Earth crust structure

Nikolaevskiy, VN. and lA Garagash, Earth crust structure as result of rock fracturing at high pt - conditions, this volume, 2004. 

EARTH CRUST STRUCTURE AS A RESULT OF ROCK FRACTURING AT HIGH PRESSURE AND TEMPERATURE CONDITIONS... 

Fractures, fissures, and joints are openings in sedimentary rocks formed by the structural (mechanical) failure of the rock under loacls caused by earth crust tectonics. This form of porosity is extremely hard to evaluate quantitatively due to its irregularity. 

The part of Earth s geosphere that is accessible to humans is the crust, which, ranging from 5 to 40 km in thickness, is extremely thin compared to the diameter of the earth. Most of the solid earth crust consists of rocks. Rocks are composed of minerals, where a mineral is a naturally occurring inorganic solid with a definite internal crystal structure and chemical composition. A rock is a solid, cohesive mass of pure mineral or an aggregate of two or more minerals. 

In this chapter, the focus is on weathering of feldspars, aluminosilicate minerals, which are the most abundant mineral species in the earth crust (Banfield Hamers, 1997). Feldspars contain aluminium and silicon, which are arranged in a tetrahedral structure, with other cations in the voids of this structure. The common feldspars have compositions ranging between albite (NaAlSisOg) and K-feldspar (KAlSigOg) (alkali feldspars) and between albite and anorthite (CaAl2Si20g) (plagioclase feldspars). 

The elements beryllium, magnesium, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, zinc, zirconium, molybdenum, silver, cadmium, tin, thallium, lead, and bismuth mainly occur in the crystal structures of rock-forming silicates and oxides of the common rocks in the Earths crust. These elements - with the exception of magnesium, iron, titanium, chromium, and zirconium - are trace elements in the minerals. They follow certain rules as reported by Goldschmidt (1954) in their ten-... 

Designs for structures subjected to earthquake loads are empirical and are based on the analyses of structures that withstood earthquakes in the past. Earthquakes have periods of vibration, but the periods are complex. They are not simple harmonic vibrations in tall steel towers. Data on some past serious earthquakes are given in Table 4-5. The horizontal acceleration, a, produced by the shift of the earth crust divided by gravitational constant, gy gives the seismic coefficient, C or... 

The global structure of the Earth crust is in accordance with residual states of rocks in an active tectonic regime, that is, when the shear intensity is reaching the rock limit strength at high temperatures and pressures. 

Minerals with Kinetic Dissolution Condition Minerals of this group are considered in everyday life insoluble. Ihey include mostly metal oxides, hydroxides, sulphides and aluminum sihcates. The mechanism of their dissolution is dominated by hydrolysis whose nature depends on the structure and composition of minerals. Their dissolution under any conditions has kinetic condition, i.e., it is controlled by extremely slow chemical reactions of surface complexation. The rate of their dissolution is noticeably lower than 10 ° mole m s and the solubility does not exceed 10" mole l Besides, both their dissolution rate and solubility depend on pH values. These minerals are most common in the Earth crust and often play a leading role in the formation of imderground water composition. It is convenient to subdivide minerals with kinetic dissolution regime into three groups 1- silica, 2 - oxides, hydroxides and sulphides of metals, 3-aluminum silicates. 

Molten silica and its mixtures with various other oxides are of central interest in geosciences, silicates that have formed fix>m such melts in the earth crust are very relevant materials. Such melts are also very important for the glass and ceramics industry, and although both of these materials are in their crystalline and amorphous forms in use for many centuries, the understanding of their structure-property relationship on an atomistic level still poses challenging scientific problems. In recent years, important progress has been made possible by atomistic molecular dynamics simulations, and a selection of problems by this method will be presented below. 

There are four commonly occurring states of stress, shown in Fig. 3.2. The simplest is that of simple tension or compression (as in a tension member loaded by pin joints at its ends or in a pillar supporting a structure in compression). The stress is, of course, the force divided by the section area of the member or pillar. The second common state of stress is that of biaxial tension. If a spherical shell (like a balloon) contains an internal pressure, then the skin of the shell is loaded in two directions, not one, as shown in Fig. 3.2. This state of stress is called biaxial tension (unequal biaxial tension is obviously the state in which the two tensile stresses are unequal). The third common state of stress is that of hydrostatic pressure. This occurs deep in the earth s crust, or deep in the ocean, when a solid is subjected to equal compression on all sides. There is a convention that stresses are positive when they pull, as we have drawn them in earlier figures. Pressure,... 

The structural complexity of the 3D framework aluminosilicates precludes a detailed treatment here, but many of the minerals are of paramount importance. The group includes the feldspars (which are the most abundant of all minerals, and comprise 60% of the earth s crust), the zeolites (which find major applications as molecular sieves, desiccants, ion exchangers and water softeners), and the ultramarines which, as their name implies, often have an intense blue colour. All are constructed from Si04 units in which each O atom is shared by 2 tetrahedra (as in the various forms of Si02 itself), but up to one-half of the Si... 

More than 90% of the rocks and minerals found in the earth s crust are silicates, which are essentially ionic Typically the anion has a network covalent structure in which Si044-tetrahedra are bonded to one another in one, two, or three dimensions. The structure shown at the left of Figure 9.15 (p. 243), where the anion is a one-dimensional infinite chain, is typical of fibrous minerals such as diopside, CaSi03 - MgSi03. Asbestos has a related structure in which two chains are linked together to form a double strand. 

Abundance of elements in earth s crust, see Elements, abundance in earth s crust Acetaldehyde structure, 332 Acetamide, 338 Acetanilide, 344 Acetic acid in biochemistry, 428 structure, 333 Acetone... 

By far the most abundant phosphate mineral is apatite, which accounts for more than 95% of all P in the Earth s crust. The basic composition of apatite is listed in Table 14-2. Apatite exhibits a hexagonal crystal structure with long open channels parallel to the c-axis. In its pure form, F , OH , or Cl occupies sites along this axis to form fluorapatite, hydroxyapatite, or chlor-apatite, respectively. However, because of the "open" nature of the apatite crystal lattice, many minor substitutions are possible and "pure" forms of apatite as depicted by the general formula in Table 14-2 are rarely found. 

In the previous paragraph, it has been stated that minerals have the same structure but different compositions (phenomenon of isomorphism of minerals) while some minerals have the same composition but different structures (phenomenon of polymorphism of minerals). Mineral composition and structure are both important in studying and classifying minerals. The major class of minerals - based on composition and structure - include elements, sulfides, halides, carbonates, sulfates, oxides, phosphates, and silicates. The silicate class is especially important, because silicon makes up 95% of the minerals, by volume, in the Earth s crust. Mineral classes are divided into families on the basis of the chemicals in each mineral. Families, in turn, are made of groups of minerals that have a similar structure. Groups are further divided into species. 

Minerals are the most abundant type of solid matter on the crust of the earth they are homogeneous materials that have a definite composition and an orderly internal structure. Minerals make up most of the bulk of rocks, the comminuted particles of sediments, and the greater part of most soils. Over 3000 minerals have been identified, and new ones are discovered each year. Only a few hundred, however, are common most of the others, such as, for example, the precious stones, are difficult to find (Ernst 1969). Table 3 lists common minerals and mineraloids. Many schemes have been devised for classifying the minerals. In the scheme presented in Table 4, minerals are arranged in classes according to their increasing compositional chemical complexity. 

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