Tephroite is the manganese endmember of the olivine group of nesosilicate minerals with the formula Mn2SiO4.

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 occurs in association with: zincite, willemite, franklinite, rhodonite, jacobsite, diopside, gageite, bustamite, manganocalcite, glaucochroite, calcite, banalsite and alleghanyite.

Tephroite has a hardness of 6 and a specific gravity of approximately 4.1, which is heavy for non-metallic minerals.