SOCGEMS Presents: Sapphires From Montana - A Historical, Geological, and Gemological Overview with Dr. Aaron Palke, Senior Research Scientist, GIA (Gemological Institute of America).
Montana’s Yogo Sapphires Unique Gemology
The first Yogo source was discovered in 1895 and by the turn of the century, production averaged 400,000 carats a year.
The mine site is located within a long dike (a geological formation of volcanic rock layered above older, pre-existing rock) that held other sapphire deposits.

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