We encourage you to double-check that information independently as populations and price guides are subject to change. The binary gold halides , such as AuCl , form zigzag polymeric chains, again featuring linear coordination at Au. The use of gold crowns in more prominent teeth such as incisors is favored in some cultures and discouraged in others. Archived from the original on 10 November
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Gold has several qualities that have made it exceptionally valuable throughout history. It is attractive in colour and brightness, durable to the point of virtual indestructibility, highly malleable , and usually found in nature in a comparatively pure form.
The history of gold is unequaled by that of any other metal because of its perceived value from earliest times. Prospectors established in the existence of a belt of gold-bearing reefs 40 miles 60 km wide centred on present-day Johannesburg.
The rapid growth of the gold-mining industry intensified processes started by the diamond boom: Gold is one of the densest of all metals. It is a good conductor of heat and electricity. It is also soft and the most malleable and ductile of the elements; an ounce 28 grams can be beaten out to square feet about 17 square metres in extremely thin sheets called gold leaf.
Because gold is visually pleasing and workable and does not tarnish or corrode, it was one of the first metals to attract human attention. Examples of elaborate gold workmanship , many in nearly perfect condition, survive from ancient Egyptian , Minoan , Assyrian , and Etruscan artisans, and gold continues to be a highly favoured material out of which to craft jewelry and other decorative objects.
Because of its unique qualities, gold has been the one material that is universally accepted in exchange for goods and services. Gold is still accepted by all nations as a medium of international payment. Gold is widespread in low concentrations in all igneous rocks.
It occurs mostly in the native state, remaining chemically uncombined except with tellurium , selenium , and bismuth. Gold often occurs in association with copper and lead deposits, and, though the quantity present is often extremely small, it is readily recovered as a by-product in the refining of those base metals. Large masses of gold-bearing rock rich enough to be called ores are unusual. Two types of deposits containing significant amounts of gold are known: Veins enriched in gold form when the gold was carried up from great depths with other minerals, in an aqueous solution , and later precipitated.
The gold in rocks usually occurs as invisible disseminated grains, more rarely as flakes large enough to be seen, and even more rarely as masses or veinlets. Masses, some on the order of 90 kg pounds , have been reported from Australia. Alluvial deposits of gold found in or along streams were the principal sources of the metal for ancient Egypt and Mesopotamia. The era of gold production that followed the Spanish discovery of the Americas in the s was probably the greatest the world had witnessed to that time.
The exploitation of mines by slave labour and the looting of palaces, temples, and graves in Central and South America resulted in an unprecedented influx of gold that literally unbalanced the economic structure of Europe. During the second era of expanding production —75 , more gold was produced in the world than in all the years since , primarily because of discoveries in California and Australia. In the late 20th century, four countries—South Africa, Russia, the United States , and Australia—accounted for two-thirds of the gold produced annually throughout the world.
In the early 21st century, China was the world leader in gold production. During this period, Australia, the United States, Russia, Canada, and South Africa also continued to supply large amounts of the precious metal. For full treatment of the mining, recovery, and refining of gold, see gold processing. Because pure gold is too soft to resist prolonged handling, it is usually alloyed with other metals to increase its hardness for use in jewelry, goldware, or coinage. Gold also produces a high output of secondary electrons when irradiated by an electron beam, and these low-energy electrons are the most commonly used signal source used in the scanning electron microscope.
The isotope gold half-life 2. Pure metallic elemental gold is non-toxic and non-irritating when ingested  and is sometimes used as a food decoration in the form of gold leaf. Although the gold ion is toxic, the acceptance of metallic gold as a food additive is due to its relative chemical inertness, and resistance to being corroded or transformed into soluble salts gold compounds by any known chemical process which would be encountered in the human body.
Soluble compounds gold salts such as gold chloride are toxic to the liver and kidneys. Common cyanide salts of gold such as potassium gold cyanide, used in gold electroplating , are toxic by virtue of both their cyanide and gold content.
There are rare cases of lethal gold poisoning from potassium gold cyanide. Gold metal was voted Allergen of the Year in by the American Contact Dermatitis Society, gold contact allergies affect mostly women. A sample of the fungus Aspergillus niger was found growing from gold mining solution; and was found to contain cyano metal complexes; such as gold, silver, copper iron and zinc.
The fungus also plays a role in the solubilization of heavy metal sulfides. From Wikipedia, the free encyclopedia. This article is about the element. For other uses, see Gold disambiguation. For the short story by Fred Hoyle, see Element 79 anthology. This section needs additional citations for verification. February Learn how and when to remove this template message. List of countries by gold production. Gold mining and Gold prospecting. Mercury cycle and International Cyanide Management Code.
Gold as an investment. Pure and Applied Chemistry. Chemical Rubber Company Publishing. The Monetary History of Gold: A Documentary History, Its scarcity makes it a useful store of value; however, its relative rarity reduced its utility as a currency, especially for transactions in small denominations. Museums, Objects, and Collections: Rarity is, nevertheless, in itself a source of value, and so is the degree of difficulty which surrounds the winning of the raw material, especially if it is exotic and has to be brought some distance.
Gold is, geologically, a relatively rare material on earth and occurs only in specific places which are remote from most other places. Retrieved 26 December Advanced Media Solutions, Inc.
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