No, they are not especially rare. There were 36.252 million issued.
They have the dubious distinction of being the most hoarded Australian coin, since they were removed from circulation in 1967 after the price of silver skyrocketed.
The next 50 cent coin issued in 1969, was made from cupro-nickel and had 12 sides, as have all Australian 50 cent coins since then.
If you refer to Australian 50 cent coins in general circulation, there are no real rarities. All years of issue of the 12 sided 50 cent coin are potentially still in circulation. The oldest Australian decimal coins are just now reaching their minimum expected useable life span of 40 to 50 years.
There are a lot of coins issued "not for general circulation" that could be considered uncommon.
The 1966 50 cent coin was not rare, but it was withdrawn from circulation, so you do not see them.
The original 1966 50 cent coin was round and had an 80% silver content. Somebody figured out that the silver content of the coin was worth more than than the coin itself (due to the value of silver at that time), so the coin was discontinued.
All subsequent 50 cent coins were 12 sided and had no silver in them at all. The silvery appearance is due to a 25% nickel content.
An Australian 1966 50 cent coin, uncirculated and in absolute mint condition could fetch up to $8 AUD.
There were 36.45 million minted.
With the exception of the round 1966 coin, all years of issue of the Australian 50 cent coin (dodecagonal) are potentially still in circulation so, unless they are part of a Proof or Uncirculated mint set or are individual Proof or Uncirculated coins and in absolute mint condition, they are worth 50 cents. Other than the odd error coin, they are neither rare nor valuable.
There are no 12 sided Australian 50 cent coins minted for general circulation that could be considered to be rare.
They do not have a mintmark, the whole 36,252,000 of them were minted at the Royal Australian Mint, Canberra.
Such a coin does not exist. The first and only round Australian 50 cent coin issued for circulation was issued in 1966. There was a round commemorative Proof coin issued in 2006, but not for circulation.
Presumably, you refer to the Australian 50 cent coin. The round Australian 50 cent coin was only ever minted for 1966. All subsequent Australian 50 cent coins are dodecagonal or 12 sided.
The Australian 2 cent coin was introduced at the changeover to decimal currency in 1966. There were no Australian "cent" coins minted prior to 1966.
Australian five-cent coin was created in 1966.
Australian twenty-cent coin was created in 1966.
The first and only round Australian 50 cent coin was minted in 1966 and was withdrawn shortly afterwards due to the steep rise in the price of silver. The 1966 round 50 cent coin had an 80% silver content. The next Australian 50 cent coin to be issued was in 1969. It was dodecagonal (12 sided) and made from a copper-nickel alloy.
Such a coin does not exist. The first Australian 10 cent coin was issued in 1966.
The 1966 Australian 50 cent coin has a diameter of 31.5mm. The area of one side of the coin is 779.3 square mm.
Such a coin does not exist. The Australian 2 cent coin was first issued in February 1966.
The Australian 1966 50 cent coin was the first and last round Australian 50 cent coin produced by the Royal Australian Mint. With the wisdom of hindsight, this coin was a bit of a blunder on the part of the Royal Australian Mint. It was only very slightly larger in size to the Australian 20 cent coin and it had an 80% silver content at a time when the price of silver was increasing rapidly. It took only three of these coins to get one ounce of silver.
Other than the 1966 coin, the only round 50 cent coin ever issued, the Australian 50 cent coin is a cupro/nickel dodecagonal (12 sided) coin of silvery appearance and is often used as a commemorative.See the link below.
There is no Australian 1954 20 cent coin. Decimal currency was introduced in 1966.