OPALIZED  Cyrenopsis

 

The Coober Pedy area of southern Australia is world-famous for its high-quality precious opal (= hydrous silica - SiO2·nH2O).  Some of the opal at Coober Pedy (pronounced “koober peedee”) has replaced fossil skeletal material.  Most of the opalized fossils here are various marine bivalve (clam) species, but Coober Pedy opal replaces other fossil remains as well (for example, snails, belemnites, crinoids, ichthyosaurs, and plesiosaurs).  Even soft parts have been preserved & replaced by opal (Kear, 2006).

 

The specimens shown below are polished & unpolished fossil clams assignable to Cyrenopsis (either C. australiensis or C. meeki) (Animalia, Mollusca, Bivalvia, Heterodonta, Veneroida, Arcticaceae, Neomiodontidae).

 

Locality: unrecorded mine field in Coober Pedy Opal Field, north-central South Australia State, southern Australia.

 

Stratigraphy: “weathered zone” of the Bulldog Shale, lower Marree Subgroup, Aptian Stage, upper Lower Cretaceous.

 

Cyrenopsis bivalves (above & below; above: 3.0 cm across; below: 3.5 cm across) from the Coober Pedy Opal Field (Bulldog Shale, Aptian Stage, upper Lower Cretaceous) of South Australia.  The unpolished valves are composed of precious opal.

 


 

Cyrenopsis bivalves (above & below) from the Coober Pedy Opal Field (Bulldog Shale, Aptian Stage, upper Lower Cretaceous) of South Australia.  The valves are polished to show the precious opal’s play of color.

 

 

 


  

Opalized molluscs from the Coober Pedy Opal Field (Bulldog Shale, Aptian Stage, upper Lower Cretaceous) of South Australia.  This is a concentration of opalized clam shells in a tempestite (storm bed).  This is a multispecies assemblage consisting principally of Cyrenopsis australiensis and Cyrenopsis meeki.  A few opalized mussel shells (Eyrena tatei) and opalized snail shells (Euspira) are mixed in as well.

(SAM P31847, South Australian Museum public display, Adelaide, Australia)

 


 

Here's another bivalve from South Australia's Coober Pedy Opal Field with its shells replaced by precious, jewelry-grade opal.  Both the left & right valves are polished to show the play of colors.  I'm not sure what bivalve it is, but it may be another Cyrenopsis (?).

 

Opalized bivalve from the Coober Pedy Opal Field, South Australia.  Specimen owned by Caitlin Sjöstrand.

 

Opalized bivalve (same specimen as above) from the Coober Pedy Opal Field, South Australia.

 

Opalized bivalve (same specimen as above) from the Coober Pedy Opal Field, South Australia.

 

Opalized bivalve (same specimen as above) from the Coober Pedy Opal Field, South Australia.  Dorsal view of hingeline.

 

Opalized bivalve (same specimen as above) from the Coober Pedy Opal Field, South Australia.  Field of view ~1.5 cm across.

 

Opalized bivalve (same specimen as above) from the Coober Pedy Opal Field, South Australia.

 

Opalized bivalve (same specimen as above) from the Coober Pedy Opal Field, South Australia.

 

Opalized bivalve (same specimen as above) from the Coober Pedy Opal Field, South Australia.

 


 

Reference cited:

 

Kear, B.P.  2006.  Marine reptiles from the Lower Cretaceous of South Australia: elements of a high-latitude cold-water assemblage.  Palaeontology 49: 837-856.

 


 

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