In this paper, we study the rheological behavior of mixtures of various sand particles suspended in model laboratory yield stress fluids. Using image analysis, we assess the morphology of the studied sand particles. We then measure the packing properties of these particles and show that, as a first approximation, the overall shape of the particles (i.e. the aspect ratio) is the dominant morphological parameter conditioning packing. We finally use magnetic resonance imaging (MRI) to assess the rheological behavior of suspensions of these sands in a water-in-oil emulsion and show that both the yield stress and consistency diverge for the same critical volume fraction, which seems to be fully correlated to both the random dense packing fraction and loose packing fraction of the grains. We finally suggest that there exists a correlation between a variation in yield stress and a variation in viscosity due to a change in the particle morphology.