A variety of different structures experience rocking motion when subjected to dynamic actions, making rocking dynamics a fundamental problem of earthquake engineering. Rocking motion presents peculiar dynamic characteristics, such as negative stiffness during pivoting and non-smooth phenomena during impacts. Hence, modelling of the rocking problem faces significant challenges. One of the most significant is related to the energy losses that occur during impacts, commonly represented by the coefficient of restitution. Despite the numerous theoretical attempts to accurately estimate the coefficient of restitution, it is apparent that experimental observations are essential in providing a direct insight into the complex and non-smooth phenomena of rocking motion. To this end, the present work conducts an extended experimental campaign on the free-rocking motion of limestone blocks. More specifically, a total of 36 blocks are tested, corresponding to 12 different geometrical aspect ratios. The free-rocking motion is thoroughly analysed, while attention is also given to three-dimensional effects. Finally, the coefficient of restitution is experimentally quantified and compared with both previous theoretical and experimental results gathered from the literature.