Striations in filled Natural Rubber (NR) have been investigated in the literature. It is thought that strain induced crystallization has an involvement in their formation, due to the anisotropy induced by the crystallites close to the crack tip. Although recent studies explained that the shape and the size of striations depends essentially on the strain level, the literature does not give a clear answer as to what triggers the striations. This work is aimed towards a better understanding of the mechanism behind these striations. Fully relaxing crack growth tests have been performed on pure shear test pieces at different maximum strains to identify the conditions required for their occurrence. Roughness of the crack tip seems to correlate with this phenomenon. Different strain histories were investigated to determine their impact on the formation of striations. Fracture surfaces were analyzed by SEM to correlate the striations with the mechanical behaviour of NR.