The geological events that created the opal have underlined how similar the geology of Australia's Red Centre is to the planet Mars.
Australia produces 95 per cent of the world's opal supply, but scientists have never been able to explain how the gemstones are formed.
Research by the University of Sydney suggests the drying out of Australia's central landscape 100 million years ago created conditions that trapped silica-rich gel in rock, which later solidified to form opals.
Associate Professor Patrice Rey says the formation of the opal is due to an extraordinary episode of acidic weathering as the inland sea dried out.
Professor Rey says Central Australia is believed to be the only place on earth where acidic weathering of that scale took place.
And he told Louisa Wright, the only other place where similar conditions have been observed is on the surface of Mars.
