|Nearly all of the rough crystals are flat, tabular pieces that can only be cut into small gems. Carat-plus sapphires are rare.||The US has never been known as a major source for gemstones. The one exception has been Montana sapphire. Montana has been an important source of blue sapphire off and on since the 1890s. Yogo sapphires feature an attractive violet to blue color. They are not heat treated – the gem-quality stones rarely respond to treatments.|
|Yogo sapphires have a distinct trace element signatures with specific values of manganese, chromium, titanium, iron and gallium that are different from other sapphires. While Yogo sapphires command premium prices, their small sizes and difficult deposits make mining uneconomic. |
In 1910 the largest sapphire ever found was revealed, a 19 carat rough that was cut into four gems, the largest 8.5 carats.