Andradite [Adr] | |
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![]() Single crystal (4.2 cm) – Diakon, Nioro du Sahel Circle, Kayes Region, Mali | |
General | |
Category | Garnet group |
Formula (repeating unit) | Ca3Fe2(SiO4)3 |
IMA symbol | Adr[1] |
Strunz classification | 9.AD.25 |
Crystal system | Cubic |
Crystal class | Hexoctahedral (m3m) H-M symbol: (4/m 3 2/m) |
Space group | Ia3d |
Unit cell | a = 12.056 Å; Z = 8 |
Identification | |
Color | Yellow, greenish yellow to emerald-green, dark green; brown, brownish red, brownish yellow; grayish black, black; may be sectored |
Crystal habit | Commonly well-crystallized dodecahedra, trapezohedra, or combinations, also granular to massive |
Cleavage | none |
Fracture | conchoidal to uneven |
Tenacity | Brittle |
Mohs scale hardness | 6.5 to 7 |
Luster | Adamantine to resinous, dull |
Streak | White |
Diaphaneity | Transparent to translucent |
Specific gravity | 3.859 calculated; 3.8–3.9 measured |
Optical properties | Isotropic, typically weakly anisotropic |
Refractive index | n = 1.887 |
Absorption spectra | demantoid – 440 nm band or complete absorption at 440 nm and below, may also have lines at 618, 634, 685, 690 nm[2] |
References | [2][3][4][5] |
Major varieties | |
Demantoid | transparent light to dark green to yellow-green |
Melanite | opaque black |
Topazolite | transparent to translucent yellow, may show chatoyancy |
Andradite is a mineral species of the garnet group. It is a nesosilicate, with formula Ca3Fe2Si3O12.
Andradite includes three varieties:
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]