Periclase: Gemstone Information

Periclase is MgO and occurs as masses or small octahedra and other forms of the cubic system with a perfect cleavage in one direction, hardness 5.5 and SG 3.56–3.68. The RI is 1.735–1.745. Periclase is usually colourless or white to pale yellow, green or brown but gem-quality adularescent orange-yellow material is known from Mt Saint Hilaire,Quebec, Canada.