Semseyite - Encyclopedia

    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.

Semseyite in the World

The best specimens come from Romania, in particular from Herja (photo on the right © Fabre Minerals) and Baia Sprie, where semseyite is known in abundance in the form of brilliant centimetric crystals, united in rosettes. Very beautiful crystals have also been brought to light in the Peruvian mines of Julcani (Huancavelica) and Bolivian mines of Itos (Oruro).

Semseyite in France

In France, the English mine near Massiac (Cantal), has provided very beautiful rosettes of crystals at most centimetric, on mauve quartz, associated with crystals of honey baryte.


No known twin for this mineral species.

Fakes and treatments

No fake identified for this mineral species.

Hardness : 2.5
Density : 6.08
Fracture : Irregular
Streak : Black

TP : Opaque
RI : Not measurable
Birefringence : Not measurable
Optical character : None
Pleochroism : None
Fluorescence : None

Solubility : None

Magnetism : None
Radioactivity : None


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