Vesuvian

Vesuvian, or IDOCRASE, a mineral composed essentially of silica (37 to 39 per cent.), alumina (13 to 16 per cent.), and lime (33 to 37 per cent.), and containing a small percentage of water and usually some oxide of iron. It occurs both massive and crystallised—the general form of the crystals being that of a rectangular prism terminated by faces of the protopyramid and basal planes. The edges of the prisms are often replaced. The hardness = 6.5, and specific gravity = 3.34 to 3.45. The mineral has a vitreous and sometimes resinous lustre, and varies in colour from brown to green; but is occasionally yellow, azure blue, or black. It was first found in dolomitic blocks ejected from Vesuvius and Somma, but occurs in granular limestone, serpentine, gneiss, and other rocks in regions where crystalline schists abound. It is often associated with garnet and pyrotoxene. It is not highly valued as an ornamental stone. The green-coloured varieties are known as Volcanic Chrysolite, and the brown as Volcanic Hyacinth.