Brucite
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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... Wikipedia
Chemical formula: Mg(OH)2
Cleavage: Perfect on
Color: White, pale green, blue, gray; honey-yellow to brownish red
Crystal class: Hexagonal crystal family (3m); H-M symbol: (3 2/m)
Crystal habit: Tabular crystals; platy or foliated masses and rosettes – fibrous to massive
Crystal system: Trigonal
Diaphaneity: Transparent