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brucite Mineral, Mg(OH)2; sp. gr. 2.4; hardness 2.5; trigonal; white, shades of pale grey, blue, or green; white streak; pearly to waxy lustre; crystals normally broad and tabular, but also occurs fibrous, massive, and foliated; cleavage perfect basal hardness; occurs in metamorphosed limestone, also in hydrothermal veins together with calcite, talc, and serpentine; soluble in hydrochloric acid. It is named after the nineteenth century American mineralogist A. Bruce.