Hnedý ihličkovitý dravit z mastencovo-magnezitového ložiska Gemerská Poloma (gemerikum, Slovensko)

Pages

164-170

Citation

BAČÍK, Peter, DIANIŠKA, Ivan, ŠTEVKO, Martin a SEČKÁR, Peter. Hnedý ihličkovitý dravit z mastencovo-magnezitového ložiska Gemerská Poloma (gemerikum, Slovensko). Bulletin mineralogicko-petrologického oddělení Národního muzea v Praze. Prague: National Museum, 2011, 19(2), 164-170. ISSN 1211-0329 (print), 1804-6495 (online). Also available from: https://publikace.nm.cz/en/periodicals/bmpholnrhmvp/19-2/hnedy-ihlickovity-dravit-z-mastencovo-magnezitoveho-loziska-gemerska-poloma-gemerikum-slovensko

Bulletin mineralogicko-petrologického oddělení Národního muzea v Praze | 2011/19/2

Brown tourmaline was found on the Gemerská Poloma talc-magnesite deposit. Fibrous tourmaline forms aggregates along with talc on the slip surface of carbonate rock containing dolomite, magnesite and accessory fluorapatite. Tourmaline (dravite) is almost homogeneous with very high XMg (0.95 - 0.96), very low X-site vacancy (up to 0.17) and Ca content (up 0.05 apfu). The Fe content is also very low (up to 0.14 apfu), the content of Al varies between 5.97 and 6.27 apfu. The calculated WO2- content correlates with the content of Al which suggests quite significant role of AlOMg-1(OH)-1 substitution and other substitutions are negligible. However, the studied dravite is rather significantly Al-Mg disordered - ZMg/(ZMg+YMg) = 0.45 až 0.50, as suggested by distribution of Al and Mg among octahedral sites calculated from the lattice parameters (a = 15.9289(7) Å; c = 7.2132(17) Å) and calculated bond lengths ( = 2.007 Å; = 1.934 Å). Dravite from Gemerská Poloma is likely a side-product of talc formation from original carbonate rock during the Permian granite intrusion. Dravite formed from granite-derived Si- and B-bearing fluids on the slip surface during/after brittle deformation of carbonate which results in its finely acicular habitus. Its high-magnesian composition is controlled by the chemical composition of the host rock

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