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This CSI is a nugget of gold. Its chemical symbol Au is derived from the Latin word for gold, "aurum." In its pure form, gold is sun yellow, but when mixed with other metals it produces alloys of different colors. White gold is produced by alloying gold with silver, palladium, nickel and copper. Yellow, green and red gold is produced by alloying gold with copper and silver.
Pure gold is soft and dense. It can be easily shaped (malleable) and stretched thin without breaking (ductile). In fact, it is the most malleable and ductile of all metals. Golds density allows it to be fairly easily separated from clay, silt, sand and gravel.
The most widely accepted hypothesis on how gold deposits form goes like this: Rain falls through cracks (fractures) into the cooler parts of the Earths crust. The water then moves laterally to areas of the Earths crust that are heated by magma. The water is then driven upward through more fractures. As it is heated, the water dissolves metals from surrounding rocks on the walls of the fractures. When the waters reach the cooler rocks, nearer to Earths surface, metallic minerals separate from the water to form veins or blanket-like ore bodies. Voila! Gold deposits.
While gold is mainly used in jewelry making and the arts, its high electrical conductivity, malleability, ductility, and resistance to corrosion favor its use in dentistry, electronic and computer circuitry, radar equipment and satellites, communications equipment, spacecraft, jet aircraft engines and much more.
Image courtesy of the California Geological Survey.