The Australian five ounces silver piece (abbreviated as 5 oz and designated with Ag for "silver") is a bullion and commemorative coin format. Uniquely, in Australia there are two mints authorised to strike legal tender: the Royal Australian Mint (which also makes the country's circulating coinage) and the Perth Mint which only makes collector and bullion coins, as well as other bullion products.
Both mints endeavour to create coins with attractive designs, and to introduce new designs and themes often, in order to raise the numismatic value of the coins over the value of previous metal used.
The mint says about this coin:
Struck from 5oz of 99.99% pure silver, this coin from the long-running Australian Kookaburra series will enhance your collection further collection further as a result of its remarkable incused design. The Australian Kookaburra series depicts annual designs of one of our most emblematic birds. Famed for its raucous laughing call, the kookaburra is heard across the nation - from the outback to the back yard.
The superbly finished proof quality coin depicts two kookaburras perched on the branches of a shrub displaying the flowers of Australian native waratah. Instead of traditional raised relief, the artistry is incused, meaning it is pressed into the surface of the blank to a depth that’s inversely related to the high relief format | 
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