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
CategoryVanadate mineral
Formula
(repeating unit)
Ba2(Mn3+,Fe3+)OH(VO4)2
IMA symbolTky[1]
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[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]

References

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  1. ^ Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine. 85 (3): 291–320. Bibcode:2021MinM...85..291W. doi:10.1180/mgm.2021.43. S2CID 235729616.
  2. ^ a b c Mindat
  3. ^ a b c Webmineral data
  4. ^ a b c 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