Abstract: Recent surveys of clay mineral assemblages in argillaceous sediments have indicated that chloritic minerals are of more frequent occurrence and of greater significance than was formerly recognized.
The wide latitude of compositional variations within the chlorite crystallization scheme introduces enough complexity into the x-ray diffraction identification and characterization of these minerals that a detailed description of a few typical clay mineral associations seems justified.
For the simplest cases, in which resolution of diffraction features from entirely chloritic grains can actually be demonstrated, analyses may be highly reliable. Further, for many unresolved instances, simple heat treatments effect reliable identifications.
For more complicated assemblages, in which coherently scattering domains are mixtures within themselves, individually planned heating or swelling reactions may become necessary.
Typical natural examples are illustrated, for which apparently proper distinctions have been made for characterizing associations on mono- and mixed-clay mineral grains.