Křemenné žíly s dumortieritem, andalusitem a dravitem od Psár u Jílového (Česká republika)
Jan Cempírek, Jan Loun
Dumortierite associated with andalusite, dravite and chlorite were found in quartz veins at Holý vrch Hill near Psáry (central Bohemia, Czech Republic), in rocks belonging to Jílové metavolcanic belt. Two macroscopically distinct varieties of dumortierite were found: dark-violet aggregates of long prismatic crystals in dark tuffitic schists and pale violet to pink aggregates of fine-grained and fibrous dumortierite in rhyolitic metatuffs. Both dumortierite varieties are chemically and structurally very similar, with high contents of Mg (0.15 - 0.2 apfu) along with low amounts of Ti (0.04 - 0.06 apfu) and Fe (0.02 - 0.03 apfu). Rare inclusions of Mg,Ti-rich dumortierite (0.17 - 0.18 apfu Mg, 0.14 apfu Ti) were observed in thick dumortierite prisms. The veins originated by reaction of B-rich fluids derived from granites of the Central Bohemian Plutonic Complex with Al-rich metavolcanic rocks. The Psáry veins are unusual in the Bohemian Massif where dumortierite typically occurs in granitic pegmatites and related rocks.