Tusionite

(repeating unit)MnSn(BO₃)₂IMA symbolTsn^[1]Strunz classification6.AA.15Crystal systemTrigonalCrystal classRhombohedral (3)
H-M symbol: (3)Space groupR3 (no. 148)IdentificationFormula mass291.26 gmColorColorless, light yellow to yellow brownCrystal habitThin platy crystals in rosettesCleavage[001] PerfectMohs scale hardness5–6LusterVitreousStreakwhiteDiaphaneityTranslucentDensity4.73Optical propertiesUniaxial (−)Refractive indexnω = 1.854 nε = 1.752Birefringenceδ = 0.102PleochroismOrange yellowReferences^[2][3][4][5]

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.

See also

• Classification of minerals
• List of minerals

References