Introduced by Great Britain in 1997, the Britannia is struck from 95.8% silver and is the world's heaviest silver bullion coin. Mintage is just 100,000 per year. In 1997 the Royal Mint started production of silver bullion coins also under the name “Britannia”. The alloy used is Britannia silver with millesimal fineness 958 (95.8 %). The silver coins are available in 1 ounce, 1/2 ounce, 1/4 ounce, and 1/10 ounce.