Image: Opalised animal fossils
A selection of opalised animal fossil specimens from the Early Cretaceous rocks of Lightning Ridge, New South Wales.
- Robert Jones
- © Australian Museum
Skeletal hard parts, such as bones, shells and teeth, are often completely replaced by silica (SiO2) in the form of opal. These examples include a plesiosaur tooth (top left), three mollusc shells (two bivalves and one gastropod, top right), turtle and crocodile vertebrae (middle row) and dinosaur and other reptile toe-bones (bottom row).