Iron Pyrite (Fool's Gold)

Iron pyrite, commonly known as fool's gold due to its misleading gold-like appearance, is a sulfide mineral with the chemical formula FeS₂. Pyrite consists of iron and sulfur, forming an iron sulfide. It crystallizes in the isometric system, typically forming cubes, pyritohedrons, or an octahedral structure, which contributes to its similar appearance to gold.

Pyrite forms in a variety of geological environments. It can crystallize during the cooling of magma, in high-temperature hydrothermal veins, and in sedimentary rocks such as shale and coal beds, where it often forms as framboids (spherical aggregates of crystals). Pyrite is well-known for its metallic luster and pale brass-yellow hue, which gives it a superficial resemblance to gold, hence the nickname "fool's gold." However, unlike gold, pyrite is brittle, and small grains or thin flakes will break instead of bending. It has a Mohs hardness of about 6 to 6.5 and a blackish-green streak.

Historically, pyrite has been used in flintlock firearms to produce the spark necessary to fire the gun. Despite its lack of precious metal value, pyrite has several industrial uses today. It is used to produce sulfur dioxide for the paper industry and is also a source of sulfuric acid. Pyrite is found worldwide, with notable deposits in Italy, Spain, Kazakhstan, the United States (Illinois, Pennsylvania, and Missouri), and Peru.