Coinage metal

The traditional coinage metals are copper, silver, and gold, elements in Group 11 (IB) of the periodic table. They are also known as the "noble metals". The name "coinage metals" is not recognized by the IUPAC.

They are all relatively inert, hard-to-corrode metals which have been used for minting coins, hence their name. Many metals form coloured compounds, (eg iron pyrite), and many metals have a coloured sheen, but (apart from caesium, which also has 1 6s-electron, similar to gold) only gold and copper are coloured.

These metals, especially silver, have unusual properties that make them essential for industrial applications outside of their monetary or decorative value. They are all excellent conductors of electricity. The most conductive of all metals are silver, copper and gold in that order. Silver is the most thermally conductive element, and is also the most light reflecting element. Silver also has the unusual property that the tarnish that forms on silver is still highly electrically conductive.

Copper is used extensively in electrical wiring and circuitry. Gold contacts are sometimes found in precision equipment for their ability to remain corrosion-free. Silver is used widely in mission-critical applications as electrical contacts, and is also used in photography, agriculture, medicine, audiophile and scientific applications.

Gold, silver, and copper are quite soft metals and so are easily damaged in daily use as coins. Precious metal may also be easily abraded and worn away through use. In their numismatic functions these metals must be alloyed with other metals to afford coins greater durability. The alloying with other metals makes the resulting coins harder to deform and more resistant to wear.

Gold coins are typically produced as either 90% gold (e.g. with pre-1933 US coins), or 22 carat (91.6%) gold (e.g. current collectible coins and Krugerrands), with copper and silver making up the remaining weight in each case.

Silver coins are typically produced as either 90% silver - in the case of pre 1965 US minted coins (which were circulated in many countries), or sterling silver (92.5%) coins for pre-1967 British Commonwealth and other silver coinage, with copper making up the remaining weight in each case.

Copper coins are often of quite high purity, around 97%, and are usually alloyed with small amounts of zinc and tin.

The rise of fiat currency has caused the face value of coins to fall below the hard currency value of the historically used metals. This had led to most modern coins being made of metals other than silver or gold - Cupro-nickel (around 80:20, silver in colour) is popular as are nickel-brass (copper (75), nickel (5) and zinc (20), gold in colour), manganese-brass (copper, zinc, manganese, and nickel), bronze, or simple plated steel.