Phyllosilicate minerals have layer structures composed of shared octahedral and tetrahedral sheets.

• plane (of atoms) - A flat (planar) array of atoms of one atomic thickness. Example: plane of basal oxygen atoms within a tetrahedral sheet.
• sheet (of polyhedra) - Flat array of more than one atomic thickness and composed of one level of linked coordination polyhedra. A sheet is thicker than a plane and thinner than a layer. Example: tetrahedral sheet, octahedral sheet.
• layer - A combination of sheets in a 1:1 or 2:1 assemblage.
• interlayer - Materials between structural layers of minerals, including cations, hydrated cations, organic molecules, and hydroxide octahedral groups and sheets.
• unit structure - The total assembly of a layer plus interlayer material.