Gold

From New World Encyclopedia
Revision as of 17:51, 6 February 2006 by Dinshaw Dadachanji (talk | contribs) (→‎Production: editing)
For other uses, see Gold (disambiguation).

Gold has long been valued as a noble metal and regarded as a symbol of purity, permanence, and royalty.

This shiny yellow substance occurs as nuggets or grains in rocks and alluvial deposits and does not react with most chemicals.

79 platinumgoldmercury
Ag

Au

Rg
Au-TableImage.png
periodic table
General
Name, Symbol, Number gold, Au, 79
Chemical series transition metals
Group, Period, Block 11, 6, d
Appearance metallic yellow
Native gold nuggets.jpg
Atomic mass 196.966569(4) g/mol
Electron configuration [Xe] 4f14 5d10 6s1
Electrons per shell 2, 8, 18, 32, 18, 1
Physical properties
Phase solid
Density (near r.t.) 19.3 g/cm³
Liquid density at m.p. 17.31 g/cm³
Melting point 1337.33 K
(1064.18 °C, 1947.52 °F)
Boiling point 3129 K
(2856 °C, 5173 °F)
Heat of fusion 12.55 kJ/mol
Heat of vaporization 324 kJ/mol
Heat capacity (25 °C) 25.418 J/(mol·K)
Vapor pressure
P/Pa 1 10 100 1 k 10 k 100 k
at T/K 1646 1814 2021 2281 2620 3078
Atomic properties
Crystal structure cubic face centered
Oxidation states 3, 1
(amphoteric oxide)
Electronegativity 2.54 (Pauling scale)
Ionization energies 1st: 890.1 kJ/mol
2nd: 1980 kJ/mol
Atomic radius 135 pm
Atomic radius (calc.) 174 pm
Covalent radius 144 pm
Van der Waals radius 166 pm
Miscellaneous
Magnetic ordering no data
Electrical resistivity (20 °C) 22.14 nΩ·m
Thermal conductivity (300 K) 318 W/(m·K)
Thermal expansion (25 °C) 14.2 µm/(m·K)
Speed of sound (thin rod) (r.t.) (hard-drawn)
2030 m/s
Speed of sound (thin rod) (r.t.) 78 m/s
Shear modulus 27 GPa
Bulk modulus 220 GPa
Poisson ratio 0.44
Mohs hardness 2.5
Vickers hardness 216 MPa
Brinell hardness 2450 MPa
CAS registry number 7440-57-5
Notable isotopes
Main article: Isotopes of gold
iso NA half-life DM DE (MeV) DP
195Au syn 186.10 d ε 0.227 195Pt
196Au syn 6.183 d ε 1.506 196Pt
β- 0.686 196Hg
197Au 100% Au is stable with 118 neutrons
198Au syn 2.69517 d β- 1.372 198Hg
199Au syn 3.169 d β- 0.453 199Hg

History

Gold (Sanskrit jval, Greek χρυσος [khrusos], Latin aurum for "shining dawn", Anglo-Saxon gold, Chinese 金 [jīn],Japanese 金 [kin]) is a chemical element and a precious metal that has been known and highly valued since prehistoric times. Early peoples used it mainly for ornamentation and rituals. It is described in Egyptian hieroglyphs dating back to 2600 B.C.E., and it is mentioned several times in the Hebrew scriptures.

Egypt and Nubia had the resources to make them major gold-producing areas for much of history. The southeast corner of the Black Sea was famed for its gold. Exploitation is said to date from the time of Midas, and this gold was important in the establishment of what was probably the world's earliest coinage in Lydia between 643 and 630 B.C.E.

Gold in antiquity was relatively easy to obtain geologically; however, 75% of all gold ever produced has been extracted since 1910.[1] 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, and Colombia.

For alchemists, gold was the king of metals. Their primary goal was to produce it from other substances such as lead or mercury—presumably by 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 their work 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, the Egyptian hieroglyph, and the ancient Chinese character for the Sun (now 日).

During the 19th century, gold rushes occurred whenever large gold deposits were discovered. They included the California, Colorado, Otago, Australia, Witwatersrand, Black Hills, and Klondike gold rushes.

