Galena, lead-sulphide (PbS), by far the most important ore of lead (q.v.), is a lead-grey metallic mineral, tarnishing somewhat on exposure, crystallising in the Cubic system, in cubes or in combinations of the cube and regular octahedron, or occurring massive. Its hardness being 2.5, it will mark paper. Its specific gravity is 7.3 to 7.6. In composition it is about 86.6 per cent. lead and 13.4 sulphur; but there is generally a proportion of silver (q.v.) present. When galena is sufficiently argentiferous, the precious metal is extracted by Pattinson's process. Galena occurs in veins, abundantly in clay-slate in Cornwall and Devon, associated with ores of copper and zinc, in the Carboniferous Limestone of Lanark, Derby, etc., and in various localities in France, Germany, Belgium, and the United States.