Tourmaline

Formula: variable. Generic formula X1Y3Al6(BO3)3Si6O18(OH)4. Where: X = Na and/or Ca, Y = Mg, Li, Al, and/or Fe
Hardness: 7-7.5
Description: Touraline is a group of isomorphic minerals with an identical crystal lattice and a hexagonal crystal system. Each member of the group has a different formula. The main forms of tourmaline are Elbaite, Schorl and Dravite, other tourmaline minerals include Uvite, Liddicoatite and Buergerite.
Specimen number: R30065