Lexikon

the silicate minerals make up the largest and most important class of rock-forming minerals, comprising approximately 90 percent of the crust of the Earth. Silicate minerals all contain silicon (silicium in Latin) and oxygen. They are classified based on the structure of their silicate group. The most predominant silicate is quartz (SiO₂). The basic chemical unit of silicates is the (SiO₄) tetrahedron shaped anionic group with a negative four charge (^-4). The central silicon ion has a charge of positive four while each oxygen has a charge of negative two (^-2) and thus each silicon-oxygen bond is equal to one half (1/2) the total bond energy of oxygen. This condition leaves the oxygens with the option of bonding to another silicon ion and therefore linking one (SiO₄) tetrahedron to another and another, etc. Mineralogically, silicate minerals are divided according to structure of their silicate anion into the following groups: nesosilicates (single tetrahedrons), sorosilicates (double tetrahedrons), inosilicates (single and double chains), cyclosilicates (rings), phyllosilicates (sheets), tectosilicates (frameworks).The phyllosilicates (sheet silicates) include the clay minerals. They are one of the primary products of chemical weathering and one of the more abundant constituents of sedimentary rocks. The basic structure of the phyllosilicates is based on interconnected six member rings of SiO₄^-4 tetrahedra that extend outward in infinite sheets. Three out of the 4 oxygen atoms from each tetrahedon is shared with other tetrahedra. This leads to a basic structural unit of Si₂O₅^-2. In case the Si⁺⁴ atom in the middle of the tetradera is replaced by lower valency atoms such as Fe⁺³ or Al⁺³, then more negative bonds become available on the surface of the sheet structured clay minerals (http://en.wikipedia.org). These bonds have primary role in plant nutrient fixation, exchange and supply. Meanwhile these bonds contribute to the sorption of inorganic contaminants, fixing of ions to the surface of the clay mineral, while in case of treatment of contaminated soil to their removal (soil washing, extraction) or even to their stabilisation (soil stabilisation, immobilisation, chemical immobilisation/stabilisation in soil, vitrification). See also fate of inorganic pollutants in soil.