Tephroite is a non-metallic manganese silicate mineral with the formula, Mn2SiO4.
It was first described for an occurrence at the Sterling Hill Mine and Franklin, New Jersey, USA. It occurs in iron-manganese ore deposits and their related skarns. It also occurs in metamorphosed manganese-rich sediments.
Tephroite has a hardness of 6 and a specific gravity of approximately 4.1, which is heavy for non-metallic minerals. Its name comes from the Greek tephros, "ash gray", for its color. It can also be found olive-green, greenish-blue, pink, or brown.