When some of Si+4 in frame work silicates are replaced by Al+3 and an additional metal ion, it results in the formation of

Three dimensional silicates having primary unit SiO2 are of two types(1) In First type of silicates, only SiO2 units are present(2)  Second type of silicates:  in three dimensional network of SiO2 , some of the Si+4 ions are substituted by uni , di , Trivalent metal ions as a result overall structure acquires a negative  charge and is balanced by cations such as Na+ , K+ or Ca+2These are of three types      (1) Feldspar ,  KAlSi3O8                                         (2) Zeolites , Na2O Al2O3 nSiO2 mH2O                                         (3) Ultramarines Na8[Al6Si6O24]S