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Healthy tropical coral reefs grow horizontally from 1 to 3 cm (0.39 to 1.18 in) per year, and grow vertically anywhere from 1 to 25 cm (0.39 to 9.84 in) per year; however, they grow only at depths shallower than 150 m (490 ft) because of their need for sunlight, and cannot grow above sea level.
At microscopic scales, precious opal is composed of silica spheres some 150–300 nm (5.9 × 10 −6 –1.18 × 10 −5 in) in diameter in a hexagonal or cubic close-packed lattice. It was shown by J. V. Sanders in the mid-1960s [ 8 ] [ 9 ] that these ordered silica spheres produce the internal colors by causing the interference and diffraction ...