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Formula: Ba2Mn3+(VO4)2OH
Vanadate, barium- and
manganese- bearing mineral,
brackebuschite supergroup
Crystal System: Monoclinic
Specific gravity: 4.62 calculated
Hardness: 4½ to 5
Streak: Deep brownish red
Colour: Red-black
Environments
Metamorphic environments
Hydrothermal environments
Localities
At the type locality, the Shiromaru mine, Okutama-cho, Nishitama district, Tokyo Metropolis, Japan, tokyoite
occurs as small aggregates (250 µm) of irregular grains less than 15 µm in size. It is red-black, translucent, and has
a vitreous lustre and a dark brownish red streak. Tokyoite was found in an outcrop of an abandoned
manganese ore deposit that occurs in
chert blocks enclosed in
sandstone.
Tokyoite occurs in brecciated
braunite or in veinlets associated with
hyalophane or tamaite
(AM 91.1468).
At the Postmasburg area, Tsantsabane Local Municipality, ZF Mgcawu District Municipality, Northern Cape, South Africa,
samples of manganese-rich rock containing two compositional varieties of
tokyoite in association with noélbensonite were retrieved from a
drill core. The samples consist of fine-grained braunite,
hematite and hausmannite. Within
this material abundant vugs are observed that are filled with witherite,
baryte and barytocalcite. In
addition, arsenic-rich tokyoite, tokyoite and
noélbensonite occur in the centre of the vugs, in fine aggregates 0.1 to
1 mm in size. Individual arsenic-rich tokyoite grains are typically
20 to 200 microns in size. The outer walls of the vugs are lined with microcrystalline
K-feldspar, witherite and/or
sérandite. Textural evidence of the
barium-rich mineral phases in association with
arsenic-rich tokyoite suggest an epigenetic mode of formation of the
observed assemblages, caused by vanadium- and
arsenic- bearing alkali-rich fluids interacting with pre-existing
manganese-rich minerals
(CM 53.6.981-990).
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