Andradite
Gemstone
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Andradite is a mineral species of the garnet group. It is a nesosilicate, with formula Ca₃Fe₂Si₃O₁₂.
Andradite includes three varieties:
Melanite: Black in color due to limited substitution of titanium for iron. Also known as "titanian andradite".... Wikipedia
Chemical formula: Ca₃Fe₃₊ ₂Si₃O₁₂
Hardness (Mohs hardness scale): 6.5 – 7.5
Refractive index: 1.888 – 1.889
Crystal class: Hexoctahedral (m3m); H-M symbol: (4/m 3 2/m)
Crystal habit: Commonly well-crystallized dodecahedra, trapezohedra, or combinations, also granular to massive
Crystal system: Cubic