Infrared spectroscopic evidence for marked interaction between nickel oxide and silica at temperatures as low as 550°C is described. An infrared absorption at approximately 1045 cm^–1 can be attributed to silicon atoms in the nickel oxide lattice. This is observed in both annealed nickel oxide + silica mixtures and nickel oxide heated in silica tubes. Electron microscopy shows that the nickel oxide particles (with incorporated silicon) are single phase. The silicon content produces a surface morphology which becomes predominantly {111}. Dissolution rates per unit surface area in dilute acid are decreased more than one hundred times by the interaction, even with < 10^–3 mol % silicon in nickel oxide. The slower dissolution is found throughout dissolution. The silicon atoms apparently enter the tetrahedral interstices in the oxygen lattice, effectively producing SiO₄ groups. The work shows that adsorption and catalytic studies of nickel oxide surfaces are markedly affected by the presence of silica even for samples pretreated at relatively low temperature.