Category Oxide mineral Strunz classification 4.FE.05 Space group P3m1 | Formula
(repeating unit) Mg(OH)2 Crystal system Trigonal | |
 | ||
Crystal class Hexagonal scalenohedral (3m)
H-M symbol: (3 2/m) | ||
Brucite is the mineral form of magnesium hydroxide, with the chemical formula Mg(OH)2. It 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.
Contents
It adopts a layered CdI2-like structure with hydrogen-bonds between the layers.
Discovery
Brucite was first described in 1824 and named for the discoverer, American mineralogist, Archibald Bruce (1777–1818). A fibrous variety of brucite is called nemalite. It occurs in fibers or laths, usually elongated along [1010], but sometimes [1120] crystalline directions.
Occurrence
A notable location in the U.S. is Wood's Chrome Mine, Cedar Hill Quarry, Lancaster County, Pennsylvania. Yellow and white brucite with a botryoidal habit has been found in Kharan District, Pakistan. Brucite also occurs in the Bela Ophiolite of Khuzdar District, Pakistan.
Industrial applications
Synthetic brucite is mainly consumed as a precursor to magnesia (MgO), a useful refractory insulator. It finds some use as a flame retardant because it thermally decomposes to release water in a similar way to aluminium hydroxide and mixtures of huntite and hydromagnesite. It also constitutes a significant source of magnesium for industry.
Magnesian attack of cement and concrete
When cement or concrete are exposed to Mg2+. The neoformation of brucite, an expansive material, induces mechanical stress in the hardened cement paste and is responsible for the formation of cracks and fissures in concrete. This kind of failure occurs upon prolonged contact between sea water or brines and concrete.
The use of dolomite as aggregate in concrete can also cause the magnesian attack and should be avoided.