​​Which gemstones are often heated, treated or enhanced?

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Aquamarine - Heated to change color​

Amethst/Citrine - Heated to change color; Irradiation to alter color

Emerald - Oil & wax to improve clarity; Heat to change color (Note: It is very rare to find a no oil Emerald)​

Kunzite - Irradiation to alter color

Morganite - Heat and occasionally irradiation

Ruby - Heat to improve color; Diffusion to produce different color; Glass and/or lead filling to improve clarity (Note: It is possible to find no-heat Rubies, which are more expensive)

Sapphire - Heat to change color; Beryllium diffusion to produce a different color (Note: It is possible to find no-heat Sapphire, which are more expensive. Also, many fancy colors like Yellow and Green are infused with Beryllium.)​​

Tanzanite - Occasionally coating to strengthen color; not permanent

Topaz - Heat to alter color; Irradiation to alter color (Note: Blue Topaz is irradiated and then heated to create its color. But Precious Topaz is not irradiated.)​

Tourmaline - Heat to alter color; Occasionally irradiation in Rubellite to alter color (Note: Most Tourmaline are heated.)