Bartelkeite
An exceptionally rare natural germanium compound, shown to share its structure with a high-pressure form of lawsonite.
Intro adapted from Wikipedia (CC BY-SA).
Bartelkeite is an IMA-recognized mineral species in the oxides & hydroxide class, with the chemical formula PbFe²⁺Ge(Ge₂O₇)(OH)₂·H₂O.
It crystallizes in the monoclinic crystal system (space group P2_1/m). It is a member of the Lawsonite structural group.
Key properties: Mohs hardness 4; specific gravity 5.36; White streak; Subadamantine luster; optically biaxial.
IMA symbol Btk, IMA status: approved, named in 1979.
Found as a very rare mineral in cavities in oxidized primary germanium ore from a dolostone-hosted hydrothermal polymetallic ore deposit.
It is found associated with Germanite, reniérite, tennantite, galena.
The mineral was named to honor Wolfgang Bartelke (b. 1949), German mineral collector and specialist in the minerals of Tsumeb, Namibia.