This is the cluster of pyrrhotite crystals with calcite. Dimensions: 3.1 x 2.6 x 2.2″ (8 x 6.7 x 5.6cm). Weight – 8oz (226 grams). Origin: Russia, Dalnegorsk.
Some information about pyrrhotite:
Pyrrhotite is an iron sulfide mineral. It is a nonstoichiometric variant of FeS, the mineral known as troilite. Pyrrhotite is also called magnetic pyrite, because the color is similar to pyrite and it is weakly magnetic. The magnetism decreases as the iron content increases, and troilite is non-magnetic.
The name pyrrhotite is derived from Greek pyrrhos, flame-colored.
Pyrrhotite has been linked to crumbling concrete basements in Quebec and Connecticut when local quarries included it in their concrete mixtures. The iron sulfide it contains can react with oxygen and water over time to cause swelling and cracking.