Idocrase was first discovered on the Italian volcano, Vesuvius, as small, perfect crystals. Also called vesuvianite, it may be red, yellow, green, brown, or purple. It is seldom used in jewellery, but it may be cut for collectors. Crystals are usually thick prisms with a square cross-section.

There are several varieties: californite from California (USA) is green; rare, blue cyprine is found in Norway; yellowish green xanthite is from New York (USA); green wiluite crystals are from the former USSR. Other localities include Austria, Canada, Italy, and Switzerland.

Vesuvianite may be confused with demantoid garnet, diopside, epidote, smoky quartz, tourmaline, zircon, and peridot.

Chemical Composition: 

Complex silicate of calcium and aluminium. Ca₁₀Mg₂Al₄(SiO₄)₅(SiO₇)₂(OH)₄ and Be, Cu, Cr, Mn, Na, K, Ti, B, U, Th, Zn, Sn, Sb and rare earth elements.

Colors / Varieties: 

• Colorless, green, brown, white, yellow, brownish, red, blue, bluish green, pink, violet, sometimes color zoned.
• Californite: massive green

Crystal System / Forms: 

Tetragonal System / Well formed crystals - prismatic with pyramidal terminations, granular, massive, and intergrown with grossular garnet.

Hardness: 

6 - 7

Specific Gravity: 

3.32 - 3.47

Cleavage / Fracture: 

Indistinct / Conchoidal

Optic Character: 

Anisotropic, D.R.; Uniaxial positive or negative

Lustre: 

Vitreous to resinous

Refractive Index / Birefringence: 

1.713 - 1.718 / 0.005; Range: 1.700 - 1.720

Pleochroism: 

Weak

Dispersion: 

0.019

Magnification: 

Crystalline and fingerprint inclusions.

U.V. Fluorescence: 

Inert.

Spectrum: 

Strong line at 461nm, weaker at 528nm

Cause of Color: 

• Iron: green, yellow, brown
• Copper: blue

Specific Tests: 

Attacked by hydrochloric acid.

Simulants (with separation tests): 

Hydrogrossular garnet (spectrum, R.I.), Jade (R.I., spectrum, structure), Epidote (birefringence, pleochroism), Hypersthene (birefringence, spectrum), Kornerupine (R.I., spectrum, pleochroism), Enstatite (R.I., spectrum), Peridot (R.I., birefringence, spectrum), etc.

Geological Occurrence: 

Contact metamorphic deposits, especially in limestone and dolomites, alkalic rocks; regionally metamorphosed rocks.

Sources: 

Canada, Pakistan, Italy, Siberia, Switzerland, U.S.A. (California), India

Cuts & Uses: 

Facetted cuts, cabochon, beads, carving, etc.