C anailian Mher alo gist, Vol. 1Z pp. 33-38 (1973)
ON THE TRANSFORMATIONOF CUBANITE*
L. l. CABRI, S. R HALL, l. T. SZYIvIANSKIarvo l. M' STEWART Mineral SciatcesDhtision, Mines Btanch, Departrnent of Energg-', Minesand Resources,555 Booth Street,Ottawa, Canada, KIA 0GI'
Aasrnecr (e.g. Buerger 1945, 1947; Azarcff &- Buoger igSS; fleJt 1970). The structure has becn de- cubanite transforms between 200' Orthorhombic by Buerger (1947) as being made up--of directly to a face-centred cubic polymorph scribed anil 2L0'C structure parallel to (010) is, in general, tryinneil along the (111) plane. slabs of ihe wurtzite which inversion The strubtural relationship between orthorhombic and arLdb/2 wide, joined to one another by cubic cubanite has been determined. The transforma- centres so thal there is a sharing of an edge tion appea$ to 6e irreversible in the laboratory and between adjacent iron co-ordination tetrahedra annealinE of cubic cubanite belornt the inversion tem- (Fig. 1). Wurtzite has a polar structure with- all perature rezults in chalcopyrite saolution This is co-ordination tetrahedra pointing one wan but opposite to the relationship in whi& orthorhombic in cubanitg half of the tetrahedra point one way latbs in cubanite is frequent'y found as "o
Frc.- -f"e, l. Diagrammatic representationol orthorhombic^cubanite(let) and of cubic cubanite (right) slow- :elative ;#;tely, the hrp ^.d ccp arrangernentsof sulphur a1&ns,.with their gPProximate oriunt"tion bef6re and after transformation.For the orthorhombic cubanite-cell, the a axis points to- ;;d;-iil-r;"dst, tt. A is horizontal and the c axis is vertical Dashed lines connectadjacent Fe ;;"*r (rfgf-ii,Jj ,, "trinversion centres.ln cubic cubanitethe small circlesrepresent the ilisordereil (C',Fei sites, ard the tllll direction ol the sphalerite.likecell is vertical. 33
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lications on this work include teports that cuba- with a wire saw into five slices for use in the nite transforms directly to a cubic phase either heating orperiments (Table 1). These slices were at 270oC (Sawada et al. 1962), at.22A"C or subsequently characterized by reflection micro- lower (Fleet 1970),or between200oC and 235'C scopy, by r-ray diffraction (Gandolfi, Debye, (Mukaiyama & Izawa 1970). A direct transforma- Scherrer, and precession eameras), and with an tion to a hexagonal phase has been suggested electron-probe microanalysei. Other cubanite (Vaasjoki 1971). It has also been proposedthat crystals wed from the same locality were too there is a tetragonal polymorph, intermediate small and could be characterized only by x-ray between orthorhombic and cubic cubanite (Yund diffraction. Annealing of specimens was done in & Kullerud 1966),but this has not been substan- horizontal furnaces (temperafure controlled with- tiated further. Sawada et aI. (1962) have re- in soc), rvith the samples contained in sealed ported that there is a decreaseof saturation mag- evacuated silica glass tubes. The annealing tem- netization at room temperature to negligible perature was determined with a calibrated Pt- values and that this transformation is accom- Pt/I|% Rh thennocouple and the samples wue panied by a disordering of Fe and Cu atomr. quenched in ice.water. Fleet (1970) compared the observed and calcu- lated intensities for high-temperature cubanite E: TABLEI. HEATINGEXPERIIVENTS ONA CUBAI,IITECRYSTAL SLICED INTO FIVE SECTIONS - Specl X-ray ldentlflcation roprobe Ana men orthorhombJccubanlte Isotropic matrix exceptfor I lanella (2x15m) smatlI area rs9Lroplc fiEtrlx smalI ar€as o mlnorchalcopyrlte lnciuslons,incluslons, all at the crystal edge. Largest lnclu- sion ls 12xl27mand ali ar€ tlio-phase(pyr.lte surrounded by pyrrhotite). cubic sotroplc matrlx with few parallel aneasof untrans cubanite> (Flg, orthorhomblccubanite ormedcubanite 2). Nocompositional dlffer- encedetected wlth mlcroprobe. cublc cuban'lte 100 (after cuDlc cuDanlfe* mnot 50tr0Dlc natrlx 230 above) cha'lcopy. (sare as #4) lamel1a of chalcopyrl te ipproxtmatety )lillL: orthorhombiccubanlte Singie-phaseCuFerSr. Downloaded from http://pubs.geoscienceworld.org/canmin/article-pdf/12/1/33/3445373/33.pdf by guest on 25 September 2021 ON T}IE TRANSFORMATION OF