Gold (Au, from the Latin word aurum) is the oldest metal known to mankind. It has always exercised an enormous power of attraction. In mythology, reference is made to the quest for the Golden Fleece by Jason and the Argonauts around 1200 BC. In Asia Minor, Midas, King of the Phrygians, was endowed by Dionysos with the power of turning everything that he touched into gold.
Croesus, King of Lydia, owed his legendary wealth to gold mines. He struck the first gold and silver coins around 550 BC. In early times gold metallurgy was based on gravimetric separation of the metal by virtue of its high density (19.3). Extraction by the amalgamation technique was introduced around 500 BC. In the 16th century the Spaniards invaded South America and discovered huge gold veins. Later, Kruger discovered the gold deposits of South Africa in 1834. Perhaps the most famous gold discovery, the Californian Gold Rush, followed shortly after.
- A bright yellow metal with a very high density.
- Along with copper and silver it is one of the best conductors of heat and electricity (conductivity of the order of 70%-that of silver)
- The most malleable and ductile of all metals.
- Can be beaten into semi-transparent foil to a thickness of 0.01 mm, and drawn into thread weighing less than 0.5 g per kilometre.
- A very soft metal (2.5 on Mohs’ scale) and must be hardened by alloying in most of its applications.
- By far the most important use is in jewelry. Being a soft metal, gold is generally used as an alloy. Grade is expressed in thousandths and in carats. Pure gold is equivalent to 24 carats. A 22-carat alloy is made up of 92% Au, 5% Ag and 3% Cu, whereas a 20-carat alloy contains 84% Au, 8–10% Ag and 3–5% Cu.
- In the electronics industry, gold is used in wires and coatings. Gold–palladium alloys offer a wide range of resistivities and are used in resistors and potentiometers.
- Gold is used in dentistry in the form of Au–Ag–Cu alloys with the addition of platinum and palladium.µ
- Gold is commonly used as an alternative investment in the form of ingots and bars
Since gold extraction and mining began thousands of years ago, less than 200,000 tonnes of gold have ever been produced, the vast majority of which is still available in aboveground stocks. This would barely fill four Olympic sized swimming pools! While recycling accounts for some 30% of the metal produced globally each year, its presence in applications like jewellery and investment bars and central bank reserves places a limit on recycling possibilities. Gold is recovered from jewellery production scrap and old jewellery, from electronic and electrical scrap among other sources. It is also recovered as a by-product from some non-ferrous metals refining as gold is often found as a trace element for example in copper concentrates.