PYRRHOTITE, MORO VELHO OURO PRETO, BRAZIL (small cabinet)

Pyrrhotite, derived from the Greek word for "flame-colored," is an uncommon iron sulfide mineral represented by the formula Fe(1-x)S, where x ranges from 0 to 0.125. This mineral is a nonstoichiometric form of FeS, commonly referred to as troilite. Often called magnetic pyrite due to its color resemblance to pyrite, pyrrhotite exhibits weak magnetism that diminishes with increasing iron content, while troilite remains non-magnetic. Typically, pyrrhotite appears tabular with a brassy or bronze hue and a metallic sheen. It is commonly found in association with mafic igneous rocks such as norites and can form from the alteration of pyrite during metamorphic events.