This subclass is also known as the framework silicates because its structure is characterized by a very strong and stable three-dimensional framework. Nearly 75% of the Earth's crust is made up of minerals of the tectosilicate class. This is because the aluminum ion can easily substitute for the silicon ion creating a -5 charge in the crystal. Since the charge must be balanced, additional cations are needed, creating the numerous minerals.
Mineral Photos courtesy of R.Weller/Cochise College