Australian Natural 8x6mm Triplet Opal Ring Size M set in 375 9K Yellow Gold. Classified by the Opal industry as Natural Opal Type 4 - Triplet Opal is Genuine Natural Australian Gem Crystal Opal, a hydrated amorphous form of silica SiO2nH2O consisting of spheres of silicon dioxide molecules arranged in regular, closely packed planes. Backed by Australian Black Opal potch and capped with a cabochon layer of silica quartz. The three layers have the same coefficient of thermal expansion and are guaranteed for life against delamination. Guaranteed free of dyes and artificial colour.