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.
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The first and only round Australian 50 cent coin was minted in 1966 and was withdrawn shortly afterwards due to the steep rise in the price of silver.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.