Comparatively rare mineral, Cu₂FeSnS₄; sp. gr. 4.3–4.5; hardness 3–4; tetragonal; steel-grey with an olive-green tinge on fresh surfaces, which become yellowish on exposure; black streak; metallic lustre; crystals rare, cubes or tetrahedra, but normally the grains are irregular or massive; occurs in hydrothermal tin-ore deposits and in association with cassiterite, chalcopyrite, and wolframite, also in stanniferous sphalerite–galena ores, and associated with sphalerite, pyrrhotite, and galena.