Kirchhoffite
Kirchhoffite is an IMA-recognized mineral species in the silicate class, with the chemical formula CsBSi₂O₆.
It crystallizes in the tetragonal crystal system (space group I4_1/acd).
Key properties: Mohs hardness 6–6.5; specific gravity 3.62; White streak; Vitreous luster; optically uniaxial.
IMA symbol Khf, IMA status: approved, named in 2009.
Found in a massif composed of a variety of granitic, alkaline granitic and syenitic pegmatites, various hydrothermal rocks (albitites, fenites) and carbonatites.
It is found associated with Quartz, pectolite, and subordinate fluorite, sokolovaite, baratovite, aegirine, polylithionite, stillwellite-(Ce), neptunite, pekovite, senkevichite.
The mineral was named to honor Professor Gustav Robert Kirchhoff (1824-1887), the German physicist at the universities of Breslau and Berlin.