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Absrracr a Comparison of the Crystal Structures of the Minerals

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Absrracr a Comparison of the Crystal Structures of the Minerals Canadian Mineralogist Vol. 13, pp. 168-112(1975) CRYSTAL STRUCTT'RES OF THE CHALCOPYRITE SERIES* S. R. HALL Mineral SciencesLaboratories, Canada Cenfte for Mineral and Energy Technology(Mines Branch), Departmentof Energy,Mines and Resources,Ottawa, Catrada, KIA AGI ABsrRAcr atoms at the interstitial sites of a sphalerite-like A comparisonof the crystal structures of the arrangement of sulphur and metals, rather than mineralschalcopyrite, CuFeSz ftIall & Stewart1973), on metal-substitution or sulphur-removal which talnakhite, CueFesSl6(Hall & Gabe 1972), mooi- are the other two structural mechanisms pos- hoekite CusFes$s(HaI & Rowland 1974) and,hay- sible for this type of cubic close-packedarrange- cockite CuaFe5Ss(Rowland & Hall 1975) is made. ment of atoms. On this basis, the compositional Tho metal-rich minerals are related to chalcopyrite data determined by electron-microprobe meth- by additional metal atoms located at interstitial sites. ods (fable 1) were consideredin terms of an in- and have structur€s consistent with stoichiometric tegral number of sulphur atoms. The resulting compositions. The interstitial metals can tre de- chemical formulae contain an integral number scribed iu terms of metal-coordination octahedra standard which vary in size according to the packing ar- of metal atoms, within the estimated rangements. deviation of the probe measurements. This was the ffust evidence that the chemical formulae for 1974). INrnooucrroN these minerals were stoichiometric Glall Interstitial metals The crystal structure of chalcopyrite, CuFeSr, was first investigatedby Burdick & Ellis in 1917, The principal structural aspect common to and has been studied by a nr:mber of workers talnakhite, mooihoekite and haycockite is the since, most recently by Hall & Stewart (1973). presence of extra metal atoms located at inter- In the last few years three new minerals closely stitial sites of the ccp sulphur lattice. Minerals related to chalcopyrite have been discovered. related in this way are sometimes referred to as They are talnakhite CusFeesro(Cabri & Harris "stuffed derivatives". In these structures each 1971), mooihoekite CusF€eSroaod haycockite additional intentitial rnetal atom has a first- CqFeoSr (Cabd & Hal|L972). The crystal struc- order tetrahedral coordination to sulphur atomsn tures of these minerals have been determined at interatomie distances of about 2.3A, and a (tlall & Gabe 1972; Hall & Rowland 1974; second-order octahedral coordination to "reg- Rowland & Hall 1975), and this paper zum- ular" metal atoms, at about 2.7A. The proxi- marizes the results of these studies and identi- mity of tle interstitial metals to the surrounding fies their relationship to eash other. "regular'n metal$ is oipificant in view of the fact that the metallic Fe-Fe and Cu-Cu distances Drscussrorv are only 2.48 and 2.56A respectively. Though these distances do not give rise to purely metal- The crystal data for chalcopyrite, talnakhite, lic properties for these minerals, the resulting mooihoekite and haycockite are su'nmarized in Table 1. For these minerals the relative unit cell volumes V/V ncreasr, with an increasing metal- TABLEl. CRYSTAL0ATA 0F CIIALCoPIRITE-LI(EI'IIHERALS to-sulphur ratro. Z is tle number of pseudo- Ptabe fu cubic sphalerite-like cells which form the basic At. U Cu 25.1e0 2) 27.19(lo) 26.41(ro) 23.s6(15) lattice Fe,Nl a.a05) 24.74(151 26.14(14) D.46(ml of these minerals. The V/Z values pro- 49.63(25) 48.1603) 47.r6(A) 46.e8(25) vided the first indication that the corrpositions EowLa CuoFegsr6 CugFesSs5 CugF€95r6 CusFe1q515 of these ,minerals were metaldch ratler tlan SWae @ora? fizd fibt ila, v2.2r,2* sulphur-poor: They also provided early evidence (A) 5.2890 ) r0.s93(3) r0.58s(5) 10.70s(5) b" 5.2890) lo.5s3(3) 10.585(5) 10.734(5) that the basic structural mechanism for 10.4A0) 10.593(3) 5.38:r(s) 31.60(15) these 8424 minerals was based on the addition of metal vtz'(Arl I 45.8 148.6 150.8 151.5 '1614 Ttb8iq 694 rcfl. 528refl. refl. 2890fsfl. R-tal,w all dsta 0.086 0.205 *Mineral Research Program - Sulphide Research 'lss. tJla6' 0.051 0.047 0-t4 Contribution No. 90. 0.031 168 CRYSTAL STRUCTURES OF THE CTIALCOPYRITE SERIES 169 second-order metal-octahedra are a most im- TABI.E2. 