Lehmannite
Lehmannite is an IMA-recognized mineral species in the arsenate class, with the chemical formula Na₁₈Cu₁₂TiO₈(AsO₄)₈FCl₅.
It crystallizes in the monoclinic crystal system (space group C2/m). It is a member of the Arsmirandite structural group.
Key properties: Mohs hardness 4.5; specific gravity 3.676; Grayish green with olive hue streak; Strong vitreous luster.
IMA symbol Leh, IMA status: approved, named in 2018.
Forms as a sublimate around an active volcanic fumarole.
It is found associated with Arsmirandite, hematite, sanidine, sylvite, halite, tenorite, cassiterite, rutile, and 40 other species.
The mineral was named to honor Johann Gottlob Lehmann (1719-1767) Academician of the Royal Prussian Academy of Sciences (1754) and the Imperial Russian Academy of Sciences (1761).