Tephroite is the manganese of the olivine minerals with the formula Mn 4. 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, United States. It occurs in iron-manganese ore deposits. It also occurs in metamorphosed manganese-rich sediments. It occurs in association with: zincite , franklinite, diopside, manganocalcite, banalsite and Sweden.
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 It can also be found olive-green, greenish-blue, pink, or brown. Other names for tephroite include mangan olivine and mangan peridot.