Stilpnomelane in the Proterozoic of the Říčany-area in Central Bohemia
Abstract
Stilpnomelane, formerly known from volcano-sedimentary sequences of Central and Western parts of Barrandian Neoproterozoic, is now reported from slightly metamorphosed greywackes and albite-rhyolite tuffs and tuffites in the easternmost area of the unit. It is the first occurrence of this mineral east of the Vltava River. This typical low-grade metamorphic silicate occurs in the prehnite-pumpellyite as well as in the chlorite zones and gradually disappears in the biotite zone. Increased Fe/Mg ratios and low K-contents in the rock together with LT/LP metamorphic regime represent the prerequisite for its origin.