Gold is a chemical element with symbol Au (from Latin: aurum) and atomic number 79, making it one of the higher atomic number elements that occur naturally. In its purest form, it is a bright, slightly reddish yellow, dense, soft, malleable, and ductile metal. Chemically, gold is a transition metal and a group 11 element. It is one of the least reactive chemical elements and is solid under standard conditions. Gold often occurs in free elemental (native) form, as nuggets or grains, in rocks, in veins, and in alluvial deposits. It occurs in a solid solution series with the native element silver (as electrum) and also naturally alloyed with copper and palladium. Less commonly, it occurs in minerals as gold compounds, often with tellurium (gold tellurides).
Gold is resistant to most acids, though it does dissolve in aqua regia, a mixture of nitric acid and hydrochloric acid, which forms a soluble tetrachloroaurate anion. Gold is insoluble in nitric acid, which dissolves silver and base metals, a property that has long been used to refine gold and to confirm the presence of gold in metallic objects, giving rise to the term acid test. Gold also dissolves in alkaline solutions of cyanide, which are used in mining and electroplating. Gold dissolves in mercury, forming amalgam alloys, but this is not a chemical reaction.
A relatively rare element,[5][6] gold is a precious metal that has been used for coinage, jewelry, and other arts throughout recorded history. In the past, a gold standard was often implemented as a monetary policy, but gold coins ceased to be minted as a circulating currency in the 1930s, and the world gold standard was abandoned for a fiat currency system after 1971.
A total of 186,700 tonnes of gold exists above ground, as of 2015.[7] The world consumption of new gold produced is about 50% in jewelry, 40% in investments, and 10% in industry.[8] Gold's high malleability, ductility, resistance to corrosion and most other chemical reactions, and conductivity of electricity have led to its continued use in corrosion resistant electrical connectors in all types of computerized devices (its chief industrial use). Gold is also used in infrared shielding, colored-glass production, gold leafing, and tooth restoration. Certain gold salts are still used as anti-inflammatories in medicine. As of 2016, the world's largest gold producer by far was China with 450 tonnes per year.[9]
Characteristics

Gold is the most malleable of all metals; a single gram can be beaten into a sheet of 1 square meter, and an avoirdupois ounce into 300 square feet. Gold leaf can be beaten thin enough to become semi-transparent. The transmitted light appears greenish blue, because gold strongly reflects yellow and red.[10] 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.[11] Gold is a good conductor of heat and electricity.
Gold has a density of 19.3g/cm3, almost identical to that of tungsten at 19.25g/cm3; as such, tungsten has been used in counterfeiting of gold bars, such as by plating a tungsten bar with gold,[12][13][14][15] or taking an existing gold bar, drilling holes, and replacing the removed gold with tungsten rods.[16] By comparison, the density of lead is 11.34g/cm3, and that of the densest element, osmium, is 22.588±0.015g/cm3.[17]
Color

Whereas most metals are gray or silvery white, gold is slightly reddish-yellow.[18] This color is determined by the frequency of plasma oscillations among the metal's valence electrons, in the ultraviolet range for most metals but in the visible range for gold due to relativistic effects affecting the orbitals around gold atoms.[19][20] Similar effects impart a golden hue to metallic caesium.
Common colored gold alloys include the distinctive eighteen-karat rose gold created by the addition of copper. Alloys containing palladium or nickel are also important in commercial jewelry as these produce white gold alloys. Fourteen-karat gold-copper alloy is nearly identical in color to certain bronze alloys, and both may be used to produce police and other badges. White gold alloys can be made with palladium or nickel. Fourteen- and eighteen-karat gold alloys with silver alone appear greenish-yellow and are referred to as green gold. Blue gold can be made by alloying with iron, and purple gold can be made by alloying with aluminium. Less commonly, addition of manganese, aluminium, indium and other elements can produce more unusual colors of gold for various applications.[21]
Colloidal gold, used by electron-microscopists, is red if the particles are small; larger particles of colloidal gold are blue.[22]
Isotopes

Gold has only one stable isotope, 197
Au, which is also its only naturally occurring isotope, so gold is both a mononuclidic and monoisotopic element. Thirty-six radioisotopes have been synthesized, ranging in atomic mass from 169 to 205. The most stable of these is 195
Au with a half-life of 186.1 days. The least stable is 171
Au, which decays by proton emission with a half-life of 30 µs. Most of gold's radioisotopes with atomic masses below 197 decay by some combination of proton emission, α decay, and β+ decay. The exceptions are 195
Au, which decays by electron capture, and 196
Au, which decays most often by electron capture (93%) with a minor β− decay path (7%).[23] All of gold's radioisotopes with atomic masses above 197 decay by β− decay.[24]
At least 32 nuclear isomers have also been characterized, ranging in atomic mass from 170 to 200. Within that range, only 178
Au, 180
Au, 181
Au, 182
Au, and 188
Au do not have isomers. Gold's most stable isomer is 198m2
Au with a half-life of 2.27 days. Gold's least stable isomer is 177m2
Au with a half-life of only 7ns. 184m1
Au has three decay paths: β+ decay, isomeric transition, and alpha decay. No other isomer or isotope of gold has three decay paths.[24]
Synthesis
The production of gold from a more common element, such as lead, has long been a subject of human inquiry, and the ancient and medieval discipline of alchemy often focused on it; however, the transmutation of the chemical elements did not become possible until the understanding of nuclear physics in the 20th century. The first synthesis of gold was conducted by Japanese physicist Hantaro Nagaoka, who synthesized gold from mercury in 1924 by neutron bombardment.[25] An American team, working without knowledge of Nagaoka's prior study, conducted the same experiment in 1941, achieving the same result and showing that the isotopes of gold produced by it were all radioactive.[26]
Gold can currently be manufactured in a nuclear reactor by irradiation either of platinum or mercury.
Only the mercury isotope 196Hg, which occurs with a frequency of 0.15% in natural mercury, can be converted to gold by neutron capture, and following electron capture-decay into 197Au with slow neutrons. Other mercury isotopes are converted when irradiated with slow neutrons into one another, or formed mercury isotopes which beta decay into thallium.
Using fast neutrons, the mercury isotope 198Hg, which composes 9.97% of natural mercury, can be converted by splitting off a neutron and becoming 197Hg, which then disintegrates to stable gold. This reaction, however, possesses a smaller activation cross-section and is feasible only with un-moderated reactors.
It is also possible to eject several neutrons with very high energy into the other mercury isotopes in order to form 197Hg. However, such high-energy neutrons can be produced only by particle accelerators.

