Opal Fossils in Australia

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Australia is the only part of the world where opalised animal and plant fossils have been found.

Opal, one of the most beautiful gemstone in the world, treasured for its unique display of flashing rainbow colors, hides out of sight in the Australian outback. For over a century, people have been to the opal mining fields to chase precious opal, finding their fortune. As it turns out, what opal miners have been uncovering is not only just opal, but also opalized fossils, like the gemstones, for 100 million years under a thin veneer of sediment.

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If it were not for the opal miners—many of whom have sharp eyes and regard the fossils with as great a sense of awe as palaeontologists do—we would not have, or know anything about, these fossils.

Jenni Brammall, palaeontologist, gemmologist and long-term resident of the Ridge

Lightning Ridge in NSW is not only famous for black opals, but also renowned as the opal mining field with the greatest number and diversity of opalised fossils in Australia. Small opalized dinosaurs and primitive early mammalian fossils have been found at Lightning Ridge in NSW, along with shallow marine shellfish and crustaceans.

An opalised tone bone of Fostoria, Lightning Ridge, Australia

Opalized freshwater mussel shells, Lightning Ridge, Australia

Eric the Pliosaur (Cretaceous age marine vertebrate) is probably the most famous opalised fossil which was found at Coober Pedy and now is part of the Australian Museum collection. Not only is the opalised skeleton of this animal preserved, but also the stomach contents of its last fish meal are replaced with opal. At Coober Pedy, SA, opalised fish bones and shelly molluscs are also commonly present.  They are valued based on the appearance of the individual specimen and the intensity of the play of colours.

Spectacular mineral replacement with opal also occurs. The so called ‘opal pineapples’ found at White Cliffs, NSW are opal pseudomorphs of the mineral ikaite. 

Opal Pineapple

Source: 

Smithsonian Magazine (2020). Scientists and miners team up to preserve opalized fossils. [online] Available at:https://www.smithsonianmag.com/science-nature/scientists-and-miners-team-up-preserve-opalized-fossils-180972734/ [Accessed 10 December 2020]

Geoscience Australia (2020). Opal. [online] Available at: https://www.ga.gov.au/education/classroom-resources/minerals-energy/australian-mineral-facts/opal [Accessed 10 December 2020]