesthat major portions ofthe yarrowite and spionko- Eight copper-sulfideminerals have beenidentified pite structures will resemblethe covelline structure. vdth to date: covellineCul.6gs, yarrowite Cu1.12S,spion- probable statistical site-occupancy.Attempts at the deter- kopite Cu,.*S, geeriteCu1.6eS, anilite Cut.75S,dige- mination of the spionkopitestructure were hamperedby the imperfection of the crystals and the partial occupancy nite Cu,.*S, djurleite Cu1.eSand chalcociteCuz.mS. of most structural positionsof copper. The geeritestruc- Partial or completestructural determinationshave ture is rhombohedral(R3n?) with a 15.77A, o 13.56,. been carried out for covelline (Oftedal 1932, Berry Z = l, and will probably resemblethe digenitestructure. 1954,Kalbskopf et al. 1975,Evans & Konnert 1976), anilite (Koto & Morimoto 1970),digenite (Donnay Keywords: yarrowite, spionkopite, geerite,copper sulfides, et al. 1958,Morimoto & Kullerud 1963),djurleite copper-iron sulfides, blaubleibender covelline, crystal (Takedaet al. 1967a,b,Evans 1979),and chalcocite structure, bonding, (Sadanagaet al. 1965,Evans l97l). The structures of yarrowite, spionkopiteand geeritehave not been SoMMAIRE determined.Yarrowite and spionkopite,two of the blaubleibenderor "blue-remaining" covellines,were On peut regrouperles sulfuresde cuivre et de cuivre r for many yearsdescribed in terms of the hexagonal fer en trois grandesfamilles: l) anilite, dig6nite,geerite, cubanite, chalcopyrite,haycockite, talnakhite, mooihoe- unit-cell of covelline,based upon similaritiesof X- kite et bornite, dont la structure contient un empilement ray powder patterns(e.9., Frenzel1959, Moh 1971, approximativement cubique compact des atomes de sou- Rickard 1972,Putnis et ql. 1977),However, Goble fre; 2) djurl6ite et chalcocite,dont la structuremontre un (1980)has shown that the unit cellsof yarrowiteand empilementhexagonal compact (6rossomodo) des atomes spionkopite are not the sameas that of covelline. de soufre, et 3) covelline,yarrowite, spionkopiteet idaite, Geeriteis a pseudocubiccopper sulfide that has only qui montrent une combinaison de I'agencementhexagonal recently been reported (Goble & Robinson 1980). compacfdes atomes de soufre avecliaisons covalentes. Pour The known structurescan be divided into three lestrois groupes,la s6parationmoyenneD descouches est generalgroups based upon the natlue of packingof 6galed I'expression2.063 + 0.654(Cu:S) + 1.183(Fe:S). the sulfur atoms: (l) anilite and digenite,with struc- Le rayon ionique.R du soufre Cansles min6raux du pre- mier groupe est 6gal d D/2 l2A. Pour les mindraux ou turesbased upon approximatecubic close-packing, deuxidmegroupe, on a .rR2: 1.856+ 0.060(Cu:S) + 0.023 (2) djurleite and chalcocite,with structuresbased (Fe:S), et pour ceux du troisiime groupe, upon approximate hexagonalclose-packing, and (3) R: = l.8SZ + 0.039 (Cu:S) - 0.020 @e:S).Les longueurs covelline, with a combination of hexagonalclose- de liaisons dans les polybdres de coordination des sulfures packing and covalentbonding of the sulfur atoms. 61 62 THE CANADIAN MINERALOGIST The resemblancebetween the well-developedyar- geeritefrom the studiesof Goble (1980)and Goble rowite and spionkopite subcellsand the covelline & Robinson (1980)were used for all single-crystal unit-cell (Goble 1980)suggests that theseminerals patterns. Precession,Weissenberg and integrated belong to group 3; the pseudocubicnature and Weissenbergphotographs were preparedfor selec- resemblanceof the geeriteunit-cell to a structurepro- ted orientations of the yarrowite and spionkopite ducedby the leachingof anilite (Goble 1981)sug- reciprocallattices. Precession photographs of covel- gest that geeritebelongs to group 1. Single-crystal line in the equivalentorientations were also prepa- X-ray studiesprovide a method of examining the