CUBANTTE 35 rhombic cubanite transforms directly to a high- sure times of 30 hours provided diffraction data temperature cubic phase between 200 and 2I0"C that could be explained entirely in terms of a and that the orthorhombic/cubic transformation single crystal of cubic cubanite with o: 5"324. is sluggish near the transition temperature. At This larger value is probably due to tlle different no time was there any evidence of a horagonal composition resulting from the exsolution of phase and this is discussed more fully below. chalcopyrite. Longer exposuretimes (- 100hours) Microscopic study of a polished section of speci- of the hk\ and 0/cl films showed additional weak men $5 (Fig. 2) shows that orthorhombic reflections which required an approximate dou- cubanite occurs as well-defined "domains" with bling of the cubic cubanite cell dimensions in respecl to the cubic cubanite matrix. The distinct each direction. A detailed mmparison of these cracksperpendicular to c and lesswell-developed data with that of dralcopyrite (Hall & Stewart cradcsparallel to c reported by Vaasjoki (1971) 1973) showed that the weak reflections were in are also clearly visible in Figure 2. fact the 101, 301, 103, and 105 reflections of three dralcopyrite single crystals oriented with their axes parallel to the principal axesof cubic cubanite. Twinning at th,e orthorhombic/cubic transformation Experiments additional to those described in Table I were performed to determine the struc- tural relationship between orthorhombic and cubic cubanite. Cubic cubanite crystals (annealed at 300oC and quenched) were o Downloaded from http://pubs.geoscienceworld.org/canmin/article-pdf/12/1/33/3445373/33.pdf by guest on 25 September 2021 36 THE CANADIAN MINERALOGIST fqrnation seemsto be similar to that of ww1r:ite/ the metals and a rmrganization of the sulphur sphalerite but, in orthorhombic cubanite. the layers to produce an ABCABC sequence of a horagonal close-packed (hcp) sulphur matri(, sphalerite-like structure. The hcp to cubic close- wi4 layers stael TABLE2. X-RAYDIFFMCTION POWDER DATA H.T. Cubanite Chalcopyri te H.T.cb. cp. l&t t dcaic r dr.u, 4n"u, dcalc dcalc r 4n.u, dcaTc t0l 2 4.71 4.711 't0 111 3.049 3.050 10 3.052 3.052 3.034 112 10 J.UJ J.UJC 'I 1 2.899 2.900 103 2,89 2.899 200 3 2.640 2.641 4 2.641 2.643 2.640 200 J 2.64 2.642 g 2.602 2.603 004 I 2.60 2.601 'I 1. Cubanite-(gp)'1972).from Strathcona mine,.0nt., heated to 30fC andquenched (gacLean et aL. Patternobtained with 57.3nm Gandotfi cameri. ;=b.rriaa2jii-:---" t. nmDebye-scherrer. ForH.r. cb. a=5.286(t); for cp. lllS.iftil^(]14.6 a=5.28(1), 3. Chalcop)'rile (cp) from Westernmines, B.C. (Cabri & Ha111912). a=5.28(l), o=10.40(l)4. B = Broad llne Downloaded from http://pubs.geoscienceworld.org/canmin/article-pdf/12/1/33/3445373/33.pdf by guest on 25 September 2021 ON TI{E TRANSFORMATION OF CUBANTTE 37 crystal) and this will give risg to a twinned occurs in the host e,halcopyrite followed zub- cubic lattice. The more nucleation points there sequentlv bv the transformation of the cubic are within a crystal, the greateris the probability cufanite to the orthorhombic structure. The of finding equal proportions o[ twins in the reverse relationship observed in our orperiments transformed lattice. If the proportion of twin in rvhidr chalcopyrite laths exsolve out of cubic components is equal, the symmetry of the t'win- cubanite matrix, rvith no apparent subsequent composite reciprocal lattice is 6/rnmm. This transformation to the orthorhombic cell, may be results in a pseudo.hexagonallattice, with o(hex) of importance to students of ore deposits. The : a(cub)/ dTand c(hex) : a(cub) X Vg ineversibility of the orthorhombic/cubic trans- This probably accounts for the report by Vaas- formation in the laboratory may be due to dlf- joki (1971) that high-temp-eraturecubanite is ferent physico-chemical conditions qn$i"S - itt hexagonal with c = 9.174. The structural natuie. On the other hand, the possibility that changes required by this transformation may naturally occurring orthorhombic cubanite ex- ot also explain why single crystals of unt'winned solved directly from a chalcopyrite matri& cubic cubanite are small. Our experience has formed by other reactions below