Solid substances in which the crystal structure has distinct layers (i.e. has a layer lattice). The micas are an example of this type of compound. Intercalation compounds are lamellar compounds formed by interposition of atoms, ions, etc., between the layers of an existing element or compound. For example, graphite is a lamellar solid. With strong oxidizing agents (e.g. a mixture of concentrated sulphuric and nitric acids) it forms a nonstoichiometric ‘graphitic oxide’, which is an intercalation compound having oxygen atoms between the layers of carbon atoms. Substances of this type are called graphitic compounds.