red in order to checkthe supposedstructural simi- structuresof yarrowite, spionkopiteand geeriteand larity of the blaubleibendercovellines to this mineral. of determiningthe true relationshipbetween these For geerite,only precessionphotographs were pre- structure$and those already known for other cop- pared. Filtered Cu-radiationwas usedfor all Weis- per sulfides. senbergfilms and Mo radiation for all precession films. The fragmentsof yarrowite, spionkopiteand PRoCEDURES geeriteused measure approximately 0.14 x 0.08 x 0.03,0.25 x 0.08 x 0.08and 0.07 x 0.06 x 0.02 Cleavagefragments of yarrowite, spionkopite and mm, respectively. For intensity determinations,0-, l- and 2level integratedWeissenberg photographs (rotation axis c), were taken of the yarrowite and spionkopite frag- ments.Exposure times for all levelswere on the order of 200 hours using a Philips fine-focus Cu X-ray tube (point-focus port) with a Philips PW 1008/85self- rectified high-voltagepower supply operatingat 40 Ft.c kV and 12 mA. Three-film packswere used, the films f being separated by one sheet of black paper. ]t Individual films of eachpack werescaled using the "film factor" of Morimoto & Uyeda(1963). Differ- ent levelswere scaled by a comparisonof reflections present on two or more of the levels, with the A. COVELUNE B. COVELUNE 0120)ptone assumptionthat the unit cellsare approximately hex- agonal. Intensitieswere estimatedby visual comparison with the {110} reflection of covellineon standard- scalefilms preparedfrom multiple exposures.Unob- servedreflections were assignedmaximum intensi- ties of one-half the minimum observableintensity at that point on the film. Raw intensity-datawere correctedfor Lorentz and polarization effectsand, in the caseof spionkopite,for the presenceof minor (= l59o) intergrownoriented yarrowite; absorption I*I correctionswere not applied. Wilson plots (Wilsgn 1942)show^overall temperature-factors of 0.45 A2 T l_Jl and 0.75 A2 for yarrowite and spionkopite, re- IT tY I spectively. -t_ l..-/.........---.....n)-) A C.'ANIUTE" D.SPHALERITE E. METASTABLE (100)phne DI6EMTE STRUCTURALDATA Frc. 1. The crystal structure of covelline(after Wuensch group-3 1974),"anilite", sphaleriteand metastabledigenite. The The crystal strucure of covelline, a "anilite" structureis an idealizedversion (see text). In mineral,is shownin Figure la (after Wuensch1974); B t,Cu and tvCu indicate copper atoms in triangular equivalentsites for all atomslie on the (l l0) plane, and tetrahedralco-ordination polyhedra, respectively; and the structure can be representedby a section S. indicates covalently bonded sulfur; lC and lI through the unit cell on this plane as shown in Figure representthe spacingsof one covalentlybonded and one lb. The crystal structure of anilite, a group-l (ionically bonded) layer, respectively.Filled tetrahedral mineral, can be representedin a similar fashion if in A, B and D indicate fully occupied triangular circles & Morimoto (1970)are co-ordination polyhedra; filled and open triangles in C the structural data of Koto and E indicate fully and partly occupiedtetrahedral co- transformed into an idealized cubic close-packed ordination polyhedra,respectively, with atomic displace- unit-cell. Copperatoms in triangularly co-ordinated ment toward the four surroundingtriangular faces. sitesare assignedto the tetrahedra of which these CRYSTAL STRUCTURE OF THE COPPER SULFIDES 63 a11.tlt3 Oooe r663 Oli3 a88e a-LZ1 .057 .T7.nn 4776 )zza .n.n.i o635 )zzt olo.fit.m a$r 415.15.15 Ods-0 oiiS .t3.f3.tz a66s- an.ji.i3 a7.t7 i" FIc. 2. The reciprocallattice of geeritewith rhombohedralindices. Both rhombo- hedral and cubic crystallographicaxes are indicated. sites form a face, and displacementof the copper cil of Canada,Ottawa, Ontario KIA 0S2.For yar- atoms from thesetetrahedrally co-ordinatedposi-