London blue topaz

Topaz is a rather rare silicate mineral with a Mohs hardness of 8. It comes in many colors from yellow to pink to purple to blue, depending on what ions are present in the crystal. It can even be colorless. However, the favorite variety is orange to brown in color and called imperial topaz. Much of the best topaz comes from Brazil. The gem called London blue topaz can be made from the colorless variety by treatment with heat and radiation. 

Irradiation Topaz is sold as Swiss blue, London blue, etc. In all cases, the material has been irradiated and heated. 

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See also in sourсe #XX -- [ , ]

See also in sourсe #XX -- [ , ]

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