Argentite, a silver sulfide mineral, is an important constituent of silver ore deposits. It contains 87% silver, and forms blackish-gray coatings or masses with a metallic luster and a shining black STREAK. Characteristic is the ease with which it is cut. Argentite is stable only above 179 deg C; thus, although few crystals found appear outwardly to be isometric, they are actually composed of acanthite, a chemically identical paramorph belonging to the monoclinic system. Argentite's hardness is 2 - 2.5 and specific gravity is 7.2-7.4.