The wonderful world of opalised fossils

Opal is a rare and precious gemstone that boasts a stunning array of colours and patterns. Australia supplies the vast majority of the world’s opal, our national gemstone. Australia is also a rich source of opalised fossils – remains of plants and animals that were buried in ancient inland waterways and seas and, over millions of years, were transformed into solid opal. Opalised fossils form in a similar way to other fossils, except that they are preserved in opal, as opposed to other minerals such as pyrite or calcite.

The Opalised Fossils stamp issue, which will be released on 17 August 2020, presents four opalised fossils from the early Cretaceous Period (125 to 100 million years ago). Learn more about the background to the stamp issue, including information about the early Cretaceous Period and the content of each stamp.

The pine cone and theropod tooth fossils featured on the stamps were found in Lightning Ridge, New South Wales, an outback opal town that is home to the Australian Opal Centre (AOC), a not-for-profit museum, research and cultural centre. The wood fossil, found in the Koroit opal fields, Queensland, also forms part of the AOC’s collection.

The moon snail fossil on the stamp was found in Coober Pedy, which has been a rich source of opalised fossils since opal was discovered in the area in 1915. It is held by the South Australian Museum. The species, Euspira reflecta, is the most common opalised fossil snail in the region and was an active sea-floor predator during the Cretaceous Period.

Invaluable during the stamp development process were Jenni Brammall, Special Projects Officer at the Australian Opal Centre, and Ben Mc Henry, Senior Collections Manager for Earth Sciences at the South Australian Museum. We interviewed Jenni and Ben, to gain further insights into the wonderful world of opalised of fossils.

As well as being a palaeontologist and gemmologist, Jenni Brammall is a writer, graphic designer, photographer, editor and jewellery designer.

“I’ve always been fascinated by science and art, the natural world and people. I’ve always picked up bones, shells, rocks, sticks, leaves, bits of dead animals, but I wasn’t a ‘dino kid’ – I was first drawn to palaeontology at university,” says Jenni.

“Fossils captured my imagination as rare, beautiful and astonishing relics from the deep past, packed with clues, quietly offering profound insights into ancient creatures, ecosystems and the complexity of life on Earth. I also loved the field work. So instead of finishing a law degree, I focused on palaeontology. Then the hunt for fossils took me to Lightning Ridge, where as well as fossils I discovered the opal fields, their landscapes, skies, geology and astonishingly beautiful opal, as well as their wonderful people and diverse, resilient communities,” adds Jenni.

The AOC was set up to protect and showcase Australia’s world-renowned opal and opalised fossils, as well as to become a world leader in opal-related science, education and tourism, creating opportunities for the broader community in the process. As well as its prized opalised fossils, the AOC has an important collection of precious opal, cultural artefacts, artworks, photographs and archival materials relating to the history and heritage of opal in Australia. The centre hosts school visits, exhibitions and courses. Its future home will be a world-class, partly-underground building designed by renowned Australian architects Wendy Lewin and Glen Murcutt that will generate its own power and collect its own water. The AOC also runs an annual fossil dig, where people from across Australia and the world join a team from the AOC, Australian Geographic Society and University of New England for the opportunity to learn about, see and search for rare opalised fossils. This year’s dig coincides with the release of the Opalised Fossils stamp issue, on 17 August 2020.

Jenni was manager of the AOC until 2019, when she took on her current role which involves managing the design and planning of the new AOC facility, running the AOC’s annual fossil dig and opal courses, managing the fossil collection and working with the external stakeholders, whether opal miners and enthusiasts, scientific researchers, gemmologist or journalists.

After specialising in micropalaeontology and petroleum geology, and working for a short time on oil rigs in Bass Strait and the Cooper Basin, Ben became an assistant to the curator of fossils of the South Australian Museum and has been there ever since, working his way through the ranks to manage the earth sciences collections.

The South Australian Museum curates the world’s largest public collection of Australian precious opal and devotes an entire display gallery to its famous opalised fossils. Here one can see a broad selection of the sea-floor-dwelling invertebrates as well as the opalised skeletons of ichthyosaurs and plesiosaurs, complemented with by life-sized reconstructions of these spectacular animals.

“Opal specimens are curated in both collections that comprise the earth sciences department – fossils and minerals. The oldest opal specimens date back to the early years of mining on the Coober Pedy fields. Our collections include material from all the South Australian fields as well as those in the other opal producing states as well as international localities. Opalised fossils are spread taxonomically throughout the separate invertebrate and vertebrate fossil collections. The strengths of these collections are in opalised molluscs as well as impressive opalised Cretaceous marine reptile remains,” says Ben.

The spectacular opalised marine reptile skeletons on display, such as the St Alban and Addyman plesiosaurs, as well as the Santos ichthyosaur, are some of the highlights of the South Australian Museum collections. Australia’s two finest opal specimens are also housed there: The Virgin Rainbow – an opalised belemnite of the finest quality opal ever seen – and the Fire of Australia, one kilogram of the highest quality opal rough in existence. These two highly significant objects were acquired with the assistance of the Australian Government's National Cultural Heritage Account.

At this major Australian scientific research institution, earth science researchers have not only studied the biodiversity of the Cretaceous Eromanga Sea (a large, shallow body of water that was home to marine molluscs, fish, and swimming reptiles such as plesiosaurs) but are also researching the very the mysterious process of opalisation itself, a conundrum which continues to puzzle scientists.

“The best quality opal is often found in fossils. This is because often they have been dissolved by groundwaters, creating a large void which was later filled with opal deposited from super saturated siliceous fluids. There are many theories as to how opal forms, but none so far can account for all occurrences of sedimentary precious opal,” says Ben.

What is it about opalised fossils that makes them both so important and so fascinating?

“They combine two super rare natural phenomena – the survival of part of a living thing as a fossil, and the formation of a rare gemstone – in the one object! And they’re beautiful!” exclaims Jenni.

“Australia’s opalised fossils provide rich insights into the history of life on our ancient continent – into how Australia, its geology, landscapes, plants and animals came to be as they are, and how fortunate we are to live in this remarkable place,” adds Jenni.

“Australia is one of the only places on Earth where fossils have been preserved in precious opal. The rainbow spectrum of colours makes these fossils more than scientific objects, they become true objects of beauty,” adds Ben.

Most opalised fossils are, perhaps unsurprisingly, discovered by opal miners, though sometimes also by people who fossick for, live near opal fields buy or collect opal.

“The AOC doesn’t have money to buy opalised fossils. Fortunately, some people donate their fossils to the AOC to keep them in Australia, create a legacy for themselves in the collection, make their fossils available for research and share them with the world. Occasionally a generous donor will help us to purchase an important fossil. Sometimes the fossils are donated through the Australian Government’s Cultural Gifts Program. So, the AOC fossil collection is a remarkable collaboration between opal miners, scientists, generous donors and the people of Australia,” says Jenni.

Both Jenni and Ben are excited to see opalised fossils on postage stamps.

“I’m excited and proud! Opal fossils are one of the nation’s wonders and this is a great chance to bring their story to the Australian public,” says Ben.

The Opalised Fossils stamp issue is available from 17 August 2020, online, at participating Post Offices and via mail order on 1800 331 794, while stocks last.

^{This content was produced at the time of the stamp issue release date and last updated 31 August 2020.}