Marcasite
Image: Didier Descouens (CC BY-SA 4.0)
Mineral NameMarcasite
Chemical FormulaFeS₂
Mohs Hardness6
Crystal Systemorthorhombic
Lustermetallic
Streak Colordark grayish-black
Cleavagepoor/indistinct on {101}
Fractureuneven
Specific Gravity4.8
Colorspale bronze-yellow, tin-white, dark gray, iridescent
Transparencyopaque
Type LocalityCap Blanc Nez, France
Mineral GroupSulfides
Usescollector, minor ore of sulfur
Associated Mineralschalk, pyrite, galena, sphalerite, calcite
Raritycommon
Description
This specimen features a cluster of dark, metallic, somewhat iridescent marcasite crystals with blocky to tabular habits, growing on a light-colored chalk matrix.
Geological Context
Marcasite typically forms in low-temperature, acidic sedimentary environments, often found in chalk, limestone, and shale deposits, and can also occur in hydrothermal veins.
