The concept of representative elementary volume (REV) is critical to understand and predict the behavior of effective properties of complex heterogeneous materials in a multiscale manner. Porosity is usually used to define the REV of a given material, if porosity is stationary over consecutive volumetric increments, the sample is considered as REV regardless of the behavior of other microstructure properties. To investigate this common assumption, the change of key microstructure parameters such as local void ratio, sphericity, angularity, and coordination number of particles was computed over different volumes of REV for porosity. X-ray computed tomography was used to obtain three-dimensional volumes of natural sand packed at four different particle fragments. Efficient and robust algorithms were used to compute the microstructure properties from three-dimensional images. Findings revealed that the REVmin for porosity may not be adequate to be considered as a REV for parameters such as particle size distribution, local void ratio and coordination number. The REVmin for these parameters was observed to be larger than the REVmin for porosity.