Zircon
Zircon has a high refractive index and is often used as a cost-effective substitute for diamond as it displays excellent fire. Most zircon is brown when mined and can be heat treated to change the colour (almost all blue and colourless zircons have been heat treated). Zircon should not be confused with cubic zirconia, which is a synthetic stone, it is not the same thing. Hardness: 6-7.5 (Mohs).
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