Beryl, Be₃Al₂(SiO₃)₆, exhibits a hexagonal crystal system in which stacked six-membered rings of Si tetrahedra form channels. Be tetrahedra and Al octahedra form the framework around these channels, while cations such as Fe²⁺, Mg²⁺ and Mn²⁺ (replacing Al³⁺), or Li⁺ (replacing Be²⁺) occupy the channels. Na and Cs, and to a lesser extent K and Rb, are the most common alkalis to occupy the channels. Although beryl is traditionally classified as a ring silicate, it may be argued that the three-dimensional connectivity of the tetrahedral distinguishes this mineral from true ring silicates, of which tourmaline is the only common mineral in its class.
Beryl is an important gemstone, colored by small impurities to green (emerald), blue (aquamarine) and pink (morganite).

Beryl crystallizes late, and at lower temperatures and pressures, and therefore occupies cavities and open spaces along fractures. It is commonly found in granite pegmatities and biotite schists and has a prismatic/columnar structure. Beryl, when colored by chromium, forms the precious gemstone emerald. Beryl can be found in Columbia, Pakistan, Zimbabwe, the Ural Mountains, Brazil and Austria.

Artioli, G., R. Rinaldi, K. Stahl, and P.F. Zanazzi. 1993. Structure refinements of beryl by single-crystal neutron and X-ray diffraction. American Mineralogist. 78:762-768