Natural arsenides

NATURAL ARSENIDES (EN: arsenides; DE: Naturarsenide; FR: arseniures naturels; ES: arseniuros naturales; RU: арсениды природные) are the class of minerals, namely, the compounds of metals (iron, cobalt, nickel, copper, silver, platinum) with arsenic. It includes 15 minerals, among which there prevail the compounds of iron, cobalt, and nickel.

The one third part of the natural arsenides (domeykite Cu3As, arsenargentite Ag3As, and others) are similar according to their structure and properties to those of the intermetallic compounds. The others are characterized by the donor-acceptor bonds between the metal and arsenic, and are more analogous to the sulphides. The main cations are isomorphically mutually substituted, especially within the Co-Ni-Fe series. They divide the natural arsenides, taking into account the type of the anion, into the two sub-classes: the compounds with As3- (nickeline NiAs, and others), and the ones with the complex anionic radicals [As2]2-, [As2]4- (loellingite FeAs2, rammelsbergite NiAs2, safflorite (Co,Fe)As2, and others), and [As4]4- (skutterudite, chloantite, smaltine). For the first ones there are characteristical the coordinative structures, for the natural arsenides with the complex radicals there are characteristical the insular structures. They crystallize into the various crystal systems. The crystals are rare, there are characteristical the granular aggregates. The prevailing coloration is tin-gray, they are opaque; the lustre is metallic. The hardness is 4-6.5 (more for the arsenides with insular structure). The density is from 5500 to 10500 kilograms per cubic metre. There are characteristical the semiconductor properties.

Natural arsenides are the typical hydrothermal minerals, which are associated with the quartz-carbonatic veins, they may be found less often within the magmatic deposits, which are associated with the basic and ultrabasic rocks, and also within the deposits of the other types (iron ore, gold ore, and lead-zinc ones). There are industrial the hydrothermal deposits of the nickel-cobalt and silver-nickel-cobalt ore formations, where natural arsenides (smaltine, rammelsbergite, nickeline, and others) are associated with various minerals of silver, bismuth, and uranium. Natural arsenides may serve as the source for the obtainment of cobalt, nickel, copper, platinum, silver, and arsenic. During the oxidation, they are substituted with the arsenates. The largest deposits of the natural arsenides within the USSR are located within the Western Siberia and Transcaucasia; abroad within the Canada, Iran, Morocco, Czechoslovakia, and East Germany.