The Olympic Australis Opal is the largest and most valuable opal yet found, valued at A$2,500,000. It was found in 1956 at the 'Eight Mile' opal field in the outback opal gemstone mining town of Coober Pedy in South Australia. South Australia is the largest producer of white opal and crystal opal gemstones in the world.
The opal was found at a depth of 9.144 m/30 ft. The Olympic Australis opal was named in honor of the Olympic Games, which were being held in Melbourne at the time. It consists of 99% gem opal with an even colour throughout the stone, and has been left in a natural organic state, unpolished and uncut with blemishes. Olympic Australis is 280 mm long, 120 mm thick, and 115 mm wide (11 in long, 4.75 in thick, and 4.5 in wide). It weighs 17,000 carats (3450 g/121.7 oz/7.6 lbs). Currently the opal is kept in Sydney, at the offices of Altmann & Cherny Ltd.