The Australian 50 cent denomination was first introduced as a silver coin with decimalisation on 14 February 1966, but was changed in 1969 to its current specifications: a large dodecagonal (12-sided) copper-nickel coin; apart from the usual design featuring the Australian Coat of Arms, the denomination is also extensively used to issue circulating commemorative coins with various reverses. It is one of the heaviest coins in regular circulation in the world.
Apart from circulating coins, the Royal Australian Mint has a range of Non-Circulating Legal Tender (NCLT) 50 cent coins issued for collectors, such as this one.
The 2nd of June 2003 marked the 50th anniversary, or Golden Jubilee of the Coronation of Her Majesty Queen Elizabeth ll.
The Royal Australian Mint commemorated the event with a two-coin set: a gold coin denominated $100, and this 50 cents coin in silver. Both were designed by Peter Soobik of Orange NSW, and continue the theme of the previous year's set which commemorated her Accession to the Throne in 1952.
The silver 50 cents were also available separately. Apart from the precious metal version, the mint also released an Aluminium-Bronze 50 cents (as opposed to the copper-nickel composition of normal 50 cent coins), in a Philatelic Numismatic Cover together with Australia Post - postmarked June 2nd 2002.
No coins of this type were released into circulation. | 
Search for Australia: Fifty Cents 2003 Coronation Golden Jubilee (NCLT) on eBay 