Emerald crystal. Animation of the crystalline structure of an emerald gemstone. Atoms are represented as spheres. This is the green form of beryl (Be3Al2(SiO3)6), a beryllium aluminium cyclosilicate. It has a hexagonal crystal system (formally dihexagonal dipyramidal) and a green colour due to trace amounts of chromium. The animation passes through the layers of the crystal, showing the hexagonal arrangement and distribution of the atoms.