Chemistry

Although gold is the most noble of the noble metals,[27][28] it still forms many diverse compounds. The oxidation state of gold in its compounds ranges from −1 to +5, but Au(I) and Au(III) dominate its chemistry. Au(I), referred to as the aurous ion, is the most common oxidation state with soft ligands such as thioethers, thiolates, and tertiary phosphines. Au(I) compounds are typically linear. A good example is Au(CN)2−, which is the soluble form of gold encountered in mining. The binary gold halides, such as AuCl, form zigzag polymeric chains, again featuring linear coordination at Au. Most drugs based on gold are Au(I) derivatives.[29]
Au(III) (auric) is a common oxidation state, and is illustrated by gold(III) chloride, Au2Cl6. The gold atom centers in Au(III) complexes, like other d8 compounds, are typically square planar, with chemical bonds that have both covalent and ionic character.
Gold does not react with oxygen at any temperature[30] and, up to 100°C, is resistant to attack from ozone.[31]
Some free halogens react with gold.[32] Gold is strongly attacked by fluorine at dull-red heat[33] to form gold(III) fluoride. Powdered gold reacts with chlorine at 180°C to form AuCl3.[34] Gold reacts with bromine at 140°C to form gold(III) bromide, but reacts only very slowly with iodine to form the monoiodide.
Gold does not react with sulfur directly,[35] but gold(III) sulfide can be made by passing hydrogen sulfide through a dilute solution of gold(III) chloride or chlorauric acid.
Gold readily dissolves in mercury at room temperature to form an amalgam, and forms alloys with many other metals at higher temperatures. These alloys can be produced to modify the hardness and other metallurgical properties, to control melting point or to create exotic colors.[21]
Gold is unaffected by most acids. It does not react with hydrofluoric, hydrochloric, hydrobromic, hydriodic, sulfuric, or nitric acid. It does react with selenic acid, and is dissolved by aqua regia, a 1:3 mixture of nitric acid and hydrochloric acid. Nitric acid oxidizes the metal to +3 ions, but only in minute amounts, typically undetectable in the pure acid because of the chemical equilibrium of the reaction. However, the ions are removed from the equilibrium by hydrochloric acid, forming AuCl4− ions, or chloroauric acid, thereby enabling further oxidation.
Gold is similarly unaffected by most bases. It does not react with aqueous, solid, or molten sodium or potassium hydroxide. It does however, react with sodium or potassium cyanide under alkaline conditions when oxygen is present to form soluble complexes.[35]
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 as 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.
Rare oxidation states
Less common oxidation states of gold include −1, +2, and +5.
The −1 oxidation state occurs in aurides, compounds containing the Au− anion. Caesium auride (CsAu), for example, crystallizes in the caesium chloride motif;[36] rubidium, potassium, and tetramethylammonium aurides are also known.[37] Gold has the highest electron affinity of any metal, at 222.8kJ/mol, making Au− a stable species.[38]
Gold(II) compounds are usually diamagnetic with Au–Au bonds such as [Au(CH2)2P(C6H5)2]2Cl2. The evaporation of a solution of Au(OH)
3 in concentrated H
2SO
4 produces red crystals of gold(II) sulfate, Au2(SO4)2. Originally thought to be a mixed-valence compound, it has been shown to contain Au4+
2 cations, analogous to the better-known mercury(I) ion, Hg2+
2 .[39][40] A gold(II) complex, the tetraxenonogold(II) cation, which contains xenon as a ligand, occurs in [AuXe4](Sb2F11)2.[41]
Gold pentafluoride, along with its derivative anion, AuF−
6, and its difluorine complex, gold heptafluoride, is the sole example of gold(V), the highest verified oxidation state.[42]
Some gold compounds exhibit aurophilic bonding, which describes the tendency of gold ions to interact at distances that are too long to be a conventional Au–Au bond but shorter than van der Waals bonding. The interaction is estimated to be comparable in strength to that of a hydrogen bond.
Well-defined cluster compounds are numerous.[37] In such cases, gold has a fractional oxidation state. A representative example is the octahedral species {Au(P(C6H5)3)}62+. Gold chalcogenides, such as gold sulfide, feature equal amounts of Au(I) and Au(III).
Medicinal uses
Medicinal applications of gold and its complexes have a long history dating back thousands of years.[43] Several gold complexes have been applied to treat rheumatoid arthritis, the most frequently used are: aurothiomalate, aurothioglucose, and auranofin. Both gold(I) and gold(III) compounds have been have been investigated as possible anti-cancer drugs. For gold(III) complexes, reduction to gold(0/I) under physiological conditions has to be considered. Stable complexes can be generated using different types of bi-, tri-, and tetradentate ligand systems and their high efficacy has been demonstrated in vitro and in vivo.[44]
Origins
Earth's mantle origins
In 2017, an international group of scientists, including José María González Jiménez and Ramón y Cajalan, in cooperation with the University of Granada and other universities, while researching the origins of gold, historically established that it "came to the Earth's surface from the deepest regions of our planet,"[45] Earth's mantle, evidenced by their findings at Deseado Massif in the Argentinian Patagonia.[46]
Celestial origin theories

Gold is thought to have been produced in supernova nucleosynthesis, and from the collision of neutron stars,[47]  and to have been present in the dust from which the Solar System formed.[48] Because the Earth was molten when it was formed, almost all of the gold present in the early Earth probably sank into the planetary core. Therefore, most of the gold that is in the Earth's crust and mantle is thought to have been delivered to Earth later, by asteroid impacts during the Late Heavy Bombardment, about 4 billion years ago.[49][50]
Traditionally, gold is thought to have formed by the r-process (rapid neutron capture) in supernova nucleosynthesis,[51] but more recently it has been suggested that gold and other elements heavier than iron may also be produced in quantity by the r-process in the collision of neutron stars.[52] In both cases, satellite spectrometers only indirectly detected the resulting gold: "we have no spectroscopic evidence that [such] elements have truly been produced," wrote author Stephan Rosswog.[53] However, in August 2017, the signatures of heavy elements, including gold, were observed by gravitational wave detectors and other electromagnetic observatories in the GW170817 neutron star merger event.[54] Current astrophysical models suggest that single neutron star merger event generated between 3 and 13 Earth masses of gold.[55]
The asteroid that formed Vredefort crater 2.020billion years ago is often credited with seeding the Witwatersrand basin in South Africa with the richest gold deposits on earth.[56][57][58][59] However, the gold-bearing Witwatersrand rocks were laid down between 700 and 950million years before the Vredefort impact.[60][61] These gold-bearing rocks had furthermore been covered by a thick layer of Ventersdorp lavas and the Transvaal Supergroup of rocks before the meteor struck. What the Vredefort impact achieved, however, was to distort the Witwatersrand basin in such a way that the gold-bearing rocks were brought to the present erosion surface in Johannesburg, on the Witwatersrand, just inside the rim of the original 300km diameter crater caused by the meteor strike. The discovery of the deposit in 1886 launched the Witwatersrand Gold Rush. Some 22% of all the gold that is ascertained to exist today on Earth has been extracted from these Witwatersrand rocks.[61]
Occurrence
On Earth, gold is found in ores in rock formed from the Precambrian time onward.[62] It most often occurs as a native metal, typically in a metal solid solution with silver (i.e. as a gold silver alloy). Such alloys usually have a silver content of 8–10%. Electrum is elemental gold with more than 20% silver. Electrum's color runs from golden-silvery to silvery, dependent upon the silver content. The more silver, the lower the specific gravity.
Native gold occurs as very small to microscopic particles embedded in rock, often together with quartz or sulfide minerals such as "Fool's Gold", which is a pyrite.[63] These are called lode deposits. The metal in a native state is also found in the form of free flakes, grains or larger nuggets[62] that have been eroded from rocks and end up in alluvial deposits called placer deposits. Such free gold is always richer at the surface of gold-bearing veins owing to the oxidation of accompanying minerals followed by weathering, and washing of the dust into streams and rivers, where it collects and can be welded by water action to form nuggets.
Gold sometimes occurs combined with tellurium as the minerals calaverite, krennerite, nagyagite, petzite and sylvanite (see telluride minerals), and as the rare bismuthide maldonite (Au2Bi) and antimonide aurostibite (AuSb2). Gold also occurs in rare alloys with copper, lead, and mercury: the minerals auricupride (Cu3Au), novodneprite (AuPb3) and weishanite ((Au, Ag)3Hg2).
Recent research suggests that microbes can sometimes play an important role in forming gold deposits, transporting and precipitating gold to form grains and nuggets that collect in alluvial deposits.[64]
Another recent study has claimed water in faults vaporizes during an earthquake, depositing gold. When an earthquake strikes, it moves along a fault. Water often lubricates faults, filling in fractures and jogs. About 6 miles (10 kilometers) below the surface, under incredible temperatures and pressures, the water carries high concentrations of carbon dioxide, silica, and gold. During an earthquake, the fault jog suddenly opens wider. The water inside the void instantly vaporizes, flashing to steam and forcing silica, which forms the mineral quartz, and gold out of the fluids and onto nearby surfaces.[65]
Seawater
The world's oceans contain gold. Measured concentrations of gold in the Atlantic and Northeast Pacific are 50–150 femtomol/L or 10–30 parts per quadrillion (about 10–30g/km3). In general, gold concentrations for south Atlantic and central Pacific samples are the same (~50 femtomol/L) but less certain. Mediterranean deep waters contain slightly higher concentrations of gold (100–150 femtomol/L) attributed to wind-blown dust and/or rivers. At 10 parts per quadrillion the Earth's oceans would hold 15,000 tonnes of gold.[66] These figures are three orders of magnitude less than reported in the literature prior to 1988, indicating contamination problems with the earlier data.
A number of people have claimed to be able to economically recover gold from sea water, but they were either mistaken or acted in an intentional deception. Prescott Jernegan ran a gold-from-seawater swindle in the United States in the 1890s, as did an English fraudster in the early 1900s.[67] Fritz Haber did research on the extraction of gold from sea water in an effort to help pay Germany's reparations following World War I.[68] Based on the published values of 2 to 64 ppb of gold in seawater a commercially successful extraction seemed possible. After analysis of 4,000 water samples yielding an average of 0.004 ppb it became clear that extraction would not be possible and he stopped the project.[69]
History

As of 1990, gold artifacts found at the Nahal Qana cave cemetery of the 4th millennium BC were the earliest from the Levant.[71] 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 artifacts.[62] Gold artifacts such as the golden hats and the Nebra disk appeared in Central Europe from the 2nd millennium BC Bronze Age.
The oldest known map of a gold mine was drawn in the 19th Dynasty of Ancient Egypt (1320–1200 BC), whereas the first written reference to gold was recorded in the 12th Dynasty around 1900 BC.[72] Egyptian hieroglyphs from as early as 2600 BC describe gold, which King Tushratta of the Mitanni claimed was "more plentiful than dirt" in Egypt.[73] Egypt and especially Nubia had the resources to make them major gold-producing areas for much of history. One of the earliest known maps, known as the Turin Papyrus Map, 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.

