Saved Bookmarks
| 1. |
How are silicates classified ? Give an example for each type of silicate. |
|
Answer» Solution :Silicates are classified into various types based on the way in which the tetrahedral units, `[SiO_(4)]^(4-)` are linked together. (i) Ortho silicates (Neso silicates): The simplest silicates which contain discrete `[SiO_(4)]^(4-)` tetrahedral units are called ortho silicates or neso silicates. Examples : Phenacite - `Be_(2)SiO_(4)` (`Be^(2+)` ions are tetrahedrally surrounded by `O^(2-)` ions) (ii) Pyro silicate (or) SORO silicates): Silicates which contain `[Si_(2)O_(7)]^(6-)` ions are called pyro silicates (or) Soro silicates. Example : Thortveitite - `Sc_(2)Si_(2)O_(7)` (iii) Cyclic silicates (or Ring silicates) : Silicates which contain `(SiO_(3))_(n)^(2n-)` ions which are formed by linking three or more tetrahedral `SiO_(4)^(4-)` units cyclically are called cyclic silicates. Example : Beryl `[Be_(3)Al_(2)(SiO_(3))_(6)]` (an aluminosilicate with each aluminium is surrounded by 6 oxygen atoms octahedrally) (iv) Inosilicates : Silicates which contain .n. number of silicate units liked by sharing two or more oxygen atoms are called inosilicates. Example : They are further classified as chain silicates and double chain silicates. (v) Chain silicates (or pyroxenes) : These silicates contain `[(SiO_(3))_(n)]^(2n-)` ions formed by linking .n. number of tetrahedral `[SiO_(4)]^(4-)` units linearly. Each silicate unit shares two of its oxygen atoms with other units. Example : Spodumene - `LiAl(SiO_(3))_(2)`. (vi) Double chain silicates (or amphiboles): These silicates contains `[Si_(4)O_(11)]_(n)^(6n-)` ions. In these silicates there are two different types of tetrahedra : (a) Those sharing 3 vertices (b) those sharing only 2 vertices. Examples : Asbestos : These are fibrous and non-combustible silicates. (vii) Sheet or phyllo silicates : Silicates which contain `(Si_(2)O_(5))_(n)^(2n-)` are called sheet or phyllo silicates. In these, Each `[SiO_(4)]^(4-)` tetrahedron unit shares three oxygen atoms with others and thus by forming two dimensional sheets. Example : Tale, MICA ETC. (viii) Three dimensional silicates (or tecto silicates) : Silicates in which all the oxygen atoms of `[SiO_(4)]^(4-)` tetrahedra are shared with other tetrahedra to form three-dimensional network are called three dimensional or tecto silicates. Examples : Quartz. |
|