Major Groups of Clay Minerals

Clay minerals are divided into three major groups. These are the important clay mineral groups. 

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As a function of their structural properties, clays interact differently with organic and inorganic contaminants. Two major groups of clay minerals are selected for discussion here (a) kaolinite, with a 1 1 layered structured aluminosilicate and a surface area ranging from 6 to 39 m g" (Schofield and Samson 1954) and (b) smectites with a 2 1 silicate layer and a total surface area of about 800m g" (Borchardt 1989). 

Table 3.1 Four major groups of clay minerals, mainly in terms of the variation in the layered structure...

TABLE 1 Major groups of clay minerals (Faheemuddin, 2008)... 

There have also been devised simple chemical pretreatments, that enable the curve to be rendered more diagnostic. Thus, gibbsite and goethite both give peaks in the 300 "C region, and these sometimes overlap. They may, however, be clearly resolved by preliminary sodium dithionite and sodium hydroxide treatments (Mackenzie and Robertson [1961]). Similarly, pretreatment with piperidine may assist in distinguishing major groups of clay minerals (Allaway [1949]). 

The following pages give a review of the chemistry of natural minerals, their typical occurrence in nature and their common mineral associations. This review is used to establish the major groupings of the common clay mineral species as a function of the chemical systems to which they can be related. Because various forms of silica as well as zeolites and organic materials are commonly associated with clays, these materials have been considered in the same manner as the phyllosilicates. It is evident that they have an influence on the clay mineralogy and that they form an integral part of clays in the broad sense of the term. However, they are not normally considered to be clay minerals. 

As mentioned in Sections 1.3.2.1 and 1.3.2.2, the CEC and specific surface area (both internal and external) are higher than those of clay minerals. The functional groups of soil organic matter (Table 1.5) can be deprotonated or protonated, depending on pH. It means that they have pH-dependent charges. The major functional groups can be deprotonated at pH values characteristic of soils (pH = 6-8) so that they can sorb cations. It has been estimated that the CEC of soils comes from the soil organic matter in 20%-70% (Stevenson 1982). 

TOT (2 1) Smectite, (Talc, Mica, Mommorillonite), Sepiolite The thickness of the layer is about 1 nm. The group includes many minerals that are major constituents of clays... 

Jackson, M. L., 1959. Frequency distribution of clay minerals in major great soil groups as related to the factors of soil formation. Proc. 6th Nat. Conf. Clays Clay Min. Vol. 6, 133-143. 

Know the general conditions of occurrence and stability of the major clay mineral groups, including the roles played by parent mineralogy, temperature, precipitation rate, soil drainage, and soil maturity in clay occurrence. 

The loosely anchored indigenous particles can be categorized into two major groups expansive authigenic clay minerals and nonexpansive clay minerals. A simple kinetic expression is set up for the generation of these indigenous fines. The variable r represents the fraction of expansive clay minerals with respect to the total releasable fines, ap. ... 

Table 1.6 Average relative concentrations [wt.%] of the principal clay mineral groups in the < 2 Dm carbonate-free fraction in sediments from the major ocean basins (data from Windom 1976).

By the value of total exchange capacity clay minerals are subdivided into the following major groups ... 

Table III summarizes the responses of the m ain clay mineral groups to various treatments and Figure 4 provides a generalized analytical procedure. These procedures outlined below are applicable for routine recognition and quantification of the major clay mineral groups. Within most of the groups there are various subgroups and species that require more elaborate XRD and chemical techniques not covered in this chapter. Brindley Brown (1980) and Thorez (1975) are excellent references that supply details about these more advanced techniques.

Table III. Response of major clay mineral groups to glycolation and healing (compiled from Brown Brindley, 1980 Thorez. 1975 and Carroll, 1970)... 

Calculation procedures Semi-quantitative calculations ofthe relative abundances of the major clay mineral groups are made using the weighted peak area method of Johns et al. (1954) ... 

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