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 angled surface on the rear of the crystal. It has a resinous to vitreous luster and a gem transparent interior. It measures 15 x 10 x 11 mm.