Snowflake Obsidian Cabochon 30X40, From Black Rock Desert, Millard County, Utah. Approximately 2.5 million years ago (late Tertiay Period). Obsidian is natural glass formed by quenching (i.e., rapidly cooling) magma of granitic/rhyolitic or similar composition.
Snowflake obsidian (also spherulitic obsidian and flowering obsidian) – dark gray to nearly black obsidian with inclusions of white, gray or rarely red spherulites, which in many specimens have been identified as cristobalite (a high-temperature polymorph of silica).