Gold is classified as a precious metal. The combination of gold’s relative scarcity and its evident beauty has made it an intrinsically valuable commodity throughout the history of humanity. It is most probably the oldest precious metal known to man. Wars have been fought over it and countless numbers have died trying to gain it or protect it.
|Previous Element: Platinum
Next Element: Mercury
|Phase at Room Temp.||solid|
|Melting Point (K)||1337.63|
|Boiling Point (K)||3081|
|Heat of Fusion (kJ/mol)||12.678|
|Heat of Vaporization (kJ/mol)||343|
|Heat of Atomization (kJ/mol)||366|
|Thermal Conductivity (J/m sec K)||318|
|Electrical Conductivity (1/mohm cm)||446.4|
|Source||Gold bearing rock (misc)|
|Number of Isotopes||54 (1 natural)|
|Electron Affinity (kJ/mol)||222.752|
|First Ionization Energy (kJ/mol)||890.1|
|Second Ionization Energy (kJ/mol)||1980|
|Third Ionization Energy (kJ/mol)||---|
|Atomic Volume (cm3/mol)||10.2|
|Ionic Radius2- (pm)||---|
|Ionic Radius1- (pm)||---|
|Atomic Radius (pm)||144|
|Ionic Radius1+ (pm)||151|
|Ionic Radius2+ (pm)||---|
|Ionic Radius3+ (pm)||99|
|Common Oxidation Numbers||+3|
|Other Oxid. Numbers||-1, +1, +2, +5|
|In Earth's Crust (mg/kg)||4.0x10-3|
|In Earth's Ocean (mg/L)||4.0x10-6|
|In Human Body (%)||0%|
|Regulatory / Health|
|OSHA Permissible Exposure Limit (PEL)||No limts|
|OSHA PEL Vacated 1989||No limts|
|NIOSH Recommended Exposure Limit||No limits|
Mineral Information Institute
Jefferson Accelerator Laboratory
Scientifically speaking, gold is an element, a metal, with an atomic number 79. Its physical and chemical properties make it ideal for a number of applications. It is very stable and as a result seldomly combines with other elements. In other words, it does not corrode or rust. It conducts electricity efficiently (only silver being a better conductor of electricity). It conducts heat very well. Gold is very malleable which means it can be hammered into shapes. Gold is so malleable that it can be hammered into a sheet so thin that light can pass through it. It is also ductile, which means it can be drawn into long, thin wires: a wire thread approximately 50 miles long can be drawn from a single troy ounce of gold (31.1 grams). It is also one of the densest metals: one cubic foot of gold weighs over 1200 pounds.
Gold’s chemical symbol is Au. It comes from the Latin word aurum which means shining dawn, a reference to its bright yellow color and shiny luster. The English word gold has its origins in Middle English.
Gold is found in two major types of deposits. Lode deposits are deposits where gold is found in cracks and veins in rocks. These are also called vein deposits. The second type of gold deposit is called a placer deposit. Placer deposits, common in the Sierra Nevada of California, are formed by moving water that has eroded gold out of lode deposits. When the speed of the water in a river slows sufficiently, the heavy gold falls to the bottom and accumulates in the sand of the riverbed. A third major source of gold is as a by-product of copper and silver mining. Gold is so valuable that it is worth the effort to recover even minute amounts from copper and silver ore.
It is estimated that the total amount of gold yet to be retrieved from the Earth is 100,000 tons. South Africa is the world’s largest producer of gold and is estimated to have half of these gold resources. Both the United States and Brazil have significant amounts of the world’s gold resources. Approximately one-fifth of the total resources of gold in the world is by-product from copper and silver ores.
In the United States, Alaska and Nevada are the main producers of gold. Nevada produces the majority of the gold produced in all of the United States. The remaining are from placer deposits in Alaska, and other gold deposits in western states. Most of the gold recovered in the United States is recovered by only about 30 mines. The largest gold mines in the United States today are located in northern Nevada.
Brazil and Canada export significant amounts of gold to the United States.
Most gold is used to make jewelry and other art items. Because it is chemically stable and conducts electricity so well, it is very important in electronics. Electronic applications represent a significant amount of the United States’ annual gold consumption, followed by dentistry and a variety of other applications.
Gold has been very important as the standard for currency. In 1792, the United States Congress established gold and silver as the standard for the nation’s money. The U.S. Department of the Treasury holds a major stockpile of gold.
Substitutes and Alternative Sources
Palladium, platinum and silver have been substituted for gold. Alloys (mixtures) of gold and other base metals are extensively used in jewelry and electronics to reduce the amount of gold used while assuring the positive features for which gold is desired.
Traditional mining of lode and placer deposits and by-product production of gold from copper and silver mining will continue to be the main sources of gold. There is gold in seawater, but recovering this gold is unlikely to ever be profitable. Recycling gold from used electronics will provide only a very small amount of gold, though some do find this venture profitable.