Photo: piatek_minerals on eBay

In Insight Into Iridescence

Some of the most beautiful patterns appear momentarily or under certain conditions, creating a fleeting moment of wonder.

In the case of iridescent bands of colour, whether in a road rainbow or in geology, like the Botryoidal Goethite above, the colours appear to shift and change depending on our viewpoint.
But how do these remarkable patterns form?
Photo from Erin O'Malley's light experiments
Iridescence is also known as goniochromism. This word originates from  the  Greek words gonia, meaning "angle", and chroma, meaning "colour" – a clue to understanding how the phenomenon is created.

The basis of most examples of iridescent patterns occur through refraction and interference of light. When two or more thin, semi-transparent surfaces layer up together (such as oil and water, or geological minerals), light can be refracted in an unusual way, creating the appearance of different colours in places where the layers vary in thickness.
Alternatively, the top structural patterns of a surface – like a peacock feather or insect wing – might be textured so that only certain parts of the spectrum of light are reflected back to the visible eye.

These are all basic scientific principles concerning shape, light and pattern, but it's always worth reminding ourselves that even the most simple structures around us can create the most magnificent of spectacles.

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