The powder X-ray diffraction pattern of fine-grained chlorite was used to obtain information about apparent chlorite “crystallinity” by M. Frey (Frey, 1987) and others, and by Arkai (1991) to correlate the reactions involving smectite-muscovite and smectite-chlorite with the Kübler index (and other metamorphic grade-indicating characteristics). Because diffraction patterns are affected by the presence of a diversity of defects, mean crystallite sizes, and other features, it is unclear if “crystallinity” is actually being measured and thus, the index should not be characterized as a “crystallinity” index.
Cf., crystalline, crystallinity index, Hinckley index, Kübler index