igneous
Obsidian with Cristobalite
Volcanic Glass (Amorphous Silicon Dioxide) with Cristobalite inclusions
Hardness of 5 to 5.5 on the Mohs scale, dark black vitreous body with characteristic conchoidal fracture, and snowflake-like or spherical white/yellowish spherulites (cristobalite) inclusions. Glassy luster.
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Physical properties
Hardness of 5 to 5.5 on the Mohs scale, dark black vitreous body with characteristic conchoidal fracture, and snowflake-like or spherical white/yellowish spherulites (cristobalite) inclusions. Glassy luster.
Formation & geological history
Formed as an extrusive igneous rock when felsic lava extruded from a volcano cools rapidly with minimal crystal growth.
Uses & applications
Used historically for sharp cutting tools, arrowheads, and blades, as well as in modern decorative items and lapidary work.
Geological facts
The spherules within snowflake obsidian are actually radial clusters of the mineral cristobalite, a high-temperature polymorph of quartz, which formed as the glass began to devitrify over long periods.
Field identification & locations
Easily identified by its jet-black, glassy appearance coupled with distinct contrasting white or yellowish star-like snowflake inclusions. Found worldwide in areas with past volcanic activity.
