11 Interesting Facts about Element 79

1. Gold is the most ductile of all metals, meaning it is the most suitable for drawing into wires.

Amazingly, one ounce of gold can be drawn into a wire 1250 miles long (thickness 1 micron). This means that you could make a gold wire long enough to go around the earth with just 20 ounces of gold. Using metric units, one gram of gold could be drawn to a length of 66 km.

2. Gold is also the most malleable of all metals, meaning it can be beaten into thinner sheets than any other metal. Gold can be beaten without any special difficulty to a thickness of 0.1 micron. A stack of one thousand sheets of 0.1 micron gold leaf is the same thickness as a typical piece of printer paper.

3. Gold is one of the densest elements. A cube of gold with each side just 14.2 inches long would weigh a ton. (37.27 cm sides give a metric ton.) The six metals denser than gold are: osmium,iridium, platinum, rhenium, neptunium and plutonium.

4. The concentration of gold below Earth’s crust is about 100 times higher than the concentration in it.

5. ‘The acid test’ has become part of everyday speech. It means a test whose result is absolutely certain. The first acid test was a drop of nitric acid on metal. Gold does not dissolve in nitric acid, so if a metal reacts with nitric acid, it is certainly not gold. The ‘acid test’ became popular in the 1849 Californian gold rush, when all sorts of shady characters tried their hand at selling fake gold.

6. The total mass of gold ever extracted from Earth is 170 000 metric tons (at the beginning of 2012). This amount of gold would fill three and a half Olympic swimming pools. About 2500 metric tons of gold is now mined every year. Two-thirds of all the gold ever taken from the earth has been taken since 1950.

7. Want to get rich quick? Nobel prize winning chemist Fritz Haber did, but not for personal gain; Haber tried to help the German economy by extracting gold from seawater, but could not do it profitably.

A 1 kg gold bar. Processing seawater equivalent to Lake Ontario’s volume might produce enough gold to make 48 bars like this one. Image by Swiss Banker.

8. As recently as the 1980s the oceans were thought to contain about 4 kg of gold for every cubic kilometer of water – that’s almost 1 kg or 2 lb of gold each for everyone on Earth today. Estimates of ocean gold keep falling, however, and it now seems likely that each cubic kilometer of ocean contains just 30 grams of gold (Nozaki, 1992). That’s 1 ounce of gold in every 264 billion gallons of water.

If you could process seawater equal in volume to draining Lake Ontario, you would capture 48 kg of gold, worth less than $3 million at today’s gold price. You cannot put that amount of water – 1600 cubic kilometers – through any chemical extraction process for $3 million. But perhaps you have an idea?

The Gold Foil Experiment: alpha particles were expected to pass through gold foil undeflected (left). In fact, some were deflected (right). Rutherford realized that atoms are mainly empty space, with a dense, positively charged nucleus. The nucleus had to be dense to deflect high-energy alpha particles. Image by Fastfission.

9. In the world-changing Gold Foil Experiment, Ernest Rutherford and his coworkers Hans Geiger and Ernest Marsden fired alpha particles at gold leaf. The experiment found that alpha particles were deflected as they passed through the gold more than they ought to have been if the gold atoms were made of smoothly spread matter.

The gold leaf used in the experiment had been pressed to about 0.6 micrometers thick – that’s a thickness of about 2000 gold atoms. By 1911 Rutherford had concluded that atoms consist of a tiny, dense point of positive charge surrounded mostly by empty space in which negatively charged electrons are present.

10. Approximately 75 percent of the world’s gold ends up in jewelry.

11. In the fourth century BC the Greek mathematician and philosopher Plato wrote: “all the gold which is under or upon the earth is not enough to give in exchange for virtue.”

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Gold

Gold is a chemical element with the symbol Au and atomic number 79. It is a dense, soft, malleable and ductile metal with a bright yellow color and luster, the properties of which remain without tarnishing when exposed to air or water. Chemically, gold is a transition metal and a group 11 element. It is one of the least reactive chemical elements, and is solid under standard conditions. The metal therefore occurs often in free elemental (native) form, as nuggets or grains, in rocks, in veins and in alluvial deposits. Less commonly, it occurs in minerals as gold compounds, such as with tellurium as calaverite, sylvanite, or krennerite.

As the metallic native element mineral, gold structurally belongs to the isometric copper group. It also forms a solid solution series with the native element silver (Ag) to which it is often naturally alloyed (electrum). Other common natural gold alloys are with copper and palladium (Pd).

Gold resists attacks by individual acids, but it can be dissolved by aqua regia (nitro-hydrochloric acid), so named because it dissolves gold. Gold also dissolves in alkaline solutions of cyanide, which have been used in mining. It dissolves in mercury, forming amalgam alloys; it is insoluble in nitric acid, which dissolves silver and base metals, a property that has long been used to confirm the presence of gold in items, giving rise to the term acid test.

This metal has been a valuable and highly sought-after precious metal for coinage, jewelry, and other arts since long before the beginning of recorded history. In the past, the Gold standard has been implemented as a monetary policy, but it was widely supplanted by fiat currency starting in the 1930s. The last gold certificate and gold coin currencies were issued in the U.S. in 1932. In Europe, most countries left the gold standard with the start of World War I in 1914 and, with huge war debts, did not return to gold as a medium of exchange. The value of gold is rooted in its medium rarity, easily handling, easy smelting, non-corrosiveness, distinct colour and non-reactiveness to other elements; qualities most other metals lack.

A total of 174,100 tonnes of gold have been mined in human history, according to GFMS as of 2012.[2] This is roughly equivalent to 5.6 billion troy ounces or, in terms of volume, about 9261 m3, or a cube 21.0 m on a side. The world consumption of new gold produced is about 50% in jewelry, 40% in investments, and 10% in industry.[3]

Besides its widespread monetary and symbolic functions, gold has many practical uses in dentistry, electronics, and other fields. Its high malleability, ductility, resistance to corrosion and most other chemical reactions, and conductivity of electricity have led to many uses, including electric wiring, colored-glass production, and gold leafing.

A schematic diagram of a NE (left) to SW (right) cross-section through the 2.020 billion year old Vredefort impact crater in South Africa and how it distorted the contemporary geological structures. The present erosion level is shown. Johannesburg is located where the Witwatersrand Basin (the yellow layer) is exposed at the "present surface" line, just inside the crater rim, on the left. Not to scale.

Most of the Earth's gold probably lies at its core, the metal's high density having made it sink there in the planet's youth. Virtually all discovered gold is considered to have been deposited later by meteorites that contained the element.[4][5][6][7][8]

The asteroid that formed Vredefort crater 2.020 billion years ago is often credited with seeding the Witwatersrand basin in South Africa with the richest gold deposits on earth.[9][10][11][12] However, the gold bearing Witwatersrand rocks were laid down between 700 and 950 million years before the Vredefort impact.[13][14] These gold bearing rocks had furthermore been covered by a thick layer of Ventersdorp lavas, and the Transvaal Supergroup of rocks before the meteor struck. What the Vredefort impact achieved, however, was to distort the Witwatersrand basin in such a way that the gold bearing rocks were brought to the present erosion surface in Johannesburg, on the Witwatersrand, just inside the rim of the original 300 km diameter crater caused by the meteor strike. This brought their rich gold deposits to the notice of humans in 1886, and launched the Witwatersrand Gold Rush. Nearly 50% of all the gold ever mined on earth has been extracted from these Witwatersrand rocks.[14]

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