Native bismuth

NATIVE BISMUTH (EN: native bismuth; DE: gediegenes Wismut; FR: bismuth natif; ES: bismuto nativo; RU: висмут самородный) is the mineral of the class of the native elements, Bi. There are noted the non-significant impurities of Sb, Pb, Te, As, S, and so on. The native bismuth crystallizes into the trigonal crystal system. The crystal structure is sub-layered; the layers are represented as the packets, which are consisting of the two contiguous slightly undulating meshes of the Bi atoms, which are bonded covalently. The crystals of the native bismuth are very rare; usually it forms the grains of the irregular shape, often the teardrop-shaped isolates, feathery and spear-shaped dendrites, continuous granular masses, foliose and tabular aggregates. There are frequent the polysynthetic twins.

There may be encountered the pseudomorphs of the native bismuth on the bismuthine. The colour of the native bismuth is silvery-white, with the pinkish tinge on the fresh fracture, and with the brown tinge on the old fracture; there is characteristic the yellowish-red iridescence. The native bismuth is easily cut using the knife. The cleavage is perfect along one direction. The hardness is 2.5. The density is 9750 ± 50 kilograms per cubic metre. The native bismuth is low-melting (the temperature of the melting point is 270 degrees Celsius). The native bismuth is the typical semimetal; its electric resistivity is approximately 1.2 • 10^-6 ohm-metres, and strongly depends on the impurities (Te is the donor impurity, Pb, Sn are the acceptor impurities). The Sb admixture changes the band structure; the Bi-Sb alloys with the content of Sb of 5-40% are semiconductors.

The native bismuth is the hydrothermal mineral, although it may also be encountered within the pegmatites and erupted rocks (as the accessory mineral). Judging by the forms of the isolates, it was formed in the series of the cases under the conditions, when the temperatures exceeded the temperature of the melting point, that is, within the droplet-liquid phase. Native bismuth exists within the quartz-veinous and greisen deposits of tin and tungsten (Bukuka, Belukha, and Ingoda within the Transbaikalia; Karaoba within the Kazakh SSR; and abroad, Tasna within Bolivia, Kingsgate, Chillagoe within Australia, and so on), within the hydrothermal tin and tin-polymetallic deposits (Oruro, Chorolque, and others within Bolivia; Akenobe, Ikuno, and others within Japan), within the arsenic-bismuth deposits (Ustarasay within the Central Asia), and within the skarns. The classic type of the native bismuth deposits is the low-temperature hydrothermal deposits, the so-called five-element formations, within which the native bismuth is associated with the Co and Ni arsenides (the Ore Mountains within the East Germany and Czechoslovakia; the Cobalt within Canada, and the multitude of others). The native bismuth belongs to the composition of the bismuth ores. Despite the broad distribution within the nature, the native bismuth relatively rarely forms the industrial clusters, which are similar to those clusters, which have been uncovered, for example, at the Ore Mountains, within Bolivia and Australia. The native bismuth is beneficiated analogously to the bismuthine.