Gems by Geography: The search for Yogo Sapphires
We’ve learned that “Olympian Blue” is one of the hot colors for fall. So what better gem to focus on for our special Gems by Geography series than the sapphire?
But, not just any sapphire. We’re going to Montana for a rare find and true natural wonder: the Yogo. It’s the most precious sapphire found in North America and considered to be among the finest in the world.
Why are they called that?
These unique gems come from only a small place, named Yogo Gulch, located in the Little Belt Mountains of Montana. They were first found accidentally by gold prospectors in the 1880s, and eventually became the primary focus of mining in the area.
Today, they are only commercially mined deep underground. These sapphires occur along a five-mile long strike in the earth. Initially, the early miners mined rock from wider veins that were up to 20 feet wide, but over time these veins were mined out.
Currently, mining is limited to the narrow veins that are left, which are only 8-10 inches wide and 400 feet underground.
What’s it made of?
Yogo sapphires are a perfect blend of aluminum and oxygen with titanium; titanium being responsible for the blue color.
The vast majority come in a very fine cornflower blue. Some will occasionally have a trace of purple color, and even more rarely, a strong violet hue. The rarest of all colors will range from magenta to true red.
They are often only found in very small sizes. Once cut, the true beauty of these gems is released.
Is it the perfect gemstone?
Pretty close. Yogo sapphires are usually free of inclusions and their color is consistent throughout the whole stone. The perfect crystallization during the geologic formation allows them to have even coloring and pristine clarity. It remains one of the few natural sapphires that never need any treatment.
Rough Yogo sapphires
Yogo Sapphires come in a range of colors from cornflower blue to deep violet.
Several are kept at the Smithsonian Institution including this large blue Yogo sapphire in the head of the Conchita Sapphire Butterfly, part of a brooch created in 2007,as well as the record-setting 10.2-carat (2.0 g) cut Yogo.
A 0.37-carat (0.074 g) brilliant cut purple Yogo sapphire. Only about two percent are purple.
Detail of the Tiffany Iris Brooch by Paulding Farnham circa 1900, currently held by the Walters Art Museum.
Yogos Fast Facts
- 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 $1,000 for less than 1 carat, but more than $10,000 for more than 1 carat