Classification of Clay Minerals

Cl minerals belong to the phyllosilicate subclass of silicate class. They have been abundantly studied by X-ray diffraction, which is the basic tool for then-identification as it is difficult to observe without using electron microscope. 

Let us know first about the silicate minerals and then the cl minerals in the silicate group. All silicate minerals have the anionic group [SiOJ consisting of one Si surrounded by four 0 . The tetrahedron obtained by joining the centres of the four O is known as [SiOJ tetrahedron. 

Each [Si04] tetrahedron has an imbalanced charge of - 4, which can be neutralized in the following two ways  

Bonding with cations An Si04 tetrahedral group can be bonded to 

Apical oxygen Basal oxygen Sheet The unpaired oxygen in a tetrahedral sheet. These oxygens lie in a plane. Any of the three shared oxygens in the tetrahedral sheet. The planes of atoms associated with either the Si/Al tetrahedra or the octahedra. Oxygens lying in the plane between the plane of Si and the plane of A1 atoms are bonded to both sets of cations and are considered to be members of both sheets. 

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Table 4.5 Simplified classification of clay minerals. After Martin et al. (1991) with kind permission from the Clay Minerals Society.

Kumada, K., and H. Kato. 1970. Browning of pyrogallol as affected by clay minerals. I. Classification of clay minerals based on their catalytic effects on the browning reaction of pyrogallol. Soil Sci, Plant Nutr. (Tokyo) 16 195-200. 

Aluminosilicates and clay minerals. Within this class, compounds are sorted alphabetically by their names. There are numerous, often multilevel, classifications of clay minerals, and different names are often assigned to the same material or to very similar materials. Such materials are listed under the names used in the original publications and interconnected by cross-references. 

Table 1.1 The classification of clay minerals and their positions in the mineral world...

Mineralov [Data on the Classification of Clay Minerals]. Inf. Byull. Kom. Isuch. Glin Otdel. Geol.-Geogr. Nauk Akad. Nauk SSSR, Moscow. 

We have already learnt that the building unit of the silicates is the Si04 pyramid. By linking these pyramids in various ways the different kinds of silicate anions are formed. The classification of the silicates is based on these kinds of ions. The silicate anions of clay minerals have a layered structure, the top view of which is again represented in figure 8.5. 

The term clay refers to fine-grained aluminosilicates that have a platy habit and become plastic when mixed with water [11], Dozens of minerals fall under the classification of clays and a single clay deposit can contain a variety of individual clay minerals along with impurities. Clay minerals are classified as phyllosilicates because of their layered structure [12], The most common clay mineral is kaolinite, although others such as talc, montmorillonite, and vermiculite are also abundant. Each of the... 

Whereas soil scientists would classify clay by considering the particle size, a chemist describes it as part of the family of silicates and more precisely as hydrated silicates of aluminium. However, the classification of minerals with a stoichiometric formula does not reflect the complexity of their structure. In order to explain the properties of clay minerals in an adequate way, the coordination of silicon has to be described first, before looking at a long-range order in the crystals. 

A classification of silicates with predominantly two-dimensional cross-linking of [SiOJ tetrahedra leads to the trichotomy presented in Figures 2 and 3. Layered silicate hydrates, disilicates, and clay minerals differ in the repetitive characteristic binding element within the layers. The silicon oxygen tetrahedra within a sheet are connected by three bridging oxygen atoms. In the case of clay minerals, the fourth valency is saturated by foreign metal ions (e.g., Mg +)... 

The classification and nomenclature of clay minerals. Clay Min, Bull 4 52. 

In order to study in more detail the clay minerals, it is first helpful to review briefly the basic structural classification of the silicates in general. Although ultimately complicated, the general progression is logical, and is based on the degree of polymerization of the basic structural unit which is the Si04 tetrahedron (see below). The sequence runs as follows ... 

Table 4.2 summarizes this basic classification and terminology of silicates. It is worth remembering that the term infinite refers here to an atomic scale of measurement, and does not imply that the chains extend to infinity in the mathematical sense of the word The terminology surrounding the silicates and clay minerals, in common with other mineralogical terms, has never been fully systematized, and so the names given are often ill-defined, or not unique to a... 

A superficial classification of the most common clay mineral groups can be based upon the number of ions present in the octahedral layer (2 diocatahedral or 3 trioctahedral) and the numbers and the kind of ions... 

Such data are necessary for calculation of parameters in the classification of coal by rank dry, mineral-matter-free volatile matter (or fixed carbon) as well as moist, mineral-matter-free gross calorific value. For volatile matter and fixed-carbon data, it is also necessary to assume that 50% by weight of the sulfur is volatilized in the volatile matter test and therefore should not be included as part of the organic volatile matter (nor should the loss from clays and carbonate minerals) ... 

Fig.30. Generalized classification of dioctahedral 2 1 clay minerals. Mixed refers to mixed-layering.

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