Science quiz: The natural artists called minerals

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This photo shows various minerals displaying ____________. Fill in the blank with the name of a phenomenon where they absorb UV light and reemit it as visible light. Credit: Hannes Grobe/AWI

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Name the optical effect where the colours on a surface appear to shift as you change the angle at which you look at them. Examples of such surfaces include oil films on water and peacock feathers. The colours are the result of structural features rather than the presence of certain pigments.

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A gemstone called moonstone is famous for its soft milky glow that seems to float just beneath its surface when light moves across it. What do gemologists call this gentle, billowing light in certain feldspar gemstones? Its name comes from a mineral first found in the Adula Alps in Switzerland.

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A feldspar mineral from Labrador in Canada is known to show brilliant flashes of blue, green, and gold colours that appear and vanish depending on how you tilt the stone. The flashes are caused by light reflected between thin internal layers. What’s this phenomenon called?

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Some gemstones show a famous “play of colours” created by small flashes and patches of light, often over a milky background because light scatters and diffracts from closely packed silica spheres inside. What is this optical effect, seen especially in opal, called?

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Car paints, some plastics, and natural nacre — all display a smooth, silky sheen that seems to change subtly as they move. This is due to an effect called X: it’s the same principle as in the answer to Q1, except most of the reflected light is white. Name X.