Silicate of calcium and iron, belonging to the garnet group. It is named after a Portuguese mineralogist, J. B. D'Andrada.
Crystal system Cubic.
Appearance Andradite occurs in crystals in the form of a rhombic dodecahedron, like all garnets, or in convex aggregates of crystals, whose color varies with slight variations in the stone's composition, and which therefore have different names: the black variety is called melanite; the honeyyellow variety topazolite; the green one, demantoid. It can also be blackish brown or blackish red. The crystals may be transparent, semiopaque, or opaque, and often have good luster.
Physical properties These vary slightly according to the composition: the density ranges from 3.81 to 3.86 g/cm3 the refractive index, from 1.882 to 1.889. The hardness in 6.5-7.5, similar to that of other garnets.
Genesis lt is found in metamorphosed limestone and,
rarely, in certain intrusive and extrusive igneous rocks. The topazolite and demantoid varieties are found in serpen
tines, often together with asbestos.
Occurrence Andradite is mainly found in alluvium in the Soviet Union (Urals) and the United States, but also in Norway and Germany.