Although the vast majority of coins are round, coins are made in a variety of other shapes, including, squares, diamonds, hexagons, heptagons, octagons, decagons, and dodecagons. They have also been struck with scalloped (wavy) edges, and with holes in the middle. Coins in the shape of polygons often have rounded edges or are Reuleaux polygons.
Squares and diamonds
Indo-Greek coins were often square.
Many countries have struck square coins with rounded corners. Some of these, such as the Netherlands 5 cent coin of World War II and the Bangladesh 5 poisha coin, are oriented as a square, while others, such as the Netherlands Antilles 50 cent and the Jersey 1 pound coin, are oriented as a diamond.
The Madagascar 10 ariary coin is seven-sided. The British twenty pence and fifty pence coins are heptagonal Reuleaux polygons, as is the United Arab Emirates 50 fils coin, the Barbados one dollar coin, and several coins from Botswana. Reuleaux polygons have constant width, which means the currency detectors in coin-operated machines do not need an extra mechanism to detect shape.
Many countries have struck twelve-sided coins. Coins currently circulating include the British one pound coin; 50 cent coins from Australia, Fiji, and the Solomon Islands; the Tongan 50 seniti coin; and the Croatian 25 kuna coin.
Many countries have coins with scalloped (wavy) edges. These usually have twelve bumps (e.g. the Vanuatu 100 vatu or the Hong Kong 20 cents), but can have other numbers such as eight (the Swaziland 10 cents or the Ang Bagong Lipunan Philippine five centavo coin) or sixteen (the Libya 50 dirhams).
Often a round coin will have a central hole. In some countries this was to allow them to be strung together, while other reasons include difficulty of counterfeiting and ability for visually impaired people to distinguish them from other coins.
- Plautz, Jason (13 May 2013). "11 Unusually Shaped Coins". Mental Floss. Retrieved 1 July 2018.
- Houston, Kevin (8 July 2011). "Curves of constant width – The 50p story". Retrieved 1 July 2018.
- "Why Do Some Ancient Coins Have Holes In Them?". Retrieved 3 July 2018.
- Gordenker, Alice (20 June 2006). "5 yen and 50 yen coins". The Japan Times. Retrieved 3 July 2018.
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