efflorescence is the formation of a gritty deposit, commonly white, on the surface. efflorescence is usually the result of mineral solutions in the capillary channels being drawn to the surface. if the water evaporates, the minerals remain as the so-called efflorescence. it also can be the result of chemical reaction; if badly prepared cement-based mortar is applied to maintain the stone in position, free calcium hydroxide may leach out. in the open air the lime reacts with carbon dioxide to form water-insoluble calcium carbonate that might take the form of powdery efflorescence or dripstone-like crusting.