The solid−liquid interface formed by single terminated muscovite mica in contact with two different ionic solutions is analyzed using surface X-ray diffraction. Specular and nonspecular crystal truncation rods of freshly cleaved mica immersed in CsCl or RbBr aqueous solution were measured. The half monolayer of the surface potassium ions present after the cleavage is completely replaced by the positive ions (Cs$^{+}$ or Rb$^{+}$) from the solution. These ions are located in the ditrigonal surface cavities with small outward relaxations with respect to the bulk potassium position. Wefind evidence for the presence of a partly ordered hydration shell around the surface Cs$^+$ or Rbs$^+$ ions and partly ordered negative ions in the solution. The lateral liquidordering induced by the crystalline surface vanishes at distances larger than 5 Å from the surface.