Kaolinite chemical formula

Hersh and coworkers (16) examined electrostatic precipitator samples using petrographic microscopy. The minerals along with their chemical formula eind mode of occurrence are given in Table VIII. Kaolinite and limonite were by far the most abundant minerals detected. 

Kaolinite. The composition of this mineral is close to the empiric formula Al20j-2Si02-2H20 while structural chemical formula of aluminium silicate is Al2(Si205](OH)4. It has triclinic syngony, PI space group, unit cell parameters are a = 0.515, b = 0.895, c = 0.737 nm, a = 9i°48, 3 = 104°30, y = 90°(z = 2). 

The phyllosilicates in soil clays can be classified into three layer types, distinguished by the numbers of tetrahedral and octahedral sheets combined, and five groups, differentiated by the kinds of isomorphic cation substitutions that occur. The layer types are shown in Fig. 1.3, and the groups are described in Table 1.3. The 1 1 layer type consists of one tetrahedral and one octahedral sheet. In soil clays, it is represented by the kaolinite group, with the unit cell chemical formula [Si4](Al4)Oio(OH)8, where the cation enclosed in brackets is in tetrahedral coordination and that enclosed in parentheses is in octahedral coordination. Normally there is no significant isomorphic substitution for Si(IV) or Al(III) in this group, and, as is common with soil clay minerals, the octahedral sheet has two thirds of its cation sites occupied (dioctahedral phyllosilicate). 

These minerals are hydrated aluminosilicates which are characterized by a sheetlike structure and can be conveniently divided into three groups (1) the kaolinite group, (2) the mont-morillonite group, and (3) the potash clay (or hydrous mica) group (Table 7.7). In the kaolinite group, all have the same chemical composition and differ only in individual crystal structures. The montmorillonite group can be represented by means of ion substitutions in the general chemical formula. For example, in montmorillonite itself, approximately 16% of the aluminum... 

Silicate clays have been particularly widely researched and commercialised. Commercially, the most widely used type is montmorillonite, with the chemical formula (AlMg)8(Si40io)3(OH)io.l2H20. It is foimd in bentonite clays and in kaolinite deposits. 

Kaolinite is a clay mineral with the chemical formula Al2(0H)4Si205 [5] or (OH)8Si4Al40io [6]. The basic unit of kaolinite consists of a single silica tetrahedral sheet and a single alumina octahedral sheet such that the oxygen atoms at the tips of the silica tetrahedrons and one of the oxygen atoms of the alumina octahedral sheet form a common layer. 

Clay minerals are classified into kaolinite, illite, smectite (montmorillonite), and palygorskite groups. The most important commercial clay minerals are kaolinite and montmorillonite. Kaolin or kaolinite, known as China clay , has the basic chemical formula Si2Al205(0H)4, and montmorillonite is AlSi205(0H) x H2O. Kaolinite was formed by various hydrothermal alterations or weathering of feldspars and other silicate minerals. 

The dioctahedral kaolin minerals have the generali2ed chemical formula Al2Si205 (0H)4- H20. In kaolinite, dickite, and nacrite, n=0 in hydrated halloysite, n=2 and in other halloysites, n varies between 0 and 2. A small amount of isomorphous substitution of A1 and Fe for Si in the tetrahedral sheets and Fe and Mg for A1 in the octahedral sheets might occur in halloysites, but has not been suggested for other dioctahedral minerals. 

Quite often fireclay is burnt to chamotte at the place where it is found. The most common clay mineral in fireclay is kaolinite with the ideal formula Al4[(OH)8/Si4O10], or in the notation applied in world of ceramics Al203.2Si0r2 H20. Kaolinite contains chemically and physically bound water. When you heat it to about 1500 °C, the physically bound form is first released and subsequently the chemically bound one. In the last phase chamotte is formed ... 

Solubility calculations were added for two allophanes, for which the equilibrium constants and formulae are a function of pH. Paces (74) found cold ground waters collected from springs in granitic rocks of the Bohemian Massif of Czechoslovakia to be supersaturated with respect to kaolinite while being unsaturated with respect to amorphous silica. He interpreted this as an indication that a metastable aluminosilicate more soluble than kaolinite was controlling the concentrations of alumina and silica in these waters. This aluminosilicate was further hypothesized to be of varied chemical composition, controlled by the mole... 

The unit formula for kaolinite has a Si/Al ratio of 1. This ratio is matched by its chemical composition, which suggests that soil kaolinites have little or no isomorphic substitution. Any differences from 1 could be due to surface coatings that were not removed during preparation of the sample. Most of the 10- to 100-mmol(+) kg-1 cation exchange capacity of kaolinite has been attributed to dissociation of OH groups at clay edges. However, if only one Si4+ of every 200 in the silica sheet were... 

The chemical composition of kaolinite can also be expressed as Al Si Oj (OH)g this formula represents better the crystal structure of the mineral as shown in Fig. 10.1 (as in a unit of the crystal (dashed line box), only two layers and two such units in each layer are shown). The crystal consists of layers of a sort of sheet which has the composition of Al Si Oj (OH)g (see more about the chemistry of rocks in Chap. 14). 

Water frequently forms an intercalate with kaolinite, in the form of the mineral halloysite which has the formula Al2Si20s(0H)2 2H2O. The addition of the two molecules of water increases the thickness of the layer from 7 A to 10 A. Kaolinite itself can be hydrated by a relatively simple chemical treatment to produce both a dihydrate, similar to halloysite, and a monohydrate with a thickness of about 8.6 A. Kaolin minerals do not form fibers as readily as do the serpentines. These minerals are described in more detail by Giese (1988). 

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