Gold is a chemical element with the symbol Au (from Latin: aurum "gold") and an atomic number of 79. Gold is a dense, soft, shiny, malleable and ductile metal. Pure gold has a bright yellow color and luster traditionally considered attractive, which it maintains without oxidizing in air or water. Chemically, gold is a transition metal and a group 11 element. It is one of the least reactive solid chemical elements. The metal therefore occurs often in free elemental (native) form, asnuggets or grains in rocks, in veins and in alluvial deposits. Less commonly, it occurs in minerals as gold compounds, usually with tellurium.
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| Gold Crystals |
Gold resists attacks by individual acids, but it can be dissolved by the aqua regia (nitro-hydrochloric acid), so named because it ...
... dissolves gold. Gold also dissolves in alkaline solutions of cyanide, which have been used in mining. Gold dissolves inmercury, forming amalgam alloys. Gold is insoluble in nitric acid, which dissolves silver and base metals, a property that has long been used to confirm the presence of gold in items, giving rise to the term the acid test.
Gold has been a valuable and highly sought-after precious metal for coinage, jewelry, and other arts since long before the beginning of recorded history. Gold standards have been the most common basis for monetary policies throughout human history, being widely supplanted by fiat currency only in the late 20th century. Gold has also been frequently linked to a wide variety of symbolisms and ideologies. A total of 165,000 tonnes of gold have been mined in human history, as of 2009. This is roughly equivalent to 5.3 billion troy ounces or, in terms of volume, about 8500 m3, or a cube 20.4 m on a side. The world consumption of new gold produced is about 50% in jewelry, 40% in investments, and 10% in industry.
Besides its widespread monetary and symbolic functions, gold has many practical uses in dentistry, electronics, and other fields. Its high malleability, ductility, resistance to corrosion and most other chemical reactions, and conductivity of electricity led to many uses of gold, including electric wiring, colored-glass production and even gold leaf eating.
Gold Characteristics
Gold is the most malleable and ductile of all metals; a single gram can be beaten into a sheet of 1 square meter, or an ounce into 300 square feet. Gold leaf can be beaten thin enough to become transparent. The transmitted light appears greenish blue, because gold strongly reflects yellow and red. Such semi-transparent sheets also strongly reflect infrared light, making them useful as infrared (radiant heat) shields in visors of heat-resistant suits, and in sun-visors for spacesuits.
Gold readily creates alloys with many other metals. These alloys can be produced to modify the hardness and other metallurgical properties, to control melting point or to create exotic colors (see below). Gold is a good conductor of heat and electricity and reflects infrared radiation strongly. Chemically, it is unaffected by air, moisture and most corrosive reagents, and is therefore well suited for use in coins and jewelry and as a protective coating on other, more reactive, metals. However, it is not chemically inert.
Common oxidation states of gold include +1 (gold(I) or aurous compounds) and +3 (gold(III) or auric compounds). Gold ions in solution are readily reduced and precipitated out as gold metal by adding any other metal as the reducing agent. The added metal is oxidized and dissolves allowing the gold to be displaced from solution and be recovered as a solid precipitate.
High quality pure metallic gold is tasteless and scentless, in keeping with its resistance to corrosion (it is metal ions which confer taste to metals).
In addition, gold is very dense, a cubic meter weighing 19,300 kg. By comparison, the density of lead is 11,340 kg/m3, and that of the densest element, osmium, is 22,610 kg/m3.
Gold Colour
Whereas most other pure metals are grey or silvery white, gold is yellow. This colour is determined by the density of loosely bound (valence) electrons; those electrons oscillate as a collective "plasma" medium described in terms of a quasiparticle called plasmon. The frequency of these oscillations lies in the ultraviolet range for most metals, but it falls into the visible range for gold due to subtle relativistic effects that affect the orbitals around gold atoms. Similar effects impart a golden hue to metallic caesium (see relativistic quantum chemistry).
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| Different colors of Ag-Au-Cu alloys |
Common colored gold alloys such as rose gold can be created by the addition of various amounts of copper and silver, as indicated in the triangular diagram to the left. Alloys containing palladium or nickel are also important in commercial jewelry as these produce white gold alloys. Less commonly, addition of manganese, aluminium, iron, indium and other elements can produce more unusual colors of gold for various applications.
