10.1 Types of Silicates

  Solid State

Silicates can be classified into different types depending upon the corners $(0, 1, 2, 3,\ or\ 4)$ of the $Si{O_4}^{4 - }$ tetrahedron shared with other tetrahedra. If some of silicon atoms in $Si{O_4}^{4 - }$ are replaced by aluminium, we get alumino-silicates.

$1.$ Orthosilicate: Simple silicates containing discrete tetrahedra e.g. $ZrSiO_4$.

$2.$ Pyrosilicate: Two tetrahedra sharing one corner.

$3.$ Cyclic or ring silicate: Two oxygen atoms per tetrahedron sharing to form closed rings with general formula $(SiO_3^{2–})_n$ or $(SiO_3)_n^{2n–}$ e.g. $Ca_3Si_3O_9$.

$4.$ Chain silicates: Two oxygen atoms per tetrahedron sharing to form long linear single strand chain of general formula $(SiO_3)_n^{2n–}$ e.g. $CaMg(SiO_3)_2$.

$5.$ Sheet Silicates: Sharing of three corners (i.e. three oxygen of each tetrahedron) resulting in an infinite two dimensional sheet structure of formula $(Si_2O_5)_n^{2n–}$ or $(Si_2O_5^{2–})_n$ e.g. clay contains these anions.

$6.$ Three dimensional silicates: If all the four corners are shared with other tetrahedra forming three dimensional network.