Iron sulfide is a chemical compound made up of iron and sulfur, typically represented by the formula FeS. It occurs naturally in various forms, including pyrite and marcasite, and is often found in sedimentary rocks. Iron sulfide is known for its metallic luster and can appear in different colors, such as yellow or brown. This compound is significant in various industrial applications, including the production of sulfuric acid and as a catalyst in chemical reactions. Additionally, iron sulfide plays a role in environmental processes, particularly in the formation of acid mine drainage, which can impact ecosystems.