MSCC3 3rd MINERAL SCIENCES IN THE CARPATHIANS ...

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Acta Mineralogica-Petrographica, Abstract Series 5, Szeged, 2006All members of the cuprobismutite family – i.e.,cuprobismutite, hodrushite, paděraite and the recently discoveredkupčíkite are represented in Romanian occurrences.Such episodes are confined to ore-deposits related to contactmetamorphicaureoles of Upper Cretaceous–Palaeocene calcalkalineigneous rocks in the so-called Banatitic Belt.Structural affinities of cuprobismutite members often reflectsin coherent intergrowths of two or three differentphases, such as hodrushite + kupčíkite ± paděraite (Fig. 6). Asimilar case of intergrowths between cuprobismutite andpaděraite from Ocna de Fier has recently been discussed byCIOBANU et al. (2004). Typical assemblages include bismuthinitederivatives, makovickyite-cupromakovickyite, emplectiteand various Bi tellurides.Fig. 6: Parallel intergrowths between hodrushite (h) and kupčíkite (Z) at Băiţa Bihor. Kupčíkite is preferentiallyaltered by emplectite (e) BSE image.Finally, not all sulphosalts may be considered rare, yetmany of the more common species reveal very peculiar aspectsof their crystal chemistry. It is the case of the bismuthinite–aikiniteseries (Bi 2 S 3 –CuPbBiS 3 ), a discrete family ofsub- and supercell structures which seemed a closed casesome ten years ago, but to which three more 4-fold and 5-foldsuperstructure members were added: salzburgiteCu 1.6 Pb 1.6 Bi 6.4 S 12 , paarite Cu 1.7 Pb 1.7 Bi 6.3 S 12 and emiliteCu 10.7 Pb 10.7 Bi 21.3 S 48 (BALIĆ-ZUNIĆ et al., 2002;MAKOVICKY et al., 2001; TOPA et al., 2005). Compositionalranges pointing to these three phases have already beenidentified in several occurrences from Romania, but they willbe in need of detailed crystal structure determinations.Cosalite – ideally Pb 2 Bi 2 S 5 – is another example of arather common sulphosalt species but with a complicatedhistory in what concerns substitutional mechanisms involvingAg and Cu, e.g. 2Pb ⇔ Bi(+Sb) + Ag; Bi(+Sb) ⇔ Pb + Cu;Pb + ⇔ Me + + Me + ; Pb + ⇔ Cu 2+ etc. Significantamounts of chemical and structural data are necessary toidentify the relevant trends for such replacement schemes.AcknowledgementsThe author wishes to thank Dr. DAN TOPA from theUniversity of Salzburg for the kindly provided support andmineralogical data, and Professor EMIL MAKOVICKY fromthe University of Copenhagen for the entire long-term supportand contribution to the topic discussed.ReferencesBALIĆ-ZUNIĆ, T., TOPA, D. & MAKOVICKY, E. (2002):Canadian Mineralogist, 40: 239–245.CHOE, W., LEE, S., O’CONNEL, P. & COVEY, A. (1997):Chemistry of Materials, 1997 (2): 2025–2030.CIOBANU, C. L., PRING, A. & COOK, N. J. (2004): MineralogicalMagazine, 68: 279–300.KARUP-MØLLER, S. & MAKOVICKY, E. (1979): Bulletinde Minéralogie, 102: 351–367.KARUP-MØLLER, S. & MAKOVICKY, E. (1992): NeuesJahrbuch für Mineralogie, Monatshefte, (12): 555–576.MAKOVICKY, E. (1989): Neues Jahrbuch für Mineralogie,Abhandlungen, 160: 269–297.MAKOVICKY, E., BALIĆ-ZUNIĆ, T. & TOPA, D. (2001):39: 1365–1376.MAKOVICKY, E., TOPA, D. & BALIĆ-ZUNIĆ, T. (2001):Canadian Mineralogist, 39: 1377–1382.MUMME, W.G. (1975): American Mineralogist, 60: 548–558.PRING, A. (1995): American Mineralogist, 80: 1166–1173.MAKOVICKY, E., TOPA, D. & BALIĆ-ZUNIĆ, T. (2001):Canadian Mineralogist, 39: 1377–1382.TOPA, D., MAKOVICKY, E. & BALIĆ-ZUNIĆ, T. (2005):Canadian Mineralogist, 43: 907–917.46www.sci.u-szeged.hu/asvanytan/acta.htm
Acta Mineralogica-Petrographica, Abstract Series 5, Szeged, 2006A NEW OCCURRENCE OF MANGANILVAITE CaFe 2+ Fe 3+ (Mn 2+ , Fe 2+ )[Si 2 O 7 ]O(OH) ATDOGNECEA, SOUTHWESTERN BANAT, ROMANIA: CHEMICAL COMPOSITION,CRYSTAL STRUCTURE AND CATION ORDERINGILINCA GH. 1 , VIZITIU, A. 1 , TOPA, D. 2 & VLAD, Ş. 31 Department of Mineralogy, University of Bucharest, Bd. N. Bălcescu, 1, RO-701111 Bucharest, RomaniaE-mail: ilinca@geo.edu.ro2 Department of Material Sciences, University of Salzburg, Hellbrunnerstrasse 34/III, A-5020 Salzburg, Austria3 Ecological University of Bucharest, Franceza str., 3, Bucharest, RomaniaSamples of ilvaite systematically exceeding 0.5 apfu