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This article is about mineral. For resident of Tokyo, see Tokyojin and Edokko.
Category Vanadate mineral
(repeating unit)
Strunz classification 8.BG.05
Crystal system Monoclinic
Crystal class Prismatic (2/m)
(same H-M symbol)
Unit cell a = 9.104 Å, b = 6.132 Å
c = 7.895 Å; β = 112.2°; Z = 2
Color Reddish black
Crystal habit Occurs as splotchy, anhedral crystals forming inclusions
Cleavage None observed
Mohs scale hardness 4.5 - 5
Luster Vitreous
Streak Deep brownish red
Diaphaneity Translucent
Specific gravity 4.62 calculated
Optical properties Biaxial (?)
Refractive index a=1.99, g=2.03
Birefringence 0.0400
Pleochroism Distinct, reddish orange to dark brownish red
References [1][2][3]

Tokyoite is a rare barium manganese vanadate mineral with the chemical formula: Ba2(Mn3+,Fe3+)OH(VO4)2. It is the manganese analogue of the iron rich gamagarite[2] and the barium analogue of the lead vanadate, brackebuschite.[3]

It occurs in low-grade metamorphosed sedimentary manganese ore deposits[1] associated with hyalophane, braunite and tamaite.[3]

It was first reported for an occurrence in the Shiromaru Mine, Okutama, Tama district, Tokyo Prefecture, Kanto Region, Honshu Island, Japan and approved by the IMA in 2003.[2] It has been found in two mines in Italy and one in Japan, for which it was named.[1]