Taking to Reddit, the user shared they were handed the 1966 coin, featuring a circular edge, and originally mistook it as a regular 20 cent coin.

“I never knew there used to be round 50 cent coins,” they wrote in the post, alongside an image of the coin.

However others online were quick to point out the “extremely valuable” find, noting the coin is worth $15 alone due to its silver value.

“Mad luck – like seriously lucky. I wish that happened to me. I had to buy a couple for my collections,” one person wrote.

“Keep it! That’s a valuable piece!” wrote another.

“Worth well over 50 cents. Haven’t seen one of these since I was a kid,” said another.

“These are extremely valuable. Please keep it,” another commented.

Before the dodecagon shaped coins we know today, 50 cent coins were originally circular when they were first introduced in Australia in 1966.

The shape of the coin changed just three years late in 1969 as it was causing too much confusion with the similarly sized 20 cent coin.

The metal in the coin was also more valuable than the actual coin value – consisting of 80 per cent silver.

“People were melting them down and making a profit so the mint stopped minting them,” Perth coin expert Joel Kandiah said in a TikTok video.

“36.45 million were minted, but only 14 million put into circulation. [The] rest were melted back into silver,” he added.

Speaking to news.com.au in September, Mr Kandiah said there are a number of valuable coins Aussies should keep an eye out for, including the 2000 $1 ‘mule’ coin or the 1966 Wavy Baseline 20 cent, both of which could be worth thousands.

A five cent coin made in 2007, which features an image of the Queen’s head on both sides, could also fetch its finder around $3000 to $5000, due to a rare printing error.

“There were a lot of 5c coins minted in 2007,” he told news.com.au.

“When the mint sets up its press to make coins, the top of the die is the head side and the bottom is the tail side. But what happened here, is the bottom die was also the tail side so it spit out a double headed 5c coin.”

For those who come across a valuable note and are looking to sell, Mr Kandiah recommends finding a coin dealer from the Australasian Numismatic Dealers Association website, which upholds a code of practice.

“The only thing is because they’re dealers, they’re going to buy and sell it, so obviously, they’re not going to give you the market price upfront, they’re going to give you maybe 20 to 30 per cent below because they need to make the profit themselves on the sale later on,” he warned.

Other options include Facebook groups, including Australian Speciality Coins and Collectors of Australia, as well as auction houses that specialise in coins.

“You will get market value and it will take time, but auction houses might be your best option.”