This is a beautiful thumbnail size Topaz from Klein Spitzkoppe, Erongo Region, Namibia.
Dimensions:
3cm (1.1”) x 2cm (0.7”)
Weight: 15.1 grams = 75.5 carats
Topaz is a silicate mineral of aluminium and fluorine
the Chemical Formula for Topaz is:
Al₂SiO₄(F, OH)₂