Abstract
The presence of clausthalite in the area of old mining works near Dziećmorowice in the Sowie Mts (SW Poland) is reported here for the first time. The identification of the clausthalite is based on macro- and microscopic observations, reflectance measurements, chemical analyses and X-ray diffraction data. The clausthalite, together with uraninite, forms veinlets in a breccia comprising <50% calc-silicate rock fragments. Different polishing hardnesses suggest some variation in the mineral structure of individual clausthalite grains. Chemical spot analyses do not reveal elements other than Pb and Se though calculated unit-cell parameters may suggest minor substitution of S for Se.