The following substances that do not belong to silicate are () A. Clay B. Diatomite C. Al 2 (Si 2 O 5) (OH) 4 D. Mg 2.

A. Clay (the chemical composition of clay rocks depends on its mineral composition and the composition of adsorbed ions in clay minerals), and its main chemical compositions are SiO _ 2, Al _ 2O _ 3 and iron oxide. , belongs to silicate, so A is wrong;

B, diatomite is composed of amorphous SiO _ 2, and contains a small amount of Fe2O3, CaO, MgO, Al2O3 and organic impurities, which is not silicate, so B is correct;

C, Al _ 2 (Si _ 2O _ 5) (OH) _ 4 can be expressed as the salt of silicon dioxide or silicic acid, which belongs to silicate, so C is wrong;

D and Mg 2 SiO 4 can represent the salt formed by orthosilicic acid and magnesium hydroxide, and can be written in the form of magnesium oxide and silicon dioxide, which belong to silicate, so D is wrong.

So choose B.