Gold is mentioned in the Amarna letters numbered 19[74] and 26[75] from around the 14th century BC.[76][77]
Gold is mentioned frequently in the Old Testament, starting with Genesis 2:11 (at Havilah), the story of The Golden Calf and many parts of the temple including the Menorah and the golden altar. In the New Testament, it is included with the gifts of the magi in the first chapters of Matthew. The Book of Revelation 21:21 describes the city of New Jerusalem as having streets "made of pure gold, clear as crystal". Exploitation of gold in the south-east corner of the Black Sea is said to date from the time of Midas, and this gold was important in the establishment of what is probably the world's earliest coinage in Lydia around 610 BC.[78] The legend of the golden fleece dating from eighth century BCE may refer to the use of fleeces to trap gold dust from placer deposits in the ancient world. From the 6th or 5th century BC, the Chu (state) circulated the Ying Yuan, one kind of square gold coin.
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, 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.
During Mansa Musa's (ruler of the Mali Empire from 1312 to 1337) hajj to Mecca in 1324, he passed through Cairo in July 1324, and was reportedly accompanied by a camel train that included thousands of people and nearly a hundred camels where he gave away so much gold that it depressed the price in Egypt for over a decade, causing high inflation.[79] 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, Kingdom of Mali[80]

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 Mesoamerica, Peru, Ecuador and Colombia. The Aztecs regarded gold as the product of the gods, calling it literally "god excrement" (teocuitlatl in Nahuatl), and after Moctezuma II was killed, most of this gold was shipped to Spain.[81] 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.[82] Rumors of cities filled with gold fueled legends of El Dorado.
Gold played a role in western culture, as a cause for desire and of corruption, as told in children's fables such as Rumpelstiltskin—where Rumpelstiltskin turns hay into gold for the peasant's daughter in return for her child when she becomes a princess—and the stealing of the hen that lays golden eggs in Jack and the Beanstalk.
The top prize at the Olympic Games and many other sports competitions is the gold medal.
75% of the presently accounted for gold has been extracted since 1910. It has been estimated that the currently known amount of gold internationally would form a single cube 20m (66ft) on a side (equivalent to 8,000m3).[83]
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 did promote an interest in systematically finding out what can be done with substances, and this laid the 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.
Golden treasures have been rumored to be found at various locations, following tragedies such as the Jewish temple treasures in the Vatican, following the temple's destruction in 70 AD, a gold stash on the Titanic, the Nazi gold train – following World War II.
The Dome of the Rock is covered with an ultra-thin golden glassier. The Sikh Golden temple, the Harmandir Sahib, is a building covered with gold. Similarly the Wat Phra Kaew emerald Buddhist temple (wat) in Thailand has ornamental gold-leafed statues and roofs. Some European king and queen's crowns were made of gold, and gold was used for the bridal crown since antiquity. An ancient Talmudic text circa 100 AD describes Rachel, wife of Rabbi Akiva, receiving a "Jerusalem of Gold" (diadem). A Greek burial crown made of gold was found in a grave circa 370 BC.
Etymology

"Gold" is cognate with similar words in many Germanic languages, deriving via Proto-Germanic *gulþą from Proto-Indo-European *ǵʰelh₃- ("to shine, to gleam; to be yellow or green").[84][85]
The symbol Au is from the Latin: aurum, the Latin word for "gold".[86] The Proto-Indo-European ancestor of aurum was *h₂é-h₂us-o-, meaning "glow". This word is derived from the same root (Proto-Indo-European *h₂u̯es- "to dawn") as *h₂éu̯sōs, the ancestor of the Latin word Aurora, "dawn".[87] This etymological relationship is presumably behind the frequent claim in scientific publications that aurum meant "shining dawn".[88]
Culture

Outside chemistry, gold is mentioned in a variety of expressions, most often associated with intrinsic worth.[38] Great human achievements are frequently rewarded with gold, in the form of gold medals, gold trophies and other decorations. Winners of athletic events and other graded competitions are usually awarded a gold medal. 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 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. A person's most valued or most successful latter years are sometimes considered "golden years". The height of a civilization is referred to as a golden age.
In some forms of Christianity and Judaism, gold has been associated both with holiness and evil. In the Book of Exodus, the Golden Calf is a symbol of idolatry, while 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 Byzantine iconography the halos of Christ, Mary and the Christian saints are often golden.
According to Christopher Columbus, 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.[89]
Wedding rings have been made of gold.[90] It is long lasting and unaffected by the passage of time and may aid in the ring symbolism of eternal vows before God and the perfection the marriage signifies. In Orthodox Christian wedding ceremonies, the wedded couple is adorned with a golden crown (though some opt for wreaths, instead) during the ceremony, an amalgamation of symbolic rites.
Production

The World Gold Council states that as of the end of 2017, "there were 187,200 tonnes of stocks in existence above ground". This can be represented by a cube with an edge length of about 21 meters.[91] At $1,349 per troy ounce, 187,200 metric tonnes of gold would have a value of $8.9 trillion.
As of 2017, the world's largest gold producer by far was China with 455 tonnes. The second-largest producer, Australia, mined 270 tonnes in the same year, followed by Russia with 250 tonnes.[9]
Mining and prospecting

Since the 1880s, South Africa has been the source of a large proportion of the world's gold supply, and about 50% of the gold presently accounted is from South Africa. Production in 1970 accounted for 79% of the world supply, about 1,480 tonnes.  In 2007 China (with 276 tonnes) overtook South Africa as the world's largest gold producer, the first time since 1905 that South Africa has not been the largest.[92]
As of 2014, China was the world's leading gold-mining country, followed in order by Australia, Russia, the United States, Canada, and Peru. South Africa, which had dominated world gold production for most of the 20th century, had declined to sixth place.[9] Other major producers are the Ghana, Burkina Faso, Mali, Indonesia and Uzbekistan.

In South America, the controversial project Pascua Lama aims at exploitation of rich fields in the high mountains of Atacama Desert, at the border between Chile and Argentina.
Today about one-quarter of the world gold output is estimated to originate from artisanal or small scale mining.[93]
The city of Johannesburg located in South Africa was founded as a result of the Witwatersrand Gold Rush which resulted in the discovery of some of the largest natural gold deposits in recorded history.  The gold fields are confined to the northern and north-western edges of the Witwatersrand basin, which is a 5–7km thick layer of archean rocks located, in most places, deep under the Free State, Gauteng and surrounding provinces.[94] These Witwatersrand rocks are exposed at the surface on the Witwatersrand, in and around Johannesburg, but also in isolated patches to the south-east and south-west of Johannesburg, as well as in an arc around the Vredefort Dome which lies close to the center of the Witwatersrand basin.[60][94] From these surface exposures the basin dips extensively, requiring some of the mining to occur at depths of nearly 4000m, making them, especially the Savuka and TauTona mines to the south-west of Johannesburg, the deepest mines on earth. The gold is found only in six areas where archean rivers from the north and north-west formed extensive pebbly Braided river deltas before draining into the "Witwatersrand sea" where the rest of the Witwatersrand sediments were deposited.[94]
The Second Boer War of 1899–1901 between the British Empire and the Afrikaner Boers was at least partly over the rights of miners and possession of the gold wealth in South Africa.
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.[95] The first major gold strike in the United States occurred in a small north Georgia town called Dahlonega.[96] Further gold rushes occurred in California, Colorado, the Black Hills, Otago in New Zealand, Australia, Witwatersrand in South Africa, and the Klondike in Canada.
Extraction and refining

Gold extraction is most economical in large, easily mined deposits. Ore grades as little as 0.5parts per million (ppm) can be economical. Typical ore grades in open-pit mines are 1–5ppm; ore grades in underground or hard rock mines are usually at least 3ppm. Because ore grades of 30ppm are usually needed before gold is visible to the naked eye, in most gold mines the gold is invisible.
The average gold mining and extraction costs were about $317 per troy ounce in 2007, but these can vary widely depending on mining type and ore quality; global mine production amounted to 2,471.1 tonnes.[100]
After initial production, gold is often subsequently refined industrially by the Wohlwill process which is based on electrolysis or by the Miller process, that is chlorination in the melt. The Wohlwill process results in higher purity, but is more complex and is only applied in small-scale installations.[101][102] Other methods of assaying and purifying smaller amounts of gold include parting and inquartation as well as cupellation, or refining methods based on the dissolution of gold in aqua regia.[103]
Consumption
The consumption of gold produced in the world is about 50% in jewelry, 40% in investments, and 10% in industry.[8][104]
According to World Gold Council, China is the world's largest single consumer of gold in 2013 and toppled India for the first time with Chinese consumption increasing by 32 percent in a year, while that of India only rose by 13 percent and world consumption rose by 21 percent. Unlike India where gold is mainly used for jewelry, China uses gold for manufacturing and retail.[105]
Pollution

