pyrite

Pyrite is an iron sulfide mineral with the chemical formula FeS2. It is the most common sulfide mineral and is widely distributed in a variety of geological environments. Pyrite typically forms metallic, brass-yellow crystals with a pale brass color and a distinctive metallic luster. The mineral crystallizes in the isometric system, most commonly as cubic crystals, but also as pyritohedra and other forms. It has a hardness of 6–6.5 and a density of about 5.0 g/cm3. Its streak is greenish-black to brownish-black.

Occurrence and formation: Pyrite forms in igneous, metamorphic, and sedimentary rocks, often in hydrothermal veins, volcanic rocks, coal beds, and sedimentary diagenetic environments. It commonly occurs with chalcopyrite, sphalerite, galena, marcasite, quartz, and easily weathered to oxides and iron oxides. It can form by direct crystallization from sulfur-bearing fluids or by replacement in sedimentary layers.

Uses and hazards: Pyrite is an important source of sulfur and sometimes of iron, but it is not a major iron ore. It has historical uses as a source of sulfur for sulfuric acid and for its ability to produce sparks when struck, hence the name “fool’s gold.” It is popular among mineral collectors. Environmental concerns arise from oxidation of pyrite, which can generate acidic drainage (acid mine drainage) and iron oxides, especially when ore bodies are exposed to air and water. Fine pyrite dust can be hazardous if inhaled.