Tephroite: Gemstones Information

Tephroite is Mn2SiO4 and forms characteristically short prismatic or anhedral transparent to translucent olive green to reddish brown crystals or compact masses of the orthorhombic system with hardness 6 and SG 4.15.The RI for the alpha, beta and gamma rays is 1.770–1.788, 1.807–1.810 and 1.817–1.825, biaxial negative with birefringence 0.037–0.047. Tephroite occurs in Fe–Mn ore deposits and related skarns, also in metamorphosed Mn-rich sediments. Ornamental-quality material is found at Franklin and Sterling Hill, Ogdensburg, Sussex County, New Jersey, USA.