Marcasite, is an Iron Sulfide, but physically and crystallographically distinct from pyrite Locality: Bell County, Texas Chemical Formula: FeS2 Crystal System: Orthorhombic, typically tabular crystals Specimen size: 1.5in x 1.25 in x 1 in Specimen weight: 25 grams In the Arthur E. Smith Collection, on display at Wheaton College, Wheaton, Illinois.