In silicates, the basic structural unit is the $[\text{SiO}_4]^{4-}$ tetrahedron. Depending on the number of oxygen atoms shared between adjacent tetrahedra, silicates are classified as follows:

• Orthosilicates: No oxygen atom is shared.
• Pyrosilicates: One oxygen atom is shared between two tetrahedra.
• Chain or Cyclic silicates: Two oxygen atoms are shared.
• Sheet (Phyllosilicates): Three oxygen atoms are shared.
• Three-dimensional (Framework) silicates: All four oxygen atoms are shared. Therefore, the silicate structure in which one oxygen atom is shared is a pyrosilicate.