The ``hexagonal ferrites'' comprise a quasipolytypic series of ferrimagnetic oxides containing Ba, Fe3+, and a divalent metal cation (Me2+). These encompass a family of hexagonal and rhombohedral mixed‐layer structures derived by thec‐axis stacking of two complex invariant building blocks, mainly ``M'' and ``Y''. TheMstacking element is a 5‐anion‐layer block, 11.6 Å in height with the composition BaFe12O19, and theYstacking element is a 6‐anion‐layer block, 14.5 Å high with the composition Ba2Me22+Fe12O22. The largest series,M2Yn(n=0 to 21), involves the stacking of twoMblocks and a variable number ofYblocks. Permutation of theMandYelements allows mixed‐layer polytypism within a given stoichiometry, i.e.,MtoYratio. More than twenty (20) mixed‐layer structures and their polytypes have been examined by electron microscopy after direct replication of the basal face.Basal faces which were etched with dilute hydrochloric acid exhibit etch steps of sub‐unit‐cell heights. The specificMandYstacking sequence of a mixed‐layer structure may be obtained by measuring the step‐height ratio,MYx/MYn−x, of two adjacent steps, provided either the shadow angle or the x‐rayc‐axis dimension is known. In addition it has been found that thec‐axis dimension and the specific stacking sequence may be uniquely determined by counting the individualMandYbuilding blocks which are replicated as separate and distinct etch‐planes on a crystal surface that has been process‐etched.