The coinage metals comprise, at minimum, those metallic chemical elements which have historically been used as components in alloys used to mint coins. The term is not perfectly defined, however, since a number of metals have been used to make "demonstration coins" which have never been used to make monetized coins for any nation-state, but could be. Some of these elements would make excellent coins in theory (for example, zirconium), but their status as coin metals is not clear. In general, because of problems caused when coin metals are intrinsically valuable as commodities, there has been a trend in the 21st century toward use of coinage metals of only the least exotic and expensive types.
Historically, many coinage metals (or alloys) are from the three nonradioactive members of group 11 of the periodic table: copper, silver and gold. However there are many more, even for coins made from intrinsically precious metals. Precious metals are always used in bullion coins and some collectable coins. Coins not intended for circulation or for intrinsic value have also been made experimentally using an even larger variety of metals, since they function as fiat money. In general coins intended for circulation must have metal values considerably less than their face values, for reasons discussed below.
Requirements for a coinage metal
Coins that are intended for circulation have some special requirements based on the conditions they will encounter. For example, a coin may be in circulation for up to 30 years, and so must have excellent wear resistance and anti-corrosion properties. Achieving this goal necessitates the use of base metal alloys. Some metals like manganese have occasionally been used in coins, but suffer from making the coins too hard to take an impression well (or metals apt to wear out stamping machines at the mint).
When minting coins, especially low denomination coins, there is a risk that the value of metal within a coin is greater than the face value. This leads to the possibility of smelters taking coins and melting them down for the scrap value of the metal. Pre-1992 British pennies were made of 97% copper; but as of 2008, based on the price of copper, the value of a penny from this period is 1.5 new-pence. Modern British pennies are now made of copper-plated steel. For similar reasons, American pennies (cents) were once made of copper alloys, but since 1982 have been made of copper-clad zinc.
This problem has led to nearly the end of use for a common base metal alloy for everyday coinage in the 20th century, called Cupro-Nickel (also cupronickel), with varying proportions of copper and nickel, most commonly 75% Cu 25% Ni. Cupronickel has a silver color, is hard wearing and has excellent striking properties, essential for the design of the coin to be pressed accurately and quickly during manufacture. In the 21st century with the prices of both copper and nickel rising, it has become more common to experiment with various alloys of steel, often stainless steel. For example, in India some coins have been made from a stainless steel that contains 82% iron, 18% chromium, and many other countries that have minted coins that contain metals now worth nearly the coin face-value, are experimenting with various steel alloys.
Chemical elements used in circulating coins
- Antimony (Used as alloy agent in one Chinese coin of 1931. Used in medallion medal alloy)
- Carbon (In all steel and iron coins. A few "coal" coins minted in the hyperinflation in post WW I Germany)
- Chromium (Used for plating coins and in some rare hard stainless steel coins)
- Manganese (Some Mn used in U.S. wartime "silver nickels" and the new US dollar coin for similar reasons—attempts to match magnetic and electrical properties of previous nickels, and previous Susan B. Anthony dollars, for vending machines)
- Magnesium (Magnesium-aluminum coins are used in India)
Chemical elements used in non-circulating (commemorative, demo or novelty) coins and medals
- Cobalt (Used in medals. A coin in Cameroon is said to be struck in cobalt)
- Hafnium (Fred Zinkann demo coin)
- Molybdenum (Demo coin – Fred Zinkann)(Mintage 250-1 troy ounce coins 2008 by Coins By Design - Murray Buckner)
- Niobium (Austria has issued a number of bimetallic 25 euro coins with a niobium center)
- Palladium (1⁄2 Hau from Tonga (98%) and some bullion coins)
- Rhenium (Demo coin – Fred Zinkann)
- Ruthenium (1967 1⁄2 Hau from Tonga was 98% palladium and 2% ruthenium)
- Selenium (Alloy medal only, to commemorate Berzelius, discoverer of the element)
- Tantalum (Used in a bimetallic silver-tantalum coin from Kazakhstan)
- Tellurium (Hungarian alloy medal only)
- Titanium (Austria has made bimetallic commemorative coins of silver and titanium)
- Tungsten (Alloys are too hard. A few private demos struck only for experimentation)
- Uranium (German medal only )
- Vanadium (Mintage 20-1 Troy ounce coins 2011 by Coins By Design - Murray Buckner)
- Zirconium (Mintage 500-1 Troy ounce coins 2012 including 50 black & 50 Rainbow by Coins By Design - Murray Buckner)