Gold
Gold is a metal element which has the atomic number 79, and an atomic weight of 196.9665. Its atomic symbol is Au which comes from its Latin name, aurum, for "shining dawn." It is relatively abundant in nature, occurring in many rocks and in seawater. Its estimated abundance in the earth's crust is 0.005 parts per million. Gold is the most malleable of elements. A single troy ounce can be hammered into a sheet that will cover 68 square feet (6.3 sq. m) only 0.00025-0.0001 inch (0.00025 cm) thick. The element is very unreactive. It is not attacked by air, oxygen, or most acids, but is dissolved by aqua regia (a mixture of concentrated hydrochloric and nitric acids) and is tarnished by sulfur.
Gold is probably the oldest of all metallic elements known to humans. The element occurs free in nature and is widely distributed. It is likely that gold was first discovered in deposits left by running water. Its brilliant golden color would have stood out from the dull earthy surroundings. For example, a sixteenth-century Spanish visitor to the New World observed that boys playing in the streets of La Paz picked up gold nuggets washed down from the hills after a heavy rain.
Some of the earliest evidence of the use of gold by humans comes from the earliest Egyptian dynasties. Fine gold jewelry shows that Egyptian goldsmiths had developed sophisticated techniques for working with the element as early as 2600 b.c. The Bible contains many references to gold. Its use as jewelry, ornamentation, and a medium of exchange--as well as a symbol of perfection--is described throughout the Old Testament.
Hindu records going back to at least 5000 b.c. suggest a familiarity with gold. The sacred book, Rig-Veda, for example, mentions the use of gold, silver, copper, lead, and bronze.
Gold was so common among early American cultures that it was valued for its beauty rather than its costliness. One Spanish observer reports that the Incas treasured copper more highly than they did gold. They used the latter metal simply for ornamentation and not as a medium of exchange. The discovery of gold in California in 1848 marked a turning point in American history. Thousands of men and women endured terrible hardships in the great Gold Rush of 1849 to make their fortunes in the California and Colorado foothills.
Techniques for working with gold have been known in most cultures for many centuries. For example, the Romans knew how to remove gold from worn-out clothing by treating it with mercury. Christopher Columbus (1446-1506) found that natives in Hispaniola were able to beat gold into very thin sheets from which they made ceremonial masks. Alchemists of the Middle Ages learned how to add gold to glass to make a beautiful gold ruby glass.
Pure gold is too soft to be used commercially for most purposes. It is usually alloyed with silver or copper for use in jewelry, coins, and decorative objects. Since it is a good conductor of electricity, it is sometimes used in electronic components. Radioactive gold (gold-198) is implanted in tissues as a means of treating some forms of cancer.
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