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There’s a reason Opal Fossils create excitement: they are as rare as prehistoric hens teeth!

If you’ve ever dug a little into the origin of opal fossils you will appreciate why they are so sought after, why they are so rare and why they are so valuable. A lot of it boils down to how lucky we are that any exist in the first place. This is because the ancient processes that lead to the development of opal fossils could just as easily not happen as happen. Lets take a closer look at where opal fossils come from, and the challenge of making them available for you.



An opalized snail, approximately 110 million years old!

(Unearthed Australian Opal Collection)


The ancient history of opal fossils.

The creation of an opal fossil begins when deceased marine life lie on the ocean floor and then are covered by sediment. Over millions of years the ocean recedes and the sediment hardens around the remaining marine life. Over time the shell, bone or teeth structure dissolves leaving just a void in the sediment that has now turned to sandstone. When conditions are just right, water and silica then collect within the voids in the sandstone which is at that time well below the earth’s surface. Again given the right conditions the water and silica can turn to opal creating a fossil of the creature or object that once existed. Opal fossils found in Australia have included bird teeth, crocodile & shark teeth, plant matter, marine life such as shells, snails and dinosaurs. Whilst still a highly debated subject these fossils are thought to be approximately 100 million years old.


The modern history of opal fossils.

One of the most famous fossils finds in Coober Pedy was Eric the Pliosaur in 1987, discovered by an opal miner!

Pliosaurs are actually aquatic carnivorous reptiles, not dinosaurs. 'Eric' was a small, short-necked pliosaur and is one of the most complete opalised vertebrates known and became part of the fossil collection of the Australian Museum in 1993 after money to purchase the specimen was raised by the school children of Australia (with the help of Akubra Hats). 'Eric' is currently on display at the Australian Museum.


"Eric" Photo credit Australian Museum


We cross our fingers that someday we find something as awesome as Eric or the well known Virgin Rainbow.

The 'Virgin Rainbow' is one of the world’s rarest and most expensive opals. This extremely rare opal exhibits incredible fluorescence with a rainbow of different colours that make opal so distinctly unique. The Virgin Rainbow was found in Coober Pedy, South Australia by miner John Dunstan, working in the opal field. It is worth over $1 million and is now owned by the South Australian Museum in Adelaide.



Searching for opal fossils is very challenging.

On our search for gem opal we typically aim to determine at what depth the “levels” occur in a certain opal field. Whilst “level” is not a geological term opal miners refer to it often. A “level” to an opal miner is a horizontal band in the ground that is either a distinct layer of separation in the ground or a band that shows signs of opal or silica within. Some opal fields have multiple levels, and some have only one.


Unlike seam opal which is nearly always located in visible faults in the ground structure on a level, opal fossils can be found almost anywhere in the sandstone. Opal surprises us on a regular basis by appearing where we least expect it to be, which is what makes it such a challenge to find. Fossils are even more challenging to target due to their usual random locations and lack of indications within the ground.


Shells, snails and belemnites (AKA “Pipes”) are the most common found fossils in Coober Pedy opal fields. Belemnites are a group of extinct cephalopods having a squid-like body and a solid, calcareous, internal, elongated, bullet-shaped skeleton called a guard. Other rarer finds include turtles, plant matter, crinoids & dinosaurs. In the Coober Pedy opal fields these fossils can be found formed just a few feet deep to around 100 feet deep.


The challenge of mining for opal fossils today.

Miners often refer to finding a “pocket of shells” which means they have come across a cluster of shells together in a group. These pockets can contain belemnites, mussel shells, pipi shells, snails, teeth and other marine life all that appear to have died together or after death have settled into a low spot on the sea in tidal movements. Whilst we do occasionally find an opal fossil by itself more often than not, there is more than one and sometimes hundreds.


Opal fossils are very rare and therefore can create a lot of excitement! A fossil in its entirety is even rarer! Removing them from the sandstone in full without fracturing or breaking them is a challenge. The unfortunate reality is that sometimes we don’t know it’s there until we hit it with the mining machinery or digging tools such as picks. With experience it’s possible to predict with some degree of certainty where a seam of opal either horizontally or vertically is likely to run behind what is visible on the face when we come to extracting it. This level of predictability allows us to avoid breaking seam opal as we try to extract it in one piece unlike the fossils.


The value of opal fossils varies significantly with factors such as rarity, size, condition, fullness, opal health and of course colour play within the piece being of importance. It is however a fact that gem opal with a fossil will command far more value than gem opal in seam.


For us, we assess what the ground shows us and we strategically mine for seam opal … If we stumble across a fossil on the journey it’s a very welcome surprise!

 







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Great site. Love opals. One correction: You use the term sandstone for the host rock. I was in Sydney in the 60's looking for a job, I am a geologist. In my spare time the guys in the geology department at the Uni of Sydney let me use their machines. I was able to show that the opal host rock was not a sandstone but from a very finely divided felsic ash fall. This ash is what yields the very mobile silica that forms the opal. I gave my data to the grad students at the Uni, but I don't know what they did with it.. It was, however, quite definitive.

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