George IV State Diadem
Part of the The Personal Jewel Collection of Elizabeth II, the George IV State Diadem or Diamond Diadem was made in 1820 by the firm Rundell, Bridge and Rundell for the coronation of King George IV. It was designed to encircle the King's velvet Cap of Estate that he wore in the procession to Westminster Abbey.
The diadem includes 1333 diamonds weighing 325.75 carats (65.150 g), and 169 pearls along its base. Its design features roses, thistles and shamrocks, the symbols of England, Scotland and Ireland respectively. It is on display at the Queen's Gallery, Buckingham Palace. 
The diadem was worn at the Coronation of Queen Victoria during the procession returning from Westminster Abbey, and later by Queen Elizabeth II. It is also worn by Queen Elizabeth II in the procession to the State Opening of Parliament. It has featured in many portraits of the Queen, including one painted by Lucian Freud in 2001, and one by Raphael Maklouf that appears on Commonwealth coinage and on British Machin series stamps. It has also featured on the banknotes of the United Kingdom, Canada, Australia, Bermuda, Hong Kong, British Honduras, the British Caribbean Territories currency board (consisting of Trinidad and Tobago, Barbados, Anguilla, Saba, St Kitts and Nevis, Antigua, St Lucia, Dominica, St Vincent and the Grenadines, British Guyana and the British Virgin Islands), Mauritius, Southern Rhodesia, Cyprus, Rhodesia and Nyasaland, Fiji, Belize, the Bahamas, Malta, Malaya and North Borneo, and Jamaica.
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- Official Royal Family website http://www.royal.gov.uk/LatestNewsandDiary/Pressreleases/2003/50factsaboutTheQueensCoronation.aspx