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Turmalinit z Velkých Žernosek (oparenské krystalinikum, severní Čechy)

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Title in English Tourmalinite from Velké Žernoseky (Oparno Crystalline Complex, northern Bohemia)


Year of publication 2014
Type Article in Periodical
Magazine / Source Bulletin mineralogicko-petrologického oddělení Národního muzea v Praze
MU Faculty or unit

Faculty of Science

Field Geology and mineralogy
Keywords dravite; trivalent iron; chemical composition; evolution; tourmalinite; Oparno Crystalline Complex; Northern Bohemia
Description Tourmalinite occurrences at Kalvárie hill near Velké Žernoseky (northern Bohemia, Czech Republic) are represented by massive tourmaline-rich layers (with minor quartz < 10 vol.%) in biotite-muscovite metapelite (phyllite to schist). Two tourmalinite assemblages were identified: a) almost monomineral tourmalinites to quartz-tourmaline rocks with accessory biotite, chlorite, fluorapatite, muscovite, calcite, and K-feldspar; b) tourmaline-epidote-quartz tourmalinites with minor garnet, muscovite and chlorite, and rare titanite and zircon. Four textural and compositional types of tourmaline containing variable contents of Fe3+, Fe2+, Ti, Ca, Na, and F were found. Other tourmalinite occurrences in the Oparno Crystalline Complex (Oparno-Černodolský mlýn, Chotiměř) are characterized by an increased amount of quartz, and typically form tourmaline-quartz veins in muscovite-biotite gneisses. Compared to the occurrence at Kalvárie hill, the tourmaline from Oparno has higher Mg, Al, and Ca contents and lower amounts of Na and OH. All rocks most likely formed by metamorphic overprint of boron-bearing protolite (biotite-muscovite metapelite with mafic admixture); however, the source of boron remain ambiguous.
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