This two-coin set was issued to mark the 50th anniversary of the Royal Australian Mint. It contains two 50-cent coins: a 1966 silver round 50 cents coin (one of the first struck by the mint), and a 2015-dated coin with a special C mint mark (the first time such a mint mark was used on the denomination).
The 2015 coin is in Proof FDC grade. The 1966 silver piece is circulated.
The mint says about the set:
"Mark this significant milestone for the Royal Australian Mint with this limited edition 50.50 Two Coin Set. Capturing the spirit of ‘fifty’ by featuring two fifty cent coins, both depicting Stuart Devlin’s iconic design of the Commonwealth Coat of Arms. The included 1966 50c Circulating Coin is an original and one of Australia’s first coins introduced after decimalisation on 14 February 1966. It carries its own unique memories, as it has been handled, spent and circulated. It sits alongside the world-renowned dodecagonal shaped 2015 50c ‘C’ Mintmark Proof Coin which for the first time in history, is adorned by a ‘C’ mintmark for Canberra, the home of Australian circulating coins." | 
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