The chemical formula of pyrite is FeS 2, isometric crystal system, space group is Fa3, a =  b =  c = 0.5390 nm, α =  β =  γ = 90°, Z = 4; light brass-yellow, often with a yellow-brownish tarnish, streaks are greenish-black, opaque, metallic luster; no cleavage, uneven fracture, brittle, Mohs hardness 6–6.5, relative density 4.9–5.27. Due to its light yellow color and bright metallic luster, it is often mistaken for gold, so it is also called “fool’s gold.”