Recently, we discovered that addition of salt plus specific types of nanoparticles, such as silica nanoparticles, to aqueous suspensions of kaolinite clay particles can induce a rapid sol-to-gel transition. A typical system exhibiting such a transition would consist of 14% vol. of kaolinite, 400 mM NaCl, and 5% vol. of 7 nm silica particles. SEM micrographs of the gels, obtained by rapid freezing and sublimation, reveal a very porous microstructure in which the disk-like clay particles are attached in an edge-to-face configuration. Rheological measurements show that the gels possess a very pronounced yield stress and that once broken, the gels will reform upon resting with reproducible properties. We propose that these gels are formed by adsorption of the nanoparticles over the entire surface of the clay particles. Addition of sufficient electrolyte screens the electrostatic repulsion between the negatively-charged nanoparticles, allowing the surfaces to contact and bond through van der Waals forces. Random motion of the clays would favor the edge-to-face alignment that is observed microscopically.