Australian Natural Boulder Opal Earrings set in solid Sterling Silver stamped 925. Boulder Opal is Classified by the Opal industry as Natural Opal Type 2 Boulder Opal is the definition applied where the Opal is naturally attached to the host rock in which it was formed and the host rock is of a different chemical composition. Genuine Natural Australian Boulder Opal consists of a hydrated amorphous form of concretions of SiO2nH2O silica consisting of spheres of silicon dioxide molecules arranged in regular, closely packed planes filling the cracks and crevices of Boulder Opal ironstone found remotely in Queensland Australia. Boulder Opal is a diminishing resource with anecdotal evidence suggesting increases in value of up to 15% per annum. 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.