Mn(in formula normalized on the basis of 6 cations) and suggestingthe presence of the recently discovered mineral manganilvaite(ZOTOV et al., 2005; BONEV et al., 2005) wereidentified in the skarn deposit at Dognecea, where they occurin association with Mn-hedenbergite and magnetite. A numberof 14 EDS chemical analyses of such ilvaites resulted inthe following ranges of variation: (in weight percents; numbersin parentheses read as average values and standard deviations,respectively): Si: 13.39–14.09 (13.92; 0.15), Al:0.00–0.27 (0.09; 0.11), Fe: 32.88–34.53 (34.62; 0.64), Mn:7.30–9.17 (7.85; 0.54), Mg: 0.00–0.26 (0.07; 0.10), Ca:9.86–10.64 (10.26; 0.22). Atomic proportions of Fe 2+ andFe 3+ for a chemical formula unit normalized for 6 cations,were calculated as Fe 2+ = 2 – Mn 2+ and Fe 3+ = Fe total – Fe 2+ .The variation domains of Fe 2+ , Fe 3+ and Mn 2+ atomic proportionswere the following: 1.34–1.48 (average 1.44; standarddeviation 0.04), 0.98–1.04 (1.01; 0.021) and 0.52–0.66 (0.56;0.04), respectively. Other varieties of Mn-poorer ilvaiteswere identified, too.Manganilvaite from Dognecea is a P2 1 /a polymorph (a =13.014 Å, b = 8.846 Å, c = 5.848 Å and β = 90.34 o ) withsignificant ordering of Fe 2+ and Fe 3+ among Me11 and Me12structural sites. The single crystal structure determination ofmanganilvaite – based on 1509 unique reflections, was refineddown to a final R = 5.41% (with single generic metals –Fe or Mn – in Me11, Me12 and Me2 positions). The crystalstructure data allowed the calculation of interatomic and perpolyhedraaverage distances for all relevant cation-oxygenpairs and the evaluation of Fe 2+ and Fe3 + occupancies inMe11 and Me12 structural sites. Statistical Fe x+ occupancieswere calculated on the basis of two classic atomic radii models,i.e. GHOSE (1966) – (G) and SHANNON (1976) – (S).Thus, Me11 structural site is 53% (G) or 84% (S) occupiedby Fe 2+ (normalized values for Me11 + Me12 = 100%). Fe 3+occupancy in Me11 and Fe 2+ occupancy in Me12 site is complementaryto these values. The corresponding ordering parameter(TAKEUCHI et al., 1983) was 0.34 (G) or 0.47 (S).Same calculations concerned the Me2 structural site andallowed indirect evaluation of Mn 2+ occupancy vs. complementaryFe 2+ . Calculation of Mn occupancy in Me2 based ona simple linear variation of Me2–O Shannon distances between2.18 Å (Fe 2+ –O) and 2.23 Å (Mn–O), resulted in 42%Mn 2+ whereas the empirical model of Carrozzini (1994)yielded 52% Mn 2+ . Similar discrepancies between the Shannonand Carrozzini models may be described in the case ofthe type manganilvaite from Ossikovo (BONEV et al., 2005).The refinement of the structure with split Me2 position (Mnand Fe) resulted in a slightly lower R = 5.33%. Attempts torefine the structure with Mn in Ca, Me11 or Me12 positionhave failed, suggesting that Mn is confined to the Me2 position.The experimental β value is slightly discrepant with regardto the ones calculated on the basis of correlated orderingparameter and degree of monoclinicity (TAKEUCHI et al.,1983 (T); FINGER & HAZEN, 1987 (FH)): 90.16 o (T) and90.27 o (FH).Local paragenetical relations and various published correlationsbetween the ordering parameter and the temperatureof formation, suggest that Mn-ilvaite from Dognecea representsa reaction product of 6 hed + 4 mgt + 3 H 2 O → 6 ilvaite+ ½ O 2 , formed at temperatures not exceeding 300 °C, and inconditions of relatively low fO 2 .ReferencesBONEV, I.K., VASSILEVA, R.D., ZOTOV, N. &KOUZMANOV, K. (2005): Canadian Mineralogist, 43:1027–1042.CARROZZINI, B. (1994): European Journal of Mineralogy,6: 465–479.FINGER, L.W. & HAZEN, R.M. (1987). Zeitschrift für Kristallographie,179: 415–430.GHOSE, S. (1969): In: WEDEPOHL, K. H. (ed.): Handbookof Geochemistry, Berlin: Springer-Verlag, II/3, 26-A, 1–14.SHANNON, R.D. (1976): Acta Crystallographica, A32: 751–767.TAKEUCHI, Y., HAGA, N. & BUNNO, M. (1983): Zeitschriftfür Kristallographie, 163: 267–283.ZOTOV N., KOCKELMAN W., JACOBSEN S.D., MITOVI., PANEVA D., VASSILEVA R.D. & BONEV I.K.(2005): Canadian Mineralogist, 43: 1043–1053.www.sci.u-szeged.hu/asvanytan/acta.htm 47
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