A microscopic extension of the phenomenological model of double-well orientational states, viz., pentagonal and hexagonal configurations of molecules, which is widely used for describing the low-temperature phase of fulleriteC60,is proposed. A simple kinetic equation and a set of thermodynamic relations connecting the crystal lattice deformation, the concentration of orientational excitations of molecules, and temperature are derived. Basic physical properties of the low-temperature phase, including orientational glass transition, heat capacity, thermal expansion, rheological properties and damping of elastic vibrations are described on a unified basis. The conclusions of the theory are compared with the experimental data, and empirical estimates are obtained for the parameters of double-well states and the lattice–orientational interaction. It is shown that the large values of thermal expansion and acoustic damping above the orientation glass-transition temperature of fullerite are due to high-intensity lattice–orientational interaction. ©1998 American Institute of Physics.