Brucite
Magnesium hydroxide mineral with industrial and concrete degradation roles.
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. It adopts a layered CdI2-like structure with hydrogen-bonds between the layers.
- chemical_formula
- Mg(OH)2
- discoverer
- François Sulpice Beudant
- named_for
- Archibald Bruce
- crystal_structure
- Layered CdI2-like structure with hydrogen-bonds between layers
- fibrous_variety
- Nemalite
- molar_volume
- 24.63 cm3/mol
Lore & Background
A fibrous variety of brucite is called nemalite. Notable locations include Wood's Chrome Mine, Cedar Hill Quarry, Lancaster County, Pennsylvania; yellow, white and blue brucite with a botryoidal habit was discovered in Qila Saifullah District of Province Baluchistan, Pakistan; and later in the Bela Ophiolite of Wadh, Khuzdar District, Province Baluchistan, Pakistan. Brucite has also occurred from South Africa, Italy, Russia, Canada, and other localities.
Reader's Guide
Synthetic brucite is mainly consumed as a precursor to magnesia (MgO), a useful refractory and thermal 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. Although generally deemed safe, brucite can be contaminated with naturally occurring asbestos fibers. In cement and concrete exposed to Mg2+ and SO2−4 ions simultaneously present in seawater, the precipitation of poorly soluble brucite contributes to enhance the formation of gypsum in sulfate attack. The precipitation of insoluble Mg(OH)2 helps drive the chemical equilibrium, exacerbating sulfate attack and forming gypsum and ettringite. However, brucite's small molar volume may clog the porous network, hindering diffusion of harmful species and delaying decalcification of C-S-H. The exact mechanism of brucite degradation remains debated; it is unclear if it causes expansion or not. Prolonged contact between seawater or Mg-brines and concrete may induce durability issues. The use of dolomite as aggregate in concrete with high alkali content can also cause brucite precipitation, driving the dedolomitization reaction, and consequently dolomite is prohibited as aggregate for concrete.
Did You Know?
- A fibrous variety of brucite is called nemalite.
- Brucite can be contaminated with naturally occurring asbestos fibers.
- The use of dolomite as aggregate in concrete is prohibited due to brucite precipitation driving the dedolomitization reaction.
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