Gold production is associated with contribution to hazardous pollution.[106][107]
Low-grade gold ore may contain less than one ppm gold metal; such ore is ground and mixed with sodium cyanide to dissolve the gold. Cyanide is a highly poisonous chemical, which can kill living creatures when exposed in minute quantities. Many cyanide spills[108] from gold mines have occurred in both developed and developing countries which killed aquatic life in long stretches of affected rivers. Environmentalists consider these events major environmental disasters.[109][110] Thirty tons of used ore is dumped as waste for producing one troy ounce of gold.[111] Gold ore dumps are the source of many heavy elements such as cadmium, lead, zinc, copper, arsenic, selenium and mercury. When sulfide-bearing minerals in these ore dumps are exposed to air and water, the sulfide transforms into sulfuric acid which in turn dissolves these heavy metals facilitating their passage into surface water and ground water. This process is called acid mine drainage. These gold ore dumps are long term, highly hazardous wastes second only to nuclear waste dumps.[111]
It was once common to use mercury to recover gold from ore, but today the use of mercury is largely limited to small-scale individual miners.[112] Minute quantities of mercury compounds can reach water bodies, causing heavy metal contamination. Mercury can then enter into the human food chain in the form of methylmercury. Mercury poisoning in humans causes incurable brain function damage and severe retardation.
Gold extraction is also a highly energy intensive industry, extracting ore from deep mines and grinding the large quantity of ore for further chemical extraction requires nearly 25 kWh of electricity per gram of gold produced.[113]
Monetary use

Gold has been widely used throughout the world as money,[114] for efficient indirect exchange (versus barter), and to store wealth in hoards. For exchange purposes, mints produce standardized gold bullion coins, bars and other units of fixed weight and purity.
The first known coins containing gold were struck in Lydia, Asia Minor, around 600 BC.[78] The talent coin of gold in use during the periods of Grecian history both before and during the time of the life of Homer weighed between 8.42 and 8.75grams.[115] From an earlier preference in using silver, European economies re-established the minting of gold as coinage during the thirteenth and fourteenth centuries.[116]
Bills (that mature into gold coin) and gold certificates (convertible into gold coin at the issuing bank) added to the circulating stock of gold standard money in most 19th century industrial economies.
In preparation for World War I the warring nations moved to fractional gold standards, inflating their currencies to finance the war effort.
Post-war, the victorious countries, most notably Britain, gradually restored gold-convertibility, but international flows of gold via bills of exchange remained embargoed; international shipments were made exclusively for bilateral trades or to pay war reparations.
After World War II gold was replaced by a system of nominally convertible currencies related by fixed exchange rates following the Bretton Woods system. Gold standards and the direct convertibility of currencies to gold have been abandoned by world governments, led in 1971 by the United States' refusal to redeem its dollars in gold. Fiat currency now fills most monetary roles. Switzerland was the last country to tie its currency to gold; it backed 40% of its value until the Swiss joined the International Monetary Fund in 1999.[117]
Central banks continue to keep a portion of their liquid reserves as gold in some form, and metals exchanges such as the London Bullion Market Association still clear transactions denominated in gold, including future delivery contracts.
Today, gold mining output is declining.[118]
With the sharp growth of economies in the 20th century, and increasing foreign exchange, the world's gold reserves and their trading market have become a small fraction of all markets and fixed exchange rates of currencies to gold have been replaced by floating prices for gold and gold future contract.
Though the gold stock grows by only 1 or 2% per year, very little metal is irretrievably consumed. Inventory above ground would satisfy many decades of industrial and even artisan uses at current prices.
The gold proportion (fineness) of alloys is measured by karat (k). Pure gold (commercially termed fine gold) is designated as 24 karat, abbreviated 24k. English gold coins intended for circulation from 1526 into the 1930s were typically a standard 22k alloy called crown gold,[119] for hardness (American gold coins for circulation after 1837 contain an alloy of 0.900 fine gold, or 21.6 kt).[120]
Although the prices 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. 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.
The ISO 4217 currency code of gold is XAU.[121] Many holders of gold store it in form of bullion coins or bars as a hedge against inflation or other economic disruptions, though its efficacy as such has been questioned; historically, it has not proven itself reliable as a hedging instrument.[122]. Modern bullion coins for investment or collector purposes do not require good mechanical wear properties; they are typically fine gold at 24k, although the American Gold Eagle and the British gold sovereign continue to be minted in 22k (0.92) metal in historical tradition, and the South African Krugerrand, first released in 1967, is also 22k (0.92).[123]
The special issue Canadian Gold Maple Leaf coin contains the highest purity gold of any bullion coin, at 99.999% or 0.99999, while the popular issue Canadian Gold Maple Leaf coin has a purity of 99.99%. In 2006, the United States Mint began producing the American Buffalo gold bullion coin with a purity of 99.99%. The Australian Gold Kangaroos were first coined in 1986 as the Australian Gold Nugget but changed the reverse design in 1989. Other modern coins include the Austrian Vienna Philharmonic bullion coin and the Chinese Gold Panda.
Price

As of September2017, gold is valued at around $42 per gram ($1,300 per troy ounce).
Like other precious metals, gold is measured by troy weight and by grams. The proportion of gold in the alloy is measured by karat (k), with 24 karat (24k) being pure gold, and lower karat numbers proportionally less. The purity of a gold bar or coin can also be expressed as a decimal figure ranging from 0 to 1, known as the millesimal fineness, such as 0.995 being nearly pure.
The price of gold is determined through trading in the gold and derivatives markets, but a procedure known as the Gold Fixing in London, originating in September 1919, provides a daily benchmark price to the industry. The afternoon fixing was introduced in 1968 to provide a price when US markets are open.[124]
History
Historically gold coinage was widely used as currency; when paper money was introduced, it typically was a receipt redeemable for gold coin or bullion. In a monetary system known as the gold standard, a certain weight of gold was given the name of a unit of currency. For a long period, the United States government set the value of the US dollar so that one troy ounce was equal to $20.67 ($0.665 per gram), but in 1934 the dollar was devalued to $35.00 per troy ounce ($0.889/g). By 1961, it was becoming hard to maintain this price, and a pool of US and European banks agreed to manipulate the market to prevent further currency devaluation against increased gold demand.[125]
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 store of value 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, which holds about 3%[126] of the gold known to exist and accounted for today, as does the similarly laden U.S. Bullion Depository at Fort Knox.
In 2005 the World Gold Council estimated total global gold supply to be 3,859 tonnes and demand to be 3,754 tonnes, giving a surplus of 105 tonnes.[127]
After the August 15, 1971 Nixon shock, the price began to greatly increase,[128] and between 1968 and 2000 the price of gold ranged widely, from a high of $850 per troy ounce ($27.33/g) on January 21, 1980, to a low of $252.90 per troy ounce ($8.13/g) on June 21, 1999 (London Gold Fixing).[129] Prices increased rapidly from 2001, but the 1980 high was not exceeded until January 3, 2008, when a new maximum of $865.35 per troy ounce was set.[130] Another record price was set on March 17, 2008, at $1023.50 per troy ounce ($32.91/g).[130]
In late 2009, gold markets experienced renewed momentum upwards due to increased demand and a weakening US dollar. On December 2, 2009, gold reached a new high closing at $1,217.23.[131] Gold further rallied hitting new highs in May 2010 after the European Union debt crisis prompted further purchase of gold as a safe asset.[132][133] On March 1, 2011, gold hit a new all-time high of $1432.57, based on investor concerns regarding ongoing unrest in North Africa as well as in the Middle East.[134]
From April 2001 to August 2011, spot gold prices more than quintupled in value against the US dollar, hitting a new all-time high of $1,913.50 on August 23, 2011,[135] prompting speculation that the long secular bear market had ended and a bull market had returned.[136] However, the price then began a slow decline towards $1200 per troy ounce in late 2014 and 2015.
Other applications
Jewelry

