Alamandine

Almandine is the most common form of the gemstone Garnet. The term Garnet describes a group name for several closely related minerals that form important gemstones, and Almandine is an individual member mineral of the Garnet group. Almandine is usually opaque and unfit for gemstones use; though the less common transparent to translucent forms make fine gemstones. In the gem trade, the term Almandine is rarely used on its own. It is either generically called "Garnet", or "Almandine Garnet".
Chemical Formula Fe3Al2Si3O12
Color Red, Black
Hardness 7.5Â -Â 8.5
Crystal System Isometric
Refractive Index 1.780Â -Â 1.810
SG 4.3
Transparency Transparent to translucent
Double Refraction None
Luster Vitreous
Cleavage None. May exhibit parting.
Mineral Class Almandine (Garnet)