Iron sulfides are chemical compounds made up of iron and sulfur. They are commonly found in nature, often in sedimentary rocks and as a result of biological processes. The most well-known iron sulfide is pyrite, also known as "fool's gold," due to its metallic luster and yellow hue. Other types include marcasite and troilite. These compounds play a significant role in various geological and environmental processes. For instance, iron sulfides can influence the availability of nutrients in soil and water systems. They are also important in the study of geochemistry and mineralogy, helping scientists understand the Earth's history and the formation of minerals.