The Australian one kilogram silver piece (abbreviated as 1kg and designated with Ag for "silver") is a massive bullion and commemorative coin format used mostly by the Perth Mint, which only makes collector and bullion coins and other bullion products.
The Australian Silver Kookaburra series was introduced in 1990 by the Perth Mint in the silver one-ounce format. Subsequently, the range was expanded in 1991 to also include 2oz silver, 10oz silver and 1 kg silver; much later, gold formats were also introduced. The Perth Mint issued a "bullion" and a "proof" two-ounce kookaburras with differing designs every year until 2009; after that, all issues are "numismatic" - not bullion but premium, like high relief and/or gold plated editions.
The coins in the series have legal tender status in Australia and are one of very few legal tender bullion silver coins to change their design every year, always featuring a kookaburra - a bird native to Australia, which is the largest member of the kingfisher family and the national bird of Australia. This and their limited annual mintage may, unlike for many other bullion coins, raise their numismatic value over the value of silver used.
The overall weight is slightly more than one kilogram so that the coins have exactly 1,000 grams of pure silver in them (32.15 Troy Oz). | 
