BRUCITE, a mineral consisting of magnesium hydroxide, and crystallizing in the rhombohedral system. It was first described in 1814 as "native magnesia" from New Jersey by A. Bruce, an American mineralogist, after whom the species was named. Brucite is usually found as platy masses, sometimes of considerable size, which have a perfect cleavage parallel to the sur face of the plates. It is white, sometimes with a tinge of grey, blue or green, varies from transparent to translucent, and on the cleav age surfaces has a pronounced pearly lustre. In general appearance and softness (H=21) it is thus not unlike gypsum or talc, but it may be readily distinguished from these by its optical character, being uniaxial with positive birefringence. The specific gravity is 2.38-2.40.
Brucite is generally associated with other magnesian minerals, such as magnesite and dolomite, and is commonly found in serpen tine, or sometimes as small scales in phyllites and crystalline schists ; it has also been observed in metamorphosed magnesian limestone, such as the rock known as predazzite from Predazzo in Tirol. (L. J. S.)