STRUCTURE

Beryl crystallizes in the hexagonal system (a=b=c=120° ; d=90° ; a:a.a:c), dihexagonal dipyramidal prism (A6, 3A'2, 3A"2, P, 3P', 3P", C). The most common habits are: prismatic, with basal pinacoid, hexagonal, and dihexagonal prism, hexagonal dipyramid and dihexagonal dipyramid. Space group P6/mcc. Hexagonal crystals' most common habit is prismatic, acicular, and rarely tabular. Beryl's structure has long been known. It consists of six hexagonal rings These rings are linked together both laterally and vertically by three tetrahedra BeO4= and two octahedra AlO6-, forming a three dimensional framework. The structure contains open channels parallel to the A6 axis, where minor beryl chemical elements can be stored. The unit cell contains two unities (Z=2) and has general reticular parameters of the order of a= 9.215 Å, c=9.218 Å, and c/a = 1.0003. It has three crystallografic sites: one tetrahedric T' occupied by Si atoms, one tetrahedric T" by beryllium and one octahedric Oh by Al.