Australian Natural 13x10mm Doublet Opal Ring Size 1??set in 925 Sterling Silver. Classified by the Opal industry as Natural Opal Type 3 - Doublet 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 or Boulder Opal Potch. The two layers have the same coefficient of thermal expansion and are guaranteed for life against delamination. Guaranteed free of dyes and artificial colour. All Australian Opal Cutters Jewellery and Loose Opal items are covered by our international warranty. Please send us an note when you check out if you would like to add any modifications or changes or have a specific colour requirement for your Opal. On request and at an additional charge we are able to change or upgrade your Opal (or change the design) of any item that we offer. The item shown online may not exactly reflect the item you receive as Opals have a living play of colour that can be difficult to capture on camera.