Schorl composition from the barren granitic pegmatites in the Western Carpathians: Two examples from the Nízké Tatry mountains, Central Slovakia
Tourmaline group minerals belong to rather uncommon accessory minerals of the Hercynian granitic pegmatites of the Central Western Carpathians, Slovakia. Black tourmaline from two barren quartz-feldspar-(biotite-muscovite) pegmatites of the Nízké Tatry Mts.: Bystrá Valley - Srdiečko (TBV) and Magurka - Adolf adit (TMA), were studied by EMPA. Both tourmalines show schorl compositions with intermediate X-site vacanies: 0.25-0.33 pfu, slight compositional zonality with increasing Fe/(Fe+Mg) ratio from center to rim of crystals, and low Ca and K contents. The most striking feature of the TMA schorl is a notably high Mn content: 0.98-1.56 wt. % MnO, 0.14-0.23 apfu, exceptional for schorl from poorly fractionated granite-pegmatite environment. Nevertheless, the TMA schorl also reveals higher Fe/(Fe+Mg) ratio in comparison to TBV: 0.69-0.83 and 0.54-0.60, respectively, and Mn values correlate positively with Fe, Fe/(Fe+Mg) and X-site vacancies. Thus, the elevated Mn content in TMA schorl is probably a consequence of local Mn-rich environment, probably due to absence of garnet as well as a relatively higher overall fractionation level.
SNIP (Scopus, 2015): 0.700
IF (ISI, 2015): 1.326
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