A structural phase transition, conductivity and dielectric permittivity anomalies, together with a polarization hysteresis loop which collapses above the Curie temperature (~150 ¿C) provide converging lines of evidence for ferroelectricity in the single and polycrystalline natural samples of chalcocite, Cu2S, investigated. Chalcocite is an important ore of copper, and its electrical properties are a factor both in exploration for the mineral and processing the ore. ¿ American Geophysical Union 1987