Silver, Native

a mineral, one of the native elements. The chemical composition of native silver varies from nearly pure Ag, with admixtures constituting no more than 1.5 percent, to natural solid solutions of Au, Hg, Sb, Bi, or Cu in Ag. Varieties of native silver include küstelite (up to 10 percent Au), kongs-bergite, arquerite, and bordosite (up to 5, 13, and 30 percent Hg, respectively), animikite and allargentum (up to 11 and 15 percent Sb), chilenite (up to 5 percent Bi), and copper-bearing silver (up to tenths of a percent Cu). Native silver has a face-centered cubic structure. Although it occasionally occurs in the form of cubes and octahedrons, it is usually found as thin, irregular plates and scales, filiform or dendriform growths, irregular grains, or larger compact aggregates or nuggets. One plate-shaped nugget, found in Chañarcillo in northern Chile, weighed 1,420 kg. A freshly made fracture is white in color, and sometimes the surface is covered with a black film. Polished sections exhibit very high reflectivity. Native silver is soft and ductile; it has a hardness of 2.5 on Mohs’ scale and a density of 10,500 kg/m³.

Native silver occurs rarely in nature. It is formed in hydrothermal vein deposits in association with silver-bearing sulfides, calcite, quartz, fluorite, adularia, the minerals of Ag, Co, Ni, Bi, and U, and arsenides of cobalt and nickel. Commercial deposits of native silver are located in Kongsberg (Norway), Cobalt (Canada), and Schneeberg and Annaberg (German Democratic Republic) and in low-temperature veins in zones containing young volcanic rocks. Such veins can be found in North America (Cordilleras), Europe (Carpathians), Japan, and New Zealand.

Native silver associated with native gold occurs in the oxidation zone of, for example, lead-zinc, pyrite, and silver deposits (Rudnyi Altai, the Urals, and Dzhezkazgan in the USSR; Potosí in Bolivia).