An experimental investigation of the deformation mechanisms acting in halite at the scale of its polycrystalline microstructure is presented. Uniaxial compression tests on centimetric samples are performed inside the chamber of a scanning electron microscope and the obtained high definition images are processed by digital image correlation (DIC) routines. A special marking procedure provides an appropriate contrast at microscale. Standard DIC routines qualitatively demonstrate the coexistence of two deformation mechanisms: crystal slip plasticity and grain boundary sliding. A specific post-processing of the DIC-evaluated displacement fields provides a first quantification of the relative contribution of these mechanisms to overall strain and a dependence with grain size can be demonstrated. A modified DIC formulation able to separate intra-grain deformation from interfacial gliding is also proposed for a better quantification and preliminary results are presented. Such data will be of primary interest for the construction of physically-based multiscale models of the mechanical properties of halite, which might be used for security assessment of deep caverns in salt-rock.