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Category Borate minerals
(repeating unit)
Strunz classification 6.AA.15
Crystal system Trigonal
Crystal class Rhombohedral (3)
H-M symbol: (3)
Space group R(3)
Color Colorless, light yellow to yellow brown
Crystal habit Thin platy crystals in rosettes
Cleavage [001] Perfect
Mohs scale hardness 5-6
Luster Vitreous
Streak white
Diaphaneity Translucent
Specific gravity 4.73
Optical properties Uniaxial (-)
Refractive index nω = 1.854 nε = 1.752
Birefringence δ = 0.102
References [1][2][3][4]

Tusionite is a rare colorless to transparent to translucent yellow brown trigonal borate mineral with chemical formula: MnSn(BO3)2. The mineral is composed of 18.86% manganese, 40.76% tin, 7.42% boron, and 32.96% oxygen. It is a late stage hydrothermal mineral and occurs rarely in granite pegmatites in miarolitic cavities.

Tusionite was named for the location where the mineral was first discovered and described in 1983 in the Tusion River Valley in the Pamir Mountains of Tajikistan. Tusionite has also been reported from Recice in the Czech Republic and in pegmatites at Thomas Mountain, Riverside County, California.

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