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Maskelynite

Maskelynite is a glassy mineral 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.

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History

The mineral was first identified in the Shergotty meteorite by G. Tschermack (1872) as an isotropic glass of an unknown origin with near labradorite composition^[1]. Similar minerals 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 ^[2]. In 1967, T.E.Bunch and others identified maskelynite in the Clearwater West and Manicouagan craters^[3].

Origin

At first, maskelynite was believed to result from solid-state transformation of plagioclase into diapletic glass by a relatively low-pressure shock wave (250 to 300 kilobars) and low-tmperature (350 °C), as in Milton and de Carli's experiment^[2]. Since 1997 this theory 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^[1].

References

^ ^a ^b M. Chen; A. El Goresy (1999). "The Nature of "Maskelynite" in Shocked Meteorites: Not Diapletic Glass but a Glass Quenched from Shock-Induced Dense Melt at High-Pressures". Proceedings of the 62nd Annual Meteoritical Society Meeting.
^ ^a ^b Daniel J. Milton (1963). "Maskelynite: Formation by Explosive Shock". Science 140: 670--671. doi:10.1126/science.140.3567.670.
^ T.E. Bunch; Alvin J. Cohen; M. R. Dence (1967). "Natural Terrestrial Maskelynite". The American Mineralogist 52: 244-253.