This specimen is a fragment of rough opalized plant material is opalized fossil plant material from Lightning Ridge in NSW, Australia. Australia is the largest producer of opals in the world. The opal fields here date to the Cretaceous when Central Australia was home to an enormous inland sea, known to science as the Eromanga Basin. It dates to roughly 110,000,000 years old.

It is a uniquely large opal, measuring 1.08" — the largest rough opal in our collection. This is a one-of-a-kind item with a beautiful multicolor look.

You can see our full collections of smaller opals here.

Unlike most gemstones, opal does not have a single crystalline lattice structure stretching throughout the material. Rather, opal is a collection of very tiny spheres of silicon-dioxide which are packed together and compressed. Scientists estimate it takes up to five million years to form a single centimeter of natural opal.

The "fire" of opal is the result of diffraction as light passes through the silicon-dioxide sphere within the stone.

As illustrated here, the spheres are aligned in an ordered network that diffracts continually the white light as it passes through each sphere and creates the shifting, brilliant colors we see.

Opal forms in areas where water comes in contact with sandstone and filters deep into the Earth, picking up more silica along the way. This silica-rich solution settles into cracks, natural fractures in the rock, or even into fossilized organic material. Under the intense heat and pressure, most of the water evaporates leaving the silica behind.

As noted above, this particular specimen is opalized fossil plant material from Lightning Ridge in NSW, Australia. Australia is the largest producer of opal in the world. The opal fields here date to the Cretaceous when Central Australia was home to an enormous inland sea, known to science as the Eromanga Basin (or Sea).

The Eromanga Basin in Central Australia was home to a great inland sea for about 95 million years during the Mesozoic Era. This sea was home to many forms of marine life including Plesiosaurs, Ichthyosaurs, and Ammonites. The deposits in Lightning Ridge date to roughly 110,000,000 years old.