A Coin found in an unused desk in Scone Palace, near Perth, has been valued at up to £15,000.
The 1813 silver piece from New South Wales was the centre punched out of a Spanish dollar - better known as "pieces of eight".
There was then no coinage in the colony and governor Lachlan Macquarie bought 40,000 silver dollars to solve the problem.
The inner circle, or "dumps" were worth 1s3d (6p) and the outers were valued at 5s (25p).
They were not in use for long before British coins were introduced and so are very rare.
The coin is being sold at Spink's next month by Palace owner, the Earl of Mansfield and Mansfield.