Gold
Gold was used more than 5,000 years ago in Mesopotamia, and has never lost its attraction. A symbol of divinity, used for religious objects; of royalty, used for the crowns and sceptres of kings and queens; and an indication of wealth, its gleam adorning the necks of the richest men and women throughout history – gold has been valued for thousands of years.
The esteem in which gold has always been held is demonstrated by the fact that it has been accepted in exchange for goods and services by all cultures throughout history. In fact, up until World War I, the gold standard was the basis for the world's currencies, and even today, 45 percent of the world's gold is held in government reserves.
The element gold is found in low concentrations in igneous rocks, and it rarely combines with other elements. It is often found in association with copper and lead, and because it does not combine, it is easily recovered. It also occurs in small amounts in hydrothermal veins, in association with quartz and pyrite. It is found in alluvial deposits, in which gold, because of its density, is separated from other minerals during weathering and transported to become concentrated in stream and other sediments, which may be loose and unconsolidated or hardened into rock. Tiny grains of gold can be carried long distances by streams and can be recovered from gravel by panning, which involves washing away all but the heavy minerals and then searching for any flecks of gold.
Gold is remarkable for its ductility and malleability – in fact, it is the most malleable metal of all. Twenty grammes (0.6 ounces) of gold can be stretched into a wire more than 1 kilometre (0.6 miles) long or beaten into a sheet of gold leaf more than 20 square metres (210 square feet). In addition to this, it does not tarnish or corrode because it is chemically inert.
Its durability and workability have inspired craftspeople and their patrons over the millennia. Beautiful jewellery and ornaments were created by the earliest cultures, and museums around the world display gold objects created by Egyptians, Minoans, Assyrians, and Etruscans. During the Middle Ages, gold objects and gold-leaf veneers adorned elaborate churches, and during the Renaissance, gold jewellery was worn by the most important people. Today, although gold is no longer the province of only the wealthy, because it is more affordable, it is no less precious for it.
The market for gold in Europe exploded with the Spanish conquest of the New World in the 15th century, with the height of gold production in the 1490s. The New World mines continued to be productive through the early 1800s, when they were overtaken by Russia as the leading source of gold. Since the end of the 19th century, however, South Africa has dominated the market and is today the source of around one-third of total global production. Russia, the United States of America, and Australia together account for a further one-third.
Because gold is so soft, it is alloyed with other metals (usually SILVER, copper and zinc) to increase its hardness so it can be used in jewellery. White gold has a higher proportion of silver than yellow gold does. Gold purity is defined by its carat value – one carat is equivalent to 1/24th, with 24-carat gold being pure gold. Most jewellery is either nine-carat or 14-carat gold.
| CHEMICAL COMPOSITION | Au |
COLOUR |
gold-yellow |
REFRACTIVE INDEX |
none |
RELATIVE DENSITY |
19.3 |
HARDNESS |
2.5 |
CRYSTAL GROUP |
cubic |
CLEAVAGE |
none |
FRACTURE |
hackly |
TENACITY |
tough yet malleable |
LUSTRE |
metallic |
TRANSPARENCY |
opaque |
DISPERSION |
none |
BIREFRINGENCE |
none |
PLEOCHROISM |
none |
LOCATION |
Worldwide, Especially Australia, Brazil, Canada, China, Indonesia, Russia, South Africa, United States |
Gold nugget
Gold on quartz
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