We were in Lightning Ridge with a small team of experts from the Australian Opal Centre (AOC) and University of New England searching for fossils from the Cretaceous, a geological period that lasted from about 145 to 66 million years ago. The fossils we were searching for were those that had been opalised. This dig is an annual science venture for the AOC and Australian Geographic Society (our Lake Mungo Conservation expedition earlier in the month had also been Australian Geographic based). Before I talk about that amazing time at Lightning Ridge, I want to tell you a smidgen about opal - because I’m a rock person! It is considered Australia’s national gemstone and is found in every colour of the rainbow. While opal is found in other countries such as Brazil, Mexico and the US, Australia produces 95% of the world's precious opal and Lightning Ridge produces the most valuable, and is the world’s major source of, black opal.
For those of you interested, opal is a non-crystalline form of mineral silica and related to the more common crystalline mineral silica such as quartz and agate. It comes in two forms – ‘common’ which can be grey, black, cream, amber-coloured and white; and ‘precious’ which has the glorious fire we all associate with opal. That brilliant colour is created by microscopic regularly-arranged spheres of silica which diffract light shone on or through it much like a prism - or that's have I understand it. Opalised fossils occur when the material of biological structures - bone, tooth, shell, plant, etc, has been replaced by opal. In some cases, opal forms in voids within those structures or perhaps, as with wood and clay, within shrinkage cracks.
It's worth having a look at this video to set the scene
https://www.youtube.com/watch?v=FWWyFEygvFQ
Opalised fossils at Lightning Ridge are about 100 million years old and date back to a time when central Australia was covered by a broad, shallow sea, the Eromanga Sea, the ancient dry bed of which we travelled across last year. The sea and land teemed with myriad life forms including dinosaurs and Lightning Ridge was heavily forested with conifers which towering over ferns, fungi, lichens, liverworts etc (I can almost picture it!). It seems that the animals inhabiting the area around Lightning Ridge then were unique even among Australian species, which means that any bones we found could conceivably have been from new and unnamed species – pretty heady stuff! These precious opalised fossils we were hunting provide a window onto deep time, Australia’s ancient past and many aspects of earth history. Whatever precious shards of time we unearthed were destined for the collection at the AOC, the world’s largest and most diverse collection of rare opalised fossils (and callooh callay these were labelled with the discoverer’s name).
Lindsay and I were 2 out of 17 diggers. When I say diggers, the hard digging work had been done by miners already but we spent many days sorting through the tailings from a number of opal mines. Six people had been on the dig a few times before but most of us were newbies. Our guides were an impressive group - a regular at the dig was a palaeontologist and dinosaur specialist from University of New England who has excavated and studied dinosaurs around the world; an amazing woman who grew up in Lightning Ridge and has a lifetime’s experience finding opals and opalised fossils; a PhD and a Masters student studying dinosaurs; and leading us all was Jenni Brammall a vertebrate palaeontologist and gemmologist among many other things who is the CEO of the Australian Opal Centre. She was a wealth of knowledge and an absolute delight to work with.
First day on our fossil ‘dig’ was orientation and getting our eye in so we would be able to recognise opal particularly the more difficult non-precious, common opal called potch in which most fossils would be found on this 'dig'. This doesn’t have the fire of precious opal but both potch and precious opal are fossil-bearing but when found the precious opal is usually snaffle by the miners - of course, it is their raison d'etre. Fantastic fun. We started with the tailings from a couple of opal mines and found quite a few interesting things - turtle shell, tiny bones, plant matter, yabby buttons, wee pine cones, molluscs. I found a tiny pinecone and a gastropod mollusc! I nearly fell over with surprise. And Lindsay found 2 bivalves (freshwater mussels). Brilliant day finished off with drinks and quite delicious nibbles looking over the black plains as the sun set. The next day we were heading out into the field.
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| We each got a box of yummy nibbles sufficient for two! |
The next morning we spent a morning with Butch (see video below) at his mining lease somewhere out of Lightning Ridge. He is a very charming and generous man and we learnt quite a lot listening to him.
Follow the link below to get a better understanding of how the opal miners and palaeontologists of Lightning Ridge work together to ensure Lightning Ridge’s iconic opalised fossils are protected.
https://www.australiangeographic.com.au/news/2021/04/saving-the-rainbow-bones-film/
After lunch we drove across the black soil plains of Lake Coocoran and went specking AKA crawling around looking for tiny fragments of opal/fossil. We were still on the hunt for opalised fossils - and joy oh joy, finding them! Much of the time we spent in the field was on the ground on our knees or reclining on the stones and rocks. It was awesome – but somewhat stressful on back and knees. On the way back to town we detoured to visit a ‘wash out’ where the material brought up from the mines is put through an 'agitator' (modified cement mixer affair) and washed. We helped out for an hour. It's slow and laborious process but rewarding sufficient to keep people like John anchored to Lightning Ridge. And we did go down one mine.