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 karat rating, typically 22k, 18k, 14k or 10k, contain higher percentages of copper or other base metals or silver or palladium in the alloy.[21] Nickel is toxic, and its release from nickel white gold is controlled by legislation in Europe.[21] Palladium-gold alloys are more expensive than those using nickel.[137] High-karat white gold alloys are 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.
By 2014, the gold jewelry industry was escalating despite a dip in gold prices. Demand in the first quarter of 2014 pushed turnover to $23.7 billion according to a World Gold Council report.
Gold solder is used for joining the components of gold jewelry by high-temperature hard soldering or brazing. If the work is to be of hallmarking quality, the gold solder alloy must match the fineness (purity) of the work, and alloy formulas are manufactured to color-match yellow and white gold. Gold solder is usually made in at least three melting-point ranges referred to as Easy, Medium and Hard. By using the hard, high-melting point solder first, followed by solders with progressively lower melting points, goldsmiths can assemble complex items with several separate soldered joints. Gold can also be made into thread and used in embroidery.
Electronics
Only 10% of the world consumption of new gold produced goes to industry,[8] but by far the most important industrial use for new gold is in fabrication of corrosion-free electrical connectors in computers and other electrical devices. For example, according to the World Gold Council, a typical cell phone may contain 50mg of gold, worth about 50 cents. But since nearly one billion cell phones are produced each year, a gold value of 50 cents in each phone adds to $500 million in gold from just this application.[138]
Though gold is attacked by free chlorine, its good conductivity and general resistance to oxidation and corrosion in other environments (including resistance to non-chlorinated acids) has led to its widespread industrial use in the electronic era as a thin-layer coating on electrical connectors, thereby ensuring good connection. For example, gold is used in the connectors of the more expensive electronics cables, such as audio, video and USB cables. The benefit of using gold over other connector metals such as tin in these applications has been debated; gold connectors are often criticized by audio-visual experts as unnecessary for most consumers and seen as simply a marketing ploy. However, the use of gold in other applications in electronic sliding contacts in highly humid or corrosive atmospheres, and in use for contacts with a very high failure cost (certain computers, communications equipment, spacecraft, jet aircraft engines) remains very common.[139]
Besides sliding electrical contacts, gold is also used in electrical contacts because of its resistance to corrosion, electrical conductivity, ductility and lack of toxicity.[140] Switch contacts are generally subjected to more intense corrosion stress than are sliding contacts. Fine gold wires are used to connect semiconductor devices to their packages through a process known as wire bonding.
The concentration of free electrons in gold metal is 5.91×1022cm−3.[141] Gold is highly conductive to electricity, and has been used for electrical wiring in some high-energy applications (only silver and copper are more conductive per volume, but gold has the advantage of corrosion resistance). For example, gold electrical wires were used during some of the Manhattan Project's atomic experiments, but large high-current silver wires were used in the calutron isotope separator magnets in the project.
It is estimated that 16% of the world's gold and 22% of the world's silver is contained in electronic technology in Japan.[142]
Medicine
Metallic and gold compounds have long been used for medicinal purposes. Gold, usually as the metal, is perhaps the most anciently administered medicine (apparently by shamanic practitioners)[143] and known to Dioscorides.[144][145] In medieval times, gold was often seen as beneficial for the health, in the belief that something so rare and beautiful could not be anything but healthy. Even some modern esotericists and forms of alternative medicine assign metallic gold a healing power.
In the 19th century gold had a reputation as a "nervine", a therapy for nervous disorders. Depression, epilepsy, migraine, and glandular problems such as amenorrhea and impotence were treated, and most notably alcoholism (Keeley, 1897).[146]
The apparent paradox of the actual toxicology of the substance suggests the possibility of serious gaps in the understanding of the action of gold in physiology.[147] Only salts and radioisotopes of gold are of pharmacological value, since elemental (metallic) gold is inert to all chemicals it encounters inside the body (i.e., ingested gold cannot be attacked by stomach acid). Some gold salts do have anti-inflammatory properties and at present two are still used as pharmaceuticals in the treatment of arthritis and other similar conditions in the US (sodium aurothiomalate and auranofin). These drugs have been explored as a means to help to reduce the pain and swelling of rheumatoid arthritis, and also (historically) against tuberculosis and some parasites.[148]
Gold alloys are used in restorative dentistry, especially in tooth restorations, such as crowns and permanent bridges. The gold alloys' slight malleability facilitates the creation of a superior molar mating surface with other teeth and produces results that are generally more satisfactory than those produced by the creation of porcelain crowns. The use of gold crowns in more prominent teeth such as incisors is favored in some cultures and discouraged in others.
Colloidal gold preparations (suspensions of gold nanoparticles) in water are intensely red-colored, and can be made with tightly controlled particle sizes up to a few tens of nanometers across by reduction of gold chloride with citrate or ascorbate ions. Colloidal gold is used in research applications in medicine, biology and materials science. The technique of immunogold labeling exploits the ability of the gold particles to adsorb protein molecules onto their surfaces. Colloidal gold particles coated with specific antibodies can be used as probes for the presence and position of antigens on the surfaces of cells.[149] In ultrathin sections of tissues viewed by electron microscopy, the immunogold labels appear as extremely dense round spots at the position of the antigen.[150]
Gold, or alloys of gold and palladium, are applied as conductive coating to biological specimens and other non-conducting materials such as plastics and glass to be viewed in a scanning electron microscope. The coating, which is usually applied by sputtering with an argon plasma, has a triple role in this application. Gold's very high electrical conductivity drains electrical charge to earth, and its very high density provides stopping power for electrons in the electron beam, helping to limit the depth to which the electron beam penetrates the specimen. This improves definition of the position and topography of the specimen surface and increases the spatial resolution of the image. 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.[151]
The isotope gold-198 (half-life 2.7 days) is used, in nuclear medicine, in some cancer treatments and for treating other diseases.[152][153]
Cuisine
Gold can be used in food and has the E number 175.[154] In 2016, the European Food Safety Authority published an opinion on the re-evaluation of gold as a food additive. Concerns included the possible presence of minute amounts of gold nanoparticles in the food additive, and that gold nanoparticles have been shown to be genotoxic in mammalian cells in vitro.[155]
Gold leaf, flake or dust is used on and in some gourmet foods, notably sweets and drinks as decorative ingredient.[156] Gold flake was used by the nobility in medieval Europe as a decoration in food and drinks,[157] in the form of leaf, flakes or dust, either to demonstrate the host's wealth or in the belief that something that valuable and rare must be beneficial for one's health.
Danziger Goldwasser (German: Gold water of Danzig) or Goldwasser (English: Goldwater) is a traditional German herbal liqueur[158] produced in what is today Gdańsk, Poland, and Schwabach, Germany, and contains flakes of gold leaf. There are also some expensive (c. $1000) cocktails which contain flakes of gold leaf.[159] However, since metallic gold is inert to all body chemistry, it has no taste, it provides no nutrition, and it leaves the body unaltered.[160]
Vark is a foil composed of a pure metal that is sometimes gold,[161] and is used for garnishing sweets in South Asian cuisine.
Miscellanea

Gold produces a deep, intense red color when used as a coloring agent in cranberry glass.
In photography, gold toners are used to shift the color of silver bromide black-and-white prints towards brown or blue tones, or to increase their stability. Used on sepia-toned prints, gold toners produce red tones. Kodak published formulas for several types of gold toners, which use gold as the chloride.[162]
Gold is a good reflector of electromagnetic radiation such as infrared and visible light, as well as radio waves. It is used for the protective coatings on many artificial satellites, in infrared protective faceplates in thermal-protection suits and astronauts' helmets, and in electronic warfare planes such as the EA-6B Prowler.
Gold is used as the reflective layer on some high-end CDs.
Automobiles may use gold for heat shielding. McLaren uses gold foil in the engine compartment of its F1 model.[163]
Gold can be manufactured so thin that it appears semi-transparent. It is used in some aircraft cockpit windows for de-icing or anti-icing by passing electricity through it. The heat produced by the resistance of the gold is enough to prevent ice from forming.[164]
Gold is attacked by and dissolves in alkaline solutions of potassium or sodium cyanide, to form the salt gold cyanide—a technique that has been used in extracting metallic gold from ores in the cyanide process. Gold cyanide is the electrolyte used in commercial electroplating of gold onto base metals and electroforming.
Gold chloride (chloroauric acid) solutions are used to make colloidal gold by reduction with citrate or ascorbate ions. Gold chloride and gold oxide are used to make cranberry or red-colored glass, which, like colloidal gold suspensions, contains evenly sized spherical gold nanoparticles.[165]
Gold, when dispersed in nanoparticles, can act as a heterogeneous catalyst of chemical reactions.
Toxicity
Pure metallic (elemental) gold is non-toxic and non-irritating when ingested[166] and is sometimes used as a food decoration in the form of gold leaf.[167] Metallic gold is also a component of the alcoholic drinks Goldschläger, Gold Strike, and Goldwasser. Metallic gold is approved as a food additive in the EU (E175 in the Codex Alimentarius). 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.[168][169] Gold toxicity can be ameliorated with chelation therapy with an agent such as dimercaprol.
Gold metal was voted Allergen of the Year in 2001 by the American Contact Dermatitis Society, gold contact allergies affect mostly women.[170] Despite this, gold is a relatively non-potent contact allergen, in comparison with metals like nickel.[171]
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.[172]
See also

Bulk leach extractable gold
Chrysiasis (dermatological condition)
Commodity fetishism (Marxist economic theory)
Digital gold currency
GFMS consultancy
Gold fingerprinting
Gold phosphine complex
Gold Prospectors Association of America
List of countries by gold production
Mining in Roman Britain
Prospecting
Tumbaga

Hart, Matthew, , New York: Simon & Schuster, 2013. ISBN9781451650020

 (MP3) from the Royal Society of Chemistry's Chemistry World:  www.rsc.org
 at The Periodic Table of Videos (University of Nottingham)
, www.lateralscience.co.uk
 at the Wayback Machine(archived 7 March 2008), www.epa.gov

What is the origin of the symbol Au for gold?


