New data on the synthesis and stability relations of glaucophane

A glass of cordierite composition was found in a highly shocked garnet gneiss collected from Otting quarry in the Ries crater. This glass varies in color from colorless to dark brown. Despite the variation in color no compositional variation from grain to grain was found. Electron microprobe analyses of several glasses revealed: SiO₂ 49.07%, Al₂O₃ 34.15%, FeO 6.07%, MgO 9.77%, CaO 0.07%, K₂O 0.11%, Na₂O 0.42%. In the sample investigated, all cordierite grains were transformed to isotropic cordierite glass.