An extremely rare 50 cent coin has sold for more than $3,000 at auction due to a mistake that happened during the minting process. If you spot an error on one of your coins, it could be worth more than its face value to collectors because of its rarity.

The 2002 50 cent coin was mistakenly struck on a Samoan Tala coin, which is seven-sided and made out of nickel brass. The coin is thought to be totally “unique”, with no other examples of the error coin seen before.

Roxbury’s director Scott Waterman, who auctioned off the coin, told Yahoo Finance there was “nothing similar” to the coin.

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“It’s a different alloy as well, which makes it quite eye-catching. It’s very, very unusual that one, unique as I understand it. So anything that is unique is literally there’s one of it,” he said.

The coin ended up selling at auction for $3,050, after being found in circulation.

Waterman said the error was “pretty crazy” and very “unusual”.

“The Royal Australian Mint strikes a lot of other countries in the region, their coins as well. So very, very occasionally one will cross over and I think that’s what’s happened here,” he said.

Waterman said error coins were a rare occurrence since decimal currency was introduced by Australia in February 1966, but they still exist.

“Relatively speaking, they’re exceptionally rare in Australia compared to other countries and they’re very well supported. We see really high prices for good error coins in Australia relative to other countries,” he said.

Other coins struck on the wrong die have also fetched more than their face value.

A 2000 $1 coin with its obverse struck with a 10 cent die sold at auction for $1,150 in uncirculated condition.

This is known as a “mule coin” where the coin is struck with mismatched dies on the heads and tails.

Another of the $1 coins with the heads side struck on a 10 cent die fetched $375 at auction in circulated condition.

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