Australia: 100-million-year-old fossil pearl discovered

Sydney. In the Australian outback, a tourist found something that at first glance appeared to be a round stone – but it was actually a treasure from a bygone era: a fossil pearl, around 100 million years old and the largest of its kind ever discovered in Australia.

The unusual discovery was made in 2019 in a fossil quarry in the small town of Richmond in northwest Queensland. Visitors are allowed to dig there themselves with a permit – on the condition that any scientifically significant finds are handed over to the Kronosaurus Korner Museum. That's exactly what a tourist did, finding a strikingly round sphere.

"There are round stones – and then there are really round stones!" reads a statement from the museum. The then curator, Michelle Johnston, immediately suspected it might be a pearl. Later examinations confirmed: The supposed stone was indeed a fossil pearl, almost two centimeters in diameter.

The pearl was formed by a bivalve of the genus Inoceramus . These bivalves were among the largest in the world during the Cretaceous period. In Australia, they reached diameters of up to 50 centimeters, and in other regions, even two meters. With their enormous size, they were able to produce very large pearls.

What's so special about the discovery: Richmond today lies in a dry grassland, hundreds of kilometers from the sea. However, 100 million years ago, the Eromanga Sea covered large parts of eastern Australia. This inland sea was home not only to mussels, but also to fish, turtles, and enormous marine reptiles such as the Kronosaurus and ichthyosaurs. Many of their fossils can be seen today in the Richmond Museum.

The pearl was examined by Gregory Webb, a paleontologist at the University of Queensland, who spent two years reviewing the find. "It is the first pearl of its kind found in Australia, but similar finds have been found in North America," the scientist explained in an email. The discovery is a stroke of luck for research: "It is really significant because it helps bridge the gap between the biology and ecology of these ancient, extinct organisms and those of today." Webb explained that this will help researchers better understand how mussels interacted with their environment and with changes in their surroundings. This knowledge could even be valuable for conservation today.

The pearl was examined using state-of-the-art technology: a neutron CT scanner, a type of tomography similar to that used in medicine, allowed the internal structure to be analyzed without damaging the find. This provided definitive proof: It was a pearl—and the largest fossil pearl confirmed in Australia to date.

What's particularly astonishing is that the fossil pearl has survived millions of years virtually intact. This is due to its material: It formed in a shell of calcite, which is more stable than aragonite, the mineral from which most modern pearls are made. While only two other fossil pearls have been discovered in Australia to date – both significantly smaller and opalescent – ​​the specimen from Richmond is a virtually unaltered "true" pearl and thus a scientific "treasure."

But the find is valuable beyond research. "Something as unusual as a fossil pearl also captures the public's imagination," says Webb. "It makes it easier to understand the value of our natural heritage. Some things have never changed—and a pearl is fascinating, whether modern or 100 million years old."

The pearl is now on permanent display in the Kronosaurus Korner—and is likely to become one of the museum's main attractions in the future. The fact that it was discovered by amateur fossil collectors makes the story particularly compelling for museum directors and scientists. After all, professional paleontologists are rare worldwide, the museum emphasizes, and many discoveries only come to light because laypeople are curious about nature and share their finds.