Opalized Wood Boulder Opal

Sources of opal
Australia produces around 97% of the world's opal. 90% is called 'light opal' or white and crystal opal. White makes up 60% of the opal productions but cannot be found in all of the opal fields. Crystal opal or pure hydrated silica makes up 30% of the opal produced, 8% is black and only 2% is boulder opal.
The town of Coober Pedy in South Australia is a major source of opal. The world's largest and most valuable gem opal "Olympic Australis" was found in August 1956 at the "Eight Mile" opal field in Coober Pedy. It weighs 17,000 carats (3450 grams) and is 11 inches (280 mm) long, with a height of 4 3⁄4 inches (120 mm) and a width of 4 1⁄2 inches (110 mm).
The Mintabie Opal Field located approximately 250 km north west of Coober Pedy has also produced large quantities of crystal opal and also the rarer black opal. Over the years it has been sold overseas incorrectly as Coober Pedy Opal. The black opal is said to be some of the best examples found in Australia.