: (i) Those sharing vertices (ii) those sharing only vertices. Figure . Structure of Chain silicates Figure . Structure of Pyro silicate Figure .
Structure of Cyclic silicates - - - - Examples: ) Asbestos: These are fibrous and non- combustible silicates. Therefore they are used for thermal insulation material, brake linings, construction material and filters. Asbestos being carcinogenic silicates, their applications are restricted. Sheet or phyllo silicates Silicates which contain (Si O ) n 2n- are called sheet or phyllo silicates.
In these, Each [SiO ] - tetrahedron unit shares three oxygen atoms with others and thus by forming two- dimensional sheets. These sheets silicates form layered structures in which silicate sheets are stacked over each other. The attractive forces between these layers are very weak, hence they can be cleaved easily just like graphite. Example: Talc, Mica etc...
Three dimensional silicates (or tecto silicates): Silicates in which all the oxygen atoms of [SiO ] - tetrahedra are shared with other tetrahedra to form three-dimensional network are called three dimensional or tecto silicates. They have general formula (SiO ) n . Examples: Quartz These tecto silicates can be converted into three dimensional aluminosilicates by replacing [SiO ] - units by [AlO ] - units. E.g.
Feldspar, Zeolites etc., . . Zeolites: Zeolites are three-dimensional crystalline solids containing aluminium, silicon, and oxygen in their regular three dimensional framework. They are hydrated sodium alumino silicates with general formula Na O.(Al O ).x(SiO ).yH O (x= to ; y= to ).
Figure . Structure of Sheet or phyllo silicates Figure . Structure of Double chain silicates - - - - Zeolites have porous structure in which the monovalent sodium ions and water molecules are loosely held. The Si and Al atoms are tetrahedrally coordinated with each other through shared oxygen atoms.
Zeolites are similar to clay minerals but they differ in their crystalline structure. Zeolites have a three dimensional crystalline structure looks like a honeycomb consisting of a network