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andradite Member of the garnet group of minerals, Ca3Fe2(SiO4)3; sp. gr. 3.75; hardness 6.5–7.5; cubic; yellow, greenish, or brownish-red, to black; greasy to vitreous lustre; most crystals dodecahedral; occurs widely in metamorphic and igneous rocks often as a result of metasomatism, also in beach sands and alluvial placers. Transparent crystals are used as gemstones, and the mineral can be used as an abrasive.