Brucite
| Brucite | |
|---|---|
 |
|
| General | |
| Category | Oxide mineral |
| Formula (repeating unit) |
Mg(OH)2 |
| Strunz classification | 04.FE.05 |
| Crystal symmetry | Trigonal, hexagonal scalenohedral H-M symbol: (32/m) Space group: P3m1 |
| Unit cell | a = 3.142(1) Å, c = 4.766(2) Å; Z=1 |
| Identification | |
| Color | White, pale green, blue, gray; honey-yellow to brownish red |
| Crystal habit | Tabular crystals; platy or foliated masses and rosettes – fibrous to massive |
| Crystal system | Trigonal |
| Cleavage | Perfect on {0001} |
| Fracture | Irregular |
| Tenacity | Sectile |
| Mohs scale hardness | 2.5 to 3 |
| Luster | Vitreous to pearly |
| Streak | White |
| Diaphaneity | Transparent |
| Specific gravity | 2.39 to 2.40 |
| Optical properties | Uniaxial (+) |
| Refractive index | nω = 1.56–1.59 nε = 1.58–1.60 |
| Birefringence | 0.02 |
| Other characteristics | Pyroelectric |
| References | [1][2][3] |
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.
Notable locations include Wood's Chrome Mine, Cedar Hill Quarry, Lancaster County, Pennsylvania, USA.
Contents
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.
Industrial applications
Brucite is used as a flame retardant because it thermally decomposes to release water in a similar way to aluminium hydroxide and mixtures of huntite and hydromagnesite.[4][5] It also constitutes a significant source of magnesium for industry.
Magnesian attack of cement and concrete
When cement or concrete are exposed to non negligible concentration of Mg2+, e.g. when these materials are left in prolonged contact with sea water or brines, Mg(OH)2 precipitates under the high pH conditions prevailing in the cement porewater. 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.
The use of dolomite as aggregate in concrete can also cause the magnesian attack and should be avoided.
See also
References
- ↑ Brucite on Mindat.org
- ↑ Handbook of Mineralogy
- ↑ Brucite on Webmineral
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