So what makes an Opal precious? What are Opal made up of? Well at the basic level the Opal is a precious stone that is comprised of silica dioxide and varying amounts of water. Where it differs to other precious stones is that the opal does not form crystals but is made up of tiny balls of silica arranged in a regular pattern. Where are Opals primarily found? Opals are found in the following areas: The major areas in Australia for opal deposits are Andamooka, Coober Pedy, Lightning Ridge, Mintabie and Queensland. In the Americas, opal is found in Brazil, Honduras, Indonesia, Mexico and the ...