Because of its historically high value, much of the gold mined throughout history is still in circulation in one form or another.

Occurrence

A gold nugget
Raw gold from California (top) and Australia (bottom), showing octahedral formations.

Scientists theorize that the gold on our planet was first formed in an ancient star shortly before it exploded as a supernova. The debris from that explosion is thought to have gone into the formation of our solar system.

Given its relative chemical inertness, gold usually occurs as the native metal or as an alloy with silver and other precious metals. Occasionally, it has been found in the form of large accumulations, or nuggets. More often, it is found as tiny grains that occur as inclusions within minerals or lie between mineral-grain boundaries. In addition, extremely minute quantities of gold are distributed across the Earth's crust and in sea water.

There are several types of primary deposits of gold; common ones are termed "reef" or "vein." Hydrothermal ore deposits of gold occur in metamorphic rocks and igneous rocks. In addition, sedimentary black shale and limestone deposits contain finely disseminated gold and other metals.

The primary deposits are weathered and eroded, with most of the gold being transported into stream beds where it congregates with other heavy minerals to form what are called "alluvial deposits" or "placer deposits." Recent research shows that microbes may also play a role in transporting and precipitating gold to form grains and nuggets that collect in alluvial deposits. [2]

Gold is commonly associated with quartz and sulfide minerals. The most common sulfide associations are pyrite, chalcopyrite, galena, sphalerite, arsenopyrite, stibnite, and pyrrhotite. Iron pyrite (FeS2), with its metallic luster and yellowish color, has been called "fool's gold"; but it may contain small amounts of actual gold.

Physical and chemical characteristics

Gold is a chemical element given the symbol Au, from the Latin word aurum. Its atomic number is 79. In the periodic table, it is placed in the same family (group 11 or 1B) as copper and silver. Also, it lies in period 6, between platinum and mercury. It occurs as one stable isotope (Au-197) and 18 radioisotopes.

Although the usual color of gold is yellow, its finely divided form may appear black or ruby-colored. Colloidal solutions (suspensions of tiny gold particles) are intensely colored and often purple.

Gold is a good conductor of heat and electricity. It is also the most malleable and ductile metal—a single gram can be beaten into a sheet of one square meter, or an ounce into 300 square feet.

Alloys of gold are often prepared to increase its strength or create a range of exotic colors. Adding copper yields a redder metal; iron, blue; silver, green; aluminum, purple; and platinum, white. When natural bismuth is added to alloys with silver, the resultant mixture is black. Native gold usually contains 8–10% silver, but often much more. An alloy containing 20% or more of silver is called electrum. As the amount of silver increases, the color becomes whiter and the specific gravity, lower.

Heat, moisture, oxygen, and most chemical reagents have very little chemical effect on gold. This relative lack of reactivity is the reason why gold is known as a noble metal. Alchemists called it the king of metals.

Gold does, however, react with halogens—such as chlorine, bromine, and iodine—to form compounds such as gold(III) chloride (auric chloride, AuCl3), gold(III) bromide (auric bromide, AuBr3), and gold(I) iodide (aurous iodide, AuI). In such compounds, gold is said to have an "oxidation number" of +3 or +1, as the case may be.

Moreover, gold can be dissolved by aqua regia (a mixture of nitric acid and hydrochloric acid in the ratio 1:3) to form chlorauric acid (HAuCl4). Aqua regia, which literally means "royal water," was so named because it could dissolve the king of metals.

Gold ions in solution are readily precipitated out as gold metal by the addition of virtually any other metal to the solution. The added metal dissolves, while the gold is displaced from the solution. The gold ions are said to be "reduced," while the added metal is said to be "oxidized." This is a way to recover gold from solution.

Under extreme conditions, gold can combine with fluorine to produce gold(V) fluoride (AuF5). In this case, gold has the oxidation number +5. Unusually for a metal, gold can also form compounds in which its oxidation number is -1. Such compounds contain the Au- anion and are called aurides. Examples are cesium auride (CsAu), rubidium auride (RbAu), and tetramethylammonium auride, (CH3)4N+ Au-.

