Cretaceous Period, 110 million years B.P. A stunning fossil bivalve shell, preserved in black opal, showing iridescent colours, including blue, greens and reds. 15.2 grams total, 41 x 34 mm including case (1 5/8 x 1 3/8 in.). From Lightning Ridge, Australia. Private Shropshire, UK collection. Opal is a spectacular gemstone, and a dazzling key to Australia’s mysterious past, because buried in the Australian opal fields are fossils of dinosaurs and other strange creatures that lived 110 million years ago, in Early Cretaceous times. These fossils are literally gems: teeth, bones, shells and pinecones which have turned to solid opal. Australia is the only country where opalised animal fossils are found. Opalised fossils are rare and precious; even more so because in Australia, it is rare to find fossils of any kind from the time of the dinosaurs. [No Reserve]