A chordate (/kɔːrdeɪt/) is an animal constituting the phylum Chordata. During some period of their life cycle, chordates possess a notochord, a dorsal nerve cord, pharyngeal slits, an endostyle, and a post-anal tail: these five anatomical features define this phylum.  Chordates are also bilaterally symmetric; and have a coelom, metameric segmentation, and a circulatory system.
The Chordata and Ambulacraria together form the superphylum Deuterostomia. Chordates are divided into three subphyla: Vertebrata (fish, amphibians, reptiles, birds, and mammals); Tunicata (salps and sea squirts); and Cephalochordata (which includes lancelets). There are also extinct taxa such as the Vetulicolia. Hemichordata (which includes the acorn worms) has been presented as a fourth chordate subphylum, but now is treated as a separate phylum: hemichordates and Echinodermata form the Ambulacraria, the sister phylum of the Chordates. Of the more than 65,000 living species of chordates, about half are bony fish that are members of the superclass Osteichthyes.
Chordate fossils have been found from as early as the Cambrian explosion, 541 million years ago. Cladistically  (phylogenetically), vertebrates - chordates with the notochord replaced by a vertebral column during development - are considered to be a subgroup of the clade Craniata, which consists of chordates with a skull. The Craniata and Tunicata compose the clade Olfactores. (See diagram under Phylogeny.)
Anatomy
Chordates form a phylum of animals that are defined by having at some stage in their lives all of the following anatomical features:[3]
A notochord, a fairly stiff rod of cartilage that extends along the inside of the body. Among the vertebrate sub-group of chordates the notochord develops into the spine, and in wholly aquatic species this helps the animal to swim by flexing its tail.
A dorsal neural tube. In fish and other vertebrates, this develops into the spinal cord, the main communications trunk of the nervous system.
Pharyngeal slits. The pharynx is the part of the throat immediately behind the mouth. In fish, the slits are modified to form gills, but in some other chordates they are part of a filter-feeding system that extracts particles of food from the water in which the animals live.
Post-anal tail. A muscular tail that extends backwards behind the anus.
An endostyle. This is a groove in the ventral wall of the pharynx. In filter-feeding species it produces mucus to gather food particles, which helps in transporting food to the esophagus.[4] It also stores iodine, and may be a precursor of the vertebrate thyroid gland.[3]
There are soft constraints that separate chordates from certain other biological lineages, but are not part of the formal definition:
All chordates are deuterostomes. This means that, during the embryo development stage, the anus forms before the mouth.
All chordates are based on a bilateral body plan.[5]
All chordates are coelomates, and have a fluid filled body cavity called a coelom with a complete lining called peritoneum derived from mesoderm (see Brusca and Brusca).[6]

Classification
The following schema is from the third edition of Vertebrate Palaeontology.[7] The invertebrate chordate classes are from Fishes of the World.[8] While it is structured so as to reflect evolutionary relationships (similar to a cladogram), it also retains the traditional ranks used in Linnaean taxonomy.
Phylum Chordata
†Vetulicolia
Subphylum Cephalochordata (Acraniata) – (lancelets; 30 species)
Class Leptocardii (lancelets)
Clade Olfactores
Subphylum Tunicata (Urochordata) – (tunicates; 3,000 species)
Class Ascidiacea (sea squirts)
Class Thaliacea (salps)
Class Appendicularia (larvaceans)
Class Sorberacea
Subphylum Vertebrata (Craniata) (vertebrates – animals with backbones; 57,674 species)
Infraphylum incertae sedis Cyclostomata
Superclass 'Agnatha' paraphyletic (jawless vertebrates; 100+ species)
Class Myxini (hagfish; 65 species)
Class Petromyzontida or Hyperoartia (lampreys)
Class †Conodonta
Class †Myllokunmingiida
Class †Pteraspidomorphi
Class †Thelodonti
Class †Anaspida
Class †Cephalaspidomorphi
Infraphylum Gnathostomata (jawed vertebrates)
Class †Placodermi (Paleozoic armoured forms; paraphyletic in relation to all other gnathostomes)
Class Chondrichthyes (cartilaginous fish; 900+ species)
Class †Acanthodii (Paleozoic "spiny sharks"; paraphyletic in relation to Chondrichthyes)
Superclass Osteichthyes (bony fish; 30,000+ species)
Class Actinopterygii (ray-finned fish; about 30,000 species)
Class Sarcopterygii (lobe-finned fish: 8 species)
Superclass Tetrapoda (four-limbed vertebrates; 28,000+ species) (The classification below follows Benton 2004, and uses a synthesis of rank-based Linnaean taxonomy and also reflects evolutionary relationships. Benton included the Superclass Tetrapoda in the Subclass Sarcopterygii in order to reflect the direct descent of tetrapods from lobe-finned fish, despite the former being assigned a higher taxonomic rank.)[9]
Class Amphibia (amphibians; 7,000+ species)
Class Sauropsida (reptiles (including birds); 19,000+ species - 10,000+ species of birds and 9,500+ species of reptiles)[10][11]
Class Synapsida (mammals; 5,700+ species)
Subphyla

Craniata (Vertebrata)

Craniates, one of the three subdivisions of chordates, all have distinct skulls. They include the hagfish, which have no vertebrae. Michael J. Benton commented that "craniates are characterized by their heads, just as chordates, or possibly all deuterostomes, are by their tails".[12]
Most craniates are vertebrates, in which the notochord is replaced by the vertebral column.[13] These consist of a series of bony or cartilaginous cylindrical vertebrae, generally with neural arches that protect the spinal cord, and with projections that link the vertebrae. However hagfish have incomplete braincases and no vertebrae, and are therefore not regarded as vertebrates,[14]
but as members of the craniates, the group from which vertebrates are thought to have evolved.[15] However the cladistic exclusion of hagfish from the vertebrates is controversial, as they may be degenerate vertebrates who have lost their vertebral columns.[16]
The position of lampreys is ambiguous. They have complete braincases and rudimentary vertebrae, and therefore may be regarded as vertebrates and true fish.[17] However, molecular phylogenetics, which uses biochemical features to classify organisms, has produced both results that group them with vertebrates and others that group them with hagfish.[18] If lampreys are more closely related to the hagfish than the other vertebrates, this would suggest that they form a clade, which has been named the Cyclostomata.[19]
Tunicata

Most tunicates appear as adults in two major forms, known as "sea squirts" and salps, both of which are soft-bodied filter-feeders that lack the standard features of chordates. Sea squirts are sessile and consist mainly of water pumps and filter-feeding apparatus;[20] salps float in mid-water, feeding on plankton, and have a two-generation cycle in which one generation is solitary and the next forms chain-like colonies.[21] However, all tunicate larvae have the standard chordate features, including long, tadpole-like tails; they also have rudimentary brains, light sensors and tilt sensors.[20] The third main group of tunicates, Appendicularia (also known as Larvacea), retain tadpole-like shapes and active swimming all their lives, and were for a long time regarded as larvae of sea squirts or salps.[22] The etymology of the term Urochorda(ta) (Balfour 1881) is from the ancient Greek οὐρά (oura, "tail") + Latin chorda ("cord"), because the notochord is only found in the tail.[23] The term Tunicata (Lamarck 1816) is recognised as having precedence and is now more commonly used.[20]
Cephalochordata: Lancelets

Cephalochordates are small, "vaguely fish-shaped" animals that lack brains, clearly defined heads and specialized sense organs.[24] These burrowing filter-feeders compose the earliest-branching chordate sub-phylum.[25][26][27]

Phylogeny
Overview

There is still much ongoing differential (DNA sequence based) comparison research that is trying to separate out the simplest forms of chordates. As some lineages of the 90% of species that lack a backbone or notochord might have lost these structures over time, this complicates the classification of chordates. Some chordate lineages may only be found by DNA analysis, when there is no physical trace of any chordate-like structures.[29]
Attempts to work out the evolutionary relationships of the chordates have produced several hypotheses. The current consensus is that chordates are monophyletic, meaning that the Chordata include all and only the descendants of a single common ancestor, which is itself a chordate, and that craniates' nearest relatives are tunicates.
All of the earliest chordate fossils have been found in the Early Cambrian Chengjiang fauna, and include two species that are regarded as fish, which implies that they are vertebrates. Because the fossil record of early chordates is poor, only molecular phylogenetics offers a reasonable prospect of dating their emergence. However, the use of molecular phylogenetics for dating evolutionary transitions is controversial.
It has also proved difficult to produce a detailed classification within the living chordates. Attempts to produce evolutionary "family trees" shows that many of the traditional classes are paraphyletic.