That night we had a fascinating lecture given by Dr Phil Bell, dinosaur specialist at the University of New England and who is involved in dinosaur research around the world. In fact, as well as visiting mines, talking to miners and doing field work we were treated to erudite lectures almost daily. We were told opal’s own story: its life cycle from volcanoes, to inland sea and rich vistas of ancient flora and fauna, how it is found, etc right on to its uses as a semi-precious gemstone as jewellery and collectors’ items – and critically as a ‘highlight’ of precious fossils. For nerdy me the lectures were wonderful.
One day we were treated to a rare sight, a fossil neck vertebra from a Sauropod – these are those big beasts which grew up to 30-40 metres long with long necks and tails (and no they don’t have a brain in their tail!). The location where this was discovered is absolutely secret for a range of reasons not least of which is to protect the miner but also to protect the site from sightseers etc. Sorry I can’t show you photos of that amazing piece of prehistory, but the illustration in the book above will give you a bit of an idea of the shape of the beast. It certainly excited us seeing this fragment if a time long long gone. That afternoon having seen and contemplated this breathtaking fragment from such an ancient and huge beast which I might ass hadn’t seen the light of day for 100 million years, we returned to rock sifting with a heightened sense of purpose and particularly so because the rock fragments we were searching through came from that same site. We found many fragments of bone they suspect were from that same sauropod. As an aside and in a lovely twist of fate, I’m finding lots of opalised plant fossils. Not as sexy as the big beastie bits but I’m happy - it all boils down to no plants, no insects, no etc etc.
All week it was go go go non-stop from first up in the morning till after dark when we fell into bed only to be up and at it first thing in the morning. Friday was no different. We headed out to ‘The Grawin’ for more fossicking and look see.
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| The red arrow points to my favourite, a translucent crystal quartz jellybean. You can see the light shining through it. Beautiful. |
On the way we travelled through a wee village of Cumborah where we visited what is called the Cumborah gravel pit which is quite extensive. This undulating plain of colourful stones, conglomerate beds of river gravel and sand, are quite old. I don’t know just how old but fossil leaf dating to the Tertiary age (60- 40 million years ago) have been found here. I had just a wonderful time finding jasper, crystal and smoky quartz, agates, a possible torpaz, fossilised wood and other colourful pebbles – it was like a landscape of glowing jellybeans. And for my efforts I got stuck by a Hudson Pear - a nasty prickly weed that has invaded the region. Extraction of the prickles is with pliers, I kid you not.
But to The Grawin. This ‘spot’ is about 70 km from Lightning Ridge and encompasses Grawin, Glengarry and Sheepyards; we visited them all albeit briefly in some cases. It is quite unique and actually hard to describe but what you see is pretty frontier-style living. The 'residents' are there for the opal - and freedom; it’s a community of very colourful characters. And they are not keen on photographs. There are three quirky pubs in the district - the Glengarry Hilton, The Club in the Scrub (which we visited a few years ago) and the Sheepyard Inn where we had lunch.
On the road to the pub we crossed paths with a car load of people from the Outback Opal Hunters (TV series) including one of the Cooke brothers. The whole area is populated with marvelous character - and odd pieces of 'junk'!
Scattered and piled everywhere through the opal fields were old cars, trucks, pieces of old machinery. Nothing is thrown away. Over the decades valuable bits and pieces have been scavenged from these wrecks to drive a machine, a pump, a hoist, etc. The miners had to be very inventive. Not so long ago there was a move to clean up the place but fortunately sense prevailed and these rusting pieces of 'scrub art' have been left just as they are as an important part of the local history
Our last day we were starting to run out of steam physically but perked up quickly when I found a Plesiosaurus tooth! And Lindsay found a piece of turtle shell.
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| On the last day, one of the miners whose lease we had visited presented Jenni with a tray of opalised fossils for the AOC. A generous gift! there were yabby buttons, gastopods, pinecones, bivalves and even shark teeth. |
The day culminated with a farewell dinner in one of the surprisingly numerous local restaurants. And so the dig finished - at least our part in it, however I suspect we will venture back some time. It was a wonderful and quite exciting experience, one which had us completely engaged for a week.
For those amateur palaeontologists among you here’s an abbreviated list of what our group of amateur diggers found transformed into opal, wholly or partially:
Bivalve shells (loads), a handful of tiny pine cones and stems, gazillions of bone fragments, seeds, my one gastropod, turtle shell and vertebrae fragments, crocodilian vertebra and scute (scales), 5 Plesiosaurus teeth and 7 yabby buttons (these are gastroliths that develop internally as the crays reabsorb minerals from their shells when they go into molt; the minerals are stored to use to rebuild their next shell). We were all very happy with our stash.
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