Sheet Silicates (also known as phyllosilicates) are formed in a process similar to chain silicates. Three of the four oxygens are shared with other tetrahedra: only the upper oxygens remain charged and not connected to a Silicon atom.
Sheet silicates tend to follow their namesake and form sheets or layers of minerals. This gives very strong intramolecular bonds, but extremely weak intermolecular bonds. The bonds between molecules in a sheet silicate are a very good representation of Van Der Waals forces.

Example: Muscovite or any of the micas.

For more general information, see silicon tetrahedra.