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Tusionite

Tusionite
Category	Borate mineral
Chemical formula	Mn Sn(B O_{3_)₂}
Identification
Color	Colorless, light yellow to yellow brown
Crystal habit	Thin platy crystals in rosettes
Crystal system	Trigonal
Cleavage	[001] Perfect
Mohs Scale hardness	5-6
Luster	Vitreous
Refractive index	nω = 1.854 nε = 1.752
Optical Properties	Uniaxial (-)
Birefringence	δ = 0.102
Streak	white
Specific gravity	4.73
Diaphaneity	Translucent
References	^[1]^[2]^[3]

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.

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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.