Mystic Topaz - Another treated stone is sold under the name "mystic" topaz. This is a stone with an iridescent appearance that is produced by vapor coating the surface of clear topaz with titanium oxide. This surface coating is not permanent and many mystic topaz gemstones quickly show signs of wear.
You can see the amazing dispersion in this high quality facetted Titanite Sphene! I don't have it in my possession, but I'd love to!
In the case of ‘Mystic Topaz’, the coating creates interference effects, displaying a rainbow effect of various colors. This is on real topaz.