Garnet, andradite - Serifos, Cyclades, Greece. — Photo: Lech Darski · CC BY-SA 3.0
Andradite
Also known as: Demantoid (green), Melanite (black), Topazolite.
The calcium-iron garnet — its varieties range from common brown colophonite to the prized green demantoid and black melanite.
Intro adapted from Wikipedia (CC BY-SA).
Andradite is an IMA-recognized mineral species in the silicate class, with the chemical formula Ca₃Fe³⁺₂(SiO₄)₃.
It crystallizes in the cubic crystal system (space group Ia3d). It is a member of the Garnet structural group.
Key properties: Mohs hardness 6.5–7; specific gravity 3.8–3.9; typically green or yellow or brown or black; White streak; Adamantine to resinous, dull luster; refractive index 1.887.
IMA symbol Adr, grandfathered status — known before the IMA’s founding, named in 1868.
Found in skarns from contact metamorphosed impure limestones or calcic igneous rocks; in chlorite schists and serpentinites; in alkalic igneous rocks, then typically titaniferous.
It is found associated with Vesuvianite, chlorite, epidote, spinel, calcite, dolomite, magnetite.
The name commemorates J.B. d'Andrada e Silva (1763–1838), Brazilian mineralogist who described a variety.
Collections: Gemstones, Collector Favorites.