Answer
When a tetrahedron occurs singly (not bonded to other tetrahedrons), it forms the $SiO_{4}^{4-}$ polyatomic anion (which has four extra electrons that satisfy the octet rule for the four oxygen atoms). These types of silicates are orthosilicates
Work Step by Step
In many silicate compounds, the oxygen atoms are not connected to two silicon atoms to form the neutral compound that is found in quartz. Instead, the oxygen atoms gain electrons from metal atoms and form polyatomic anions, such as $SiO_{4}^{4-}$ tetrahedrons.
When a tetrahedron occurs singly (not bonded to other tetrahedrons), it forms the $SiO_{4}^{4-}$ polyatomic anion (which has four extra electrons that satisfy the octet rule for the four oxygen atoms). These types of silicates are orthosilicates
