Demantoid

Variety Ca3Fe2(SiO4)3

About it

Green andradite garnet with more fire than diamond. Russian stones from the Ural Mountains often hold curving "horsetail" fibres; Namibia and Madagascar also produce it.

Type
Variety
Group
Andradite variety (garnet)
Formula
Ca3Fe2(SiO4)3
Hardness (Mohs)
6.5–7
Specific gravity
3.8–3.9
Streak
white
Lustre
adamantine (diamond-like), vitreous (glassy)
Crystal system
Isometric (cubic)
Colours
yellowish green, emerald green
Transparency
transparent
Cleavage and fracture
none; conchoidal to uneven fracture

Typical values: real specimens vary. For more, see mindat.org.