Australia mines 97% of the world’s different types of opals. The other 3% come from Mexico, Brazil, and Hungary but are not the same quality that Australian Opal is world renowned for. The Australian opal fields were once an inland sea. As the ages passed and the seas receded, sea creatures were isolated, marooned, and opalised. Eventually the area dried out completely and is now dry desert country. In time the ground waters, holding silica solution, also evaporated (with some artesian springs still active deep “underground”). In a few spots they left behind the phenomenon known as ‘opal’.