| Semseyite | |
| Category: | Sulfosalt mineral |
| Formula: | Pb9 Sb 8 S21 |
| Imasymbol: | Ssy[1] |
| Strunz: | 2.HC.10d |
| System: | Monoclinic |
| Class: | Prismatic (2/m) (same H-M symbol) |
| Symmetry: | C2/c |
| Unit Cell: | a = 13.64 Å, b = 11.96 Å c = 24.46 Å; β = 105.87°; Z = 4 |
| Color: | Dark gray to black |
| Habit: | Tabular, elongated prismatic crystals, commonly twisted; rosettelike groups |
| Cleavage: | Perfect on |
| Tenacity: | Brittle |
| Mohs: | 2.5 |
| Luster: | Metallic |
| Diaphaneity: | opaque |
| Gravity: | 6.15 |
| References: | [2] [3] [4] |
Semseyite is a rarely occurring sulfosalt mineral and is part of the class of lead antimony sulfides. It crystallizes in the monoclinic system with the chemical composition Pb9Sb8S21. The mineral forms dark gray to black aggregates.
Semseyite was first described for an occurrence in the Felsöbánya mine in Baia Sprie, Romania in 1881 by József Sándor Krenner (1839–1920). The mineral was named after Hungarian mineralogist Andor von Semsey (1833–1923).
Semseyite forms in hydrothermal solutions at temperatures between 300 and 350 °C.[5] It occurs in association with bournonite, jamesonite, sphalerite, zinkenite, sorbyite, guettardite, jordanite, diaphorite, galena, pyrite, chalcopyrite, tetrahedrite, arsenopyrite and siderite.[2]