semseyite
Semseyite is a rare lead antimony sulfosalt mineral with the chemical formula Pb4Sb6S13. It was first described in 1908 and named in honor of Hungarian mineralogist Géza Semsey. Semseyite typically occurs as small, prismatic to acicular crystals or as massive aggregates. Its color is dark steel-gray to black. It has a metallic luster and is opaque. The mineral is relatively soft, with a Mohs hardness of 3.5, and has a specific gravity of approximately 5.7. Semseyite is an uncommon mineral found in hydrothermal veins and often associated with other lead and antimony minerals, as well as other sulfosalts. Notable occurrences include the Felsőtárkány mining district in Hungary, the Botes mine in Romania, and various localities in Mexico and Japan. Due to its rarity, semseyite has limited economic significance, but it is of interest to mineral collectors and geologists studying ore-forming processes. Its crystallography is monoclinic. The presence of both lead and antimony in its structure makes it a member of the sulfosalt group of minerals.