Idocrase (Vesuvianite)

Chemistry: Calcium aluminum silicate.
Crystal system: Tetragonal; Vesuvianite: well-developed square prisms capped with bipyramidal and often basal pinacoid; Californite: massive; Cyprine: massive.
Color: Vesuvianite: transparent, yellow to brown and greenish shades; Californite: transparent to opaque; massive green (mixture of idocrase and grossular garnet); Cyprine: very rare blue variety (Cu).
Hardness: 6 - 7
Cleavage: Indistinct; Fracture: sub-conchoidal.
Specific gravity: 3.35
Refractive index: 1.70 – 1.73 (changes from negative to positive with increasing R.I); 0.005
Luster: Vitreous.
Dispersion: Low
Dichroism: Indistinct.
Occurrence: Canada, Italy, Switzerland, Siberia; Californite: California, USA.

Notes
Vesuvianite cut for collectors; crystals similar to zircon, except zircon rarely shows the basal pinacoid; massive green Californite may look like nephrite jade; massive idocrase often mixed with hydrogrossular; may show rare earth spectrum, strong band at 461nm in the blue; transparent varieties faceted; Californite: cabochon and beads.