The reaction of single-crystal NaCl(100) with dry HNO3 was monitored using atomic force microscopy in contact mode. Initial exposure to dry HNO3 results in the growth of a two-dimensional metastable layer of NaNO3 to nearly complete surface coverage. Exposure of this metastable NaNO3 layer to small amounts of H2O produces deliquescence of the surface with concomitant rearrangement of the NaNO3 adlayer to form unusual mobile "strings" presumed to contain NaNO3. These strings are transient and eventually crystallize to form rhombohedral NaNO3 crystals sitting on top of the NaCl surface.