Pyrite, or iron sulfide (FeS₂), is a metallic mineral known for its brassy yellow color and high luster, often mistaken for gold, earning it the nickname "fool's gold." It crystallizes in the isometric system, commonly forming cubic, octahedral, or pyritohedral shapes. With a Mohs hardness of 6-6.5, it is relatively hard but brittle, making it unsuitable for faceted jewelry. Pyrite forms in a variety of geological environments, including hydrothermal veins, sedimentary rocks, and coal beds, with major sources in Spain, Peru, the United States, and China. It has industrial applications in sulfuric acid production and is also popular in mineral collections and decorative carvings.