Other compounds formed by gold include:

  • gold chalcogenides (formed with O, S, Se, or Te);
  • gold cluster compounds (in which two or more metal atoms are attached to one another);
  • gold hydrazide (AuN2H3): an olive-green powder, it is one of several explosive compounds known archaically as aurum fulminans.

Symbolism

Historically, gold has been associated with royalty, sanctity, and durability. The New Testament records that gold was one of the gifts offered by the three magi who visited the newborn Jesus. Later, Christian kings wore golden crowns to symbolize their divinely inspired authority. Also, the rituals of various faiths have involved the use of items made of gold. The tombs of the pharaohs of ancient Egypt were filled with items made of or plated with gold.

Wedding rings are traditionally made of gold, as a metaphor for the unchanging commitment of love between the partners in marriage. Also, gold is associated with notable anniversaries, particularly in a 50-year cycle, such as the golden wedding anniversary or golden jubilee.

Gold medals and decorations are often used to honor those who have made great contributions to society or have won great competitions. Examples are medals awarded to winners of the Nobel Prize and champions in the Olympic Games. Also, many award statuettes are plated in gold, such as those given at the Academy Awards, the Emmy Awards, and the British Academy Film Awards.

A person who is particularly kind-hearted and generous is said to have a "heart of gold." The eminent orator John Chrysostom was said to have a "mouth of gold with a silver tongue."

On the other hand, hearkening back to the time of Moses, worshipping the Golden Calf has become a symbol of idolatry and revolt against God. Native Americans of the Sioux tribe called gold "the yellow metal that makes the white man crazy." In Communist propaganda, the gold pocket watch and its fastening gold chain were classified as accessories of the class enemy, namely, the bourgeoisie and industrial tycoons.

Applications

Pure gold is too soft for ordinary use and is hardened by alloying with silver, copper, and other metals. Gold and its many alloys are most often used in jewelry and coinage, and as a standard for monetary exchange in many countries. Given its high electrical conductivity, resistance to corrosion, and other properties, gold emerged in the late 20th century as an essential industrial metal.

Gold and its compounds now have a wide range of applications, a number of which are listed below.

  • Gold can be made into thread and used in embroidery.
  • Gold is used in restorative dentistry, especially in tooth restorations such as crowns and bridges.
  • Being resistant to oxidation, thin layers of gold are electroplated on the exposed surfaces of electrical connectors to ensure good connections.
  • Gold performs critical functions in computers, communications equipment, spacecraft, jet aircraft engines, and a host of other products.
  • Being a good reflector of both infrared and visible light, gold is used for protective coatings on many artificial satellites.
  • Gold is used as a coating that enables biological material to be viewed under a scanning electron microscope.
  • The gold isotope Au-198 (half-life 2.7 days) is used as a treatment for cancer and other diseases.
  • Colloidal gold (containing nanoparticles of gold in suspension) is being studied in many labs for medical, biological, and other applications. It is also the form used as gold paint on ceramics prior to firing.
  • Chlorauric acid is used in photography for toning the silver image.
  • Gold(III) chloride is used as a catalyst in organic chemistry. It is also the usual starting point for making other gold compounds.
  • A gold compound known as disodium aurothiomalate is a treatment for rheumatoid arthritis (administered intramuscularly). It can, however, also cause photosensitive rashes, gastrointestinal disturbance, and kidney damage.
  • Gold flake is added to some gourmet sweets and drinks. Called varak (or varaq) in India, it has no reactivity and adds no taste but is taken as a delicacy. Some use it to create super-expensive cocktails.
  • White gold (an alloy of gold with platinum, palladium, nickel, and/or zinc) serves as a substitute for platinum.
  • Green gold and rose gold are alloys of gold with silver and copper, respectively, and are used in specialized jewelry.

It should be noted that the human body does not absorb gold very well. As a result, compounds of gold are normally not very toxic. In dentistry, gold is regarded as the safest and most successful form of restorative material. On the other hand, liver and kidney damage has been reported for up to 50% of arthritis patients treated with gold-containing drugs.

