Bixbyite with Hematite after Garnet

specimen number:
2063407

location:
Thomas Range, Juab Co., Utah, USA

description:
Interesting thumbnail specimen from this prolific locality was sharp lustrous mirror bright crystals of metallic bixbyite measuring to 0.4 cm on ads, these across crystals of what were once a member of the garnet family now replaced by hematite. All on a matrix of rhyolite. In good condition.

Situated in Juab County, western Utah, the Thomas Range is composed of Tertiary volcanic rocks, notably topaz-bearing rhyolite flows and tuffs that erupted around twenty-one million years ago. As these silicic magmas cooled, fluorine-rich vapor trapped within cavities and gas vesicles allowed gem-quality topaz crystals to crystallize alongside other minerals. Indigenous populations and early pioneers were long aware of these deposits, but formal mineral collecting exploded in the mid-twentieth century when the area became famous as Topaz Mountain. Today, the location remains a world-renowned public collecting site, actively managed for rockhounds and amateur miners who search the weathered rhyolite and gravels for sherry-colored topaz crystals that bleach to clear or pale amber upon exposure to sunlight.

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