Marcasite is an iron sulfide mineral with an orthorhombic crystal structure. It is very brittle and unsuitable for jewelry. What we call “marcasite” in jewelry is actually pyrite – “fools gold” – that has been faceted to imitate diamonds. Popular from around 1700 onward, marcasite is usually found mounted in silver. Because of its golden yellow color and metallic luster, Marcasite has remained popular in higher-quality fashion jewelry. In antique jewelry, marcasite can be distinguished from cut steel faux gems because marcasites are usually bead or prong-set as a gemstone would be and cut steel is riveted.