Production

The entrance to an underground gold mine in Victoria, Australia
Gold ore

In large, easily mined deposits, economic gold extraction can be achieved from ore grades as low as 0.5 g/1000 kg (0.5 ppm), on average. Typical ore grades in open-pit mines are 1–5 g/1000 kg (1-5 ppm); ore grades in underground or hard rock mines are usually at least 3 g/1000 kg (3 ppm), on average. Ore grades of 30 g/1000 kg (30 ppm) are usually needed before gold is visible to the naked eye. Thus, in most gold mines you will not see any gold. It has been estimated that all the gold in the world that has ever been refined would form a single cube 20 m (66 ft) on each side.

Since the 1880s, South Africa has produced a large proportion of the world's gold supply. Production in 1970 accounted for 79% of the global supply, corresponding to about 1,000 tonnes. In 2004, however, production fell to 342 tonnes. This decline was a result of the increasing difficulty of extraction and changing economic factors affecting the industry in South Africa.

The city of Johannesburg was built atop the world's greatest gold finds. Gold fields in the Orange Free State and the Transvaal are deep and require the world's deepest mines. The Second Boer War of 1899–1901, between the British Empire and the white Boers, was at least partly over the rights of miners and possession of the gold wealth in South Africa.

Other major producers are Canada, the United States, and Australia. Mines in South Dakota and Nevada supply two-thirds of the gold used in the United States. The Siberian regions of Russia used to be significant in the global gold mining industry. The Kolar Gold Fields of India is another example of a city built on a great gold deposit. In South America, the controversial project Pascua Lama aims at exploitation of rich fields in the high mountains of Atacama, at the border between Chile and Argentina.

While alchemists attempted to produce gold from other elements via chemical reactions, modern science has proven the impossibility of doing so. It is, however, possible to obtain minuscule amounts of gold by artificial nuclear transformations in particle accelerators. The product would likely be one or more radioactive isotopes of gold.

The world's oceans hold a vast amount of gold, but at very low concentrations (perhaps 1-2 parts per billion). Fritz Haber (the German inventor of the Haber process) attempted commercial extraction of gold from seawater in an effort to help pay Germany's reparations following the First World War. Unfortunately, his assessment of the concentration of gold in seawater was unduly high, probably due to sample contamination. The effort produced little gold and cost the German government far more than the commercial value of the gold recovered. No commercially viable mechanism for performing gold extraction from seawater has yet been identified.

Value

File:3sovriegns.jpg
Three Gold Sovereigns with a Krugerrand
Gold bars with Krugerrands in the background.

Like other precious metals, gold is measured by troy weight and by grams. When it is alloyed with other metals the term carat or karat is used to indicate the amount of gold present, with 24 carats being pure gold and lower ratings proportionally less. The purity of a gold bar can also be expressed as a decimal figure ranging from 0 to 1, known as the millesimal fineness, such as 0.995.

The price of gold is determined on the open market, but a procedure known as the Gold Fixing in London, originating in 1919, provides a twice-daily benchmark figure to the industry.

Historically gold was used to back currency in an economic system known as the gold standard in which one unit of currency was equivalent to a certain weight of gold. As part of this system, governments and central banks attempted to control the price of gold by setting values at which they would exchange it for currency. For a long period the United States government set the price of gold at $20.67 per troy ounce ($664.56/kg) but in 1934 the price of gold was set at $35.00 per troy ounce ($1125.27/kg). By 1961 it was becoming hard to maintain this price, and a pool of US and European banks began to act together to defend the price against market forces.

On March 17 1968, economic circumstances caused the collapse of the gold pool, and a two-tiered pricing scheme was established whereby gold was still used to settle international accounts at the old $35.00 per troy ounce ($1.13/g) but the price of gold on the private market was allowed to fluctuate; this two-tiered pricing system was abandoned in 1975 when the price of gold was left to find its free-market level. Central banks still hold historical gold reserves as a reserve asset although the level has generally been declining. The largest gold depository in the world is that of the U.S. Federal Reserve Bank, in New York.

