Although the source rocks of alluvial sapphires in Montana have never been discovered, inclusions and geochemistry of material from this location may give clues to their original source. Mineral inclusions in alluvial Montana sapphires, mainly from Rock Creek, were identified and compared with existing data. Topaz was a remarkable find in one of these samples; other newly identified mineral inclusions in Montana sapphire were allanite, anatase, chalcopyrite, and monazite.
This story originally published by Gemological Institute of America and written by Andrew Lucas, Tao Hsu, Shane McClure, and Kevin Schumacher
Montana’s rich history of gold and sapphire goes back to the late 1800s. A GIA field team traveled to the Rock Creek and Missouri River areas, where sapphire mining is still underway, to document the current industry and collect rough sapphire samples for our research reference sample collection. During our time in Montana we visited three mining operations, each with its own business model and its own exciting story.