Ussingite: Gemstones Information

Ussingite is Na2AlSi3O8(OH) and forms transparent to translucent pinkto dark violet-red triclinic pseudocubic crystals or fine-gained compact masses with two directions of perfect cleavage, hardness 6– 7, SG 2.46–2.49. The RI for the alpha, beta and gamma rays is 1.503–1.504,1.506–1.508, 1.543–1.545, biaxial positive with birefringence 0.039.Ussingite occurs as a secondary mineral in pegmatites associated with sodalite syenite. At Mt Saint Hilaire, Quebec, Canada, ussingite is found in sodalite xenoliths in an intrusive alkalic gabbro-syenite complex.