Gold is often found in free elements (native state), in the form of nuggets or grains, in rocks, veins and alluvial deposits. It comes in a series of solid solutions with the native element silver (such as electrum), naturally alloyed with other metals such as copper and palladium, and mineral inclusions such as pyrite. Some gold can be found in rock minerals. It comes in the form of scales, as a pure native element, and with silver in the natural electrum alloy.
Erosion frees gold from other minerals. Because gold is heavy, it sinks and accumulates in stream beds, alluvial deposits and the ocean. Traces of gold are found almost everywhere, but large deposits are only found in a few places. Although there are about twenty different gold ores, all of them are quite rare.
Therefore, most of the gold found in nature is in the form of native metal. Gold began to serve as a backup for paper currency systems when they became widespread in the 19th century and, from the 1870s until the First World War, the gold standard was the basis of the world's currencies. Like copper, gold has only one electron outside of a complete shell, but despite the similarity between electronic structures and ionization energies, there are few close similarities between gold, on the one hand, and copper, on the other. Alloys of gold with silver or copper are used to make gold coins and gold items, and alloys with platinum or palladium are also used in jewelry.
Gold-enriched veins form when gold is transported from great depths with other minerals, in an aqueous solution, and then precipitated. The artisans of ancient Egypt, Minoan, Assyrian and Etruscan preserve examples of elaborate gold work, many of them in almost perfect condition, and gold is still a highly appreciated material for making jewelry and other decorative objects. It's also soft and the most malleable and ductile of the elements; an ounce (31.1 grams; gold is weighed in troy ounces) can be converted to 187 square feet (about 17 square meters) into extremely thin sheets called gold leaf.