Yellow crystal aggregates of tusionite, a very rare Mn-Sn borate, from one of the only three known localities worldwide: Řečice, Vysočina Region, Moravia, Czech Republic. — Photo: David Hospital · CC BY-SA 4.0
Tusionite
A rare manganese-tin borate — colorless to yellow-brown trigonal crystals.
Intro adapted from Wikipedia (CC BY-SA).
Tusionite is an IMA-recognized mineral species in the borate class, with the chemical formula Mn²⁺Sn(BO₃)₂.
It crystallizes in the hexagonal crystal system (space group R-3). It is a member of the Calcite-Dolomite structural group.
Key properties: specific gravity 4.73; Vitreous luster; optically uniaxial.
IMA symbol Tsn, IMA status: approved, named in 1982.
Of late-stage hydrothermal origin, rare in granite pegmatites, typically in miarolitic cavities.
It is found associated with Tetrawickmanite, hambergite, danburite, tourmaline, orthoclase, albite, quartz (along the upper Tusion River, Tajikistan); tourmaline, hambergite, danburite.
The name refers to its first-noted occurrence along the upper Tusion River, Tadjikistan.