Idocrase

wiluite
Rough wiluite

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.

Cause of Color :
  • Iron: green, yellow, brown
  • Copper: blue
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.

Crystal System / Forms :

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

Cuts & Uses :

Facetted cuts, cabochon, beads, carving, etc.

Dispersion : 0.019
Hardness : 6 - 7
Lustre : Vitreous to resinous
Magnification :

Crystalline and fingerprint inclusions.

Optic Character :

Anisotropic, D.R.; Uniaxial positive or negative

Pleochroism : Weak
Refractive Index / Birefringence :

1.713 – 1.718 / 0.005; Range: 1.700 – 1.720

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.

Sources :

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

Specific Tests :

Attacked by hydrochloric acid.

Spectrum :

Strong line at 461nm, weaker at 528nm

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