Moche gold necklace depicting feline heads. Larco Museum Collection. Lima-Peru
Because of the softness of pure (24k) gold, it is usually alloyed with base metals for use in jewelry, altering its hardness and ductility, melting point, color and other properties. Alloys with lower caratage, typically 22k, 18k, 14k or 10k, contain higher percentages of copper, or other base metals or silver or palladium in the alloy. Copper is the most commonly used base metal, yielding a redder color.
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| Moche gold necklace depicting feline heads.Larco Museum Collection. Lima-Peru |
Fourteen and eighteen carat gold alloys with silver alone appear greenish-yellow and are referred to as green gold. White gold alloys can be made with palladium or nickel. White 18-carat gold containing 17.3% nickel, 5.5% zinc and 2.2% copper is silvery in appearance. Nickel is toxic, however, and its release from nickel white gold is controlled by legislation in Europe.
Alternative white gold alloys are available based on palladium, silver and other white metals, but the palladium alloys are more expensive than those using nickel. High-carat white gold alloys are far more resistant to corrosion than are either pure silver or sterling silver. The Japanese craft of Mokume-gane exploits the color contrasts between laminated colored gold alloys to produce decorative wood-grain effects.
Gold History
Gold artifacts found at the Nahal Kana cave cemetery dated during the 1980's, showed these to be from within the Chalcolithic, and considered the earliest find from the Levant (Gopher et al. 1990). Gold artifacts in the Balkans also appear from the 4th millennium BC, such as those found in the Varna Necropolis near Lake Varna in Bulgaria, thought by one source (La Niece 2009) to be the earliest "well-dated" find of gold artefacts. Gold artifacts such as the golden hats and the Nebra disk appeared in Central Europe from the 2nd millennium BC Bronze Age.
Egyptian hieroglyphs from as early as 2600 BC describe gold, which king Tushratta of the Mitanni claimed was "more plentiful than dirt" in Egypt. Egypt and especially Nubia had the resources to make them major gold-producing areas for much of history. The earliest known map is known as the Turin Papyrus Map and shows the plan of a gold mine in Nubia together with indications of the local geology. The primitive working methods are described by both Strabo and Diodorus Siculus, and included fire-setting. Large mines were also present across the Red Sea in what is now Saudi Arabia.
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| The Turin Papyrus Map |
In Roman metallurgy, new methods for extracting gold on a large scale were developed by introducing hydraulic mining methods, especially in Hispania from 25 BC onwards and in Dacia from 106 AD onwards. One of their largest mines was at Las Medulas in León (Spain), where seven long aqueducts enabled them to sluice most of a large alluvial deposit. The mines at Roşia Montană in Transylvania were also very large, and until very recently, still mined by opencast methods. They also exploited smaller deposits in Britain, such as placer and hard-rock deposits at Dolaucothi. The various methods they used are well described by Pliny the Elder in his encyclopedia Naturalis Historia written towards the end of the first century AD.
The Mali Empire in Africa was famed throughout the old world for its large amounts of gold. Mansa Musa, ruler of the empire (1312–1337) became famous throughout the old world for his great hajj to Mecca in 1324. When he passed through Cairo in July 1324, he was reportedly accompanied by a camel train that included thousands of people and nearly a hundred camels. He gave away so much gold that it depressed the price in Egypt for over a decade. A contemporary Arab historian remarked:
Gold was at a high price in Egypt until they came in that year. The mithqal did not go below 25 dirhams and was generally above, but from that time its value fell and it cheapened in price and has remained cheap till now. The mithqal does not exceed 22 dirhams or less. This has been the state of affairs for about twelve years until this day by reason of the large amount of gold which they brought into Egypt and spent there [...]
—Chihab Al-Umari
The European exploration of the Americas was fueled in no small part by reports of the gold ornaments displayed in great profusion by Native American peoples, especially in Central America, Peru, Ecuador and Colombia. The Aztecs regarded gold as literally the product of the gods, calling it "god excrement" (teocuitlatl in Nahuatl). However, for the indigenous peoples of North America, gold was considered useless, and they saw much greater value in other minerals, which were directly related to their utility, such as obsidian, flint, and slate.
Although the price of some platinum group metals can be much higher, gold has long been considered the most desirable of precious metals, and its value has been used as the standard for many currencies (known as the gold standard) in history. Gold has been used as a symbol for purity, value, royalty, and particularly roles that combine these properties. Gold as a sign of wealth and prestige was ridiculed by Thomas More in his treatise Utopia. On that imaginary island, gold is so abundant that it is used to make chains for slaves, tableware and lavatory-seats. When ambassadors from other countries arrive, dressed in ostentatious gold jewels and badges, the Utopians mistake them for menial servants, paying homage instead to the most modestly dressed of their party.
