Phase Diagram for the Illite-Glauconite Mixed Layered Minerals

H = illites VO, M, MC - glauconites from various authors (see Velde and Odin, 1975). 

One should notice the possibility of producing single-phase illite materials by the same type of process. If, for reasons unknown at the moment, the path of chemical change leads to aluminous illite instead of iron glauconite, i.e., parallel to the K axis with low initial iron content, one could produce single phase illite or mixed layered mineral assemblage. These are apparently rare, but such an explanation could be used to explain the illite and mixed layered mono-mineral layers of metabentonite deposits which cannot be explained as recrystallization of an eruptive rock. Mono-mineral layers in carbonate rock the so called 

It is obvious then that A1 is not synonymous with Fe in sedimentary mica-like minerals. The increasing influence of trivalent iron in a sedimentary system will obviously provoke the crystallization of a specific mineral series which is not contiguous with illite and which would not be present otherwise. The development of glauconite in sediments should be due to specific local conditions which permit the chemical evolution of an initial montmorillonite material to celadonite mica-like phase. In fact previous observations have consistently led to this conclusion as to the origin of glauconite in sediments and sedimentary rocks. 

It would appear that the different types of potassic mica-like phases can be distinguished on the basis of alkali and iron content and geologic occurrence  

Normal aluminous illite common in pelitic sediments, altered volcanic ash beds, hydrothermal alterations of acidic rocks and weathering products of these rocks. 

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