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Andradite

melanite
Melanite garnet (variety of andradite garnet) about 10 cm long in white calcite

Garnets containing titanium and manganese are grouped as andradite garnet. The most valuable is demantoid, whose emerald-green color is due to the presence of chromium. It has a higher dispersion than diamond and can be recognized by the characteristic “horsetails”, which are fine, hair-like inclusions of asbestos. Topazolite, the yellow variety of andradite garnet, varies from pale to dark yellow. Only small crystals are found. Melanite is a generally black form, but can also be dark red.

The best demantoid is found in the Urals in Russia, and is associated with gold-bearing sands and metamorphic rocks. Other localities include northern Italy, Zaire, and Kenya. Topazolite crystals are found in the Swiss and Italian Alps in metamorphic rocks. Melanite is found in metamorphic rocks and volcanic lavas; fine crystals are found on the island of Elba (Italy), and in France and Germany.

Andradite Pictures

Demantoid garnet (variety of andradite garnet)

Cause of Color :
  • Green: Chromium
  • Yellowish-green: Chromium, Iron
  • Black: Titanium, Iron
  • Yellow, brown: Iron

Chemical Composition :

Calcium Iron Silicate – Ca3Fe2(SiO4)3


Cuts & Uses :

Facetted, cabochon, beads, carvings, etc.


Dispersion : 0.057
Hardness : 6.5
Magnification :
  • Demantoid: Horse-tail pattern of byssolite / asbestos fibers, fingerprints.
  • Topazolite: Liquid and crystal inclusion.

Refractive Index / Birefringence :

1.800 – 1.940


Simulants (with separation tests) :

Natural Zircon (optic character, spectrum, inclusions), Synthetic Cubic Zirconia (lustre, inclusions, spectrum), Y.A.G. (inclusions, spectrum, fire), Sphene (optic character, spectrum, fire doubling), Chrysoberyl (optic character, R.I., spectrum, inclusions, fire), Tourmaline (optic character, pleochroism, life, fire), etc.


Sources :

Russia (Ural Mountains), Namibia, Pakistan, U.S.A. (California, Arizona)


Spectrum :

Demantoid: Strong band at 443nm (may appear as a cut off), 622nm & 640nm, 693nm & 701nm.


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