(named after the American mineralogist A. Bruce, died 1818), a mineral of the hydroxide group; chemical composition, Mg(OH)₂. The magnesium may be partially replaced by Fe²⁺ or Mn²⁺ (ferroand manganobrucites). Brucite crystallizes in a trigonous system and consists of colorless or white (rarely bluish) mica-like crystals, or masses of them, with a layered structure, or sometimes fine-fibered (so-called nemalite) or dense, sinter-like aggregates. Its hardness on the mineralogical scale is 2.5; its density, 2,370-2,400 kg/m³. Formed during hydrothermal changes in ultrabasic magnesial rocks and metamorphosis of dolomites, brucite is found with asbestos in veins of serpentine dunites or peridotites. It may be used as a magnesium ore. In the USSR deposits of brucite have been discovered in massifs of serpentinites and metamorphosed dolomites in the Urals, the Caucasus, and Siberia. Abroad the best known deposits are in the USA, Canada, Italy, and Yugoslavia.