View source for Australian fifty-cent round coin

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=== Production ===
The Australian round fifty-cent coin was introduced with decimal currency on 14 February 1966 and was struck for that year only. It holds a unique place in Australian decimal coinage: it is the only round fifty-cent coin, the only decimal circulation coin struck in silver (80% silver and 20% copper), and the only issue of the new currency that did not survive the decade. The reverse carried Stuart Devlin's Commonwealth Coat of Arms design, while the obverse bore Arnold Machin's effigy of Queen Elizabeth II.

The coin's downfall was its precious metal content. After the silver price was freed and began rising sharply in the late 1960s, the bullion value of the coin's 10.6 grams of fine silver (approximately 0.34 troy ounces) exceeded its fifty-cent face value. Speculators and melters hoarded the coin out of circulation, and the public found its round shape too easily confused with the twenty-cent piece. The Fraser government approved a replacement, and in 1969 a new dodecagonal fifty-cent coin in copper-nickel was introduced, ending the round coin's production after a single year.

Despite its withdrawal, the round fifty-cent coin has never been demonetised and remains legal tender for amounts not exceeding $5. Because so many were melted for their silver, circulated examples trade comfortably above their face value even in modest grades, with value driven by both silver content and collector demand. Mint-state examples, particularly those with full lustre and attractive toning, command substantial premiums.

All 1966 round fifty-cent coins were struck at the Royal Australian Mint in Canberra. No mint marks appear on the coin.
{| class="wikitable"
|+
! align="center" |'''Value'''
! align="center" |Mass
! align="center" |'''Diameter'''
! align="center" |'''Edge'''
!'''Composition'''
|-
| align="center" |$0.50 AUD
| align="center" |13.28 g
| align="center" |31.65 mm
| align="center" |Milled
| align="center" |80% silver<br />20% copper
|-
! align="center" |'''Obverse'''
! align="center" |'''Design'''
! align="center" |'''Designer'''
! colspan="2" align="center" |'''Design date'''
|-
| align="center" |[[File:Australian 50cr AM Coin.jpg|79px]]
| align="center" |Elizabeth II
| align="center" |Arnold Machin
| colspan="2" align="center" |1966
|-
! align="center" |'''Reverse'''
! align="center" |'''Design'''
! align="center" |'''Designer'''
! colspan="2" align="center" |'''Design date'''
|-
| align="center" |[[File:Australian 50cr Coin.jpg|79px]]
| align="center" |Commonwealth Coat of Arms
| align="center" |[[Stuart Devlin AO CMG|Stuart Devlin]]
| colspan="2" align="center" |1966
|-
|}

=== Mintage Figures ===
{|class="wikitable"
|+
!Mintage year
|1966
|-
!Mintage (Mil)
|36.5
|-
!Mint
|RAM
|}
{| class="wikitable"
|+
|<small>RAM = Royal Australian Mint. The Royal Australian Mint reports a figure of 36.5 million; some catalogues cite 36,270,000. Large numbers were melted after the coin's withdrawal, so surviving examples are considerably scarcer than the mintage suggests.</small>
|}

=== Mint Marks ===
All round fifty-cent coins were struck at the Royal Australian Mint in Canberra, and no mint marks or distinguishing varieties between dies have been documented for the circulation issue. This simplicity is welcome for collectors: any genuine 1966 round fifty-cent piece originated from a single mint and a single production run, so condition and authenticity, rather than die attribution, determine value.

Because the coin carries a silver value above its face value, underweight or base-metal counterfeits do appear from time to time. Collectors should verify weight (13.28 grams), diameter (31.65 millimetres), and the soft grey lustre characteristic of 80% fine silver. A coin that is significantly underweight, or which shows a brassy or steel-like colour, should be treated with suspicion.

=== Varieties and Errors ===
No significant die varieties have been widely documented for the 1966 round fifty-cent circulation coin. Genuine mint errors of the usual types (off-centre strikes, brockages, lamination flaws and clipped planchets) do exist for the issue and attract strong interest from error collectors, precisely because the parent coin itself carries a silver premium.

The coin's great collecting stories instead concern survival. Since 1966 the round fifty-cent has been hoarded, melted and traded as bullion through every silver price cycle, and each cycle removed more examples from the pool. Finding one in change today is increasingly uncommon, and many collections regard a well-preserved 1966 round fifty-cent as an essential anchor for any decimal type set. For further detail on the coin's replacement, see [[Australian fifty-cent coin|Australian fifty-cent coin (1969 - present)]].