What is "tumchaite"

n. (context mineralogy English) A monoclinic-prismatic colorless mineral containing hydrogen, oxygen, silicon, sodium, tin, and zirconium.

Tumchaite, Na(Zr,Sn)SiO•HO, is a colorless to white monoclinic phyllosilicate mineral. It is associated with calcite, dolomite, and pyrite in the late dolomite-calcite carbonatites. It can be transparent to translucent; has a vitreous luster; and has perfect cleavage on {100}. Its hardness is 4.5, between fluorite and apatite. Tumchaite is isotypic with penkvilksite. The structure of the mineral is identified by silicate sheets parallel {100}, formed by alternation of clockwise and counterclockwise growing spiral chains of corner-sharing SiO tetrahedra. Tumchaite is named for the river Tumcha near Vuoriyarvi massif.