Infrared Spectra of Foreign Molecules in Beryl

Thirty infrared absorption lines in beryl between 1500 and 11 000 cm−1 are assigned to vibrations of two types of water and to CO2 all in the axial voids of the structure. The spectrum of Type-I water arises from molecules which are capable of libration and are located between the silicate rings which make up the crystal. The spectrum of Type-II water arises from molecules in the same sites, but with alkali ions nearby. These molecules are also capable of libration, but at a higher frequency. The Type-I molecules have their C2 symmetry axes perpendicular to the crystal C6 axis, while the Type-II molecules have their symmetry axes aligned parallel to the crystal C6 axis. The CO2 molecules are oriented with their long axes prependicular to the crystal C6 axis. Modification of the spectra by heat and hydrothermal treatments was not feasible and the identity of the alkali ions apparently does not influence Type-II spectrum.