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This beautiful cockle shell has had its original calcite shell replaced by precious opal. Large numbers of these cockles lived on the cold sea floor of the Eromanga Sea. Cyrenopsis meeki |
Gems from a desert ocean
The opal fossils of South Australia are both jewels of science and beautiful gems.
The Eromanga Sea that covered the interior of Australia 100-120 million years ago was rich in marine life. Ichthyosaurs, plesiosaurs, fish, sharks, ammonites and belemnites swam in the open water. Slow-moving and sedentary animals, such as starfish, crinoids, cockles, mussels, snails and tube-worms lived on the seafloor.
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An opalised ichthyosaur backbone recovered from a mine in Andamooka by V. Simudvarak of Andamooka. The opal appears to have filled the cavities left behind after the buried vertebrae had dissolved away in the rock. |
Only those bones and shells that became trapped in seafloor sediment had a chance of becoming fossils. Some were replaced by clear silica, and others by precious opal.
Cretaceous Shellfish:
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