andradite

Andradite is a calcium-iron garnet mineral in the garnet group with the chemical formula Ca3Fe2Si3O12. It is the iron-rich endmember of the garnet family and crystallizes in the isometric cubic system.

It forms under high-temperature, calcium-rich conditions, typically during contact metamorphism and in skarns associated with carbonate rocks. Andradite occurs with calc-silicate minerals such as wollastonite and calcite, and is commonly found with other garnets and magnetite.

Gem varieties include demantoid, a bright green variety prized for its brilliance and dispersion; and topazolite, a yellow to yellow-green variety; and melanorite, a black variety. The colors arise from trace elements such as chromium, iron, and titanium.

Notable gem-quality andradite has been found in the Ural Mountains of Russia, with other sources including Madagascar, Namibia, and the United States.

In geology and jewelry, andradite is valued both as a gem material (primarily demantoid) and as a mineral specimen. Hardness is similar to other garnets, and the mineral has a relatively high specific gravity, contributing to its weight and luster in cut stones.