Tunneling states in mineral crystals

We report on an acoustic study at low temperature of two natural mineral cr ystals (olivine and cordierite). These samples are single crystals of very good quality and have in their unit cells 28 atoms and 116 atoms, respectiv ely. We have observed the specific acoustic properties expected from tunnel ing states (TSs): logarithmic velocity variation and phonon echoes. These r esults suggest that TSs are intrinsic in crystals with a large number of at oms in the unit cell.