Facts about Pyrite
The pyrite/marcasite pair is probably the second most well-known pair of polymorphs, after the diamond/graphite pair.
Adding to the confusion between marcasite and pyrite is the use of the word "marcasite" as a jewelry trade name.
The sulfur atoms in marcasite occur in similar pairs, and the formal oxidation states of the atoms in marcasite are the same as for those in pyrite.
Marcasite is metastable relative to pyrite and slowly changes to pyrite over time, or if heated.
Pyrites can show negative resistance and have been used experimentally in oscillator circuits as radio detectors.
The ferric iron in turn reacts with pyrite to produce ferrous iron and sulfuric acid.
Pyrite is often confused with the mineral marcasite (named from the Arabic word for pyrite), due to their similar characteristics.
Bravoite is a variety of pyrite enriched in nickel, with more than 50 percent substitution of Ni2+ for Fe2+.
Small, polished, faceted stones of pyrite may be inlaid in sterling silver, but they are erroneously called marcasite.
Marcasite is a polymorph of pyrite, which means they have the same chemical formula but different structures.
From the perspective of classical inorganic chemistry, which assigns formal oxidation states to each atom, pyrite is probably best described as Fe2+S22-.
Ironically, small quantities of actual gold are occasionally associated with pyrite.
Pyrite is often used to make necklaces, bracelets, and other types of jewelry.
Pyrite exposed to the environment during mining and excavation reacts with oxygen and water to form sulfuric acid.
