![]() The vast majority of the world's opals are common opal. This stone is known as common opal.Ĭommon opal which is opaque can be found in many different colours but does not exhibit iridescence (play of colour). When the shape and size of the silica spheres in the structure of opal differ and the pattern they form is random, there's no diffraction of light. The only difference is one exhibits an optical phenomenon known as 'play of colour', the other does not. Precious opal and common opal are virtually the same stone. With smaller spheres blue and violets can be seen whilst larger spheres produce reds and orange. The most common colours seen in opal are red, orange, green and blue.Īs an opal stone is gently moved around, depending on the size of the spheres light reflects from different angles. The more uniform the shape and size, the brighter and more intense the colour. ![]() The quality of the iridescence correctly known as 'play of colour' is dependant on the size of the spheres and the space between them. They must also be arranged in a neatly arranged pattern. Refraction is the slowing down of light as it enters an object.ĭiffraction only happens when the minute silica spheres share a similar shape and size. Light diffracts off the spheres as it passes through the stone which produces a rainbow of colours.ĭiffraction is the bending of light as it goes around an object. The spaces between the spheres contains water. The silica in opal forms uniformly sized closely packed spheres that come together in a regular repeating arrangement. Over long periods of time as it dissolves the mineral-rich water dries into a gel. Under the right geological conditions, as certain rocks break down silica is released into groundwater trapped in cracks and voids. Opal is form of silica that contains a significant amount of water. Opal Properties Facts and Photos Contents
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