Chalcopyrite,Copper,iron sulphide.CuFeS2. Geufron mine, Central Wales Orefield. A nugget of massive chalcopyrite with a fractured face displaying the usual pale yellow colour. The rest of surface of the specimen has weathered and taken on the green colour of copper exposed to air. The chalcopyrite does not have any discernible crystals and is intermixed with a minor amount of quartz and very small pieces of host rock.