Yes, the 10 cent coin is smaller.
The Australian 10 cent coin is 23.60 mm in diameter.
The Australian 20 cent coin is 28.52 mm in diameter.
The 5 cent coin is smaller in diameter than the Two Dollar coin. The Australian 5 cent coin is 19.41 mm in diameter. The Australian Two Dollar coin is 20.62 mm in diameter.
No, the Two Dollar coin is heavier. An Australian 10 cent coin weighs 5.66 grams. An Australian 2 Dollar coin weighs 6.6 grams.
Other than the 1966 coin, the only round 50 cent coin ever issued, the Australian 50 cent coin is a cupro/nickel dodecagonal (12 sided) coin of silvery appearance and is often used as a commemorative.See the link below.
The original Australian 1966 50 cent coin was made from 80% silver, and after the steep increases in the price of silver in the 1960's, the silver in the coin was worth more than the coin. It took only three 50 cent coins to make one ounce of silver. The coin was no longer cost effective to produce. The 1967 issue was halted and the coins melted down. The next, and all subsequent Australian 50 cent coins were dodecagonal and made from cupro-nickel. The change in shape was to make them more distinguishable from the slightly smaller 20 cent coin.
Other than the initial Australian 1966 50 cent coin which was round, all subsequent Australian 50 cent coins from 1969 have been dodecagonal or 12 sided. Because they are of a similar size to the 20 cent coin, they were made 12 sided so that vision impaired people could feel the difference.
The Two Dollar coin was the most recent addition to Australia's circulating coinage and had to fit in with, and be distinguished from, 7 existing types of circulating coin. Circulating coins are no longer made of precious metals, so there is no longer a need to make them to any particular size for any particular metal or denomination. There was also a need to consider the visually impaired. The Two Dollar coin is slightly larger than the 5 cent coin and slightly smaller than the 10 cent coin, and significantly thicker than both.
Any genuine coin with a genuine flaw would be worth something more than usual. The Australian 1966 10 cent coin has no documented occurence of any minting flaws. A reputable coin dealer should be able to give a valuation.
The round Australian 50 cent coin was only ever issued once, in 1966. Three of these 50 cent coins contained one ounce of silver and, as the price of silver increased, the silver content was worth much more than the face value of the coin. The round 50 cent coin at 31.5 mm was also considered to be too similar in size to the 20 cent coin at 28.52 mm. The replacement 12 sided (dodecahedronal) 50 cent coin first issued in 1969 is still 31.5 mm, but its distinctive shape makes it stand out in appearance and feel from other Australian coins.
The first Australian 50 cent coin was issued on the 14th of February, 1966, along with the rest of the initial release of Australian decimal coins and banknotes. The original 1966 50 cent coin was round and had an 80% silver content. Due to steep increases in the proce of silver, somebody figured out that the silver was worth more than 50 cents, so the coin was discontinued. All subsequent 50 cent coins were 12 sided and had no silver in them at all.
With the exception of the 1966 round 50 cent coin, all issues of the Australian 50 cent coin are potentially still in circulation, so unless they are Mint Uncirculated, not much more than face value. A reputable coin dealer will be able to give a more accurate valuation.
The first, last and only year the round Australian 50 cent coin was issued was in 1966. They were made with an 80% silver content. The price of silver skyrocketed around this time and the silver was worth more than the coin, so they were withdrawn from circulation in 1967. The next Australian 50 cent coin was issued in 1969. It was dodecagonal (12 sided) and made from the more commonplace and cheaper copper-nickel alloy.
A two cent US coin is larger in size than a ten cent US coin.