Plane defects including polytypism are easily treated by an X-ray diffraction analysis, or more recently, by HRTEM, which is a highly effective technique for the detection of line defects.
Polytypism of phyllosilicates is a phenomenon where fundamental 1:1 (kaolinite minerals, serpentines), 2:1 (micas, vermiculites, smectites, pyrophyllite, talc) or 2:1:1 (chlorites) structural layers of identical structure, symmetry, and composition reveal different stacking along the c axis, namely by an axial or rotational shifting.
The discovery of disorder and polytypism in the chemically simple kaolinite subgroup is a good example of specialized crystallographic research starting in 1938 and continuing for decades.
Modern geologists and sedimentary petrologists wishing to study some parts of argillosphere in more detail should have in their research team a specialized crystallographer for the investigation of order-disorder states and polytypism of phyllosilicates.
Already in 1959-1963, Radoslovich with his coworkers drew the crystallographers' attention (quoted in detail above, and by Konta, 2005) to the fact that the energetic state expressed in "local balance of forces" in layer structures may provide a means of structural control over polytypism.