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The Gemstone Andradite (Garnet)

Andradite is the most is the most lustrous of the Garnets and has several gemstone varieties. The term Garnet describes a group name for several closely related minerals that form important gemstones, and Andradite is an individual member mineral of the Garnet group. Andradite is a common mineral but is usually opaque and not fit for gemstone use; the transparent gemmy forms are rare and valued. The term Andradite is strictly a mineral term and is rarely used in the gem market. The gem forms of Andradite are known by their variety names of Demantoid, Topazolite, and Melanite.

Color

Red, Green, Yellow, Orange, Brown, Pink, Gray, Black, Multicolored

Hardness

6.5 - 7.5

Chemical Formula

Ca₃Fe³⁺₂Si₃O₁₂

Mineral Class

Andradite (Garnet)

Additional Properties

Crystal System
Isometric

Refractive Index
1.888 - 1.889

Double Refraction
None

Transparency
Transparent to opaque

SG
3.8 - 3.9

Luster
Adamantine, submetallic

Cleavage None

All About

The green Demantoid variety is a rare and valuable form of Garnet. The original deposits of Demantoid were from Russia, and these types of Demantoid almost always contains inclusions of asbestos, which are known as horsetail inclusions. Large gemstones of Demantoid, which display a brilliant luster and fire are extremely rare and can be very valuable.

The yellow to orange-yellow variety of Andradite, Topazolite, seldom occurs in crystals large enough to be worth faceting, and is not commonly seen in jewelry. The black opaque variety Melanite has become a popular black gemstone, with a highly reflective submetallic luster. It is the most well-known black Garnet and is often simply known as "Black Garnet".

Uses

Andradite Garnets are not commonly used as gemstones. Demantoid was more popular in the 19th century, but its popularity has decreased because of its lack of widespread availability and low hardness. Topazolite is also seldom used in jewelry and is mostly faceted for collectors. With an increased interest of black gemstones on the market, Melanite makes a very good and inexpensive black gemstone, and is used in bracelets, rings, earrings, pendants, and beads.

Varieties

Demantoid - Olive-green to emerald-green gem variety of Andradite Garnet.
Mali Garnet - Garnet gemstone from the African country of Mali that ranges in color from green to yellow to brown (though most often a greenish-yellow). The deposit of these Garnets was discovered in Mali in 1994, and this form of Garnet is a relatively new gemstone. The scientific classification of the Mali Garnets are not clearly identified; they can be either Grossular or Andradite, though are usually an intermediary form closer in chemical structure to Grossular.
Melanite - Lustrous, opaque black or very dark red variety of Andradite Garnet.
Topazolite - Yellow to brownish-yellow variety of Andradite Garnet.

Treatments & Enhancements

Andradite Garnet gemstones are naturally colored and not enhanced.

The Gemstone Andradite (Garnet) Sources

The original historical deposits of Demantoid were in Russia. A new more extensive deposit of Demantoid is in Namibia, with other lesser-scale deposits in Madagascar, Afghanistan, Iran, and Italy.

Deposits of the other forms of Andradite, including Topazolite and Melanite, are in Russia, Azerbaijan, Italy, Mali, Mexico, and the U.S. (Arizona and California).

Similar Gemstones

Demantoid: Similar to Peridot, Tsavorite, and Emerald.
Topazolite: Similar to Topaz, Citrine, Yellow Sapphire.
Melanite: Similar to Onyx, Schorl Tourmaline, Black Sapphire.