Since 1968 the price of gold on the open market has ranged widely, with a record high of $850/oz ($27,300/kg) on 21 January 1980, to a low of $252.90/oz ($8,131/kg) on 21 June 1999 (London Fixing). Prices have risen to the $500/oz mark in late 2005, due to a depreciation of the US dollar and inflation due to rising energy costs.

Gold and the money supply

In January 1959 US M3 money supply was $288.8 billion, and the Official Gold Holdings of the United States was then 17,335.1 Tonnes, or about 557 million ounces (there are 32,150.7 Troy Ounces in a Tonne). That means that in 1959, there were $518 in circulation for every ounce of gold reserves held by the USA. Although the theoretical price should then have been $518 per ounce, the actual price, as fixed under the gold standard was only $35 an ounce.

By August 2005, the US M3 money supply had risen to $9,873.9 billion, whilst at the same time the Official Gold Holdings of the United States had fallen to just 8,133.5 Tonnes, or about 261 million Troy Ounces. This means that today, in 2005, there are $37,831 in circulation for every ounce of gold held by the United States.

The above numbers show the falling influence of gold in the monetary system of the world today. Goldbugs believe, or even hope, that one day gold's importance will return as the printing of paper money gets out of control and we end in a hyper-inflationary fiat money collapse.

Restrictions on gold ownership

Because of its use as a reserve store of value, the possession of gold is sometimes restricted or banned. Within the United States, the private possession of gold except as jewelry and coin collecting was banned between 1933 and 1975. President Franklin D. Roosevelt expropriated gold by Executive Order 6102, and President Richard Nixon closed the gold window by which foreign countries could exchange American dollars for gold at a fixed rate.


Gold in investment portfolios

As a tangible investment, gold is sometimes held as part of a portfolio because it has an extensive history of maintaining its value over the long term. In the last century, it has gained ground in relation to fiat currencies owing to inflation. Gold becomes particularly desirable in times of extremely weak confidence and during hyperinflation because it maintains its value even as fiat money becomes worthless. People who enjoy investing in gold are known as goldbugs.

In some countries such as Switzerland, it is possible to hold physical gold as part of an investment portfolio. In other countries, however, portfolio managers may hold gold shares or gold bullion securities as proxies for the metal itself. Exchange-traded funds (ETFs), such as gold bullion securities, are sponsored by the World Gold Council and are fully backed by allocated gold held by a custodian.

Futures contracts based on gold are traded on various exchanges around the world. In the United States, speculation about the future price of gold and other commodities is carried on at COMEX (Commodity Exchange), a subsidiary of the New York Mercantile Exchange. Recently, gold-based ETFs like GLD have emerged as a more convenient investment vehicle.


References
ISBN links support NWE through referral fees

See also

  • Gold prospecting
  • Gold as an investment
  • Colloidal gold
  • Socialism and Gold
  • 22/22k

External links

Commons
Wikimedia Commons has media related to::

af:Goud bg:Злато ca:Or cs:Zlato cy:Aur da:Guld de:Gold et:Kuld es:Oro eo:Oro fr:Or hr:Zlato io:Oro id:Emas is:Gull it:Oro he:זהב ku:Zêr la:Aurum lv:Zelts lt:Auksas lb:Gold li:Goud hu:Arany ms:Emas nl:Goud ja:金 no:Gull nn:Gull oc:Aur pl:Złoto pt:Ouro ru:Золото simple:Gold sk:Zlato sl:Zlato sr:Злато fi:Kulta sv:Guld ta:தங்கம் th:ทองคำ vi:Vàng tr:Altın uk:Золото zh:金

Credits

New World Encyclopedia writers and editors rewrote and completed the Wikipedia article in accordance with New World Encyclopedia standards. This article abides by terms of the Creative Commons CC-by-sa 3.0 License (CC-by-sa), which may be used and disseminated with proper attribution. Credit is due under the terms of this license that can reference both the New World Encyclopedia contributors and the selfless volunteer contributors of the Wikimedia Foundation. To cite this article click here for a list of acceptable citing formats.The history of earlier contributions by wikipedians is accessible to researchers here:

The history of this article since it was imported to New World Encyclopedia:

Note: Some restrictions may apply to use of individual images which are separately licensed.