Ortho silicates: The simplest silicates which contain discrete [SiO4]4- tetrahedral units are called ortho silicates or neso silicates.
Examples: Phenacite – Be2SiO4 (Be2+) ions are tetrahedrally surrounded by O2- ions). Olivine – (Fe/Mg)2 SiO4 (Fe2+ and Mg2+ cations are octahedrally surrounded by O2- ions).
Pyro silicates: Silicates which contain [Si2O7]6- ions are called pyro silicates (or) Soro silicates They are formed by joining two [SiO4]4- tetrahedral units by sharing one oxygen atom at one comer, (one oxygen is removed while, joining).
Example: Thortveitite – SC2Si2O 7.