Formula: Pb9Sb8S21
Sulfosalt, plagionite group
Specific gravity: 6.08
Hardness: 2½
Streak: Black
Colour: Steel-grey to black

Hydrothermal environments

Semseyite occurs in hydrothermal veins formed at moderate temperature, associated with sorbyite, jamesonite, bournonite, zinkenite, guettardite, jordanite, diaphorite, sphalerite, galena, pyrite, chalcopyrite, tetrahedrite, bournonite, arsenopyrite and siderite.

At the Van Silver Property, Vancouver Mining Division, British Columbia, Canada, semseyite has been observd in co-deposition with fizelyite and on calcite. More frequently it appears on quartz, pyrite and sphalerite.

At Yaogangxian, Hunan, China, semseyite is associated with freibergite, and stannite.

Common impurities: Ag,Cu,Fe