Complex sentence: A silicon-oxygen tetrahedron is the SiO 4 anionic group, 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.
Split into simpler sentences: A silicon--oxygen tetrahedron is the SiO 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.