Shock metamorphism and petrography of the Shergotty achondrite

The shock history of the Shergotty meteorite has been evaluated by analyzing the observable shock effects. In addition, the results of petrographic and mineralogical analyses of new Shergotty subsamples are presented. The overall modal composition of these subsamples is similar to that of the other Shergotty samples, except for the rather high whitlockite content. The shock effects observed in the mineral constituents include mosaicism, deformation bands, planar fractures, and mechanical twin lamellae in clinopyroxene; isotropization of plagioclase with very rare remnants of birefringence; and planar deformation structures, mosaicism, and strongly reduced birefringence in quartz. Other shock effects include mechanical twinning of ilmenite, and localized in situ melting of neighboring minerals at the contact of low and high density phases. The observed shock effects could be explained by a single shock event.