Phenomena occurring at the surfaces of calcium silicates in alkaline solutions have been studied. This knowledge is very important in understanding the behavior of suspensions of glazes, felspars or clay minerals. This behavior has been found to depend partially on whether the surface of the materials in question has a high degree of order or not - in other words, whether the solid is crystalline or vitreous. It is also found that surfaces of crystalline materials which have been disturbed or destroyed, by grinding for instance, show a behavior between the extremes of the completely crystalline or completely vitreous systems. An analysis is given for the manner in which the net change of the surface layers of åkermanite (Ca2MgSi2O7), pseudowollastonite (CaSiO3) and anorthite (CaAl2Si2O8) are built up in alkaline CaCl2 solutions and which processes occur during their formation. Special attention is given to the mutual stimulation of adsorption of Ca2+ and OH- ions by pseudowollastonite.