Mineral: Cristobalite
Locality: Egypt
Description: Alignment of the cristobalite crystals within the lamellae results in birefringence producing a variety of patterns, including Maltese cross, when spherulites are viewed between crossed polarizers in an optical microscope.It is not possible to see the fibro-radiated cristobalite crystals but the Maltese cross proves their texture. The size of the spherule is a bit large to have a well-defined Maltese cross in this slide.It would be interesting to correlate this texture of cristobalite with the temperature. I do not know the origin of the Libyan glass, but the thermal shock should not have been produced by a meteorite impact.

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