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Phyllosilicates

Authored by: Hideomi Kodama

Handbook of Soil Sciences Properties and Processes

Print publication date:  November  2011
Online publication date:  November  2011

Print ISBN: 9781439803059
eBook ISBN: 9781439803066
Adobe ISBN:

10.1201/b11267-24

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Abstract

Phyllosilicates, in other words, layer silicates, occupy one of six subclasses under the silicates class (Table 21.1). Phyllo- is after the Greek word describing the state of leaves, like a bed or heap of leaves. Thus in science, often the word is used as a prefix to express thin layer or paper sheet like in a book. This reflects general crystal habits and morphological features of the phyllosilicates. The silicates are abundant on the earth and of greater importance than any other minerals, which is easily understood from the fact that oxygen and silicon constitute nearly 75% of the elements in the earth’s crust (Figure 21.1). The fundamental unit in all silicate structures is the silicon-oxygen tetrahedron (Figure 21.2). As Bragg (1950) stated, the bonds between silicon and oxygen are so strong that the four oxygen atoms are always found at the corners of a tetrahedron of nearly constant dimensions and regular shape whatever the rest of the structure may be like. The Si–O distance is about 0.16 nm, and the O–O distance 0.26 nm. Besides the crustal abundance of these two elements, the ionic radius of Si4+, 0.042 nm, is conveniently accommodated in surroundings with four oxygens to form the fundamental structural unit of all silicates, the tetrahedron having the chemical formula (SiO4)4−. This unit can occur independently with compensating cations like Mg2+ and Fe2+. And also these SiO4 tetrahedra may be linked together by having one or more oxygen atoms shared in common by neighboring tetrahedra to form indefinitely extended and more complicated structural units to cover the existing silicate minerals. This mechanism of linking together is known as polymerization, and the classified structural units with their compositions are given in Table 21.2. Table 21.1 Six Subclasses under the Silicate Mineral Class

Subclass (Commonly Used)

Subclass (in Other Name)

Nesosilicates

Orthosilicates

Sorosilicates

Disilicates

Cyclosilicates

Ring silicates

Inosilicates

Chain silicates–;Single chain and double chain

Phyllosilicates

Layer silicates

Tectosilicates

Framework silicates

Table 21.2 Unit Compositions of Six Subclasses, Mineral Group, and Species Examples

Subclass

Unit Composition

Mineral Group Example

Mineral Species Example

Nesosilicates

(SiO4)4−

Olivin

Forsterite

Sorosilicates

(Si2O7)6−

Epidote

Zoisite

Cyclosilicates

(Si6O18)12−

Tourmaline

Elbaite

Inosilicates

 Single chain

(SiO3)2−

Pyroxene

Diopside

 Double chain

(Si4O11)6−

Amphibole

Actinolite

Phyllosilicates

(Si2O5)2−

Mica

Muscovite

Tectosilicates

(SiO2)0

Feldspar

Albite

Figure 21.1 The 12 most abundant elements in the earth’s crust. (Modified graph from Vanders, I., and P. Kerr. 1967. Mineral recognition. John Wiley & Sons, Inc., New York.) Figure 21.2 Close-packing representation of the SiO4 tetrahedron. (From Klein, C., and C.S. Hurlbut, Jr., 1985. Manual of mineralogy. John Wiley & Sons, Inc., New York.)

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