IRON IN KAOL IN ITE: I I. THE RELAT IONSHIP BETWEEN KAOL IN ITE CRYSTALL IN ITY AND IRON CONTENT

A B STRACT: Calibration of the internal and external signals appearing at geff ~ 4 in the electron paramagnetic resonance (EPR) spectra of twenty-four kaolinites, has led to the recognition of two types of kaolinite-iron. The amount of iron associated with the internal signal (I iron) shows good inverse correlations with parameters used to describe the degree of crystalline perfection in kaolinite. Iron associated with the external signal (E iron) is insensitive to crystalline order. By considering both the amount and nature of the iron, the kaolinites investigated are placed in three groups. The first contains well-crystallized varieties characterized by tow total iron and EPR spectra consisting mainly of an E signal. Poorly-crystallized kaolinites contain more iron and are characterized by a fifty-fifty partition of this iron into E and I sites. The third group contains samples which are intermediate with respect o both the amount and nature of the iron. Since the recognition by Brindley & Robinson (1946) of the existence of a series of kaolinites with different amounts of structural defects, several methods for characterizing the extent of these defects have been proposed. Though the most common ones rely on the examination of selected areas of the X-ray diffraction diagram (Murray, 1954; Murray &amp