What are silicates? Discuss briefly their structures.

Silicate is the general name given to a group of minerals which have silicon - oxygen bonds. Rocks, soils and clays consist of almost entirely silicate minerals such as quartz, mica, asbestos, feldspars and zeolites.
(i) Quartz is a crystalline form of silica (SiO₂).
(ii) Mica is a potassium aluminium silicate KAl₃Si₃O₁₀(OH)₂.
(iii) Feldspar is a potassium silicate KAlSi₃O₈.
(iv) Asbestos is a calcium magnesium silicate CaMgSi₂O₆.
Structure: All silicates involve silicon-oxygen single bonds. These may either Si - O bonds or Si - O - bonds. The basic structural unit of all silicates is the  In this ion, silicon is sp³ hybridised. Each sp³ hybridised orbital of silicon combines with an orbital of the oxygen atom to form silicate ion which is tetrahedral in structure. 

Such tetrahedral units  are linked together in different ways to give chains, rings, sheets and three-dimensional networks.