Marcasite is a mineral composed of iron sulfide, often found in sedimentary rocks. It has a metallic luster and a pale brass-yellow color, resembling pyrite, which is commonly known as "fool's gold." Marcasite typically forms in low-temperature environments and can be found in various geological settings, including coal deposits. This mineral is often used in jewelry and decorative items due to its attractive appearance. However, marcasite can be brittle and may tarnish over time, making it less durable than other gemstones. Its unique properties and historical significance make it a subject of interest for collectors and mineral enthusiasts.