Where Gold Comes From

In many cultures the word “golden” is associated with something good: golden rule, golden hands, golden medal, golden words, and just about anything else if it is “worth its weight in gold.” Let's look into why this precious metal has become a metaphor and where it came from on our planet.

Gold is a noble metal of a pure yellow color. Its familiar reddish hue results from the impurities in the jewelry. It is very soft and heavy metal at the same time. It is number 79 in the periodic table. The density of gold is 19.32 g/cm³. To put that into perspective, a golden ball of 4 centimeters in diameter weighs about 1 kilogram. Yet gold is very malleable. On the Mohs scale, its hardness is only 2.5, so scientists often experiment on how to thin gold.

Origin

There are various myths and legends about the origin of gold. They are wonderful, yet have little to do with science. According to one version, the Sun, orbiting the Earth millions of times, wove golden threads around it. According to the Egyptians, golden rain once fell on the earth and the drops were left there as nuggets. The Scandinavians believe the golden deposits are the tears of Freya, the goddess of love, who longed for her spouse. However, there are different interpretations not only among folk tales, but also among scientists. Here are a few scientific hypotheses as to where gold came from on Earth:

1. Along with the formation of the planets

According to one version, gold appeared on Earth billions of years ago during the formation of the planet during the stage of high volcanic activity. Gold precipitated together with other heavy metals under high temperature and pressure and came close to the Earth's interior. So precious metals appeared long before the origin of living organisms. However, so far there is no direct spectroscopic evidence that such elements are actually formed.

2. In the composition of meteorites

Gold fragments are also found in meteorites. It is possible that meteorites falling on Earth formed scattered gold reservoirs and deposits. Given the fact that the atmosphere was forming over millions of years, a lot of gold could “fall” to the planet during this time. There are broader versions of the cosmic origin of gold, suggesting that the Earth collided with large asteroids.

3. Space dust

There was a theory that gold was formed by the nucleosynthesis of a supernova. But that has changed over time. Now scientists suggest that gold and other elements heavier than iron were formed by the collapse of neutron stars. The hypothesis has its advantages because it can explain the geographic spread of gold on the Earth. Gold is present in micro- and macro-doses in the earth, water, plants, animal bodies, and even the human body.

4. Золотопроизводящие бактерии

Бактерии, которые могут синтезировать золото. Есть одноклеточные микроорганизмы без ядра (прокариоты), которые вырабатывают энергию с помощью реакции окисления неорганических соединений. Такой способ существования называют хемолитотрофией, а микроорганизмы –  хемолитотрофными бактериями. Они были открыты русским микробиологом С.Н. Виноградским. Биогидрометаллургическая технология позволяет окислять сульфидные минералы и вскрывать тонкое вкрапленное золото, а также мышьяк и сурьму, которые часто находятся по соседству с драгоценными металлами. Но процесс такой добычи золота совсем не быстрый. Позже в золоторудных месторождениях России были открыты новые группы таких микроорганизмов, бактерий рода Sulfobacillus.

1. Gold-producing bacteria

Bacteria that can produce gold. There are single-celled microorganisms without a nucleus (prokaryotes) that produce energy through the oxidation reaction of inorganic compounds. This mode of existence is called chemolithotrophy and the microorganisms are called chemolithotrophic bacteria. They were discovered by Sergei N. Winogradsky, a Russian microbiologist. Biohydrometallurgical technology makes it possible to oxidize sulfide minerals and uncover fine disseminated gold, as well as arsenic and antimony, which are often found next to the precious metals. But the process of such gold mining is not fast at all. Later, new groups of such microorganisms, bacteria of the genus Sulfobacillus, were discovered in Russian gold deposits.

Applications

Naturally, gold is most commonly used in the jewelry industry. Since ancient times, it has been used to make jewelry and insignia. However, in addition to its aesthetic use, gold is used in many other areas.

• Investing

Gold is the most important element of the financial system. This metal is not susceptible to corrosion, has many technical applications and is limited in quantity. Currently, the world's bank reserves of gold are estimated at 32,000 tons.

• Currency

For many years gold was used as money. However, gold coins only became a single monetary commodity in the 19^th century. Until the First World War, they served only as gold certificates. The gold standard lost its relevance in our country in 1937, when a new chervonets, even theoretically non-convertible to gold, was put into circulation. Today the issue of money is controlled by GDP indicators. However, the concept of the Gold and Foreign Exchange Reserve remains; it is essential for the sustainability of the national currency, maintaining the state's creditworthiness and stability.

• Manufacturing industry

Gold is used as a material for electrical contacts. Gold conductors and gold plating of contact surfaces, connectors, and printed circuit boards are widely used in microelectronics.

Gold is also used as a target in nuclear research, as a coating for far-infrared mirrors, and as a special shell in a neutron bomb. A thin layer of gold (20 nm) on the inner surface of window and stained-glass windows reduces unwanted heat loss in winter and protects the interior of buildings and vehicles from heating by infrared rays in summer.

Gold solders are used in the brazing of metals. Thin pads made of soft gold alloys are used in ultra-high vacuum techniques. Gold plating of metals is widely used to protect against corrosion.

• Dentistry

Gold is used in the fabrication of crowns and dentures together with silver, copper, nickel, platinum, and zinc. These alloys are corrosion-resistant and have excellent mechanical properties. 

• Pharmacology

Gold compounds are included in some medicines used to treat tuberculosis, rheumatoid arthritis, and so on. The radioactive isotope Au is used in radiotherapy.

• Food industry

It is also possible to decorate cakes with gold. The food additive code is E175. It is very expensive, of course, so it is rarely used in cooking and food production. In addition, large amounts of gold are harmful to the human body, because gold compounds are toxic and their microelements accumulate in kidneys, liver, and spleen. However, gold can be consumed in food if all regulations are followed. Scientists have confirmed that the food additive E175 does not affect the digestive system and is absolutely hypoallergenic. Switzerland has a confectionery factory that makes candy in an edible gold wrapper. The French have introduced “wholesome” water, which contains colloidal gold.

Prospects

In 2019, Russian researchers obtained “two-dimensional” gold, a thin sheet less than 10 nanometers (nm) thick. Nanometers are tiny units of measurement (one billionth of a meter) comparable to molecules. Scientists have gone even further and found that gold can be made into a two-dimensional structure 3–4 nm thick. However, this experiment wasn't conducted just for the sake of interest. Such a gold sheet could be used to create future transparent electronic devices.

The article is based on open sources.

Photo: Яндекс. Дзен