Unusual Coins

Some mediaeval coins, called bracteates, were so thin they were struck on only one side.
The Royal Canadian Mint is now able to produce holographic-effect gold and silver coinage. However this procedure is not limited to only bullion or commemorative coinage. The 500 yen coin from Japan, was subject to a massive amount of counterfeiting. The Japanese government in response produced a circulatory coin with a holographic image.
The Canadian Mint has also released several coins that are coloured, the first of which was in commemoration of remembrance day. The subject was a coloured poppy on the reverse of a 25 cent piece.
For a list of many pure metallic elements and their alloys which have been used in actual circulation coins and for trial experiments.