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Formula: NaFe3+3(Al4Mg2)(Si6O18)(BO3)3)(OH)3)O
Cyclosilicate (ring silicate), tourmaline group, forms a complete
substitution series from oxy-schorl via
oxy-dravite and bosiite to
povondraite, limited substitution series between
oxy-schorl and bosiite
(HOM)
Crystal system: Trigonal
Specific gravity: 3.23 measured, 3.26 calculated
Hardness: 7
Streak: Pale brown
Colour: Dark brown to black
Luminescence: No fluorescence under UV
Common impurities: Ca,Fe(II)
Environments
Localities
At the type locality, the Darasun mine, Vershino-Darasunskiy, Tungokochensky District, Zabaykalsky Krai, Russia,
bosiite formed as a hydrothermal phase in a gold-bearing
quartz vein spatially related to a
granodiorite-porphyry
intrusion. Ores of this deposit are enriched in sulphides. Bosiite is intimately associated with other
tourmalines. The first
tourmaline generation is bosiite, which is followed by a second
generation of oxy-dravite and a third generation of
dravite. Bosiite also coexists with
quartz and pyrite; further associated
minerals in the vein are gangue minerals
(quartz, calcite and
dolomite), sulphides (pyrite,
arsenopyrite, chalcopyrite,
pyrrhotite, tetrahedrite,
sphalerite and galena) and
native gold. Crystals of bosiite are dark brown to black with a pale brown
streak
(EJM 28.581–591).
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