There is an age-old tradition of biting gold to test its authenticity. Although this is certainly not a professional way of examining gold, the bite test should score the gold because gold is a soft metal, as indicated by its score on the Mohs' scale of mineral hardness. The purer the gold the easier it should be to mark it. Painted lead can cheat this test because lead is softer than gold (and may invite a small risk of lead poisoning if sufficient lead is absorbed by the biting).
Gold in antiquity was relatively easy to obtain geologically; however, 75% of all gold ever produced has been extracted since 1910. It has been estimated that all gold ever refined would form a single cube 20 m (66 ft) on a side (equivalent to 8,000 m3).
One main goal of the alchemists was to produce gold from other substances, such as lead — presumably by the interaction with a mythical substance called the philosopher's stone. Although they never succeeded in this attempt, the alchemists promoted an interest in what can be done with substances, and this laid a foundation for today's chemistry. Their symbol for gold was the circle with a point at its center (☉), which was also the astrological symbol and the ancient Chinese character for the Sun. For modern creation of artificial gold by neutron capture, see gold synthesis.
During the 19th century, gold rushes occurred whenever large gold deposits were discovered. The first documented discovery of gold in the United States was at the Reed Gold Mine near Georgeville, North Carolina in 1803. The first major gold strike in the United States occurred in a small north Georgia town called Dahlonega. Further gold rushes occurred in California, Colorado, the Black Hills, Otago in New Zealand, Australia, Witwatersrand in South Africa, and the Klondike in Canada.
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| Jason returns with the golden fleece on an Apulian red-figurecalyx krater, ca. 340–330 BC. |
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| Funerary mask of Tutankhamun |
The consumption of gold produced in the world is about 50% in jewellery, 40% in investments, and 10% in industry.
India is the world's largest single consumer of gold, as Indians buy about 25% of the world's gold, purchasing approximately 800 tonnes of gold every year, mostly for jewelry. India is also the largest importer of gold; in 2008, India imported around 400 tonnes of gold. Indian households hold 18,000 tonnes of gold which represents 11 per cent of the global stock and worth more than $950 billion.
Gold jewellery consumption by country (in Tonnes).
Country 2010 2009 %Change
India 745.70 442.37 +69Greater China 428.00 376.96 +14
United States 128.61 150.20 -14
Turkey 74.07 75.16 -1
Saudi Arabia 72.95 77.75 -6
Russia 67.50 60.12 +12
United Arab Emirates 63.37 67.60 -6
Egypt 53.43 56.68 -6
Indonesia 32.75 41.00 -20
United Kingdom 27.35 31.75 -14Other Gulf Countries 21.97 24.10 -10
Japan 18.50 21.85 -15
South Korea 15.87 18.83 -16
Vietnam 14.36 15.08 -5
Thailand 6.28 7.33 -14Total 1805.60 1508.70 +20
Other Countries 254.00 251.60 +1
World Total 2059.60 1760.03 +17
Symbolism
Gold has been highly valued in many societies throughout the ages. In keeping with this it has often had a strongly positive symbolic meaning closely connected to the values held in the highest esteem in the society in question. Gold may symbolize power, strength, wealth, warmth, happiness, love, hope, optimism, intelligence, justice, balance, perfection, summer, harvest and the sun.
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| Gold bars at the Emperor Casino in Macau |
Great human achievements are frequently rewarded with gold, in the form of gold medals, golden trophies and other decorations. Winners of athletic events and other graded competitions are usually awarded a gold medal (e.g., the Olympic Games). Many awards such as the Nobel Prize are made from gold as well. Other award statues and prizes are depicted in gold or are gold plated (such as the Academy Awards, the Golden Globe Awards, the Emmy Awards, the Palme d'Or, and the British Academy Film Awards).
Aristotle in his ethics used gold symbolism when referring to what is now commonly known as the golden mean. Similarly, gold is associated with perfect or divine principles, such as in the case of the golden ratio and the golden rule.
Gold is further associated with the wisdom of aging and fruition. The fiftieth wedding anniversary is golden. Our precious latter years are sometimes considered "golden years". The height of a civilization is referred to as a "golden age".
