Silica Polymorphs Formation in the Jänisjärvi Impact Structure: Tridymite, Cristobalite, Quartz, Trace Stishovite and Coesite

The study of silica polymorphs in impactites is important for determining the pressure and temperature impact rock formation. Silica modifications melt rocks Janisjärvi structure (Karelia, Russia) are presented by tridymite, cristobalite, quartz, trace stishovite coesite. were characterized studied scanning electron microscopy (SEM), probe microanalysis (EPMA), Raman cathodoluminescent spectroscopy. Investigations carried out order to clarify formation mechanisms search signs transition certain structural others. For first time, a description tridymite with ballen-like texture from given. A sequence modification textural transformation after event suggested. We conclude that 40 GPa more than 900 °C achieved structure.