Any gemstone that has been heated to change its color or improve the color, such as blue zircon, hyacinth, burnt amethyst, white chalcedony, smoky quartz and many aquamarines.
See Alexandrite Tsarstone collectors guide, Definition of Heated stone, http://m.alexandrite.net/viewpage.html?id=GG-093-00002 (Any gemstone that has been heated to change its color or improve the color, such as blue zircon, hyacinth, burnt amethyst, white chalcedony, smoky quartz and many aquamarines. ) (as of Apr. 03, 2026, 15:36 GMT).