They may exhibit pleochroism or double refraction.
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A quartz wedge also may be calibrated by determining the amount of double refraction in all parts of its length.
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He succeeded in explaining the colour of thin and of thick plates, and the inflexion of light, and he wrote on double refraction, light polarization and binocular vision.
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If all the sections are of the same thickness as is nearly true of well-made slides, the minerals with strongest double refraction yield the highest polarization colors.
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Birefringence, or double refraction, is the decomposition of a ray of light into two rays when it passes through certain anisotropic materials, such as crystals of calcite or boron nitride.
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Anisotropic crystals have double refraction of light where light of different polarizations is bent different amounts by the crystal, and therefore follows different paths through the crystal.