This “London” blue topaz crystal from Minas Gerais Brazil. Topaz is a silicate and it contains the elements Al, Si, O, F, and H. It can be found in a variety of colors which are created by different trace impurities in the crystal lattice. This crystal has water worn prism faces and a sawed surface on the base of the crystal. It has a mostly frosty luster and has a gem transparent interior. It measures 18 x 13 x 12 mm.