American Mineralogist, Volume61, pages260-265, 1976 57Fe Miissbauereffect study of and lreSnin stannite, stannoidite,and mawsonite Tnrlurrsu YnvnNnrn Mineralogical Institute, Faculty of Science Uniuersityof Tokyo, Il3 Hongo, Tokyo, Japan nNp Arrne Ke.ro Departmentof Geology,National ScienceMuseum Tokyo, Japan Abstract The valencyformulae of mineralsin the systemCu-Fe-Sn-S were determined with the aid of electronprobe microanalysisand of the Mdssbauereffect study of s?Feand rleSnat temperaturesof 80"K and 293'K. The formulaeof stannite,stannoidite, and mawsonite can be expressedas Cu!+(Fe2+,Zn"*) Sno*S?-,Cul+Fe!+(Fe,*, Znt*1Sn!+S!r-, and Cul+FeB+ Sno+S3-respectively. Zn wasfound to substituteonly for thefeirous ion. Mawsonitecontains no zlnc. The quadrupolesplittings and isomershifts could be rationalizedwith crystalfield effects causedby thedifferences in sitesymmetry around the Fe andSn atoms. Quadrupole splittings and isomershifts o[ ""Sn indicatethat the (SnSo)-tetrahedronof these specimens is strongly covanentlybonded, and that it may be regardedas a chemicalradical bearingspt hybrid orbitals.Site symmetries around tin atomsin thesestructures are similar. The most probablespace group of mawsoniteis I42m, l4mm, 1422,or 14,22,based on its X-raypowder diffraction pattern and the site symmetries of tin andiron ionsdetermined from the Miissbauereffect study. Introduction The crystal structure of stannite analyzed by Mawsonite, stannoidite, stannite, and rhodostan- Brockway ( 1934)is closelyanalogous to that of chal- nite are mineralsin the systemCu-Fe-Sn-S. Some of copyrite. Further, the crystal structureof stannoidite their crystalstructures are saidto be similar to that of has recently been analyzedby Kudoh and Tak6uchi chalcopyrite.Markham and Lawrence (1965) stated (1974\.This structure indeed resemblesthat of chal- that mawsonite was pseudocubic,with the chemical copyrite, but is more delormed comparedto stannite formula CurFerSnS,o.Kato and Fujiki (1969) de- because of the presence of additional interstitial scribed stannoidite as orthorhombic with chemical cations. Stannoidite has four copper sites,two iron composition CuuFerSnSr. Boorman and Abbott sites,and one tin site. The structuresof other minerals (1967),Springer (1968), and Petruk (1973)reexam- in the above-mentionedsystem are still not defined. ined the chemical compositions of these specimens The cation valencesof theseminerals are still am- and defined stannoidite as Cur(Zn,Fe)rSnrS, and biguous, becausechemical analyseshave not been mawsonite as Cu.FerSnS.. conducted in considerationof the valency statesof Springer(1972) showed in his work on phaseequi- cations. Since iron, copper, and tin may all have librium diagram for CurFeSnSn-CurZnSnSothat at a severalvalencies in crystallinephases, complications temperatureabove 680oC syntheticstannite forms a arise in defining the valenciesof thesecations. solid solution with synthetic kesteritein the whole Pauling and Brockway (1932) and Hall and Stew- range of zinc-iron substitution; that the former has art ( 1973)discussed the valencyformula of chalcopy- polymorphic structuresof a-phase and B-phase;and rite from the bond lengthsdetermined by X-ray crys- that the increasedZn substitution in stannite will tal analysis,and they reported that chalcopyriteis a reducethe temperatureof transition betweenthe two mixture of two statesCu'+Fe3+S3- and Cu2+Fe2+S!-. phases. But the neutron diffraction study by Donnay et al. 260 ,L9SN 261 MOSSBAUER EFFECT STUDY OF 57FCAND IN STANNITE of specimens (1958) and Mdssbauer effect study by Chandra and TlsLe 2. Cell dimension Puri ( 1968)show that the iron ion in chalcopyritehas Stannite Stannoidite l"lawsonite a singletrivalent state. The M6ssbauer effect can determine the charge 5.461+0.002 a= 10.789 + 0.009 a=70.?45+0.00I valenciesof iron ions. The cation valenceof Fe in 5.413 + 0.004 + c=10.711+0.006 stannitehas beendetermined by severalinvestigators 10.726+0.007 c= I6.155 0.009 (1967), Eibschutz et al. Marfunin and Mkrtchyan S,G. S.G. PTeswable S.G. (1968). (1967),and Greenwoodand Whitfield 742n(7) rzzzQ) r42n, r+*(3) The presentstudy eliminatesthe ambiguity about 1422, 14r22 the valencyformulae of stannoiditeand mawsoniteas (1) Brocl<'tay (1934) well as stannitewith the aid of the Miissbauerspectra (2) ktdoh ml lakeuchi (1.974) of both u'Fe and 1leSn.It also discussesthe site sym- (3) Present assmrptLon metriesof iron and tin and of the characterof Fe-S and Sn-S bonds in theseminerals in comparisonwith synthetic samples and some other sulfidessuch as 1970), stannoidite (Petruk, 1973) and mawsonite chalcopyriteand sphalerite. (Petruk, 1973;Kulichikhina and Vyal'sov,1969). Cell dimensionsof stannite,stannoidite, and maw- were obtained by X-ray powder diffractometry Material and