Gold is a highly prized precious metal, having been used as money, in jewelery, in sculpture, and for ornamentation since the beginning of recorded history. The metal occurs as nuggets or grains in rocks, underground veins and in alluvial deposits. Pure gold is dense, soft, shiny and has a bright yellow color traditionally considered attractive.
It has been known and highly valued since prehistoric times. It may have been the first metal used by humans and was valued for ornamentation and rituals. Egyptian hieroglyphs from as early as 2600 BC describe gold. The earliest known map is known as the Turin papyrus and shows the plan of a gold mine in Nubia together with indications of the local geology. Large mines also occurred across the Red Sea in what is now Saudi Arabia.
The Romans developed new methods for extracting gold on a large scale using hydraulic mining methods. One of their largest mines was in Spain, where seven long aqueducts enabled them to sluice most of a large alluvial deposit. The legend of the golden fleece may refer to the use of fleeces to trap gold dust from placer deposits in the ancient world.
The Mali Empire in Africa was famed throughout the old world for its large amounts of gold. Mansa Musa, ruler of the empire, gave away so much gold that it took over a decade for the economy across North Africa in 1324 to recover, due to the rapid inflation that it initiated. The European exploration of the Americas was fueled in no small part by reports of the gold ornaments displayed in great profusion by Native American peoples, especially in Central America, Peru, and Colombia.
One main goal of Medieval alchemists was to produce gold from other substances, presumably by the interaction with a mythical substance called the philosopher’s stone. Although they never succeeded in this attempt, the alchemists promoted an interest in what can be done with substances, and this laid a foundation for today’s chemistry.
During the 19th century, gold rushes occurred whenever large gold deposits were discovered. The first documented discovery of gold in the United States was at the Reed Gold Mine near Georgeville, North Carolina in 1803. Further gold rushes occurred in California, Colorado, and Klondike.
Gold is the most malleable and ductile metal. A single gram can be beaten into a sheet of one 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.
In various countries, gold is used as a standard for monetary exchange. Gold formed the basis for the gold standard of international currency used before the collapse of the Bretton Woods system in 1971. Pure gold is too soft for ordinary use as coins and is typically hardened by alloying with copper or other base metals. The gold content of gold alloys is measured in carats (k), pure gold being designated as 24k.
High quality pure metallic gold is tasteless. Some modern esotericists and forms of alternative medicine assign metallic gold a healing power. Gold flake was used by the nobility in Medieval Europe as a decoration in foodstuffs and drinks, either to demonstrate the host’s wealth or in the belief that something that valuable and rare must be beneficial for one’s health. Goldwasser is a traditional herbal liqueur produced in Schwabach, Germany, and contains flakes of gold leaf.
Gold alloys are used in restorative dentistry, especially in tooth restorations, such as crowns and permanent bridges. The gold alloys’ slight malleability facilitates the creation of a superior molar mating surface with other teeth and produces results that are generally more satisfactory than those produced by the creation of porcelain crowns. The use of gold crowns in more prominent teeth such as incisors is favored in some cultures and discouraged in others.
Because of its historically high value, much of the gold mined throughout history is still in circulation in one form or another. 75% of all gold ever produced has been extracted since 1910. It has been estimated that all the gold in the world that has ever been refined would form a single cube 66 feet wide on each side.
Recent research undertaken by Sir Frank Reith of the Australian National University shows that microbes play an important role in forming gold deposits, transporting and precipitating gold to form grains and nuggets that collect in alluvial deposits.