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from BBC News

Wildlife Photographer of the Year - People's Choice

Rainbow wings by Victor Tyakht, Russia

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An enlarged view of the iris agate specimen with backlighting. This view is at a slightly different angle than the other backlighted view also pinned. It demonstrates that the spectral colors change with the angle of incident light and observation.

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Two views of a specimen of iris agate. The photo on the left was taken in normal light and displays the color of light reflected from the agate. The photo on the right shows the agate with backlighting. The backlighting reveals the diffraction grating or "iris" effect produced when light passes through the very fine banding of the agate. This specimen is a thin slice of Brazilian agate that measures about 25 mm high, 14 mm wide and 3 mm in thickness.

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opal - The cause of the brilliant play of colors in opal was an enigma until relatively recently. Scanning electron microscope studies show that opals consist of transparent spheres of silica that are tightly packed. The voids or spaces between the spheres contain air or water. The regular arrangement of spheres acts as a diffraction grating, breaking visible white light into separate colors.

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Opal. The cause of the brilliant play of colors in opal was an enigma until relatively recently. Scanning electron microscope studies show that opals consist of transparent spheres of silica that are tightly packed. The voids or spaces between the spheres contain air or water. The regular arrangement of spheres acts as a diffraction grating, breaking visible white light into separate colors.

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A Scapolite gem from Dodoma, Tanzania with a series of parallel Magnetite inclusions. The tightly-spaced inclusions act as a diffraction grating, causing the shimmering iridescent effect which gives these gems their commercial name, Rainbow Scapolite. This cushion shaped specimen weighs 7.54 carats.

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A 43.19 carat faceted Scapolite from Dodoma, Tanzania with a series of parallel rows of dotted inclusions running through the stone at angles which follow the crystals growth. The tightly spaced inclusions, assumed to be Pyrrhotite, serve as a diffraction grating, causing a vivid iridescent display. This unique effect gives rise to the term "Rainbow Scapolite" being used by some gem enthusiasts to describe these rare and unusual gemstones.

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