Tokyoite

Formula: Ba₂Mn₃(VO₄)₂OH

Origin of name: Named after the prefecture of occurrence, Shiromaru Mine, Okutama, Nishi-Tama-gun, Tokyo Prefecture, Kanto Region, Honshu Island, Japan

Crystal system: Monoclinic

Crystal class: 2/m

Twinning: 

Unit cell: a = 9.10, b = 6.13, c = 7.89, β = 112.2°

Colour: Black-red

Diaphaneity: Translucent

Luster: Vitreous

Habit: Small aggregates of irregular grains

Hardness: 4.5-5

Specific gravity: 4.62

Cleavage: Not observed

Tenacity: 

Streak: Deep brownish red

Synonyms/varieties:

Comments:  Member of the brackebuschite group. Found in metamorphosed low-grade sedimentary manganese ore