Origin of β-cristobalite in Libyan Desert Glass: The hottest naturally occurring silica polymorph?

Abstract

Identifying and determining the origin of ß-cristobalite, a high-temperature silica polymorph, in natural samples is challenging as it is rarely, if ever, preserved due to polymorphic transformation to α-cristobalite at low temperature. Formation mechanisms for ß-cristobalite in high silica rocks are difficult to discern, as superheating, supercooling, bulk composition, and trace element abundance all influence whether cristobalite crystallizes from melt or by This is the peer-reviewed, final accepted version for American Mineralogist, published by the Mineralogical Society of America.The published version is subject to change. Cite as Authors (Year) Title. American Mineralogist, in press.

Libyan Desert Glass: New evidence for an extremely high-pressure-temperature impact event from nanostructural study

“…Evidence for (ii) impact-related melting has been presented in a series of papers (Kleinmann 1968;Koeberl 1997Koeberl , 2000Pratesi et al 2002;Greshake et al 2010Greshake et al , 2018, where the LDG is suggested to be the product of a high-temperature impact process. The occurrence of lechatelierite, α-and β-cristobalite, mullite, and possible tridymite enclosed in silica glass matrix provides evidence for high-temperature impact conditions (e.g., Urey 1957;Barnes and Underwood 1976;Greshake et al 2018;Cavosie et al 2022). Lechatelierite and αcristobalite indicate heating of the source rock to at least 1550 °C followed by rapid cooling (Greshake et al 2010).…”

“…Kleinmann 1968;Greshake et al 2018;Cavosie et al 2022) and thus are not able to resolve the existing argument. The suggested former presence of reidite in LDG (in the form of granular zircon) would allow shock pressures above 30 GPa, favoring the impact model(Cavosie and Koeberl 2019).…”