5ETECTEI}AVEMOE IUTERAMfiIC.DISIANEE5 portant'component in relating the chalcopyrite- <t--N', 2.548(2ta.a.a like structures. An examination of the metal- ?:s3[l] :., t..Z1|,lil,;,i:8s[ 6] ;., octahedra packing in these structures (see Fig. ,,i:ut i.llilll 1) illustrates clearly their fundamental structural ##, i,fril,itri,ifif1fl character. There are, of course, a number of :*:: i:u?fi\ i.t\tA ,.22843:S[ll] other structural differences, such as metal-type soure brackets. slt6 u', lf , vi' and l/ @cuPy xnat 8re l@ m- ordering but these tend to be of lesser impor- ridsl'. "w@nt', "lsolat!d' and "llnked" mtal-octahedra' l[ ls a tance. In every structure the presence of an in- gllar Estal sits. tsrstitial metal displaces the surrounding six (M- o'regular" metals outwards from the positions raspective unit cells of the minerals. The they occupy when this site is vacant. Distortion -l> Cistanse would then be half the length of of the sphalerite-like lattice due to the addition the pseudo-cubic cells which make up eaoh of interstitial metals is conveniently described in struciure (V n Table 1 gives the number of terms of the second-order octahedral coordina- these cells). tion surrounding each interstitial metal site or The metal-octahedra coordinating each M', each interstitial metal site. For the Mo, M+ and M* site are referred to as "ideal", "potential" oovacant'nn sake of brevity each of fhe "regular" metal atoms "isolated" lad "linkgd", tespectively. at the vertices of the metal-octahedra is denoted A summary of the metal-metal distances for by aa M; interstitial sites which are unoccupied, the different structures is given in Table 2. T:he by an Mo; occupied interstitial sites which are similarity of. the <M*Iuf) for the "ideal" met' not adjacent to other interstitial metals, by an al-octahedra is, of course, consistent with the 71/+; and occupied intentitial sites which are ad- common struotural feature of these minsls'ls, jacent to other interstitial metals, by an M*. For the sphalerite-like arrangement of metals and comparative puqposesit is also useful to qonsider sulphurs. Metal-occupied octahedra which are one other octahedral site, lul'based on the hypo- isolated in the lattice (i.e' coordinated to M") thetical position of an interstitial metal in the are significantly larger than those that are tol '29 cp 557 mh 1r Frc. 1. The crystal structgres of chalcopyrite (cp), talnakhite (ral), mooihoeklle (mh) and haycockite (hc) aro shown scfiematically in terms of sfraterite-type "cubes" of metals and sulphurs. (detailed in the upper-left corner), and in terms of interstitial metal-octalredra. The a, b alord c dimensions of the "cubes" are given (in angstroms) for each structure. 170 THE CANADIAN MINERALOGIST "linked". That is, LM-M+ 2 are greater than an antiferromagnetic structure from its struc- <M4iI4> .This is because the addition of the tural similarity to the ofher .minerals in the intentitial metal into an "isolated" site is facili- S€fI9S; tated by an outward movement of the M-atoms The antiferromagnetic i+=zd stucture of chal- which is not prevented by an opposing distor- copyrite arises from the two Fe(4b) atoms being tion from adjacent occupied metal-oCtahedra. tetrahedrally (with ,,vacanf, arranged two Cu(4a) atoms) The contraction of all surrounding about each sulphur atom and having opposed octshedra is ryitnessed by the relatively smaller moments aligned along the c-axis. The magnetic <M-Mo> distances. For structures containing coupling between the Fe atoms is via tle sul- only isolated metal-octahedra, the contraction phur atom and is generally referred to as an of adjacent vacant metal-octahedra enables the Anderson superexohange interaction. The sul- repeat unit of the sphalerite-like lattice to re- phur coordination-tetrahedra of two irons and main essentially unchanged. The 1M-Mr7 two coppers also form significant portions of distances show tlat this is the case for all lat- the structures of talnakhite and mooihoekite, tice direstions in talnakhite, the r and y direc- and this is expected to account for the antiferro- tions in mooihoeki.te. and the e direction in hav- magnetic aspect of these minerals. cockite. When two'ooccupied" metal-octahedia aro adjacent (i.e. "linked") expansion in the di Thermal motion rection of the sommon M atorn ocsur without The relative rnagnitude of the thermal motion an over-all expansion of lattice in this direction. for the Cu, Fe and S atoms in these minerals The increased energy required for lattice expan- is remarkly consistent. The average isotropic sioq results in significantly srnaller <M-M'p> temperature factors, <B>, summarized for than <M-M*> distancesfor these directions. these atoms in Table 3, show that the thermal This is the case for the e direction of mooihoe- motion of the iron atoms is consistentlv lower kite, and the r and y directions of haycockite. than that for copper atoms. This was also found The extent of the lattice expansion due to the to be the case for cubanite CuFezSls(Szymanski adjacent interstitial metals san be gauged by the 1974), The relative difference for Fe and Cu difference between the two <M--Mr> distances atoms may be expected for several reasons: the for mooihoekite and havcockite. stronger covalent interaction between iron and sulphur over copper and sulphur, as Magnetic structure witnessed by the consistently shorted Fe-S distances over The magrretic structure of chalcopyrite has Cu-S (see Table 2); the magnetic exchange in- been established as antifemomagnetic by Don- teraction between the Fe atoms but not the Cu n.ay et al.
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