Silicate, chemical formula Lattice

FIGURE 7.7 The crystal structure of garnet. The general formula is AsBsC004)3 where C is Si for the silicates. The B cation sits in an octahedral site while the largest cation A is located in a dodecahedron. The bcc unit cell has a lattice parameter of -1.1 nm. With 20 atoms in the chemical formula there ate 160 atoms in the unit cell. 

Crystalline layered sodium disUicates are the most recent development in the field of detergent silicates. In contrast to hydrous sodium polysilicates and metasilicates, they display a three-dimensional crystal lattice characterized by corrugated silicate layers, which are separated by sodium ions. The chemical formula is NajSijO,. This reflects that the material is anhydrous and has a formal molar ratio of 2. Several crystal phases differ in the kind of corrugation of the silicate layers [3,21,66,86-88]. 

Within the context of a general proposal for all the silicates, Berman (1937) suggested a general formula for the mica group which is still valid today. It was Berman who introduced the crystal-chemical symbols W, X, Y, Z for the different lattice sites, thus changing symbols previously suggested by Bragg (1930). 

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