In Christianity gold has sometimes been associated with the extremities of utmost evil and the greatest sanctity. In the Book of Exodus, the Golden Calf is a symbol of idolatry. In the Book of Genesis, Abraham was said to be rich in gold and silver, and Moses was instructed to cover the Mercy Seat of the Ark of the Covenant with pure gold. In Christian art the halos of Christ, Mary and the Christian saints are golden.
Medieval kings were inaugurated under the signs of sacred oil and a golden crown, the latter symbolizing the eternal shining light of heaven and thus a Christian king's divinely inspired authority.
Those who had something of gold, were in possession of something of great value on earth and a substance to even help souls to paradise
—according to Christopher Columbus (quoted in Bernstein - p.1)
Wedding rings have long been made of gold. It is long lasting and unaffected by the passage of time and may aid in the ring symbolism of eternal vows before God and/or the sun and moon and the perfection the marriage signifies. In Orthodox Christianity, the wedded couple is adorned with a golden crown during the ceremony, an amalgamation of symbolic rites.
In popular culture gold holds many connotations but is most generally connected to terms such as good or great, such as in the phrases: "has a heart of gold", "that's golden!", "golden moment", "then you're golden!" and "golden boy". Gold also still holds its place as a symbol of wealth and through that, in many societies, success.
Gold Purity - Millesimal fineness
Millesimal fineness is a system of denoting the purity of platinum, gold and silver alloys by parts per thousand of pure metal by mass in the alloy. For example, an alloy containing 75% gold is denoted as "750". Many European countries use decimal hallmark stamps (i.e. '585', '750', etc.) rather than '14K', '18K', etc., which is used in the United Kingdom and United States.
It is an extension of the older carat (karat in North American spelling) system of denoting the purity of gold by fractions of 24, such as "18 carat" for an alloy with 75% (18 parts per 24) pure gold by mass.
The millesimal fineness is usually rounded to a three figure number, particularly where used as a hallmark, and the fineness may vary slightly from the traditional versions of purity.
The most common millesimal finenesses used for precious metals:
Platinum
- 999 (also known as three nines fine)
- 995 (what most dealers would buy as if 100% pure; the most common purity for platinum bullion coins and bars)
- 950 (the most common purity for platinum jewellery)
- 900 (also known as one nine fine)
- 850
Gold
- 999.999 (The purest gold ever produced. Refined by the Perth Mint in 1958.)
- 999.99 (The purest type of gold in the market)
- 999.9 Four-nine purity, e.g. Canadian Gold Maple Leaf and Panda-Pagoda investment coins
- 999 (Fineness equivalent to 24 carat, also known as three nines fine)
- 995 the minimum allowed in Good Delivery gold bars
- 990 also known as two nines fine
- 986 also known as ducat fineness, formerly used by venetian and Holy Roman Empire mints, still in use in Austria and Hungary
- 958.3 (equivalent to 23 carat)
- 916 (equivalent to 22 carat) gold is used in the Krugerrand investment coins
- 900 part gold was mostly used in Latin Monetary Union mintage (e.g. french and swiss "Napoleon coin" 20 francs)
- 833 (equivalent to 20 carat)
- 750 (equivalent to 18 carat)
- 625 (equivalent to 15 carat)
- 585 (equivalent to 14 carat)
- 417 (equivalent to 10 carat)
- 375 (equivalent to 9 carat)
- 333 (equivalent to 8 carat; minimum standard for gold in Germany after 1884)
Silver
- 999.9 (Ultra-fine silver used by Royal Canadian Mint in the Canadian Silver Maple Leaf)
- 999 (Fine silver used in Good Delivery bullion bars, also known as three nines fine)
- 980 (common standard used in Mexico ca.1930 - 1945)
- 958 (equivalent to Britannia silver)
- 950 (equivalent to French 1st Standard)
- 925 (equivalent to Sterling silver)
- 900 (equivalent to Coin silver in the USA, also known as one nine fine)
- 835 (a standard predominantly used in Germany after 1884)
- 833 (common standard used in continental silver especially among the Dutch, Swedish, and Germans)
- 830 (common standard used in older Scandinavian silver)
- 800 (minimum standard for silver in Germany after 1884; Egyptian silver; Canadian silver circulating coinage)
- 750 (uncommon silver standard found in older German, Swiss and Austro-Hungarian silver)
(Gold Article Source - Wikipedia)
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