The Marcasite Group is composed of minerals with a similar orthorhombic structure and related chemistry. It is named for its most common member, marcasite. The general formula for this group is AX2. The A can be either iron, cobalt, nickel, osmium, iridium and/or ruthenium. The X can be either sulfur, arsenic, selenium and/or tellurium. Marcasite's formula is FeS2 for example. The members of the Lollingite Group are sometimes placed in the Marcasite Group. Marcasite is the only common member of this group.

The following are members of the Marcasite Group of minerals:
  • Anduoite (Ruthenium Osmium Arsenide)
  • Ferroselite (Iron Selenide)
  • Frohbergite (Iron Telluride)
  • Hastite (Cobalt Selenide)
  • Iridarsenite (Iridium Ruthenium Arsenide)
  • Kullerudite (Nickel Selenide)
  • Marcasite (Iron Sulfide)
  • Mattagamite (Cobalt Telluride)
  • Omeiite (Osmium Ruthenium Arsenide)
  • The Lollingite Group:
    • Costilbite (Cobalt Antimonide Sulfide)
    • Lollingite (Iron Arsenide)
    • Nisbite (Nickel Antimonide)
    • Rammelsbergite (Nickel Arsenide)
    • Safflorite (Cobalt Arsenide)
    • Seinajokite (Iron Nickel Antimonide Arsenide)
Popular Members of the Sulfides Class


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