Tokyoite

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]

This article is about mineral. For resident of Tokyo, see Tokyojin and Edokko.
Tokyoite
General
CategoryVanadate mineral
Formula
(repeating unit)		Ba2(Mn3+,Fe3+)OH(VO4)2
Strunz classification8.BG.05
Crystal systemMonoclinic
Crystal classPrismatic (2/m)
(same H-M symbol)
Unit cella = 9.104 Å, b = 6.132 Å
c = 7.895 Å; β = 112.2°; Z = 2
Identification
ColorReddish black
Crystal habitOccurs as splotchy, anhedral crystals forming inclusions
CleavageNone observed
Mohs scale hardness4.5 - 5
LusterVitreous
StreakDeep brownish red
DiaphaneityTranslucent
Specific gravity4.62 calculated
Optical propertiesBiaxial (?)
Refractive indexa=1.99, g=2.03
Birefringence0.0400
PleochroismDistinct, reddish orange to dark brownish red
References[1][2][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, Kantō 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]

References
  1. Mindat
  2. Webmineral data
  3. Matsubara, Satoshi, et. al., Tokyoite, Ba2Mn3+(VO4)2(OH), a new mineral from the Shiromaru mine, Journal of Mineralogical and Petrological Sciences, V. 99, pp. 363-7, 2004
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