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The Play of Colour

Precious opal is composed of minute spheres of silica arranged together in an orderly 3D grid. The colour emitted from opal is dependent on the size of the spheres, which determines the wavelengths. For example, where the spheres are smaller you will see blue light and where they are larger you will perceive red and orange light (colours at the other end of the spectrum). This display of shifting colours in opal is called the 'play of colour'. The intensity and brilliance of the opal also depends upon the size and uniformity of the silica.