the transition shown that, of the many cubic cubanite crystals tempsature, cannot be excluded. examined, only the smallest (-0.05 mm) was found to be single with no twin component. Concr.usroNs Intensity data have been collected for this crystal Cubanite transforms between 200 and 2l0oc and a detailed structure analysis is in progress. directly to a face-centred cubic polymorph of The exsolution of chnlcopwite from CuFezSa composition. This cubic cubanite is often twinned along the (ll1) plane which is - e high t emper atur e cubanit the a,b plane of orthorhombic cubanite. The The presenceof single-crystaldomains of chal- mechanism of the transformation, though not copyrite in specimen $7, oriented along the fullv understood, is thought to be similar to that principal axes of cubic cubanite, seeunsto be of the wurzite/sphalerite transformation. consistentwith the localized ordering of Cu and Annealing experiments on cubic cubanite be' Fe atoms with decreasingkinetic energy. Under low the transformation temperatwe results in such conditions the metal atoms, starting at ran- the ocsolution of chalcopyrite laths from the dom nucleation points, may be located in specific cubic cubanite matix. This relationship is the interstices in the face-centred cubic sulphur reverse of that commonly found in some ore matrix, in an order that is dictated by the anti deposits, where orthorhombic cubanite laths ferromagnetic and/or ionic covalent interactions. occur in a dralcopyrite matrix. This suggeststhal The single-crystal domains of chalcopyrite e:<- in nature, orthorhbmbic cubanite may crystallize pand from these points until inhibited by dis- from a ciralmpyrite matrix below 200-210oC' continuities or fractures in the sulphur matrix, proportion or by the unavailability of an equal AcrNowr-nPcrun.trs of Cu and Fe atoms at the chalcopyrite-cubic 'We cubanite interface. The availability of an equal are grateful to IVIr. D.R. Owens for the proportion of metal atoms depends,in large parl carefrrl eleLonprobe analyses and to I\[r. I.H.G. on the ability of these atoms to diffuse through Laflamme for assistancewith the heating experi- the sulphur matrix at t}le time of chalcopyrite ments and the polished sections. We would like formation. Two factors, namely, temperatrue and to thank Dr. ].S. White Jr. of the Smithso$an the rate of cooling, are probably critical in the Institution, Washington, D.C. and Dr. t.D. Scott mobility of metal atoms in such a solid-statedif- of Queen'i University, Kingston' Ontariq both fusion transformation. Such a formation process of ihom generously provided us with the cuba- would account for the small amounts of chalco- nite crystal"sfrom the Strathcona mine. We would of pyrite present in specimens#4 and f7. Indeed, also like to thank Dr. Howard T. Evans tr. chalcopyrite was observedonly as a single lath the U.S. Geological Survey, Washington, D.C'' (2 X 10 plm) in specimen #7 but could not for critical reading of our manuscript. be observedin specimen#4 which had been an' nealed for a shorter period of time, though it Rerms.Icns was detectedby x-ray diffraction. Azanorr, L.V. & BumcsR,M.J. (1955): Refinementof ftr mineral deposits,cubanite often occurs as the structureof cubanite,CuFe2S3. Amer. Mineral. laths in a chalcopyrite matrix, which is the 40, 2t3-225. revef,se of the situation discussed above, The Bannrirr,C.S. (1952) : Imperfectionsin NearlgPerfect former textural relationship suggestsa subsolidus Crgstals(ed. W. Shockley)J. Wiley, New York' proce$$ whereby exsalutio.n of -cubic cubanite Chapter3, 9l Downloaded from http://pubs.geoscienceworld.org/canmin/article-pdf/12/1/33/3445373/33.pdf by guest on 25 September 2021 38 TI{E CANADIAN MINBRALOGIST Bmav, L.G. & Tnouesom, R.M. (1962) : X-ray pow_ Mec:Lraq WJ{.,. Carnr, L.J. & Gnr., l.E. (1922) : der data for ore minerals. Geol.'Soc.'A*n. itS. E:aolution products in heated chalcopfrite. Can.' !. Buancr4 M.J. (1945) : The structure of cubanire. Earth Sci. 9, 1305-1317. CuFe2Ss, and the co-ordination of ferromametic Maxaxoq E.F., Manrurm, A.S., MrnrcrryAN, AR, iron. l. Amer. Chern, Soc. 67, 2056. Povns Downloaded from http://pubs.geoscienceworld.org/canmin/article-pdf/12/1/33/3445373/33.pdf by guest on 25 September 2021