Silicate tetrahedron. A silicon–oxygen tetrahedron is the Si O 4 anionic group, or a silicon atom with four surrounding oxygen atoms arranged to define the corners of a tetrahedron. This is a fundamental component of most silicates in the Earth's crust.n this group the tetrahedra don't share any oxygen atoms and are independent. Attraction between the tetrahedra and positive ions holds minerals of this structure together. The positive ions could be metal cations such as iron or magnesium. a common mineral in this group is Olivine.