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early 14c., metathesized from Old French grenat "garnet," originally an adjective, "of a dark red color," from Medieval Latin granatum, originally an adjective, "of dark red color," perhaps abstracted from pomegranate (q.v.), from the stone's resemblance either to the shape of the seeds or the color of the pulp. But perhaps the word is from Medieval Latin granum "grain," in its sense of "cochineal, red dye."
Any of several common red, brown, black, green, or yellow minerals having the general chemical formula A3B2SiO8, where A is either calcium (Ca), magnesium (Mg), iron (Fe), or manganese (Mn) and B is either aluminum (Al), manganese, iron, chromium (Cr), or vanadium (V). Garnet crystals are dodecahedral in shape, transparent to semitransparent, and have a vitreous luster. They usually occur in metamorphic rocks but also occur in igneous and sedimentary rocks.