Gold is a chemical element with the symbol Au (Latin: aurum) and an atomic number of 79. It is a precious metal used for coinage, jewelry, and other arts since the beginning of recorded history. Gold is seen as a safe haven in times of financial and political uncertainty, since it is not at risk of becoming worthless, unlike currency and other assets. It is increasingly being used to diversify investment portfolios, as a currency and as a hedge against inflation.
It was estimated, that by 2009 a total of 161,000 tonnes of gold have been mined throughout all human history.
The metal occurs as nuggets or grains in rocks, in veins and in alluvial deposits. Most of the time, it appears as an alloy with silver, usually with a silver content of 8–10%. Electrum is a natural alloy with more than 20% of silver. Its color runs from golden silvery to silvery, dependent upon the silver content.
In gold extraction, ore grades as little as 0.5 g/1000 kg can be economical. 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).
Eight countries produce more than 100.000 kilograms of gold per year, or 67 percent of world mine production (order in 2007: China, South Africa, Australia, USA, Peru, Russia, Indonesia, Canada). From 1905, South Africa has been the largest producer of gold, in 1970 it was over 1000 tonnes annually, then 60 percent of world production. It has declined down to 252 tonnes in 2007, and China become first, with 276 metric tons of gold mined. Other traditionally dominant gold producers, including Australia, USA and Canada, are rapidly losing ground to new producers. Indonesia has experienced an exceptional rise in production from only three tonnes in 1985 to 143 tonnes in 2005. Peru, which is now the world’s fifth largest gold producer, has increased production from 24 tonnes in 1992 to more than 200 tonnes in recent years, but declined to a low of 170 tonnes.
Gold is the most malleable and ductile of all metals; a single gram can be beaten into a sheet of 1 square meter, or an ounce into 300 square feet. Gold leaf can be beaten thin enough to become translucent. The transmitted light appears greenish blue, because gold strongly reflects yellow and red.
Gold is a good conductor of heat and electricity and reflects infrared radiation strongly. Chemically, it is unaffected by air, moisture and most corrosive reagents, and is therefore well-suited for use in coins and jewelry and as a protective coating on other, more reactive, metals. Free halogens will react with gold, and aqua regia can dissolve it. Gold also dissolves in alkaline solutions of potassium cyanide and in mercury, forming a gold-mercury amalgam. High quality pure metallic gold is tasteless; in keeping with its resistance to corrosion (it is metal ions which confer taste to metals).
In addition, gold is very dense, a cubic meter weighing 19300 kg. By comparison, the density of lead is 11340 kg/m3, and that of the densest element, osmium, is 22610 kg/m3.
The color of pure gold is metallic yellow. Gold readily creates alloys with many other metals. Common colored gold alloys such as rose gold can be created by the addition of various amounts of copper and silver, as indicated in the triangular diagram on the right. Alloys containing palladium or nickel are also important in commercial jewelry as these produce white gold alloys. Less commonly, addition of manganese, aluminium, iron, indium and other elements can produce more unusual colors of gold for various applications.
Gold has a wide range of industrial uses, dominated by the electrical sector, in which it is valued for its excellent thermal and electrical properties. A significant amount of gold is consumed in dentistry and it also has medical applications. New applications for gold including catalysts and in nanotechnology are researched.
Gold is increasingly being used to diversify investment portfolios, as a currency and as a hedge against inflation. The centre of world gold trading is the London Bullion Market, on which the gold price is fixed twice daily. The fix is used as a benchmark for pricing the majority of gold products and derivatives throughout the world's markets. Jewellery production accounts for the largest use of gold, representing around 70 per cent of total demand. In Asia and the Middle East gold jewellery is commonly bought as an investment or store of value. 
Pure gold is too soft for day-to-day monetary use and is typically hardened by alloying with copper, silver or other base metals. The gold content of alloys is measured in carats (k). Pure gold is designated as 24k. Gold coins intended for circulation from 1526 into the 1930s were typically a standard 22k alloy called crown gold, for hardness.
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, the British gold sovereign, and the South African Krugerrand continue to be minted in 22k metal in historical tradition. The special issue Canadian Gold Maple Leaf coin contains the highest purity gold of any bullion coin, at 99.999% or .99999 finess, while the popular issue Canadian Gold Maple Leaf coin has a purity of 99.99%. Several other 99.99% pure gold coins are available.
The ISO 4217 currency code of gold is XAU.
- ↑ 1.0 1.1 1.2 British Geological Survey. World Mineral Production (pdf), 2003-2007, p. 37-41, referenced 2009-12-12.
- ↑ Brook Larmer. National Geographic: "The Real Price of Gold" by Brook Larmer. Published: January 2009. See also The World's Cumulative Gold and Silver Production for other production estimates. Referenced 2010-05-15.
- ↑ Webexhibits.org / Causes of Color. "Gold: causes of color", referenced 2009-12-11.
- ↑ Utilisegold.com. "Gold Jewellery Alloys > Utilise Gold.", Scientific, industrial and medical applications, products ,suppliers from the World Gold Council, posted on 2000-01-20, referenced 2009-12-11}}