experimentalmethod sonite and were calculated with the aid of least-squares Stannite from Gyojayama, Kyoto Prefecture,and method using UNICS computer program. The cell stannoiditeand mawsonitefrom the Akenobe mine, dimensionsof the samplesare presentedin Table 2. Hyogo Prefecture,were separatedfrom the ores un- Mawsonite was reportedto be pseudocubicby Mark- der the ore microscopeand by the subsequentcrush- ham and Lawrence(1965), Levy (1967),and Kuli- ing, magnetic, and specificgravity separations.The chikhina and Vyal'sov (1969)' Better indexing of the occurrenceand paragenesisof these minerals were mawsonitepattern usingthe computer program writ- reported by Lee et al. (1974). Synthetic CuzFeSnSa ten by Evans et al. (1963) implied tetragonal symme- and CurFeaSn2Sl2were preparedin an evacuatedsil- try as shown in Table 3. u'Fe r'eSn ica tube and identifiedby the ore microscopicand X- Mdssbauerspectra of and in the natural ray powder diffraction methods.Their homogeneities and syntheticmaterials were obtained at 80'K and at wereconfirmed by electronmicroprobe. Chalcopyrite room temperature (293"K) by using a HITACHI/ u'Co from the Arakawa mine, Akita Prefecture,and cuba- RAH/-403, 400 channel analyser. diffused in llemsn nite from the Kohmori mine, Kyoto Prefecture,were metallic copper (10 millicuries) and doped in employed for reference.Some of the natural samples BaSnOs(2 millicuries) were used as sources.These were analyzed by the electron microprobe method, y-ray sources have fairly large recoilless fractions using a computer program modified on the basisof and give absorption peaks with very narrow-line the correction formula devised by Sweetman and widths. The line widths of the inner two lines of the the Long (1969), as shown in Table l. Their recalcula- spectrum of "Fe in metallic iron and those of tions gave an empirical formula for each specimen. spectrumof treSnin SnOzmeasured at room tempera- These were in good agreementwith the previously ture were 0.30 mm/sec and 0.83 mm/sec, respec- reported formula of stannite (Ramdohr, 1960;Oen, tively, with these sources. Spectra were taken by the mechanismof moving Teslr I . Chemical analysisof specimensin the system the source at both temperatures.Measurement at Cu-Fe-Sn-S 80oK was conductedwith both source and absorber in a cryostat. Stannite Stannoidite Mailsonite The intensity of the 14.4 keV emitted from wtt rclt ut? mol% wt% nol? 7-ray u'Co and the 23.8 keV from were de- Cu 30.11 24.77 38.49 31.69 44.15 35.48 7-ray "'*Sn t3 44 12.58 10.04 9 4r 12.95 11.84 tected by a Nal scintillation counter. The spectraof Zn 1.07 0.86 3,62 2 90 0.00 0 00 '?Fe obtained at constantDoppler velocitycalibrated 8.33 14.58 6.27 Sn 28 55 t2 59 18.89 in metallic iron were analyzedwith the aid of 30.l8 49.21 29.21 47 -67 29,14 46.41 by those program which performed least mean t03.35 100.00 100 26 100.00 100.82 100 00 a computer fits of the experimentaldata to the Lorent- htrpirical squares Cu2(Fe, Zn)SnS4 Cu^(Fe, zn) ^ Cu6Fe2SnSS Fomula "Sn^s, zian function. This calculation did not employ a T. YAMANAKA AND A. KATO Tnalr 3. X-ray powder pattern of mawsonites from Mt. Lyell, d-electrondensity in iron ion. The orbits of p- and d- Tasmania,and the Akenobe Mine, Hyogo prefecture,Japan electrons play the role of screeningthe s-electron from the positive electric charge of the nuclei. Fd+ t. 2. (3d), which has one more 3d-electronthan Fe8+ d(A) d. (At' d rA) I. hkl obs' carc' ' oDs (3d), shows a larger screeningeffect and a decreased 7.62 7.60 3 110 electrondensity around the iron nuclei,which causes 5.37 20 5.38 5.37 l0 200 the (Walker 4.37 20 4.38 4.38 t5 7 7 2 larger isomer shift for Fe'+, et al., 1962; 3.80 r0 3.80 3.80 I 220 Simaneket al.,1968; Watson, 1960a,1960b). 3.34 l0 3.378 5.388 4 103 3.09 r00 3.099 3.099 I00 222 Covalency of Fe-anion bonds also influencesthe 2.87s 20 2.868 2.869 10 312 isomer shift. Increasein the ionic character of the 2.680 50 2.684 2.686 2s 400 2.462 2.46I 3 114 bonds causesa decreasein the density of s-electrons 2.395 l0 2.401 2.40r 8 402 around iron nuclei and raisesthe isomer shift in both 2.287 l0 2.29L 2.289 J JJZ 2.I85 5 2.792 2.L92 3 422 ferric and ferrous ions. 2.098 s The quadrupole splitting u?Fe r. 959 5 r.962 r.962 3 s2r of dependson the l. 895 80 r.899 1.900 440 electric field gradient at the iron nuclei, which is l. 788 s 1. 791 t.790 3 442 L.739 5 7.742 7.742 3 523 induced from the valency electrons and from the r .618 80 1.620 L.620 40 622 surroundinganions. The electricfield gradient is also L.s47 10 1.549 I .549 7 444 1.460 5 L.463 1.462 3 72r attributed to distortion of electron orbits due to the r. 366 r. 565 3 651 crystal field and the covalent bonding character,(ln- r.343 20 1.344 L.343 15 800 1.318 1.319 3 tl8 galls, 1962, 1964;Sternheimer, 1963).