Brucite: Gemstone Information
Brucite is Mg(OH)2 and forms transparent tabular crystals, platy orfoliated or granular masses of the trigonal system with one direction of perfect cleavage, hardness 2.5 and SG 2.39. The RI for the ordinary and extraordinary rays is 1.56–1.59 and 1.58–1.60, uniaxial positive (anomalously biaxial) with birefringence 0.010–0.020. The colour ranges from white through pale green or blue to brownish red and brown. Brucite occurs as a common alteration of periclase in marble and in low-temperature hydrothermal veins in metamorphic limestones and chlorite schists. Good examples are found at Asbestos,Quebec, Canada.