The most valuable Australian coins and how to spot a fake

Australians are the world's most avid coin collectors. For many it is simply a hobby, but for real enthusiasts there is a financial incentive, as some of the rarest coins are known to appreciate in value and potentially be worth thousands of dollars.

Australians are renowned for being the world's most enthusiastic coin collectors.

For many, it's simply a hobby, but for the truly passionate, there's a financial incentive. Some of the rarest coins are known to appreciate in value and can potentially be worth thousands of dollars.

There are coins of a particularly low circulation that can be worth their weight in diamonds today - but on the other hand some coins thought to be valuable are hardly worth more than the denomination stamped on the side.

Scammers have even capitalised on the hype surrounding certain coins, using nail polish remover to trick potential unsuspecting buyers into parting with their cash.

As a general rule, the most valuable coins tend to be the products of mistakes or even sabotage at the mint, says Tomas Rodriguez, the director of Aussie Coins and Notes who is a member of the Coin Dealers Association of Australasia.

'It's an illegal thing from the employee but that's what creates the intrigue and the interest,' the Canberra-based coin dealer tells me.

'Error coins is a whole category of collector.'

Errors have been very rare since the Royal Australian Mint opened in February 1965, in the Canberra suburb of Deakin, in time for the start of decimal currency in February 1966.

A 2000 $1 coin with a double rim is a particularly valuable 'error coin', with examples in mint condition even fetching $10,000 to $12,000

But that's exactly why certain coins produced unintentionally have become expensive collector's items.

'This is what we call "mint sport" - someone's been cheeky at work and we think intentionally made a coin that was an error,' Mr Rodriguez says.

'They're not supposed to: they do get into trouble, they can even face legal consequences for that but for that to be done, the Mint has to know who did it and that can be difficult to work out.

'Normally, we accuse the junior toolmakers - the 18-year-olds or 19-year-olds - of being cheeky as they are learning how to become toolmakers.

'We never know what caused it - it's all speculation. We have robots that literally scan every coin - it's not easy to get error coins out.'

The $1 coin from 2000

A 2000 $1 coin with a double rim is a particularly valuable error coin, with examples in mint condition fetching $10,000 to $12,000.

'That is a pretty collectable coin,' Mr Rodriguez says.

To collectors, this coin is known as the '2000 $1, 10-cent mule' - describing how a mould meant for the 10 cent coin was used to stamp $1 coins.

'You know how mules carry loads?'

On the head side, featuring the late Queen, there is a double rim that's different to the standard rim of the usual $1 coin.

Only 3,000 to 5,000 of these error coins were believed to have been made when a worker at the Mint put the wrong mould, also known as a die, into the coin-making machine.

'That mold was fitted into the machine only for a portion of the year 2000,' Mr Rodriguez says.

'What they actually did, they put the die for the 10-cent coin went striking the $1 coin.'

A junior toolmaker was rumoured to have caused the error.

'They think it was someone working at the Mint - maybe a junior toolmaker; they do something to cause an error and a few thousand of them escaped the Mint unnoticed,' Mr Rodriguez says.

The most valuable $1 error coin from 2000 has a double rim that goes all the way around, and not just part of the way.

'On this particular one, what you're looking for is for the doubling to go the entire way around the rim,' he says.

'The ones that are graded by their authentication - the highest grade ones, they're worth up to $10,000 - even $12,000.

'As the coin is more perfectly centred, or as the condition increases to a higher condition, then all the way up to $12,000 on the highest end of the scale.

'You're not going to find one anymore in that condition.'

The coins fetching top dollar would need to be certified by the Professional Coin Grading Service, an American third-party group that gives a coin a grading based on wear.

A particularly valuable coin would have an MS60 grade signifying no circulation wear.

Collectors began gathering at Perth's Crown Casino