Class : Sulphides and sulfosalts
    Subclass : Sulfosalts
    Crystal system : Monoclinic
    Chemistry : Pb₉Sb₈S₂₁
    Rarity : Fairly common

Semseyite is a common lead-antimony sulfosalt in mid-temperature hydrothermal veins. Its name was given to it in honor of the Hungarian aristocrat Andor von Semsey, a former mineral collector (1833-1923). It is found, like the boulangerite, jamesonite, zinkenite or plagionite with which it is associated, in veins with a dominant stibnite invaded by lead fluids, or in veins with galena and sphalerite infiltrated by antimony fluids. Gray to black in color, it appears as lamellar crystals, elongated along [010] and flattened on {001}, sometimes twisted, often united in radiated aggregates. Semseyite weathers easily at outcrops giving mixtures of antimony oxides and lead oxides. Semseyite is locally mined as an ore of antimony and lead. At La Rode (Ally, Haute-Loire, France) for example, it constituted an important ore of lead and silver.

No known twin for this mineral species.

No fake identified for this mineral species.