# 3.6 Framework silicates

Framework silicates are the most abundant silicates in the Earth's crust. They have complex crystal structures, with each SiO4 tetrahedron joined to four others, producing a three-dimensional framework. In feldspars, some of the silicon atoms are replaced by aluminium, and singly charged cations (e.g. Na+ or K+) are required to maintain charge balance.

OpenLearn - An introduction to minerals and rocks under the microscope
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