Shock-induced transition of NaAlSi3O8 feldspar into a hollandite structure in a L6 chondrite

Abstract

Natural NaA1Si3O8 hollandite was found in the Tenham chondrite. It occurs as aggregates of extremely fine grains of several tens of nanometers. The hollandite phase seems to have formed from host feldspar in a solid-state reaction during the shock event. It is very sensitive to electron beam irradiation and easily becomes amorphous, similar to MgSiO3 perovskite contained in the same chondrite. The existence of crystalline silicate perovskite and hollandite in Tenham indicates that the peak pressure and the post-shock temperature were much lower than previously believed.