Deuterostomes

Ambulacraria

Hemichordates
EchinodermsChordates

CephalochordatesOlfactores

Tunicates
Craniates (vertebrates)
Diagram of the family tree of chordates[4]
While this has been well known since the 19th century, an insistence on only monophyletic taxa has resulted in vertebrate classification being in a state of flux.[30]
The majority of animals more complex than jellyfish and other Cnidarians are split into two groups, the protostomes and deuterostomes, the latter of which contains chordates.[31] It seems very likely the  million-year-old Kimberella was a member of the protostomes.[32][33] If so, this means the protostome and deuterostome lineages must have split some time before Kimberella appeared—at least million years ago, and hence well before the start of the Cambrian million years ago.[31] The Ediacaran fossil Ernietta, from about  million years ago, may represent a deuterostome animal.[34]

Fossils of one major deuterostome group, the echinoderms (whose modern members include starfish, sea urchins and crinoids), are quite common from the start of the Cambrian, million years ago.[35] The Mid Cambrian fossil Rhabdotubus johanssoni has been interpreted as a pterobranch hemichordate.[36] Opinions differ about whether the Chengjiang fauna fossil Yunnanozoon, from the earlier Cambrian, was a hemichordate or chordate.[37][38] Another fossil, Haikouella lanceolata, also from the Chengjiang fauna, is interpreted as a chordate and possibly a craniate, as it shows signs of a heart, arteries, gill filaments, a tail, a neural chord with a brain at the front end, and possibly eyes—although it also had short tentacles round its mouth.[38] Haikouichthys and Myllokunmingia, also from the Chengjiang fauna, are regarded as fish.[28][39] Pikaia, discovered much earlier (1911) but from the Mid Cambrian Burgess Shale (505 Ma), is also regarded as a primitive chordate.[40] On the other hand, fossils of early chordates are very rare, since invertebrate chordates have no bones or teeth, and only one has been reported for the rest of the Cambrian.[41]

The evolutionary relationships between the chordate groups and between chordates as a whole and their closest deuterostome relatives have been debated since 1890. Studies based on anatomical, embryological, and paleontological data have produced different "family trees". Some closely linked chordates and hemichordates, but that idea is now rejected.[4] Combining such analyses with data from a small set of ribosome RNA genes eliminated some older ideas, but opened up the possibility that tunicates (urochordates) are "basal deuterostomes", surviving members of the group from which echinoderms, hemichordates and chordates evolved.[42] Some researchers believe that, within the chordates, craniates are most closely related to cephalochordates, but there are also reasons for regarding tunicates (urochordates) as craniates' closest relatives.[4][43]
Since early chordates have left a poor fossil record, attempts have been made to calculate the key dates in their evolution by molecular phylogenetics techniques—by analyzing biochemical differences, mainly in RNA. One such study suggested that deuterostomes arose before million years ago and the earliest chordates around million years ago.[43] However, molecular estimates of dates often disagree with each other and with the fossil record,[43] and their assumption that the molecular clock runs at a known constant rate has been challenged.[44][45]
Traditionally, Cephalochordata and Craniata were grouped into the proposed clade "Euchordata", which would have been the sister group to Tunicata/Urochordata. More recently, Cephalochordata has been thought of as a sister group to the "Olfactores", which includes the craniates and tunicates. The matter is not yet settled.
Diagram
Phylogenetic tree of the Chordate phylum. Lines show probable evolutionary relationships, including extinct taxa, which are denoted with a dagger, †. Some are invertebrates. The positions (relationships) of the Lancelet, Tunicate, and Craniata clades are as reported[46][47][48][49]

Chordata

Cephalochordata

AmphioxusOlfactores

Haikouella†Tunicata

Appendicularia (formerly Larvacea)
Thaliacea
AscidiaceaVertebrata/

Agnatha/

Myxini (hagfish)
Hyperoartia (Petromyzontida) (Lampreys)Cyclostomata

Myllokunmingia fengjiaoa†
Zhongjianichthys rostratus†
Conodonta†
Cephalaspidomorphi†
Pteraspidomorphi†
osteostracan†

Gnathostomata/

Antiarchi†

Petalichthyida†

Arthrodira†
Ptyctodontida†Crown

Acanthodii, incl ChondrichthyesOsteichthyes

Actinopterygii (ray-finned fish)

Sarcopterygii

Actinistia (coelacanths)

Dipnoi (lungfishes)

Tetrapoda

AmphibiaAmniota

MammaliaSauropsida

Lepidosauromorpha (lizards, snakes, tuatara, and their extinct relatives)

Archosauromorpha (crocodiles, birds, and their extinct relatives)GnathostomataPlacodermiCraniata
Closest nonchordate relatives

Hemichordates

Hemichordates ("half chordates") have some features similar to those of chordates: branchial openings that open into the pharynx and look rather like gill slits; stomochords, similar in composition to notochords, but running in a circle round the "collar", which is ahead of the mouth; and a dorsal nerve cord—but also a smaller ventral nerve cord.
There are two living groups of hemichordates. The solitary enteropneusts, commonly known as "acorn worms", have long proboscises and worm-like bodies with up to 200 branchial slits, are up to 2.5 metres (8.2ft) long, and burrow though seafloor sediments. Pterobranchs are colonial animals, often less than 1 millimetre (0.039in) long individually, whose dwellings are interconnected. Each filter feeds by means of a pair of branched tentacles, and has a short, shield-shaped proboscis. The extinct graptolites, colonial animals whose fossils look like tiny hacksaw blades, lived in tubes similar to those of pterobranchs.[50]
Echinoderms

Echinoderms differ from chordates and their other relatives in three conspicuous ways: they possess bilateral symmetry only as larvae - in adulthood they have radial symmetry, meaning that their body pattern is shaped like a wheel; they have tube feet; and their bodies are supported by skeletons made of calcite, a material not used by chordates. Their hard, calcified shells keep their bodies well protected from the environment, and these skeletons enclose their bodies, but are also covered by thin skins. The feet are powered by another unique feature of echinoderms, a water vascular system of canals that also functions as a "lung" and surrounded by muscles that act as pumps. Crinoids look rather like flowers, and use their feather-like arms to filter food particles out of the water; most live anchored to rocks, but a few can move very slowly. Other echinoderms are mobile and take a variety of body shapes, for example starfish, sea urchins and sea cucumbers.[51]
History of name
Although the name Chordata is attributed to William Bateson (1885), it was already in prevalent use by 1880. Ernst Haeckel described a taxon comprising tunicates, cephalochordates, and vertebrates in 1866. Though he used the German vernacular form, it is allowed under the ICZN code because of its subsequent latinization.[2]
See also
Chordate genomics
List of chordate orders

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Does an animal with vertebrae have to be a chordate?


A global city, also called world city or sometimes alpha city or world center, is a city which is a primary node in the global economic network. The concept comes from geography and urban studies, and the idea that globalization is created, facilitated, and enacted in strategic geographic locales according to a hierarchy of importance to the operation of the global system of finance and trade.
The most complex node is the "global city", with links binding it to other cities having a direct and tangible effect on global socio-economic affairs.[1] The term "global city", rather than "megacity", was popularized by sociologist Saskia Sassen in her 1991 work, The Global City: New York, London, Tokyo.[2] "World city", meaning a city heavily involved in global trade, appeared in the May 1886 description of Liverpool, by The Illustrated London News.[3] Patrick Geddes later used the term "world city" in 1915.[4] More recently, the term has focused on a city's financial power and high technology infrastructure, with other factors becoming less relevant.[5][6]
Criteria

