Water molecules in the channel-like cavities of osumilite

Abstract

The crystal structure of osumilite is characterized by channel-like cavities that are composed of double six-membered rings along the c-axis, which is similar to the channels of beryl and cordierite. Beryl and cordierite generally include water molecules in the channel, and these have been extensively investigated using mainly infrared (IR) spectroscopy. Two major types of water molecules have been determined, however, the water molecules in the channel-like cavities of osumilite have not been reported. Polarized IR absorption spectra of water molecules in osumilite are presented here. The polarized IR absorption spectra of oriented osumilite that was hydrothermally treated at 600 °C and under 100 MPa for 72 h revealed three pairs of split peaks with equivalent intensity. They can be assigned to ν₃-I and ν₁-I (3651 cm^-1 and 3554 cm^-1), ν₃-II_a and ν₁-II_a (3635 cm^-1 and 3601 cm^-1), and ν₃-II_b and ν₁-II_b (3603 cm^-1 and 3551 cm^-1) as well as water molecules in the channels of cordierite and beryl.