Australian Opal Cutters Triplet Opal 8 x 10m Pendant Stainless Steel, with side design. Triplet Opal is classified as Genuine Natural Australian Opal Type 3. It is an assembly of 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.