And before I get onto those, the 1966 round 50 cent is not rare and nor is it particularly valuable. It does have real silver in it though which is different to all the other 50 cent coins issued and makes it worth a bit even if it is a banged up circulated coin. So what is the round 50 cent coin worth? It depends on the silver price of the day.
Are there any rare 50 Cent Coins in Australia?
The other problem is that the public at the time hoarded these things so there are tens of thousands of money boxes loaded down with uncirculated or near uncirculated examples of them. So sadly most Australian 50 cent coins are anything but rare.