TY - JOUR A1 - Houzar,S. A1 - Novak,M. A1 - Selway,J.B. T1 - Compositional variation in tourmaline from tourmalinite and quartz segregations at Pernstejn near Nedvedice (Svratka Unit, western Moravia, Czech Republic) JF - Journal of the Czech Geological Society JA - J. Czech Geol. Soc. Y1 - 1998 VL - 43 IS - 1-2 SP - 53 EP - 58 CY - Prague PB - Czech Geological Society SN - 1803-1943 (online), 1802-6222 (print) AV - Free UR - http://www.jgeosci.org/index.php?pg=detail&ID=JCGS.750 L1 - http://www.jgeosci.org/content/JCGS.750_Houzar.pdf KW - dravite KW - schorl KW - electron microprobe analyses KW - tourmaline KW - quartz segregations KW - Svratka Unit AB - The Pernstejn tourmalinite is situated in the southern part of the Svratka Unit near the border with Moldanubicum. It underwent a retrogressive low-to-medium grade regional metamorphism which produced quartz segregations within the tourmalinite. Fine-grained tourmalinite dominantly consits of quartz and tourmaline (dravite-schorl). The tourmaline is elongated, euhedral to subhedral grains are typically < 0.5 mm in size. Tourmaline (dravite-schorl) from quartz segregations forms euhedral grains, from 0.5 to 10 mm in size, locally associated with kyanite, andalusite, muscovite, apatite and accessory rutile. There is only a negligible difference between tourmaline from tourmalinite and quartz segregations. Tourmaline of both paragenetic types is characterized by moderate to high vacancies in the X-site, up to 45 at.%, and moderate to high F contents varying from 0.32 to 0.56 apfu. It also exhibits Fe/Mg ratios and Al contents typical for tourmaline in metapelites and metapsammites with an Al-saturating phase (eg kyanite, andalusite). Formation of the quartz segregations with coarse-grained tourmaline and kyanite began during a retrogressive kyanite grade metamorphic event at P > 3-4 kbar and T > 400-500 °C through the kyanite-andalusite transition to the andalusite grade. The presence of tourmaline as the only ferro-magnesium mineral and the presence of Si-, Al- and Ti-saturating phases, ie quartz, kyanite/andalusite and rutile, respectively, buffered these elements during the mobilization process which produced the quartz segregations. ER -