Opal Belemnite: Cretaceous Period (145-66 million years ago), beautiful specimen from Coober Pedy in South Australia, completely opalised with lovely irridescence, 97 mm long. Gorgeous! [Belemnites are an extinct order of squid-like cephalopods. Cooper Pedy is known as the 'opal capital of the world': since the first opal was discovered in 1915 it has been supplying most of the world's gem-quality opal]