Earth Materials. John O'Brien. Читать онлайн. Newlib. NEWLIB.NET

Автор: John O'Brien
Издательство: John Wiley & Sons Limited
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Жанр произведения: География
Год издания: 0
isbn: 9781119512219
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Hydroxides (OH)−1 Tungstates (WO4)−2 Carbonates (CO3)−2 Silicates (SiO4)−4

      Oxygen (O) and silicon (Si) are the two most abundant elements in Earth's continental crust, oceanic crust and mantle. Under the relatively low pressure conditions that exist in the crust and the upper mantle, the most abundant rock‐forming minerals (Chapter 5) are silicate minerals. Silicate minerals, characterized by the presence of silicon and oxygen that have bonded together to form silica tetrahedra, are utilized here to show how coordination polyhedra are linked to produce larger structures with the potential for the long‐range order characteristic of all minerals.

      2.5.1 The basics: silica tetrahedral linkage

      Many factors influence the type of silica tetrahedral structure that develops when silicate minerals form; the most important is the relative availability of silicon and other cations in the environment in which the mineral crystallizes. Environments with abundant silicon (and therefore silica tetrahedra) tend to favor the linkage of silica tetrahedra through shared oxygen ions. Environments depleted in silicon tend to favor the linkage of the oxygen ions in silica tetrahedra to cations other than silicon. In such situations, silica tetrahedra tend to link to coordination polyhedral elements other than silica tetrahedra.

      If none of the oxygen ions in a silica tetrahedron bond to other silicon ions in adjacent tetrahedra, the silica tetrahedron will occur as an isolated tetrahedral unit in the mineral structure. If all the oxygen ions in a silica tetrahedron bond to other silicon ions of adjacent tetrahedra, the silica tetrahedra form a three‐dimensional framework structure. If some of the oxygen ions in the silica tetrahedra are bonded to silicon ions in adjacent tetrahedra and others are bonded to other cations in adjacent coordination polyhedra, a structure that is intermediate between totally isolated silica tetrahedra and three‐dimensional frameworks of silica tetrahedra will develop.

      Because the silicate groups constitute the most significant rock‐forming minerals in Earth's crust and upper mantle they are discussed more fully in Chapter 5. In Chapter 3, we will further investigate significant aspects of mineral chemistry, including substitution solid solution and the uses of isotopes and phase stability diagrams in understanding Earth materials.

      1 Explain the difference between:An isotope and an ion.A cation and an anion and the reason the latter two types of ions exist.A stable isotope and an unstable isotope and how the latter evolve through time.

      2 Detail the major factors that determine the effective radii of different atoms and ions.

      3 What is the diagonal rule and how does it help to predict the electron configuration of most major elements whose atomic number is known? Use the diagonal rule to write the “ground state” electron configurations for the following elements.(a)Figure 2.21 Major silicate structures: (a) nesosilicate, (b) sorosilicate, (c) cyclosilicate, (d) single‐chain inosilicate, (e) double chain inosilicate, (f) phyllosilicate, (g) tectosilicate.Source: Wenk and Bulakh (2004). © Cambridge University Press.helium (H)carbon (C)oxygen (O)aluminum (Al)argon (Ar)iron (Fe).

      4 Referring to the periodic table of the elements (Table 2.3), which of the reactive (non‐Noble) elements is the most metallic (electropositive) and which of these is the most nonmetallic (electronegative). Use their electron configurations and position on the periodic table to explain why.

      5 Explain the differences between ionic, covalent, metallic, and transitional (hybrid) bonds and the properties that commonly characterize materials that possess that type of bond.

      6 Using the periodic table of the elements (Table 2.3), calculate the electronegativity difference and then predict the bond type and properties for each of the following minerals:Native platinum (Pt)Periclase (MgO)Sylvite (KCl)Pyrite (FeS2)Sphalerite (ZnS).

      7 Explain the concepts of radius ratio and electrostatic valency and use them to explain why silica tetrahedra tend to link by sharing oxygen ions. Then describe and explain the basic differences between nesosilicate, sorosilicate, cyclosilicate, nesosilicate, phyllosilicate and tectosilicate structures.

      1 Klein, C. and Dutrow, B. (2007). Manual of Mineral Science (Manual of Mineralogy), 23e. New York: Wiley 704 pp.

      2 Pauling, L. (1929). The principles determining the structure of complex ionic structures. Journal American Chemical Society 51: 1010–1026.

      3 Railsback, L.B. (2003). An earth scientist's periodic table of the elements and their ions. Geology 31: 737–740.

      4 Wenk, H.R. and Bulakh, A. (2004). Minerals: Their Constitution and Origin, 3e. Cambridge, UK: Cambridge University Press 646 pp.

      5 Wenk, H.R. and Bulakh, A. (2016). Minerals: Their Constitution and