This rare and precious Australian opal shell is a valuable discovery found in cavities of rocks. These cavities formed when a part of a living organism was buried in sand or clay, eventually turning into stone and then opal. While fossils from the time of dinosaurs are not commonly unearthed in Australia, this country was once covered by "The Eromanga Sea," a shallow inland sea, during the Cretaceous era, which covered about one-third of its landmass. These specific pieces are believed to be from the Paleocene period (656-56 million years ago) to the Eocene period (56-33.9 million years ago).