Gold is one of the least abundant elements on Earth and is found in small quantities almost everywhere. It can be found in seawater, rivers, soil, volcanic dust, meteorites, rocks from the moon, and other planets. However, despite this widespread availability in nature, gold isn’t that easy to find!
Naturally occurring gold has the atomic number 79 and the chemical symbol Au (from the Latin word for gold, aurum). As a pure substance, it is a bright, somewhat yellow color with red tints metal that is dense, soft, flexible, and stretchy. Gold, precious metal and a relatively scarce element has been utilized for coins, jewelry, and other artistic endeavors since the beginning of humanity.
Gold may be uncommon, but it is found in over a hundred minerals and at least fifty different types of local deposits. Its solid form can be discovered in rocks, faults, and alluvium as granules or grains. Less often, it occurs in telluride ores. Gold’s eponymous origin can be traced back to the Old English word geolo, which meant “yellow” in that language.
Gold is found in nature in a variety of ways. Quartzite is the most common gold ore, often refractory and challenging to process. Other sources include hydrothermal vein and replacement deposits, placer gold, and colluvium. Most gold ore contain small amounts of impurities such as sulfur, arsenic, antimony, or mercury. Processing gold ore is usually done using several methods: cyanidation, flotation, gravity concentration, or amalgamation.
There are many different processing methods for separating gold from rock, with the goal being to extract the metal from its natural alloying agents. Amalgamation is the oldest method for extracting gold from its ores. It involves combining mercury with ore and heating it until the two forms an alloy that can be easily smelted at a lower temperature than it would take to smelt either metal alone.
Gold has been mined for centuries, and the methods used to extract it have changed very little over time. The most common way for gold extraction is through cyanide leaching, where cyanide is used to dissolve the gold from the ore.
This process was first developed in 1887 and is still in use today. Gold is also sometimes extracted using mercury, which was historically used to amalgamate the gold with other metals. Due to the dangers to human health posed by mercury, this technique is no longer practiced. One of the world’s largest open-pit mines, the Carlin Trend, can be found near Elko, Nevada, in a region known as the mother lode. Other significant gold-producing areas include Australia, Canada, Russia, and South Africa.
Due to the wavelength dependence of light absorption and re-emission, metals have different colors. The color indicates yellow, and red are preferentially reflected, while gold and copper have low reflectivity at short wavelengths. The density difference between air and water also influences how light is absorbed.
Simplified, gold’s electrons move so fast that they show a phenomenon called “relativistic contraction,” which changes the wavelength of the light they absorb to blue and makes them reflect the opposite color, golden.