Illite crystallinity

The illite-crystallinity (IC) method was developed during the early 1960s, first in Texas and later in France. It was applied in petroleum exploration to detect diagenetic stages, but essentially to characterize the ultimate evolution stages before metamorphism. This empirical approach had no precis e theoretical support for clay mineralogists or crystallographic scientists . With the development of computerised XRD treatments, the application fiel d of the IC method has essentially been for the anchizonal and its immediat e limits, for which the method is most accurate. It corresponds to an indir ect measurement of the mean consecutive illite layers contained in coherent scattering domains of mixed-layer illite-smectite. Its application field w ent beyond petroleum exploration to be applied to regional geology in studi es of low-metamorphic orogenic belts. (C) 2000 Academie des sciences/Editio ns scientifiques et medicales Elsevier SAS.