Topaz. View of a blue topaz in celandite. Topaz is a silicate mineral made of aluminium silicate. Topaz is a very hard stone, often transparent or translucent with a vitreous lustre. It is often colourless, but can be coloured, yellow, blue (as here), pink, green, violet or reddish-yellow. Clear or finely coloured varieties have always been used as gemstones. This specimen was found in the Ural Mountains, Russia.