Opal Geology

You could only find our precious opals in very few locations as it required a very special combination of geological, climate and biological phenomena for opal formation. This is the great desert regions of central Australia, where is the origin of 90% of world's precious opals.

Fine marine sands rich in silica were deposited around the shoreline. The great Artesian Basin formed when the sea receded. During the mid-Tertiary period around 30 million years ago, deep weathering caused changes to the sediments releasing large quantities of soluble silica. This solution traveled along faults and joints in the ground infilling cracks and voids. The gel eventually hardened to form common opal, and in rare circumstances it formed precious opal. It was estimated that it takes 5 million years for an opal to form one centimeter thick!