Extremely rare mineral from Tsumeb! The mineral, that is only known from this locality worldwide, was labeled as "RRR: extremely rare: single occurrence with less than 10 specimens known" and "brown aggregates of minute crystals on the type specimen" in G.Gebhard Tsumeb II book (1999) when the mine was already closed (1996), so new discoveries will not take place in the future. This sample was in Gebhard collection and it's part of the type specimen, as proved by the label enclosed. Second oxidation zone. It occurs in this specimen as at least 5 typical brown balls on matrix. — Photo: David Hospital · CC BY-SA 4.0
Gerdtremmelite
Gerdtremmelite is an IMA-recognized mineral species in the arsenate class, with the chemical formula ZnAl₂(AsO₄)(OH)₅.
It crystallizes in the triclinic crystal system.
Key properties: specific gravity 3.3; White streak; Adamantine luster.
IMA symbol Gtm, IMA status: approved, named in 1983.
A very rare secondary mineral from the deep oxidized zone of a dolostone-hosted hydrothermal polymetallic ore deposit.
It is found associated with Powellite, betpakdalite, scorodite, wilhelmkleinite, adamite, hematite, kaolinite, quartz.
The mineral was named to honor Dr. Gerd Tremmel (1940–), of Overath-Steinbrück, Germany, who submitted the mineral for identification.