The physical element of opal is silica. It was formed in the Cretaceous period (65-140 million years ago) under a very special series of geological conditions. The inland sea of today’s Australia rose. Deep weathering caused the sediments to release a lot of soluble silica which eventually went in the faults, joints, cracks and voids underground. The gel hardened to form opal. Rarely could it become gem quality precious opal!

The “play of colours” of opal results from the diffraction of white light passing through the extremely tiny silica particles. To have brilliant colours, it is necessary to have the particles orderly arranged and their size determines the dominant colours of the opal. Blue fire comes from the shortest wavelength while red fore from the longest one. As silica particles seldom exceed 0.0003mm which results in the longest wavelength, red opals are extremely rare.