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(i) Discuss the ortho and pyro silicates. (ii) Compare lanthanides and actinides. |
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Answer» Solution :(i) Ortho 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), Olivine - `(Fe//Mg)_(2) SiO_(4) (Fe^(2+) and Mg^(2+)` cations are octahedrally surrounded by `O^(2-)` ions.) Pyro silicates : Silicates which contain `[Si_(2)O_(7)]^(6-)` ions are called pyro silicates (or) Soro silicates. They are formed by joining two `[SiO_(4)]^(4-)` tetrahedral units by sharing one oxygen ATOM at one CORNER. (one oxygen is removed while joining). Example: Thortveitite `-Se_(2) Si_(2)O_(7)`.  (ii) 
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