Distinctly Montana Magazine

Sapphires are hard, beautiful, and rare, all the qualities that make a first-class gemstone. Most have come from remote exotic locations like Kashmir, Sri Lanka, and Madagascar, and in the United States a few sapphires oc- cur in North Carolina. But the Treasure State harbors sapphires that measure up with the best in the world, and sapphire is so distinctly Montana that it was designated a state gem, together with Montana agate, in 1969. Yellow, pink, green, and purple corundum specimens are all sapphire (red corundum is called ruby), but the most valued varieties are deep blue. Gem dealers seek cornflower blue, nearly a reflection of Montana’s Big Sky. Yogo Gulch, in Judith Basin County on the flank of the Little Belt Mountains, produces elegant gems of just this color, beautiful enough that Yogo sapphires found their way into Tiffany jewelry and the Smithsonian’s gem collection, which holds a 10.2-carat cut stone believed to be the largest cut Yogo ever made. Dick Berg, industrial minerals geologist with the Yogos are America’s premier gemstone Montana Bureau of Mines and Geology in Butte, is clear on one thing: after studying them for a decade, he doesn’t know why the 48-million-year-old Yogos are deep blue while other Montana sapphires such as those from the Rock Creek District west of Philipsburg are much lighter shades, requiring heat treatment to create gems. But he speculates that the rocks’ cooling history may have something to do with it. Longer cool- ing times might allow the titanium and iron to spread more uniformly through the crystals, affecting the color. Yogos result from the luck of geology—just the right elements and just the right cooling history mak- ing a “Goldilocks” gem that is just about perfect. Early gold prospectors discarded the curious blue stones that concentrated in their gold pans and sluices, but by 1895 sapphire gem mining at Yogo Creek was a real- ity. The first almost accidental mining reportedly earned Jake Hoover $3,750—a fortune, and five times what Hoover made on gold—from the Tiffany Company. Tiffany’s gemolo- gist, George F. Kunz, had written Gems and Precious Stones of North America just five years earlier and had known of the lower-quality Missouri Riv- er sapphires for 30 years. He recognized quality when he saw it in Hoover’s Yogos. Hoover sold his share in the “mere gold mine,” as Kunz called it, for $5,000, but within a few months, British investors bought the property for $100,000. Thanks in part to the British connec- tion and European gem cutting centers, a few Yogos probably made their way into the personal collections of British royalty in the 1910s, but a popular suggestion that the Crown Jewels of England contain Yogos is likely a myth. In 1998, the late Montana ge- ologist David Baker contacted Leslie Field, expert on the Crown Jewels. She told Dr. Baker, “I am not aware of any Yogo Gulch sapphires set in any piece of jewelry belonging to a member of the British family.” The suggestion that Princess Diana’s engagement ring con- tains a Yogo sapphire is likewise probably not true—the stone is much too large and probably SAPPHIRES • Composition: Aluminum oxide, Al2O3 • Hardness: #9, second only to diamond • Color: pink, yellow, purple, green, blue • Cause of color: traces of titanium and iron YOGOS • Not heat-treated (only 5% to 10% of sapphires boast natural deep blue color) • Free of inclusions • Uniform high brilliance • Rarer than diamonds • Typically priced at under $1000 for less than 1 carat, but more than $10,000 for more than 1 carat www.distinctlymontana.com 41

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