Native metal

A native metal is any metal that is found in its metallic form, either pure or alloyed, in nature. Metals that can be found as native deposits singly or in alloys include aluminium, antimony, arsenic, bismuth, cadmium, chromium, cobalt, indium, iron, manganese, molybdenum, nickel, rhenium, selenium, tantalum, tellurium, tin, titanium, tungsten, vanadium, and zinc, as well as two groups of metals: the gold group, and the platinum group. The gold group consists of gold, copper, lead, aluminium, mercury, and silver. The platinum group consists of platinum, iridium, osmium, palladium, rhodium, and ruthenium. Amongst the alloys found in native state have been brass, bronze, pewter, German silver, osmiridium, electrum, white gold, and silver-mercury and gold-mercury amalgam.

Only gold, silver, copper and the platinum metals occur in nature in large amounts. Over geological time scales, very few metals can resist natural weathering processes like oxidation, which is why generally only the less reactive metals such as gold and platinum are found as native metals. The others usually occur as isolated pockets where a natural chemical process reduces a common compound or ore of the metal, leaving the pure metal behind as small flakes or inclusions.

Non-metallic elements occurring in the native state include carbon and sulfur. Silicon, a semi-metal, has been found in the native state on rare occasions as small inclusions in gold.

Native metals were prehistoric man's only access to metal, since the process of extracting metals from their ores, smelting, is thought to have been discovered around 6500 BC. However, they could be found only in relatively small amounts, so they could not be used extensively. So while copper and iron were known well before the copper age and Iron Age, they would not have a large impact on humankind until the technology to smelt them from their ores, and thus mass-produce them appeared.

Gold is the most well known of the native metals. Most gold is mined as native metal and can be found as nuggets, veins or wires of gold in a rock matrix, or fine grains of gold, mixed in with sediments or bound within rock. The iconic image of gold mining for many is gold panning, which is a method of separating flakes of pure gold from river sediments due to their great density. Native gold is the predominant gold mineral on the earth. It is sometimes found alloyed with silver and/or other metals but true gold compound minerals are uncommon, mainly a handful of selenides and tellurides.

Native silver occurs as elongated dendritic coatings or irregular masses. It may also occur as cubic, octahedral, or dodecahedral crystals. It may occur alloyed with gold as electrum. It often occurs with silver sulfide and sulfosalt minerals. Various amalgams of silver and mercury or other metals and mercury do occur rarely as minerals in nature. An example is the mineral eugenite (Ag11Hg2) and related forms. Silver nuggets, wires, and grains are relatively common, but there are also a large number of silver compound minerals owing to silver being more reactive than gold.

This page was last edited on 14 February 2018, at 14:41.
Reference: under CC BY-SA license.

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