A Natural Australian Opal Triplet Pendant Sterling SIlver (Stamped 925) Triplet Opal Pendant. Triplet Opal is classified as Genuine Natural Australian Opal Type 3. It is an assembly of Gem Light Opal, a hydrated amorphous form of silica SiO2?nH2O 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.