A rare 5 cent coin has sold for thousands more than its face value due to a key “accident” made during the minting process. Error coins can be very valuable because they are an “exceptionally rare” occurrence in Australia compared to other countries.

The 2007 5 cent coin has a double obverse error, meaning it has the head of Queen Elizabeth on both sides of the coin. The coin went to auction today and was sold by Roxbury’s Auction House for $1,250.

Roxbury’s director Scott Waterman told Yahoo Finance the double header coin was popular among collectors and this is what led to its “strong price”.

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“The fact that it is double heads is really what makes it desirable and valuable,” he said.

The error coin was due to an accident by the Royal Australian Mint at the time, with the coins mistakenly released into circulation.

The Royal Australian Mint made 59 million 5 cent coins in 2007. While the exact number of double header coins is not unknown, Waterman said, as a guess, there could be 1,500 to 3,000 out there.

The 2007 5 cent coins are the most popular example of a double-headed coin.

“You get single coins, occasionally double heads or double tails. But very rarely do you get that many that are released into circulation,” Waterman said.

The coin went up for auction along with 2,500 other items, including the Holey Dollar, which is the first coin struck in Australia. It is expected to sell for between $90,000 and $100,000 over the coming days.

The Rainbow Pound, which was created during note shortages in World War I, is also up for sale and expected to sell for between $16,000 and $20,000. A total of 32 notes are known to have survived.

Error coins can be valuable

Waterman said most of the classic rarities were accidents.

“The 1930 Penny, for instance, was an accident. So it’s quite often not by design and they’re not even aware of it until sometimes 20 years later. In the case of the 1930 Penny, no one knew they existed until the 50s, so that’s kind of what makes the legend of it,” he told Yahoo Finance.

The 1930 Penny is known as ‘the King of Australian Coins’ and there are thought to be 1,500 of them in existence. The coin was not meant to be struck as the Melbourne Mint received no orders from the government for new coins during the depression.

Waterman said error coins were a rare occurrence since decimal currency was introduced.