Abstract
The building blocks of any silicate crystal are the silicium based tetrahedron SiO4; they form chains, rings, frameworks, etc., with tetrahedron, octahedron, dodecahedron, etc., sites in the crystal network. Such polyhedral sites are usually occupied by cations of different nature. Of course, changing such cations in a given polyhedral site, the properties of the crystal are changed.In …