Natural gold Gold production Gold alloys Modern gold

Throughout history, gold has been unequalled in its value. Gold has several qualities that have made it so attractive as a currency, adornment and technological metal.

• Its yellow colour and brightness
  
• Its inertness to chemical reaction, it does not tarnish or corrode
  
• It is highly malleable and ductile
  
• It can be found in nature in pure form
  
• Its high density
  
• It is a good conductor of heat and electricity

Gold's highly visual appeal and workability made it one of the first metals to attract man's attention. Examples of gold workmanship and coins have survived from ancient Egypt, Greece, Syria and Etruscia.

Gold is universally accepted in exchange for goods and services, with approximately 45% of the world's gold held by governments and central banks in the form of coins and bullion as a medium of international exchange.

Natural gold
Gold is found in low concentrations in all igneous rocks. It's abundance in the Earth's crust is estimated at about 0.005 parts per million. Gold often occurs in copper and lead deposits. Gold can be found in underground veins associated with quartz and pyrite (or fool's gold) and as alluvial deposits created by the weathering of gold-bearing rocks and the deposit of gold in river beads and lakes. Gold in igneous rock is usually found as near invisible grains, more rarely as flakes large enough to be seen, and even more rarely as nuggets. The largest nuggets, up to 90 kg, come from Australia.

Gold production
Because gold is found naturally as a metal, little is required to extract it from its surrounding rock. Production usually starts with crushing the rock to release the gold, this can then be washed to separate the gold from the rock. With the gold being much denser than normal rock it will sink to the bottom of a pan or slats of a sluice.

Gold can also be dissolved from the crushed rock ore using a mixture of cyanide and acids and then recovered from solution formed. Another method passes the crushed ore through a bath of liquid mercury. The dense gold sinks in the mercury, forming an alloy, while the lighter rock floats on the surface of the mercury.

Gold alloys
Because pure gold is very soft it is usually alloyed with other metals to increase its hardness for use in jewellery and coinage. Gold is alloyed with silver, copper, nickel and zinc to produce various shades of yellow gold. Alloys with platinum and palladium are also used in jewellery to form "white gold".

The gold content of gold alloys is expressed in karats. 1 karat = 1/24^th of the content being gold, 24-karat gold being pure gold. A 18 karat gold alloy is 75% gold, 12 karat is 50% gold and 9 karat is 38% gold.

Modern gold

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