What is "bartelkeite"

n. (context mineral English) A monoclinic mineral containing germanium, iron, lead, and oxygen.

Bartelkeite is an exceptionally rare mineral, one of scarce natural germanium compounds. The formula was originally assumed to be PbFeGeO, bartelkeite was later shown to be isostructural with a high-pressure form of the mineral lawsonite. Thus, its correct formula is PbFeGe(GeO)(OH)•HO. Bartelkeite and mathewrogersite are minerals with essential (dominant) lead, iron and germanium. Both come from Tsumeb, Namibia - a world's "capital" of germanium minerals.