Shock-induced thermal transformations of ries-biotites

Thermal transformations in biotites depending on increasing postshock temperatures were studied.A decrease of the unit cell volume, caused by oxidation of octahedral Fe²⁺ to Fe³⁺ at temperature rangings of about 400–500° C was observed.In the same temperature range (500° C) the biotite lattice becomes thermodynamically unstable. Intersheet and octahedral layers are decomposed, whereas individual SiO₄-tetrahedra are more resistant to thermal vibrations. The decomposition of the biotite leads to the formation of new minerals and amorphous phases. By X-ray analysesmagnetite, hercynite, pyroxene, feldspar, and quartz were identified.Thermal transformations of biotite induced by shock waves are characterized by states of distinct disequilibrium.