50 Cents - Elizabeth II 2nd Portrait - Pattern

Australia's 1966 decimal changeover was originally planned around a silver 50-cent piece, and this pattern represents that intention before the economics collapsed. Silver prices rose sharply enough in the years immediately following that the circulating .800 silver coins — already released — were being melted by the public for bullion profit. The mint pulled the composition within two years, replacing it with a dodecagonal cupro-nickel design in 1969.

This pattern predates even that short-lived circulation issue, struck during the design approval process for the new decimal series.