Of all the things the opal fields give up, the ones that stop me in my tracks are the fossils. An opalized fossil is exactly what it sounds like: something that was once alive, a shell or a bone or a pine cone, that has slowly turned to opal. You end up holding a creature that lived a hundred million years ago, glowing with the same fire as a fine gem. After fifty years I still find them astonishing, and they are worth understanding even if you never own one.
What an opalized fossil is
When a shell or bone is buried in the right ground, it can slowly dissolve away and leave a void in the shape of the original. If silica-rich water later seeps into that space and sets, as it does anywhere opal forms, the silica fills the mold and takes on the exact shape of what was there before. Sometimes the result is plain common opal, and sometimes it is precious opal with full play-of-color. Either way, nature has made a faithful copy of a living thing in stone. For how that silica gets there in the first place, see my guide to how are opals made.
What gets opalized
The Australian fields, which formed in the beds of an ancient inland sea, are full of marine life turned to opal. Seashells and the bullet-shaped fossils called belemnites are common. So are the shells of small clams and snails. More rarely the fields turn up bones, and Lightning Ridge in particular has produced opalized dinosaur bones and teeth that are important to science as well as beautiful to look at. At White Cliffs, collectors prize the so-called “pineapples,” clusters of crystals that opalized into a knobbly pineapple shape.
Drawn to opal with a story? Browse the handcrafted opal rings in my collection, or talk to me about a custom piece built around a special stone.
Why they matter
An opalized fossil is two rare things at once: a fossil and a gem. The best opalized dinosaur material is so scientifically important that it belongs in museums rather than jewelry, and serious specimens can change hands for very large sums. Most opalized shells are more modest, and a bright one makes a wonderful collector’s piece or, now and then, a one-of-a-kind pendant.
Can you wear an opalized fossil?
Some of it, yes. An opalized shell with good color can be set into a pendant, which is the gentlest way to wear any opal since it sees so little knocking about. Larger or scientifically important pieces are better kept as specimens. As with all opal, the stone is soft, around 5.5 to 6.5 on the Mohs scale, so it wants the same gentle care I set out in caring for opal jewelry.
Frequently asked questions
What is an opalized fossil? It is a fossil in which the original shell, bone or wood has been replaced by opal, so the fossil keeps its shape but is now made of gem material, sometimes with full play-of-color.
Are opalized fossils valuable? They can be very valuable, especially opalized dinosaur bone or a bright shell with strong play-of-color. Plainer common-opal fossils are more affordable and still lovely.
Where are opalized fossils found? Mostly in the Australian opal fields, especially Lightning Ridge, Coober Pedy and White Cliffs, where an ancient sea left shells and bones in just the right ground.
If the idea of wearing something a hundred million years old appeals to you, talk to me about it. For the wider family of opal, start with my guide to understanding opal, or browse the current opal rings in my collection.
