Andradite
Andradite
Nesosilicate mineral species of garnet
Andradite is a mineral species of the garnet group. It is a nesosilicate, with formula Ca3Fe2Si3O12.
Andradite includes three varieties:
- Colophonite: a historical variety found in the Scandinavian islands, brownish or reddish in color, often opaque or translucent.[6]: 61
- Demantoid: Vivid green in color, one of the most valuable and rare stones in the gemological world.[7]
- Melanite: Black in color due to limited substitution of titanium for iron. Also known as "titanian andradite". Forms a solid solution with morimotoite and schorlomite depending on titanium and iron content.[8]
- Topazolite: Yellow-green in color and sometimes of high enough quality to be cut into a faceted gemstone, it is rarer than demantoid.[7]
It was first described in 1868 for an occurrence in Drammen, Buskerud, Norway.[3][4][7] Andradite was named after the Brazilian statesman, naturalist, professor and poet José Bonifácio de Andrada e Silva (1763–1838).[3][7]