Idocrase

Idocrase is an alternative name for vesuvianite, a calcium-magnesium-aluminium sorosilicate first described from the volcanic blocks of Mount Vesuvius, Italy — the origin of both of its names. It typically occurs in green, yellow-green and brown, and a compact green massive form is sometimes cut as a jade substitute (the 'californite' of California).

Properties

Vesuvianite is tetragonal and commonly forms stout prismatic crystals with a vitreous lustre and a hardness of 6–7. Transparent material is occasionally faceted, while the massive material is carved.

Occurrence

It forms mainly in contact-metamorphosed and skarn limestones, often with grossular garnet, diopside and wollastonite. Classic localities include Vesuvius and the Italian Alps, the Jeffrey Mine in Quebec, and skarns in Russia and the United States. It is the same species as vesuvianite.