Tephroite forms a series with the olivine mineral fayalite. Tephroite is the manganese rich member of the series and fayalite is the iron rich member with a formula of Fe 2 SiO 4 . Unlike fayalite which is more commonly found in volcanic rocks, tephroite is a contact metamorphic and hydrothermal replacement mineral. Luster is vitreous to greasy.
Crystals are transparent to translucent.
Crystal Habits include short prismatic to blocky crystals Also massive, granular and compact. Cleavage is good in two directions at 90 degrees. Fracture is uneven to conchoidal. Streak is off white to gray. Associated Minerals are calcite , quartz , spessartine , rhodonite , willemite , franklinite and pyroxmangite .