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Gold is a chemical element with the symbol Au (from Latin: aurum) and the atomic number 79. Its purest form is bright, reddish yellow, dense, soft, malleable and malleable metal. Chemically, gold is a transition metal and a group of 11 elements. It is one of the chemical elements with the lowest reactivity and is solid under standard conditions. Gold usually occurs in the form of free elements (NATURAL), such as gold or grains, rocks, veins, and alluvium. It appears as a series of solid solutions with the natural element silver (as electron), and is also naturally alloyed with copper and palladium. Less commonly, it occurs in minerals in the form of gold compounds, usually with tellurium (gold telluride).
It is believed that gold is produced by the collision of neutron stars in supernova nucleosynthesis and exists in the dust formed in the solar system. Since the earth was molten at the time of its formation, almost all the gold that existed in the early days of the earth may have sunk into the core of the planet. As a result, asteroids are believed to have struck most of the gold in the earth's crust and mantle during the late heavy bombardment, some 4 billion years ago.
Although gold does dissolve in aqua regia (a mixture of nitric acid and hydrochloric acid) to form a soluble tetrachloroacid anion, gold is resistant to most acids. Gold is insoluble in nitric acid, which dissolves silver and base metals, a property that has long been used to extract gold and confirm the presence of gold in metallic objects, hence the term "acid testing.". Gold is also dissolved in an alkaline solution of cyanide, which is used in mining and electroplating. Gold dissolves in mercury to form an amalgam, but this is not a chemical reaction.
Historically, gold has been valued for its relative rarity, ease of handling and casting, ease of smelting and manufacturing, corrosion resistance and other chemical reactions (aristocracy) and its unique color. Throughout the recorded history, gold has been used as a precious metal for coinage, jewelry and other arts. In the past, the gold standard was usually used as monetary policy, but in the 1930s, gold coins were no longer used as currency. After 1976, the world gold standard was abolished as legal currency system.
As of 2015, there were 186700 tons of gold on the ground. The consumption of newly produced gold in the world accounts for about 50% of jewelry, 40% of investment and 10% of industry. Gold's high ductility, ductility, corrosion resistance and most other chemical reactions, as well as electrical conductivity, have led to its continued use in corrosion-resistant electrical connectors in all types of computer equipment (major industrial applications). Gold is also used for infrared shielding, stained glass production, gold foil relief and tooth restoration. Some gold salts are still used as anti-inflammatory drugs in medicine. As of 2014, the largest gold producer in the world so far is China, with a production capacity of 450 tons.
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