Wikipedia:Today's featured article/June 30, 2012

Yogo sapphires are a variety of corundum found only in Yogo Gulch, Montana, part of the Little Belt Mountains in Judith Basin County, on land once inhabited by the Piegan Blackfeet people. Yogos are typically cornflower blue in color, a result of their containing trace amounts of iron and titanium. Many gemologists consider them among the finest sapphires in the world. 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) of Yogos are still in the ground. The Smithsonian Institution first reported on Yogos in the museum's annual report on June 30, 1899. Jewelry containing Yogos was given to First Ladies Florence Harding and Bess Truman; in addition, many gems were sold in Europe. Today, several Yogo sapphires are part of the Smithsonian Institution's gem collection. In 1969, the sapphire was co-designated along with the agate as Montana's state gemstones. (more...)

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