Brucite is the mineral form of magnesium hydroxide, with the chemical formula Mg(OH)2. It is pearly white or pale green in colour, translucent, with perfect cleavage, and tabular crystals or massive. It has a hardness of 2.5.

Brucite is a common alteration product of periclase in marble; a low-temperature hydrothermal vein mineral in metamorphosed limestones and chlorite schists; and formed during serpentinization of dunites. Brucite is often found in association with serpentine, calcite, aragonite, dolomite, magnesite, hydromagnesite, artinite, talc, and chrysotile. Notable locations include Wood's Chrome Mine, Cedar Hill Quarry, Lancaster County, Pennsylvania.

Brucite was first described in 1824 and named for the discoverer, American mineralogist, Archibald Bruce (1777-1818).