How do I determine that a sapphire has not been heated?

Determining conclusively that a sapphire has not been heat-treated is something that only a very experienced gemologist can do. Gemologists examine internal structures under high magnification and look for the presence of crystal structures that would be altered by heat treatment, since many charactertistic inclusions such as rutile and zircon crystals have a lower melting point than corundum. Some laboratories also use high tech tools such as Raman spectroscopy and laser tomography.

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