Andradite Garnet

Andradite is the calcium-iron end-member of the garnet group and the most fiery of all garnets, with a dispersion that exceeds even diamond. It occurs in several gem varieties: green chromium-bearing demantoid, golden-yellow topazolite, and opaque black melanite.

Demantoid, in particular, is among the most valuable of all garnets, prized for its vivid green and spectacular fire. Andradite gets its name from the Brazilian mineralogist José de Andrada.

Its high refractive index gives all andradite varieties a strong, adamantine luster.

Andradite forms in skarns and contact-metamorphosed limestones, in serpentinites (where demantoid develops with chromium), and in alkaline igneous rocks (where melanite occurs). It also forms in some metamorphosed iron deposits.

The iron-rich composition develops where calcium-rich rocks interact with iron- and silica-bearing fluids.

Notable sources include the Ural Mountains of Russia (classic demantoid), Iran and Namibia (demantoid), Italy (topazolite), and various alkaline complexes for melanite.

Andradite is recognized by its high luster, strong dispersion (fire), and singly refractive garnet character.

• Hardness: 6.5-7 (slightly softer than other gem garnets).
• Crystal system: isometric; no pleochroism.
• Streak: white (melanite may give a brownish streak).
• Demantoid often shows characteristic 'horsetail' inclusions of byssolite fibers.

Distinguish demantoid from emerald and peridot by single refraction and its intense fire; black melanite resembles black tourmaline or schorl but is isometric and singly refractive.

Gem andradite is highly valued in jewelry: demantoid is among the priciest garnets, set in fine rings and pendants; topazolite and melanite are cut for collectors, with black melanite used in mourning jewelry.

Andradite has minimal industrial use, being primarily a gemstone and mineral-specimen material.

Its exceptional fire makes demantoid a connoisseur's favorite. Metaphysical traditions link andradite to strength and grounding, a traditional belief.