Nanocrystals of MgO (4 nm) exist as polyhedral structures with high surface concentrations of edge/corner sites. In powder form the crystallites weakly agglomerate into porous weblike structures of approximately 1400 nm according to small-angle X-ray scattering. Upon consolidation of these fine powders under pressure, pellets can be readily prepared that maintain their high surface areas, and small crystallite sizes. In addition, large pore volumes and pore size openings can be controllably decreased with pelletization pressure increase. The pellets retain their voracious adsorbent affinities and capacities for a wide variety of organic molecules and acid gases. Quantitative measurements on the adsorption of a series of alcohols vs pelletization pressure reveal a pattern of molecular size selectivity.