1984 saw the introduction of the dollar coin denomination in Australia, replacing the earlier banknotes.
As the introductory information by the Royal Australian Mint in 1984 explains:
"The coin has several distinctive features; it has a golden colour which distinguishes it from cupro-nickel or bronze coins; the coin is thicker compared to other coins of similar diameter, and the edge, comprised of seven plain and seven milled segments, makes the new coin distinctive visually and to the touch. However, the unusual edge design does not inhibit the coin's ability to roll, so that it can be used in vending machines.
The reverse design, by featuring the kangaroo, continues the Australian fauna theme of the current circulating coinage. The kangaroo is Australia's best known native animal, and is instantly identifiable with Australia. Its ability to hop long distances and jump high obstacles has made this marsupial world famous."
The coin type is known in Australia as the "mob of roos" type ("roo" being short for kangaroo).
The composition is 92% copper, 6% aluminium and 2% nickel.