earth crust is composed of silicate minerals and silica. The glass and ceramic industries are based on the chemistry silicates. Types of Silicates: Silicates are classified into various types based on the way in which the tetrahedral units, [SiO ] - are linked together. Ortho silicates (Neso silicates): The simplest silicates which contain discrete [SiO ] - tetrahedral units are called ortho silicates or neso silicates.
Figure . Structure of Ortho silicates - - - - Examples : Phenacite - Be SiO (Be + ions are tetrahedrally surrounded by O - ions), Olivine - (Fe/Mg) SiO ( Fe + and Mg + cations are octahedrally surrounded by O - ions), Pyro silicate (or) Soro silicates): Silicates which contain [Si O ] - ions are called pyro silicates (or) Soro silicates. They are formed by joining two [SiO ] - tetrahedral units by sharing one oxygen atom at one corner.(one oxygen is removed while joining). Example : Thortveitite - Sc Si O Cyclic silicates (or Ring silicates) Silicates which contain (SiO ) n 2n- ions which are formed by linking three or more tetrahedral SiO - units cyclically are called cyclic silicates.
Each silicate unit shares two of its oxygen atoms with other units. Example: Beryl [Be Al (SiO ) ] (an aluminosilicate with each aluminium is surrounded by oxygen atoms octahedrally) Inosilicates : Silicates which contain 'n' number of silicate units linked by sharing two or more oxygen atoms are called inosilicates. They are further classified as chain silicates and double chain silicates. Chain silicates (or pyroxenes): These silicates contain [(SiO ) n ] 2n- ions formed by linking ‘n’ number of tetrahedral [SiO ] - units linearly.
Each silicate unit shares two of its oxygen atoms with other units. Example: Spodumene - LiAl(SiO ) . Double chain silicates (or amphiboles): These silicates contains [Si O ] n 6n- ions. In these silicates there are two different types of tetrahedra