Polytypes Paragenesis - hydrothermal alteration of ultrabasic rocks . The vacant and filled octahedra distort the hexagonal pattern.
Vacant sites are larger and filled sites are smaller.
Note in the figure below that the top of octahedral sheet is composed of all hydroxyls. Bonding to basal oxygens of tetrahedral sheet is by hydrogen bonding. Click here for an idealized representation of tetrahedral sheet distortion. Orientation of central hydroxyl. There is also lots of disorder between layers.