Corundum

specimen number:
1605083

location:
Missouri River Placers, Montana, USA

description:
A loose yellow translucent hexagonal crystal of corundum.

The Missouri River placers in Montana, particularly along the stretch near Helena known as Confederate Gulch and various bars upstream and downstream, have a rich history of gold and sapphire extraction dating back to the gold rush era of the 1860s. Geologically, the sapphire-bearing gravels are alluvial deposits where gem-quality corundum, weathered from ancient igneous dikes and regional metamorphic rocks, was transported and concentrated by river action over millions of years. Mineralogically, these deposits are famous for producing unique, pastel-colored sapphires--ranging from light blues and greens to yellows and pinks--which became a cornerstone of the American gemstone industry after commercial mining and systematic recovery operations began in the late 19th century.

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