Class : Sulfides and sulfosalts
    Subclass : Sulfides
    Crystal system : Cubic
    Chemistry : (Ni,Co)₃S₄
    Rarity : Rare

Siegenite belongs to the linnaeite group, named after the most common mineral in this group. This group, with the general formula X₃S₄ (with X = Co, Ni, Fe or [Co+Cu]), can be compared with that of spinels, with sulphur replacing oxygen; the octahedral facies is also the most common in both groups. The linnaeite group is composed of three solid solutions : Co (linnaeite in the strict sense) - Ni (polydymite) - Fe (greigite), the intermediate term being violarite. The solid solution [Co+Cu] is the only one to be incomplete and stops at carrollite. Siegenite is a rare cobalt sulfide from hydrothermal cobalt-nickel deposits, including veins and deposits in carbonate contexts. Its name comes from its discovery location : the Siegen mining region (Germany). Siegenite is bright gray to steel gray with a slightly pinkish hue. Very sensitive to alteration, siegenite gradually transforms into asbolane, which is black in color. It is sometimes an important ore of cobalt and nickel.

Main photo : Siegenite from Victoria Mine, Littfeld, Siegen, Germany © Norbert Stötzel

Twinning is known on {111}.

No fakes listed for this mineral species.