Tokyoite

This article is about mineral. For resident of Tokyo, see Tokyojin and Edokko.

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^[3] and the barium analogue of the lead vanadate, brackebuschite.^[4]

Tokyoite
Tokyoite ore displayed at the Mining Museum of Akita University, Japan
General
Category	Vanadate mineral
Formula	Ba2(Mn3+,Fe3+)OH(VO4)2
IMA symbol	Tky[1]
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
Identification
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	[2][3][4]

It occurs in low-grade metamorphosed sedimentary manganese ore deposits^[2] associated with hyalophane, braunite and tamaite.^[4]

It was first reported for an occurrence in the Shiromaru Mine, Okutama, Tama district, Tokyo Prefecture, Kantō region, Honshu Island, Japan and approved by the IMA in 2003.^[3] It has been found in two mines in Italy and one in Japan, for which it was named.^[2]