Gold is an ancient metal. Too soft for use in its native state, it was alloyed with silver, zinc, copper, or nickel for use in jewelry or coinage. Now it is deposited into integrated circuits in tiny quantities, used in dentistry, to protect satellites from radiation, and in astronaut’s helmets for the same purpose. It’s dissolved to make dark red stained glass. Its cost, of course, limits its use.
Gold’s symbol is Au, from the Latin word for gold, aurum. It has an atomic number of 79, meaning there are 79 protons in its nucleus. This places it in the copper family, which includes copper of course, and silver, all of which were in use before history. Its melting point is 1063 degrees Celsius and its boiling point at 2966 Celsius. There are 19 isotopes of gold. The most ductile and malleable of metals, it is impervious for attack by almost all solvents.
Gold does occur in natural compounds, but many important sources are gold in the free state, sometimes as nuggets, but generally as fine grains, often in quartz veins or in alluvial deposits eroded out of the mother lode. Most modern gold mines have a concentration of gold in ore so low that the gold cannot be seen before processing. There is an ecological issue with gold cyanidation, a method of recovering gold from low grade ore by dissolving it out with cyanide. Trouble can occur when there are leaks, when river life may be disrupted far downstream.
As everyone knows, gold is a warm buttery color, though it may be alloyed with other elements to strengthen, harden and stretch it. Pure gold is twenty four karats. (Carats are a measure for precious stones.) Eighteen karat gold that is 75% gold and 25% copper produces rose gold with a distinct reddish cast, sometimes found in ancient jewelry. Fourteen karat gold in which 58.33% gold is alloyed with copper, produces a rosy shade identical with some bronze. Blue gold is produced by alloying with iron, but it is brittle. Purple gold is gold alloyed with aluminum. Green gold can be produced by alloying with silver. Lovely white gold can produced by adding nickel, usually, or a combination of metals, or palladium, which is expensive but considered less toxic.
The price of gold can function as a sort of thermometer for the health of the world economy, or the safety of world politics. The current high price of gold may be taken as an indication of fevered conditions. Many people believe that the price of gold is an important barometer of inflation, too. Historically the Gold Standard, the practice of tying the price of gold to a unit of currency, has been hailed by some as the path to stability, and scorned by others as a “barbarous relic”. The economist John Maynard Keynes called it that.
Gold is a symbol of beauty, permanence, and value, and the foundation of some great art, but it is not really of much practical use. How much easier it would be to live without gold than without oxygen, or carbon, or many another element.
http://www.webelements.com/gold
http://www.utilisegold.com/jewellery_technology/colours/colour_alloys/
http://www.dendritics.com/scales/carat-def.asp
http://www.science.gold.org/
http://en.wikipedia.org/wiki/Summitville_mine