Global city status is considered beneficial and desirable. Competing groups have developed multiple alternative methods to classify and rank world cities and to distinguish them from non-world cities.[4]  Although there is a consensus upon leading world cities,[7] the chosen criteria affect which other cities are included.[4]  Selection criteria may be based on a yardstick value (e.g., if the producer-service sector is the largest sector then city X is a world city)[4] or on an imminent determination (if the producer-service sector of city X is greater than the combined producer-service sectors of N other cities then city X is a world city.)[4]
Cities can fall from ranking, as in the case of cities that have become less cosmopolitan and less internationally renowned in the current era.
Characteristics
Although criteria are variable and fluid, typical characteristics of world cities are:[8]
A variety of international financial services,[9] notably in finance, insurance, real estate, banking, accountancy, and marketing
Headquarters of several multinational corporations
The existence of financial headquarters, a stock exchange, and major financial institutions
Domination of the trade and economy of a large surrounding area
Major manufacturing centres with port and container facilities
Considerable decision-making power on a daily basis and at a global level
Centres of new ideas and innovation in business, economics, culture, and politics
Centres of media and communications for global networks
Dominance of the national region with great international significance
High percentage of residents employed in the services sector and information sector
High-quality educational institutions, including renowned universities, international student attendance,[10] and research facilities
Multi-functional infrastructure offering some of the best legal, medical, and entertainment facilities in the country
High diversity in language, culture, religion, and ideologies.
Rankings
Global Economic Power Index
In 2015, the second Global Economic Power Index, a
meta list compiled by Richard Florida, was published by The Atlantic (distinct from a namesake list[11] published by the Martin Prosperity Institute), with city composite rank based on five other lists.[11][12]
Global Power City Index
The Institute for Urban Strategies at The Mori Memorial Foundation in Tokyo issued a comprehensive study of global cities in 2017. They are ranked based on six categories: economy, research & development, cultural interaction, livability, environment, and accessibility, with 70 individual indicators among them. The top ten world cities are also ranked by subjective categories including manager, researcher, artist, visitor and resident.[13]
Global Power City top 10: 1. London, 2. New York City, 3. Tokyo, 4. Paris, 5. Singapore, 6. Seoul, 7. Amsterdam, 8. Berlin, 9. Hong Kong, 10. Sydney.
GaWC study

Jon Beaverstock, Richard G. Smith and Peter J. Taylor established the Globalization and World Cities Research Network (GaWC). A roster of world cities in the GaWC Research Bulletin 5 is ranked by their connectivity through four "advanced producer services": accountancy, advertising, banking/finance, and law.[7] The GaWC inventory identifies three levels of global cities and several sub-ranks,[14] although the authors caution that "concern for city rankings operates against the spirit of the GaWC project"[15] (emphasis in original).
The 2004 rankings added several new indicators while continuing to rank city economics more heavily than political or cultural factors. The 2008 roster, similar to the 1998 version, is sorted into categories of Alpha world cities (with four sub-categories), Beta world cities (three sub-categories), Gamma world cities (three sub-categories) and additional cities with High sufficiency or Sufficiency presence. The cities in the top two classifications in the 2018 edition are:[16]
Alpha ++

 London
 New York City

Alpha +

 Hong Kong
 Beijing
 Singapore
 Shanghai
 Sydney
 Dubai
 Paris
 Tokyo

Global Cities Index
In 2008, the American journal Foreign Policy, in conjunction with the consulting firm A.T. Kearney and the Chicago Council on Global Affairs, published a ranking of global cities, based on consultation with Saskia Sassen, Witold Rybczynski, and others.[17] Foreign Policy noted that "the world’s biggest, most interconnected cities help set global agendas, weather transnational dangers, and serve as the hubs of global integration. They are the engines of growth for their countries and the gateways to the resources of their regions."[18] The ranking is based on 27 metrics across five dimensions: business activity, human capital, information exchange, cultural experience, and political engagement and was updated in 2010, 2012, 2014, 2015, 2016, and 2017. Since 2015 it has been published together with a separate index called the Global Cities Outlook: a projection of a city’s potential based on rate of change in 13 indicators across four dimensions: personal well-being, economics, innovation, and governance.[19]
The Wealth Report
"The Wealth Report" (a global perspective on prime property and wealth) is made by the London-based estate agent Knight Frank LLP together with the Citi Private Bank. The report includes a "Global Cities Survey", evaluating which cities are considered the most important to the world’s HNWIs (high-net-worth individuals, having over $25 million of investable assets). For the Global Cities Survey, Citi Private Bank’s wealth advisors, and Knight Frank’s luxury property specialists were asked to name the cities that they felt were the most important to HNWIs, in regard to: "economic activity", "political power", "knowledge and influence" and "quality of life".[20][21]
Global City Competitiveness Index
In 2012, the Economist Intelligence Unit (The Economist Group), ranked the competitiveness of global cities according to their demonstrated ability to attract capital, businesses, talent and visitors.[22]
See also

Ecumenopolis
Financial centre
List of cities by GDP
Megalopolis (city type)
Metropolis
Primate city
Ranally city rating system

 by Jeffrey Kentor and Michael Timberlake of the University of Utah and David Smith of University of California, Irvine

What city is considered  the most advanced?


Windex is a glass and hard-surface cleaner. Windex was invented by the Drackett Company in 1933 and has been marketed throughout the intervening decades.[1] Windex was originally sold in glass containers before adding plastic and metal containers over time.
Drackett sold Windex to Bristol-Meyers in 1965.[2] S. C. Johnson acquired Windex in 1993 and has been manufacturing it since.[3]
The original Windex was colored a light, translucent shade of blue.Today, there are varieties marketed in several colors (ocean fresh blue, sunshine lemon and citrus orange) and fragrances (spring bouquet, ocean mist, lavender and tea tree), with a number of additives such as vinegar, lemon, lime, or orange juice.
Ingredients
On August 26, 1969, Melvin E. Stonebraker and Samuel P. Wise received U.S. patent #3,463,735[4] for a glass cleaning composition, listing example formulae, one of which is 4.0% isopropyl alcohol, 1% ethylene glycol monobutyl ether, 0.1% sodium lauryl sulfate (a surfactant), calcium (Ca) 0.01%, tetrasodium pyrophosphate (a water softener), 0.05% of 28% ammonia, 1% of a dye solution, and 0.01% perfume.  This formula was not only inexpensive to manufacture but allowed the product to be packaged in glass bottles and dispensed with a plastic sprayer. In 1989, Windex was a 5% ammonia solution.[5] The product was reformulated in 2006.[6] In 2009, S.C. Johnson started publishing ingredients for all of its products, including Windex.[7] The S.C. Johnson website lists Windex's ingredients as water, 2-hexoxyethanol, isopropanolamine, sodium dodecylbenzene sulfonate, lauramine oxide, ammonium hydroxide, fragrance, and Liquitint sky blue dye.[8]

, S.C. Johnson press release, Racine, Wisconsin, Thursday, January 17, 2008
"Philip W. Drackett: Earned profits, plaudits" by Barry M. Horstman, Cincinnati Post, May 21, 1999.


This article is part of a series on thePolitics of
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vt
France has a multi-party political system: one in which the number of competing political parties is sufficiently large as to make it almost inevitable that in order to participate in the exercise of power any single party must be prepared to negotiate with one or more others with a view to forming electoral alliances and/or coalition agreements.
The dominant French political parties are also characterised by a noticeable degree of intra-party factionalism, making each of them effectively a coalition in itself.
Up until recently, the government of France had alternated between two rather stable coalitions:
on the centre-left, one led by the Socialist Party and with minor partners such as Europe Ecology – The Greens and the Radical Party of the Left.
on the centre-right, one led by The Republicans (and previously its predecessors, the Union for a Popular Movement, Rally for the Republic) and the Union of Democrats and Independents.
This was the case until the 2017 legislative election, when Emmanuel Macron's party, La République En Marche!, won a large majority in parliament. This caused a political upset, as it was the first time in French history when one of the two main contemporary parties had not won.
Another political party that has had sizable successes is National Rally (RN) (previously known as the National Front before a name change in 2018). Since 2014, the party has established itself as the third sizable party, finishing in 1st place in the 2014 European elections as well as in the 2015 local elections,[1] although it still didn't manage to win any executives mostly due to the last-ditch alliance between the centre-left and the centre-right coalitions in Hauts-de-France region as well as in the South of France.[2] Now many political observers talk about the "tripartisme" (English: tripartism) of the French political landscape.[3][4][5] In the 2017 presidential election, Emmanuel Macron, under the banner of En Marche!, defeated Marine Le Pen.
Elected parties

Major nationwide represented parties

Other nationwide represented parties

Region only parties

Non-elected parties

French Revolution
Jacobin Club
Girondist - Centre-left
Maraisards - Centrism
Montagnards - Left-wing
Cordeliers Club
Feuillants Club
Historical parties
Red Republicans
Socialist Party of France (1902)
French Socialist Party (1902)
French Socialist Party (1919)
Socialist Party of France – Jean Jaurès Union
Radical Party (France)
French Section of the Workers International
Democratic Republican Alliance
Political parties in French overseas possessions
List of political parties in French Guiana
List of political parties in French Polynesia
List of political parties in Guadeloupe
List of political parties in Martinique
List of political parties in Mayotte
List of political parties in New Caledonia
List of political parties in Reunion
List of political parties in Saint-Pierre and Miquelon
List of political parties in Wallis and Futuna
Historical parties
French India Socialist Party
Mahé Socialist Party
See also
Liberalism and radicalism in France
List of political parties

What is the leading political party in France?