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
- Aluminium (First issued 1907 for circulation by East Africa & Uganda Protectorates, though earlier patterns exist)
- Antimony (Used in Kweichow, China 10 cents coin of 1931. Used in medallion medal alloy)
- Carbon (In all steel and iron coins. A few "pressed galvanic coal" Notgeld coins were 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 were issued in 1943 for the Łódź (Litzmannstadt) Ghetto in Poland, and are used in India)
- Palladium (The 1967 Tonga 3-coin set celebrating the coronation of King Taufa Ahau Tupou IV is often called a "circulation issue" although it was issued in a presentation case and had a very limited issue of 1500 sets)
- Platinum (Russia 3, 6, and 12 Ruble coins of Nicholas I issued 1828-1845)
Chemical elements used in non-circulating (commemorative, demo or novelty) coins, medals, patterns, and trial strikes
- Cadmium (1828 medal made by G. Loos for the marriage of Heinrich von Dechen, "of Silesian cadmium" )
- Cobalt (2005 Cameroon 750 CFA francs struck in cobalt-plated iron.)
- Hafnium (Fred Zinkann demo coin.)
- Iridium (2013 1⁄25 oz 10 franc bullion coin issued by Rwanda as part of "Noble Five" precious metals set)
- Molybdenum (Demo coin – Fred Zinkann)(Mintage 250-1 tr oz coins 2008 by Coins By Design - Murray Buckner.)
- Niobium (Austria has issued a number of bimetallic 25 euro coins with a niobium center.)
- Palladium (First issued 1966 by Sierra Leone. Also presentation sets from Tonga, bullion coins of various countries,)
- Rhenium (Demo coin – Fred Zinkann)
- Rhodium (Cohen Mint bullion round)
- Ruthenium (1967 1⁄2 Hau from Tonga was 98% palladium and 2% ruthenium)
- Selenium (1862 medal in UK Science Museum, commemorating Berzelius, discoverer of the element.)
- Silicon (Privately struck US quarter patterns dated 1964 (Pollock-5380) in nickel-silicon alloy.)
- Tantalum (Used in a bimetallic silver-tantalum coin from Kazakhstan.)
- Tellurium (1896 Hungarian mining medal. Reproductions exist from 1975.)
- Titanium (First issued 1999 by Gibraltar. Austria has made bimetallic silver/titanium commemoratives.)
- Tungsten (Alloys are too hard. A few private demos struck only for experimentation. Fred Zinkann US half eagle patterns.)
- Uranium (Two types of a German medal of native uranium.)
- 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.)
Element Series "Coins"
Beginning in 2006, Dave Hamric (Metallium)  has been attempting to strike "coins" (technically tokens or medals, about the size of a US cent) of every possible chemical element. To date he has struck tokens of the following elements.
- Barium (reactive, sealed in glass capsule)
- Boron (mixed with binder, sealed in resin cast)
- Calcium (reactive, sealed in glass capsule)
- Carbon (mixed with binder, sealed in resin cast)
- Cerium (reactive, sealed in glass capsule)
- Europium (reactive, sealed in glass capsule)
- Lanthanum (reactive, sealed in glass capsule)
- Neodymium (reactive, sealed in glass capsule)
- Phosphorus (mixed with binder, sealed in resin cast)
- Praseodymium (reactive, sealed in glass capsule)
- Samarium (reactive, sealed in glass capsule)
- Strontium (reactive, sealed in glass capsule)
- Tellurium (mixed with binder, sealed in resin cast)
- Thallium (extremely poisonous. Lead token clad on one side with thallium foil and sealed in resin.)