IRB is the initials of the designer (Ian Rank-Broadley) of the Fourth Portrait of Queen Elizabeth II used on many coins of the Commonwealth countries, including Australia.
The Australian 50 cent coin from 1969 to present is a cupro-nickel coin with 12 sides. The image of Queen Elizabeth II on all Australian coins from 1999 to present was designed by Ian Rank-Broadley (IRB).
The only thing different about the 2006 Australian Two Dollar coin from any other Australian Two Dollar coin minted from 1999 to 2009, is the year. The obverse has a portrait of Queen Elizabeth II with the words "QUEEN ELIZABETH II AUSTRALIA 2006". Underneath the Queen is the designers initials IRB (Ian Rank-Broadley). The reverse has the usual Aboriginal elder, grass tree and Southern Cross design with the inscription "2 DOLLARS".
on the Australian 20 cent coin it the platypus
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 Australian 5 cent coin has an echidna on it?
Such a coin does not exist. The Australian 1 cent coin was first issued in 1966. The Australian One Penny coin was issued from 1911 to 1964 inclusive.
The first Australian Dollar coin was issued in 1984.
Australian two-dollar coin was created in 1988.
Australian five-cent coin was created in 1966.
Australian twenty-cent coin was created in 1966.
Australian one-dollar coin was created in 1984.
There is no silver in any circulating Australian decimal coin.