The Silica Tetrahedron and the Architecture of Silicate Minerals

With oxygen and silicon comprising approximately 85% of the atoms in Earth’s crust, most minerals in the crust include these two elements, and form the class of minerals called silicates. The basic building block of all silicate minerals is the silica tetrahedron, in which one silicon ion bonds with four oxygen ions. This arrangement of ions (coordination number of 4) is dictated by the ratio of ionic radii. It allows the silicon ion to fit snuggly in the middle of the oxygen ions, but results in a charge imbalance. The resulting complex ion is SiO4 -4 .