Almandine-Spessartine

specimen number:
2063401

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

description:

A loose dark complete lustrous crystal of almandine-spessartine without matrix. In good condition all around. Collected by Ray DeMark in June, 1977.

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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