Yellowish crystals of the extremely rare mineral feinglosite associated to also yellowish helmutwinklerite, both minerals typical of Tsumeb, but in this case from Vouves, Thasos Island, Macedonia Department, Greece. Both in a matrix of massive adamine. Specimen analyzed by SEM/EDS. — Photo: David Hospital · CC BY-SA 4.0
Helmutwinklerite
Helmutwinklerite is an IMA-recognized mineral species in the arsenate class, with the chemical formula PbZn₂(AsO₄)₂·2H₂O.
It crystallizes in the triclinic crystal system (space group P-1). It is a member of the Helmutwinklerite structural group.
Key properties: Mohs hardness 4.5; specific gravity 5.3; White streak; Vitreous, resinous on fracture surfaces luster; optically biaxial.
IMA symbol Hwk, IMA status: approved, named in 1979.
Found as a very rare secondary mineral in corroded tennantite ore from a dolostone-hosted hydrothermal polymetallic ore deposit.
It is found associated with Tennantite, willemite, quartz.
The mineral was named to honor Professor Helmut G.F. Winkler (1915–1980), University of Göttingen, Göttingen, Germany, for his contributions to petrology, mineralogy, and crystallography.