The pyrite/marcasite pair is probably the second most well-known pair of polymorphs, after the diamond/graphite pair.
Pyrite (or iron pyrite) is the most common of the sulfide minerals.
Such auriferous pyrite is a valuable ore of gold.
Adding to the confusion between marcasite and pyrite is the use of the word "marcasite" as a jewelry trade name.
The name pyrite is from the Greek word pyr, meaning "fire."
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.
Pyrite is brittle and has a slightly uneven, conchoidal fracture.
Pyrites can show negative resistance and have been used experimentally in oscillator circuits as radio detectors.
The sulfur atoms in pyrite occur in pairs, with clear S-S bonds.
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.
Whereas pyrite has S2 subunits, arsenopyrite has AsS units.
Arsenopyrite is a mineral with the chemical formula FeAsS.
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.
Pyrite is often used in jewelry such as necklaces and bracelets.