The properties of the incommensurate (inc) phase of quartz are briefly recalled and the new studies performed during the last year are presented. When a symmetry breaking uniaxial compressive stress is applied along Y axis, another inc phase appears, with a single modulation wave along Y axis. New inelastic neutron scattering experiments indicate that the origin of the inc phases of quartz come probably from a gradient interaction between the optical soft mode and acoustic modes. Finally simultaneous measurements of birefringence and of γ-ray diffraction have shown the existence of irreversible effects (thermal hysteresis, pinning, memory effects, oscillatory behavior).