How do opalised fossils form?


What’s cooler than a fossil of something that lived millions of years ago? One that shines all the colors of the rainbow! There’s a region in Australia famous for it’s opal mines called Lightning Ridge. Sometimes they uncover fossilized shells, wood, and even bit’s of dinosaurs!

Fossilization takes place when an organism decays in a soft clay or mud. The tissues are replaced with minerals of the surrounding sediment. In the case of these specimens, the sediment is silica dissolved in water. Over millions of years, the silica/water mixture solidified into a cement of crystals that obscures light in every direction. Sometimes during the process, the crystals form in the shape of internal structures so that the details inside the organism are visible.

Opals are beautiful and pricy gems used in jewelry, so when a fossil is made of the mineral, it becomes even more valuable. To researchers, these samples offer information about the organism, especially when it’s see-through. According to the National Geographic, a new species of dinosaur was identified when a miner uncovered a piece of opalized jaw bone.

Fossils and opals are pretty cool on their own, and together is even better!


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