Opalised Fossils at Crystal World Shop OPAL BELEMNITE FOSSIL OPLBEL00022 Early Cretaceous, Bulldog Shale Formation, Coober Pedy, South Australia buy Support the preservation of rare opal fossils with The Australian Opal Centre! At the heart of the Australian Opal Centre is a magnificent collection of 110-million-year-old fossils, from a period of time called the Early Cretaceous.