Ceramics-Silikáty 52, (1) 49 - 53 (2008)

Natural Pb₉Sb₈S₂₁, known as the mineral semseyite, was newly identified in the Kutná Hora ore district, Central Bohemia, Czech Republic. Chemical compositional data and X-ray powder diffraction data are presented in the paper. Chemical composition was determined by electron microprobe analysis which revealed increased content of Bi and Se. Unit cell parameters have been calculated. Semseyite has a monoclinic unit cell with a = 13.626(18), b = 11.960(12), c = 24.325 (45), β = 105.83 (11), V = 3813.96 A³ , space group C2/c. Lenghtening of a and b parameters compared to the published structure is accompanied by shortening of the c parameter reflecting the actual chemical composition.