Andradite

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.
Chemical Formula Ca3Fe3+2Si3O12
Color Red, Green, Yellow, Orange, Brown, Pink, Gray, Black, Multicolored
Hardness 6.5Â -Â 7.5
Crystal System Isometric
Refractive Index 1.888Â -Â 1.889
SG 3.8Â -Â 3.9
Transparency Transparent to opaque
Double Refraction None
Luster Adamantine, submetallic
Cleavage None
Mineral Class Andradite (Garnet)