100 Dollars - Elizabeth II 4th Portrait - Platypus - Platinum Bullion Coin

Australia's platinum bullion program has always occupied a niche well below its gold and silver counterparts in mintage terms, and the annual figures for this denomination rarely exceeded a few hundred pieces in any given year. Perth's decision to use the platypus for the platinum series was deliberate — the animal's electroreceptive bill, used to detect the electrical fields of prey underwater, drew an implicit parallel to platinum's own role in precision sensing and catalytic technology, where the metal does genuine scientific work rather than sitting in vaults.