Magnesium hydroxide is a white powder or crystal with the chemical formula Mg(OH)₂. It is a common weak alkaline substance found in laboratories.
Brucite, the naturally occurring mineral form of Mg(OH)₂, possesses a layered structure of the CdI₂ type. Neutron diffraction studies have shown that within a single layer, each Mg²⁺ ion is surrounded by six OH⁻ ions; each OH⁻ group forms bonds with three Mg²⁺ ions in the same layer and makes contact with three OH⁻ ions in the adjacent layer.
The OH⁻ ions are oriented perpendicular to the layers.
Due to the electropositive nature of the Mg²⁺ ions, the protons are repelled toward the opposite side of the layer; consequently, no hydrogen bonds form between the layers, and the layers are held together by van der Waals forces. Mg(OH)₂ crystals are formed through the hydration of reactive MgO; even colloidal Mg(OH)₂ precipitated from magnesium salt solutions is revealed by X-ray diffraction analysis to consist of coarse crystals.
