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Canary Yellow Tourmaline
Tourmaline is a gemstone famed for occurring in nearly every color of the rainbow. Some of the colors are quite rare, such as the vivid purplish-red of rubellite, the neon blue of paraiba and the rich green of chrome tourmaline. But one of the rarest colors in tourmaline -- and one of the least known -- is a bright yellow known in the trade as canary tourmaline.
Brown or black tourmaline, known as dravite, is quite common. The black tourmalines are colored by iron, while the brown and gold colors are due to manganese. Only rarely does a pure yellow occur, when the tourmaline is manganese-rich (up to 9%) with traces of titanium while very low in iron.
The colors of canary tourmaline can range from a pale yellow to deep golden, but the most valuable are the bright yellows, usually with just a touch of green.
Yellow tourmaline can occur wherever tourmaline is found, but the finest specimens have been found in Africa, particularly in Malawi, Zambia, Mozambique and Nigeria. Specimens have also been found in Afghanistan and Pakistan.
Though tourmaline is a gem that can sometimes be found in large sizes, yellow tourmaline is usually found in smaller sizes, with the vast majority of cut stones under 1 carat. Thus yellow tourmalines over 2 carats count as especially rare.
Like rubellite, yellow tourmaline tends to have significant inclusions. But even slightly included gems can be very attractive with good brilliance if the color is strong. An eye-clean yellow tourmaline would count as very fine.
The best yellow tourmalines have exceptional brilliance with an almost neon-like quality. Since tourmaline has very good hardness (7 to 7.5 on the Mohs scale), this is a gem suitable for any type of jewelry.
Usually yellow tourmaline is completely untreated, but some specimens are heated at low temperature (500 to 700 degrees celsius) to try to reduce the green or brown component.