Yes, there were many dollar coins with errors. One of the best known dollar error coin was the Sacagawea dollar coin and Washington quarter mule error. Only 12 of these coins were made and they can be up to $100,000.
The number 51.2 is known as a decimal. The decimal is in the 10th place.
The collection and/or study of coins is called Numismatics.
No.
A terminating decimal or a decimal that, after a finite number of digits, settles into a repeating pattern (known as a recurring decimal). This need not happen straight after the decimal point.
There are two well known clubs that specialize in error coins. One of those are American Coin Collectors and the other being American Numismatic Society.
Yes, there were many dollar coins with errors. One of the best known dollar error coin was the Sacagawea dollar coin and Washington quarter mule error. Only 12 of these coins were made and they can be up to $100,000.
The answer will probably never be known. The Royal Australian Mint (RAM) Canberra opened in 1965. By 1984 had the sole responsibility for minting all of Australias circulating coins. Some coins had previously been minted by the Melbourne and Perth Mints and a few overseas Mints such as the Royal Mint and the Canadian Mint. The Royal Australian Mint also produces coins for a number of other countries in addition to bullion coins, medals, medallions, tokens and other privately commissioned articles. The Royal Australian Mint (RAM) has the production capacity to produce 2 million coins per day.
The Australian Dollar coin was first issued in 1984. There was a One Dollar coin minted in 1967, but it was not for general circulation, and it is not even regarded as an official Australian coin. It was known as the "Swan Dollar". It was a very limited mintage, Proof coins in silver and gold specifically for collectors. The obverse depicts a swan in flight, the with the word "AUSTRALIA", a crown and 1967. The reverse has a design of Australian flora with a large 1.00 across the coin. In their original condition and packaging, the silver coins could get up to $1,000 AUD. The gold coins could get up to $12,000 AUD. Only ten were minted and two are known to have been destroyed in the Ash Wednesday bushfires.
No error coins of that nature are known. Also, starting in 2009 the mint mark appears on the coins' edge instead of on the front.
It is extremely unlikely that an Australian decimal coin with minting errors survived the inspection process and went into general circulation. The closest acknowledgement of an error on an Australian 2 cent coin is that in 1967, 1968 and 1981, the designers initials were left off the reverse of the coin. If it turns out that you do have an Australian coin with a genuine minting error, take it to a reputable coin dealer for a valuation.
The rarest Australian Halfpenny issued for general circulation would be the 1923 Halfpenny. It is thought that there were only 15,000 minted. One of these coins, even in poor condition, might fetch over $1,000 AUD. The rarest of all Australian Halfpennies is the 1916 "mule". It has the reverse of the Australian Halfpenny and the obverse of the Indian Quarter Anna coin struck on an Australian Halfpenny blank (or planchet). These are an error coin and should never have made it into circulation. It is thought that less 10 were struck and are worth tens of thousands of Dollars AUD. All known examples of this coin are accounted for.
No Australian general circulation coin has ever been minted with a hole in it. During the Second World War, Australia produced some coins for use in the Internment Camps. These coins will have "Internment Camps" inscribed on them. The Australian Colonies were suffering from a shortage of coinage since England was unable to keep the Colonies supplied during the early 19th century. To resolve the problem, Governor Lachlan Macquarie acquired some 40,000 Spanish Dollars in 1812. These coin had their centres punched out to make them unusable in any other country. They became known as the "Holey Dollar" and "Dump", the "dump" being the centre that was punched out. The "Holey Dollar" had a face value of 5 Shillings and the Dump, a face value of Fifteen Pence. Although these coins were not Australian coins and they were not minted with a hole in them, they are amongst the most famous of Australian and were used until 1829 in the Australian Colonies.
It's also known as the 'mala'. It's an Australian marsupial. Incidentally, you made a slight error in the Latin name - it's Lagorchestes hirsutus.
The Australian Capital Territory is sometimes simply known as the ACT.
There were no official Australian coins issued until 1910. In 1813, Australia was a largely unexplored group of colonies under the jurisdiction of the British Government. The coins in use were mostly British coins, but due to the problems confronting Britain due to years of war, British currency was scarce and they had to improvise. The Australian colonies were a very low priority, being regarded as little more than an outdoor prison. Coins from many foreign countries were used and were known as Proclamation coins. Many of these coins were overstamped or otherwise altered and given new local values. The "Holey Dollar" is an example of the coins used during this period. The centre of Spanish Dollars were punched out, the outer part was valued at Five Shillings, the dump or the centre was valued at 15 Pence.
The Australian state of Queensland is known for its crops of both of these fruit.