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

Natural NaAlSi3O8 hollandite was found in the Tenham chondrite. It occurs a s aggregates of extremely fine grains of several tens of nanometers. The ho llandite phase seems to have formed from host feldspar in a solid-state rea ction during the shock event. It is very sensitive to electron beam irradia tion and easily becomes amorphous, similar to MgSiO3 perovskite contained i n the same chondrite. The existence of crystalline silicate perovskite and hollandite in Tenham indicates that the peak pressure and the post-shock te mperature were much lower than previously believed.