Silicates as the base of the Earth crust Silica and compounds derived from it, silicates, constituteca. 90% of the Earth crust substances. Silica gives rise to a beautiful meterial-glass. Nobody knows exactly how glass was discovered. There is a well-favoured story related to phoenician sailors who fused occassionally sea sand and soda ash. It is likely that they discovered the secret of "liquid glass" (LGL) sodium metasilicate (Na_(2)SiO_(3)) soluble in water. Using the same strategy as in 3.3 to 3.5 depict a fragment of the layered structure joining 16 tetrahedra (i). Note that 10 tetrahedra have shared vertices with 2 neighbours each, and the rest 6 have shared vertices with 3 neighbours each. Being placed into the LGL solution, salts of transition metals give rise to fancy "trees" tinted relevant to the colour of the salt of the the corrsponding transition metal. Crystals of CuSO_(4).5H_(2)O produce "trees" of blue colour whereas those of NiSO_(4).7H_(2)O form green "trees".