A 0.65-carat (0.130 g) cornflower blue Yogo sapphire
Yogo sapphires are blue sapphires, a colored variety of
corundum, found in
Montana, primarily in Yogo Gulch (part of the
Little Belt Mountains) in
Judith Basin County, Montana. Yogo sapphires are typically
cornflower blue, a result of trace amounts of
iron and
titanium. They have high uniform clarity and maintain their brilliance under artificial light. Because Yogo sapphires occur within a vertically
dipping resistive igneous dike, mining efforts have been sporadic and rarely profitable. It is estimated that at least 28 million carats (5.6 t or 5.5 long tons or 6.2 short tons) of Yogo sapphires are still in the ground. Jewelry containing Yogo sapphires was given to First Ladies
Florence Harding and
Bess Truman; in addition, many gems were sold in Europe, though promoters' claims that Yogo sapphires are in the
crown jewels of England or the engagement ring of
Princess Diana are dubious. Today, several Yogo sapphires are part of the
Smithsonian Institution's gem collection.
Yogo sapphires were not initially recognized or valued. Gold was discovered at Yogo Creek in 1866, and though "blue pebbles" were noticed alongside gold in the stream
alluvium by 1878, it was not until 1894 that the "blue pebbles" were recognized as sapphires. Sapphire mining began in 1895 after a local rancher named Jake Hoover sent a cigar box of gems he had collected to an assay office, which in turn sent them to
Tiffany's in New York, where an appraiser pronounced them "the finest precious gemstones ever found in the United States". Hoover then purchased the original
mother lode from a sheepherder, later selling it to other investors. This became the highly profitable "English Mine", which flourished from 1899 until the 1920s. A second operation, the "American Mine", was owned by a series of investors in the western section of the Yogo dike, but was less profitable and bought out by the syndicate that owned the English Mine. In 1984, a third set of claims, known as the Vortex mine, opened. (
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