Sodium silicate is a white solid that is readily soluble in water, producing an alkaline solution. It is one of a number of related compounds which include sodium orthosilicate, Na4SiO4; sodiumpyrosilicate, Na6Si2O7, and others. All are glassy, colourless and dissolve in water.

Sodium silicate is stable in neutral and alkaline solutions. In acidic solutions, the silicate ion reacts with hydrogen ions to form silicic acid, which when heated and roasted forms silica gel, a hard, glassy substance.