Garnet

Garnet is the name given to a large, chemically complex X₃Z₂(TO₄)₃
X = Ca, Fe, etc., Z = Al, Cr, etc., T = Si, As, V, etc. family of stones; due to the complexity in trace elements garnets come in almost every colour imaginable, some being very rare. All the different types of garnets form according to an isometric crystal system and have a hardness of 6.5 to 7.5 on the Mohs scale.