Formed in a similar way to other fossils, Opalised Fossils are created when plant or animal material are preserved in rock as silica, which opal is a hydrated amorphous form of. These beautiful and colourful fossils include opalised bones of dinosaurs, marine life such as molluscs, bony fish, freshwater crayfish, frogs and turtles, and plant material like pine cones, stems and seeds.