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 Si44). 

These are built of isolated Si04 tetrahedra, bonded to metal cations as in olivine (Fig. 4.4b) and garnet. The basic unit of the polymer, the Si04 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. 

Hence the chlorine atom carries a slight negative charge and the hydrogen atom a slight positive charge. Extreme polarization means that the bond becomes ionic in character. A bond is considered ionic if it has more than 50% ionic character. 

Elements that donate electrons (e.g. magnesium, calcium, sodium and potassium) rather than attract them are called electropositive. 

Ion Electro- negativity % Ionic character Ion Electro- negativity % Ionic character Ion Electro- negativity % Ionic character 

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