Tephroite is the manganese endmember of the olivine group of nesosilicate minerals with the formula Mn<sub>2</sub>SiO<sub>4</sub>. A solid solution series exists between tephroite and its analogues, the group endmembers fayalite and forsterite. Divalent iron or magnesium may readily replace manganese in the olivine crystal structure.
It was first described for an occurrence at the Sterling Hill Mine and Franklin, New Jersey, United States.