Opalized Dinosaur Tooth

Opalized Dinosaur Tooth:

Photo: Carl Bento/Australian Museum

Surely you've seen fossils in museums, but what about this: opalized
dinosaur tooth. Opalized fossils occur when silica settled into cracks
in the dinosaur bone and then hardened into opal. This one above is a
particularly fantastic specimen: an opalized
theropod dinosaur tooth from the Australian Museum.