Like the revolving mirrored ball that reflects a spotlight on a dance floor, a crystal of beryl fragments a beam of x-rays. The narrow beam was projected through the beryl, and the black spots reflect the regular lattice of atoms within the crystal. This technique of x-ray diffraction is used to work out the atomic structure of different elements. A similar technique was used to decode the double-helix spiral of DNA molecules. In geology, beryl is a mineral composed of beryllium aluminium cyclosilicate. The hexagonal crystals of beryl may be very small or range to several meters in size. Terminated crystals are relatively rare. Pure beryl is colorless, but it is frequently tinted by impurities; possible colors are green, blue, yellow, red, and white.