Semseyite Locality: Herja Mine (Kisbánya), Baia Mare (Nagybánya) , Maramures County , Romania ( Locality at mindat.org ) Size: 3 x 2.3 x 2.2 cm. A fine cluster of radial Semseyite crystals with superb metallic luster and brightness. The main cluster of well-terminated and bladed 1.4 cm crystals all line up in an undulating fan that looks somewhere between a crown and the fan of a peacock's tail. This is the type locality for the species, in 1881. Ex. Charlie Key stock. — Photo: Robert M. Lavinsky · CC BY-SA 3.0
Semseyite
A rare monoclinic lead-antimony sulfosalt of the plagionite group.
Intro adapted from Wikipedia (CC BY-SA).
Semseyite is an IMA-recognized mineral species in the sulfosalt class, with the chemical formula Pb₉Sb₈S₂₁.
It crystallizes in the monoclinic crystal system (space group C2/c).
Key properties: Mohs hardness 2.5; specific gravity 6.03; Black streak; Metallic, tarnishes to dull luster; optically biaxial.
IMA symbol Ssy, grandfathered status — known before the IMA’s founding, named in 1881.
Found in hydrothermal veins formed at medium temperature.
It is found associated with Sorbyite, jamesonite, bournonite, zinkenite, guettardite, jordanite, diaphorite, sphalerite, galena, pyrite, chalcopyrite, tetrahedrite, bournonite.
In honor of Andor von Semsey (1833–1923), a Hungarian nobleman much interested in minerals.