Serpentine is a magnesium silicate mineral with a hardness ranging from 2 to 5.5. Its crystal structure can be monoclinic, orthorhombic or hexagonal, but it does not form macroscopic crystals. Rather, it occurs in dense masses or fibrous form. Serpentine derives its name from the similarity of its green color and often smooth surfaces to the skin of some snakes. Some varieties contain spots of Magnetite. The famous Connemara marble of Ireland is a mixture of Serpentine with a marble. Serpentine is found widely, including important deposits in Great Britain, South Africa, Brazil and the USA.