it would probably maybe be a 50 cent coin
They are not the rarest of coin like miss print but they are uncommon.
Please be more specific, no one coin is known to be the rarest, even if there is only one.
In America? the 1933 double eagle, or 20$ coin. By the orders of FDR, !1 was made. It is worth up to $2,000.
The rarest British Penny would be the 1954 Penny. There is one known to exist, maybe two, but there could be some doubt about the second.
The rarest coin is the 1933 saint gaudens double eagle. It was sold at a auction for more than 7 million!
That would have to be the 19336 (Karlsruhe) issue, of which only 61,000 were made.
One of the rarest is the 1894-S Barber dime, with only nine known specimens.
The rarest Australian coin minted for general circulation would be the 1930 Penny of which there were only 3,000 minted. It is currently esitmated that there are still about 1,500 of these still being traded in the market.
A example of the 1873cc Liberty Seated Dime in the grade of MS-65 sold for $891,250.00 in July-2004 The coin has a mintage of 12,400 but records show that most were melted shortly after they were made and no one knows how many still exist. In my opinion this coin qualifies as the rarest.
In terms of minted as general currency, the Waitangi Crown of 1935 is definitely one of the rarest. Only 1128 of these were minted, and in good condition can be worth in excess of 7000 New Zealand dollars.
The rarest Australian Halfpenny is the 1916 (mule) coin, the 1923 coin is rare, and 1915, 1918 and 1939 (kangaroo reverse) coins are considered to be scarce.