Six common species of garnet are recognized based on their chemical composition. These species are pyrope, almandine, spessartite, grossular, uvarovite and andradite.
One of the rarest of all the garnet varieties is andradite, the calcium iron garnet. It has the highest refractive index of all the garnets (1.89-1.94). The most famous of the andradite garnets is the very rare demantoid, whose name means "diamond-like luster." In fact demantoid is among the rarest and most expensive of all colored gemstones.
Andradite was named after the Portuguese mineralogist José Bonifácio de Andrade e Silva (1763-1838). He discovered and described four minerals during his life, including spodumene and petalite. A geology professor in Portugal, he spent many years in the Portuguese colony of Brazil. When the independence of Brazil was declared, Andrade was made minister of the interior and of foreign affairs.
The andradite species includes two other rarely-seen varieties: the yellow topazolite and the black melanite. Melanite is an opaque black stone with excellent luster. At one time it was rarely faceted as a gemstone. However, with the interest in black diamond, and the general scarcity of black gemstones, melanite has become popular for jewelry.
The black color of melanite is the result of titanium replacing some of the iron in its composition, and melanite is sometimes known as titanian andradite. Because garnet has excellent gemstone characteristics -- good hardness and luster, and no cleavage - melanite is used in rings, pendants, earrings and bracelets. It is fairly inexpensive, selling at approximately the same price as black tourmaline. It is a very good alternative to more expensive gems such as black sapphire and black spinel, and superior to less expensive black gems such as onyx and jet.