Turtmannite
Turtmannite is an IMA-recognized mineral species in the silicate class, with the chemical formula Mn₂₅O₅(VO₄)₃(SiO₄)₃(OH)₂₀.
It crystallizes in the hexagonal crystal system (space group R-3c). It is a member of the Hematolite structural group.
Key properties: specific gravity 3.6–4; Colorless streak; Vitreous luster; optically uniaxial.
IMA symbol Tt, IMA status: approved, named in 2000.
Found in metamorphosed (upper greenschist facies) jacobsite-rich Fe-Mn ores in paleokarst.
It is found associated with Jacobsite, kutnohorite, baryte, tephroite, spessartite.
The name refers to the Turtmann Valley that hosts the type locality.
Index entry. This entry combines official IMA/RRUFF species data with published physical-property data — a full written entry hasn’t been published yet.
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