The gravimetric ratio in the earth crust is even more significant, silicates constitute in it approximately 75 % of the volume. The significance of the element silica in geochemistry of the earth crust is rising by including additional 12 % of free SiO2 (silica, opal).
The silicates are ranked among the silica compounds. These substances are almost insoluble in water, except for the silicates of alkaline metals Na2SiO3 (sodium water glass) and K2SiO3 (potassium water glass). All silicates are dissolvable in concentrated solutions of alkaline hydroxides or at high temperatures in its meltings. The silicates as minerals are of non-metallic appearance and are usually a part of rocks. They are the most extensive salts in the earth crust. Many silicates are the most important rock-forming minerals. The silicates are significantly represented almost in all deposits of utility minerals, not only as a supporting minerals of ore deposits (waste rock), but are also frequently represented as the carriers of precious metals (Ni, Zn, Be, Zr, Li, Cs, Rb, U, precious soils etc.). Some silicates are precious utility non-metallic minerals – asbestos, kaolin, clay and felspar, as raw material for fire-resistant products and ceramics, various construction substances and others. Many silicates have been used since long ago as precious and decorative gems – emerald, aquamarine, tourmaline, topaz, rodonite, jade, garnets and others. Main elements taking part on forming the siliciates are: Na, K, Li, Ca, Mg, Fe2+, Fe3+, Mn2+, Be, Al, B, Si, Zr, Ti, O, F, H (as H+, [OH]- and H2O).