Gold was first smelted by the ancient Egyptians around 6,000 years ago and was most famously used to make the funeral mask of the pharaoh Tutankhamen 1,400 years later. Gold was first used in dentistry by the Etruscans in around 600BCE; it still used to make teeth and fillings today. By the turn of the 15th Century many European gold mines had been depleted. Over the next two hundred years kingdoms such as Venice, Spain and Portugal explored Africa, Asia and the Americas in search of new sources.
The familiar site of prospectors panning for gold is because it is often found in sediments of clay or silt in river beds. These alluvial sediments can also indicate larger deposits of gold further upstream. Gold is also found in veins in rocks with deposits of copper, lead, quartz or pyrite. Unlike aluminum or iron, gold naturally occurs naturally in its elemental form. South Africa is the world's largest gold producer, followed by the United States, Australia, Canada and China.
Gold is extracted chemically using cyanide. A cyanide salt added to an aqueous slurry containing gold causes the cyanide ions to chelate to gold atoms to form gold dicyanide complex ions. These ions are easily separated from the slurry by using filtration and are then reacted with zinc to given pure gold and zinc tetracyanide ions. This is a very efficient and long-established means of extracting gold. However, it has serious environmental repercussions, as cyanide dissolved in water is extremely toxic to plant and animal life.
Gold is a strong conductor of electricity, but does not corrode and is generally chemically non-reactive. Because of this gold is used in non-corroding contacts in electrical circuits. The metal is soft and malleable, meaning it is easy to shape and its non-corroding properties means that it does not have any adverse affects when placed in the body. It is also highly resistant to bacteria. For this reason gold has been used in dentistry for thousands of years. More recent medical applications include treating rheumatoid arthritis and cancer.