Structural organization in silicate minerals

Silicate minerals are classified by the degree to which silicon-oxygen bonded networks (polymers) form (Fig. 4.4). The degree of polymerization is measured by the number of non-bridging oxygens (i.e. those bonded to just one Si4+).

Monomer silicates

These are built of isolated SiO4 tetrahedra, bonded to metal cations as in olivine (Fig. 4.4b) and garnet. The basic unit of the polymer, the SiO4 tetrahedra, is uncombined or single (mono), giving rise to the term monomer. These minerals have four non-bridging oxygens and are also known as orthosilicates.

Chain silicates

If each SiO4 tetrahedron shares two of its oxygens, chains of linked tetrahedra form (Fig. 4.4c). Chain silicates have two non-bridging oxygens and an overall Si:O ratio of 1:3, giving the general formula SiO3. The pyroxene group of minerals provides the most important chain silicates—for example, enstatite

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