Tephroite

Formula: Mn₂SiO₄

Origin of name: from Greek for ash- gray coloured

Crystal system: Orthorhombic

Crystal class: 2/m 2/m 2/m

Twinning: Uncommon on {110}, polysynthetic, rare trillings

Unit cell: a = 4.76, b = 10.2, c = 5.98

Colour: Gray, olive-green, bluish green, red, reddish brown

Diaphaneity: Transparent to translucent

Luster: Vitreous to greasy

Habit: Crystals short prismatic, modified, elongated along c-axis, disseminated grains, massive, compact

Hardness: 6

Specific gravity: 4.11

Cleavage: 2; {010} distinct, {001} imperfect

Tenacity: Conchoidal to uneven fracture, brittle

Streak: Pale gray

Synonyms/varieties:

Comments: series with fayalite