Native metal
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A native metal is any metal that is found in its metallic form, either pure or as an alloy, in nature. Metals that can be found as native deposits include bismuth, cadmium, chromium, indium, iron, nickel, tellurium, tin, titanium, and zinc, as well as two groups of metals: the gold group, and the platinum group. The gold group consists of gold, copper, lead, mercury, and silver. The platinum group consists of platinum, iridium, osmium, palladium, rhodium, and ruthenium. Only gold, silver, copper and the platinum metals occur in nature in larger 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.
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.
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Occurrence
Gold
Gold is the most well known of the native metals. Mined gold is almost invariably portrayed as solid nuggets or veins. Indeed, 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
Platinum
The platinum mined in Colombia and Russia was found as nuggets and as small grains in placer deposits. It is usually found alloyed with iron, iridium, osmium, or palladium.
Copper
The term Old Copper Complex is used to describe an ancient North American civilization that utilized native copper deposits for weapons, tools, and decorative objects. This society existed around Lake Superior, where they found sources of native copper and mined them between 6000 and 3000 BC.[1] Copper would have been especially useful to ancient man as it was much stronger than gold, hard enough to be made into useful items such as fishhooks and woodworking tools, but still soft enough to be easily shaped, unlike meteoric iron.
Iron-Nickel
Most of the native iron on earth is actually not in fact "native", in the traditional sense, to earth. It mainly comes from iron-nickel meteorites that formed millions of years ago but were preserved from chemical attack by the vacuum of space, and fell to the earth a relatively short time ago. Metallic meteorites are composed primarily of the nickel-iron alloys: taenite - high nickel content, and kamacite - low nickel content. However, there are a very few areas on earth where truly native iron can be found.[2]
Others
All other native metals occur only in small quantities or are found in geologically special regions. For example metallic cadmium was only found at two locations. One place where metallic cadmium can be found is the Vilyuy River basin in Siberia[3]
GoldNugget.jpg | Native Copper Macro Digon3.jpg | SilverUSGOV.jpg |
Platinum nuggets.jpg | Widmanstatten-patterns-3.jpg | Naturkundemuseum Berlin - Gediegen Gold in Quarz, Eagles Nest Mine, Placer County, Kalifornien, USA.jpg Native gold partially embedded in the quartz ore |
References
- ^ Thomas C. Pleger (2000). "The Old Copper Complex of the Western Great Lakes". UW–Fox Valley Anthropology. http://www.uwfox.uwc.edu/academics/depts/tpleger/oldcopper.html. Retrieved 2007-08-15.
- ^ http://www.galleries.com/minerals/elements/iron/iron.htm
- ^ Fleischer, Michael; Cabri, LouisJ.; Chao, Georg Y.; Papst, Adolf (1980). "New Mineral Names". American Mineralogist 65: 1065–1070. http://www.minsocam.org/ammin/AM65/AM65_1065.pdf.
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