Australian Opal Cutters Light Opal Earring Stainless Steel 0.39 ct Classified by the Opal industry as Natural Opal Type 1 - Australian Light Opal is defined when the Opal is presented in one piece in its natural state apart from cutting or polishing, and is of substantially homogenous chemical composition. Genuine Natural Australian Light Opal occurs in limited quantity in all of the Australian Opal fields but is predominantly from Coober Pedy in South Australia. A hydrated amorphous form of silica SiO2nH2O consisting of spheres of silicon dioxide molecules arranged in regular, closely packed planes. The Opal is pure hydrated silica SiO2nH2O which has elements of Magnezium Oxide present so it has a white base tone. Precious Australian Light Opal shows a variable interplay of internal colors, and though it is a mineraloid, it has an internal structure. At microscopic scales, precious Opal is composed of silica spheres some 150 to 300 nm in diameter in a hexagonal or cubic close-packed lattice.