Tsilaisite
A manganese-rich variety of elbaite tourmaline named for Tsilaisina, Madagascar.
Intro adapted from Wikipedia (CC BY-SA).
Tsilaisite is an IMA-recognized mineral species in the silicate class, with the chemical formula NaMn²⁺₃Al₆(Si₆O₁₈)(BO₃)₃(OH)₃(OH).
It crystallizes in the hexagonal crystal system (space group R3m). It is a member of the Tourmaline structural group.
Key properties: Mohs hardness 7; specific gravity 3.133; White streak; Vitreous luster; optically uniaxial.
IMA symbol Tsl, IMA status: approved, named in 2011.
Found in an aplitic dike in an LCT-type pegmatite.
It is found associated with Quartz, K-feldspar, plagioclase, elbaite, schorl. Tsilaisite.
The name refers to the Tsilaisina mine in the Sahatany Valley, Madagascar, from where the first Mn-rich tourmalines were described.