Marcasite

Marcasite, often confused with its close relative pyrite due to their similar appearance, is a striking mineral known for its metallic luster and intricate crystal formations. Chemically, marcasite is an iron sulfide (FeS₂), just like pyrite, but it crystallizes in a different structure. This structural variation gives marcasite its unique properties and distinguishes it from pyrite in both appearance and behavior.

Marcasite typically exhibits a pale brass-yellow to silvery-white metallic sheen that can tarnish over time to display iridescent colors, such as gold, green, or blue. It often forms in fascinating shapes, including tabular, spear-like crystals or radiating, fibrous aggregates known as “cockscomb marcasite.” These formations make it a favorite among mineral collectors and jewelry enthusiasts.

Marcasite forms in low-temperature, high-pressure environments, often found in sedimentary rocks like limestone and shale, as well as in hydrothermal veins and coal beds. It commonly occurs alongside other sulfide minerals, such as galena and sphalerite. Major deposits of marcasite can be found in regions like France, the Czech Republic, Germany, and Peru, as well as parts of the United States.