Maskelynite

Maskelynite (Meteoritic glass)
General
Category	Glass
Identification
Luster	Vitreous

Maskelynite is a glassy phase found in some meteorites and meteorite impact craters. Typical samples are similar in composition to plagioclase feldspar, and revert to that mineral when melted and recrystallized. It was named after British geologist M.H.N. Story-Maskelyne.

The Dhofar 378 meteorite is 47% maskelynite by volume.

The phase was first identified in the Shergotty meteorite by G. Tschermak (1872) as an isotropic glass of an unknown origin with near labradorite composition. Similar phases were found in chondrites and Martian (SNC) meteorites. In 1963, D. J. Milton and P. S. de Carli produced a maskelynite-like glass by subjecting gabbro to an explosive shock wave. In 1967, T. E. Bunch and others identified maskelynite in the Clearwater West and Manicouagan craters.

At first, maskelynite was believed to result from solid-state transformation of plagioclase into diaplectic glass by a relatively low-pressure shock wave (250 to 300 kilobars) and low-temperature (350 °C), as in Milton and de Carli's experiment. Since 1997 this hypothesis has been challenged, and now it is believed that the glass is formed by the quenching of dense mineral melts produced by higher-pressure shock waves.

...
Wikipedia