Variable Structures and Continuous Scattering of X-Rays from Layer Silicate Lattices

Crystals of some micas and related compounds having "layer" lattices show pronounced continuous scattering of x-rays together with normal interference maxima. Continuous scattering is explained as arising from destruction of the lattice periodicity normal to the perfect cleavage of these types of substances. This is a result of translation of some layers along the $b$ axis and parallel to the cleavage by $\frac{n{b}_0}{3}$, where $b_0$ is the unique lattice periodicity and $n$ is an integer. Various crystals differ in their degree of randomness and four general types are recognized; (1) no irregularity, (2) most elements of the crystal mosaic have a few irregular layers, (3) some elements have a regular sequence of layers while others have many irregular layers, (4) all elements have many irregular layers which leads to a small pseudo unit of structure. The phenomenon is illustrated by reproductions of photographs.