An opalized clam shell from Coober Pedy, South Australia, is a rare and striking example of natural fossilization where the original shell has been replaced or coated with opal. Formed around 100 million years ago during the Cretaceous period, when the region was covered by a vast inland sea, these fossils are the result of silica-rich water seeping into buried marine remains over millions of years. Under the right conditions, this process leads to the creation of precious opal, sometimes displaying vivid flashes of color. Coober Pedy, often called the “opal capital of the world,” is one of the few places on Earth where such opalized fossils are found, making these clam shells highly sought after by collectors and prized for their unique blend of natural history and gemstone beauty.