Differential interference contrast (DIC) light micrograph of cocaine crystals. Under a light microscope cocaine crystals appear as small, shiny, translucent or white particles with a characteristic elongated or rectangular shape. The crystals can vary in colour depending on the purity of the cocaine, with higher purity cocaine generally appearing whiter. One of the most distinctive features of cocaine crystals under the microscope is their birefringence, or double refraction, which is the splitting of light into two beams with different polarizations. This property is due to the anisotropic nature of the cocaine crystal lattice, which causes light to travel at different speeds in different directions.