Gold facts

Gold is a precious chemical element

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Gold, like silver, platinum and other precious metals is a natural chemical element, which means it cannot be manufactured. Gold's chemical symbol is Au, which is short for the Latin word for gold, 'Aurum' (meaning 'Glowing Dawn'). Gold has a melting point of 1064 degrees centigrade and a boiling point of 2808 degrees centigrade. The word 'gold' is derived from the Indo-European root 'yellow'.

Interesting features of gold are that it is an element remarkable for its rarity (gold is extremely rare), density, softness, and its very good electrical conductivity. It is also largely inert, and therefore is almost totally immune to decay, and thus can be stored cheaply for long periods.

Gold is a very dense metal with a density of 19.32 g/cm3 which gives it a very heavy atomic weight of 196.9665 g/atom. In practical terms, this means that a litre carton of gold weighs 19.3 kg, so it's nearly 20 times heavier than water. A one tonne cube of gold would have edges of around 37 centimetres - a bit over a foot. It would store value of well over $12 million in very little space.

It is so distinctively heavy that solid gold offers its own immediate qualitative verification in the hand. Gold's heaviness is also important in that it means large amounts of gold can be stored in relatively small spaces, like bank vaults, in which the same value of gold can be stored in one hundredth of the space which would be required for silver.

Gold weights and measures

By tradition gold is quoted and traded in troy ounces, these having been adopted by the U.S. Mint for the regulation of coinage in 1828. Unlike 'normal' pounds and ounces, there are 12 troy ounces to the troy pound rather than 16. But a troy pound weighs less than in imperial pound ( 0.82 British/US pounds). In short, a troy ounce is approximately 0.031kg or 31 grams.

The following table gives an approximate conversion between traditional and metric weights:
Troy ouncesKilogramsGrams
The following table converts prices in troy ounces to prices in kilograms:
$ per troy ounce$ per kilo
$ 260$8,359
$ 270$8,681
$ 280$9,002
$ 290$9,324
$ 300$9,645
$ 310$9,967
$ 320$10,288
$ 330$10,610
$ 340$10,931
$ 350$11,253
$ 360$11,574
$ 370$11,896
$ 380$12,217
$ 390$12,539
$ 400$12,860
$ 420$13,503
$ 440$14,146
$ 460$14,789
$ 480$15,432
$ 500$16,075
$ 520$16,718
$ 540$17,361
$ 560$18,004
$ 580$18,647
$ 600$19,290

In jewellery, carat grade is used to express the proportion of gold in an alloy or the quality of a gold alloy. A Carat (or Karat in USA) was originally a unit of mass (weight) based on the Carob seed or bean used by ancient merchants in the Middle East. The carat is now used for measuring the purity of gold, with pure gold defined as 24 carats. The carat is still used for the weight of gem stones (1 carat is about 200 mg).

All jewellery is required by law to be stamped so consumers will know the quality of gold used. Jewellery made in North America is typically marked with the karat grade (e.g. 10K, 14K), while jewellery made in other countries may be marked with its fineness (e.g. 417, 583). So jewellery should either have a karat grade stamped on it, or a 3-digit fineness number.

Parts Gold to Alloy

Uses and applications for Gold

Gold finds a small number of industrial uses arising from its physical qualities. Gold based products are used in the electronics, chemical and dental industries, which require high quality non-corrosive material, as well as new emerging materials like gold nanopowders and gold catalysts. However together its industrial uses are numerically insignificant and only account in total for a consumption of approximately 450 tonnes of gold per annum. Gold's principal use is decorative, i.e. in the production of jewellery.

The jewellery trade is a permanent and global marketing initiative for bullion, and has for thousands of years gone hand in hand with un-worked metal in promoting gold as a store of material value. It creates a significant barrier to entry for any rival material and contributes to the security of gold, in bullion form, as a form of money. Because gold is ductile and malleable in its pure form, it is often alloyed with various other metals to harden it, which in some cases, change its color. Metals commonly used in the alloying process include silver, copper, nickel, zinc, tin and manganese.

One of gold's important properties is psychological. Most people readily associate gold's distinctive colour with wealth, and many even consider the colour beautiful - possibly because it is so closely associated with money. This gives it an immeasurable advantage over other tangible and portable stores of wealth.

Gold extraction and purification

At different points concentration of minerals within the earth's crust varies from their average, and it is those variations which produce workable ores. Iron, for example, accounts for an average 5.8% of the content of the Earth's crust. It needs to be concentrated by natural variations to about 30% to be considered an ore, indicating a required geological concentration of about 5 times. Gold's average concentration in the Earth's crust is 0.005 parts per million. A lower grade gold ore would contain something like 5 grams per tonne (5 parts per million). So gold ore needs to be concentrated by about 1,000 times above the average to become viable.

The process of gold concentration happens both above and below the surface of the Earth. On the surface there is alluvial gold which has been concentrated by the effects of running water, for example in rivers. Because of its extreme density gold will readily fall out of suspension as water slows down. So where a river cuts through gold bearing rock, and then slows down as it hits a flatter/wider river bed, gold will concentrate in a 'placer' deposit, allowing extraction of gold particles by panning and the modern day industrial equivalents.

Underground gold veins or 'lodes' are produced in association with various metallic deposits, often including sulphides and pyrites. Gold concentration may occur as other minerals are leached away over a long period. Ore of sufficient yield is very rare.

Because of gold's inertness some 80% of gold within ore is in its elemental state. There are several processes for extracting, and then purifying it.

Amalgamation is a mercury based process which works because of gold's willingness to be dissolved by mercury. The mercury is applied on an ore, picks up the gold, and the resulting amalgam is distilled, with the mercury being boiled off to remove it. Mercury is highly toxic and therefore environmentally sensitive, making the industrial plant to perform this type of extraction expensive.

The most important process for gold extraction is cyanidation. Sodium cyanide solution in the presence of air causes gold to enter into solution. Good quality ores give up their gold under cyanidation in what is called vat leaching. Lesser quality ores require heap leaching, which involves huge piles of ore being repeatedly re-sprayed with the cyanide solution over a prolonged period.

Relatively raw gold is purified in two main ways. The cheaper first stage of purification is the Miller process which uses chlorine gas and reaches purification of 99.5%, and then there is the more expensive Wohlwill process which electrolyses gold to purities of 99.99%. London Good Delivery Bars - the main trading unit of bullion - are specified at 99.5% pure. Pure gold is 24 karats, or 99.999% pure. 100% pure gold is nearly impossible to refine.

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