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.
This coin was part of the five-coin mint set called 50th Anniversary of the 50c Coin (marking 50 years of the dodecagonal coin; the 1966 50 cents coin was round and made of silver). The set - with a mintage of 20,000 - features five 50-cent coins with identical reverses (the Australian Coat of Arms design), and five different obverses using each of the effigies of Queen Elizabeth II that have been in circulation in Australia on its decimal currency.
The first coin in the set is gold-plated and has the Queen's Second Portrait by Arnold Machin, used in Australia between 1966 and 1984.
The second coin has the Queen's Third Portrait by Raphael David Maklouf, used in Australia between 1985 and 1998.
The third coin has the Queen's Fourth Portrait by Ian Rank Broadley, used in Australia between 1999 and 2019 (this coin was also issued for circulation).
This fourth coin has the Queen's Gottwald portrait by Australian artist Vladimir Gottwald which was only used once for a circulation coin, on the 50 Cents commemorative coin for the 2000 Royal Visit.
The fifth coin has the Queen's Fifth Portrait by Jody Clark, which was introduced in Australia in 2019 (this coin was also issued for circulation).
There is no coin in the set representing Mary Gillick's First Portrait of the Queen, which was used in Australia between 1953 and 1964 on the pre-decimal currency.