The first coins to be used in Australia were George III Pennies minted in 1797. …

The first coins to be used in Australia were George III Pennies minted in 1797. More than 4 tonnes of them were shipped to the colony in the early 1800s.
The George III Penny was about 1.5 times the size and 3 times the weight of the later pennies that were in use in Australia until decimalization was introduced in 1966.