Silicalite is an inorganic compound with the formula SiO 2. It is one of several forms (polymorphs) of silicon dioxide. It is a white solid. It consists of tetrahedral silicon centers and two-coordinate oxides. It is prepared by hydrothermal reaction using tetrapropylammonium hydroxide followed by calcining to remove residual ammonium salts. The compound is notable in being ca. 33% porous. It is useful because the material contains (SiO) 10 rings that allow sorption of hydrophobic molecules of diameter 0.6 nm.