Geochemistry

Geochemistry: Pathways and Processes

Harry Y. McSween
Steven M. Richardson
Maria E. Uhle
Copyright Date: 2003
Edition: 2
Pages: 432
https://www.jstor.org/stable/10.7312/mcsw12440
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  • Book Info
    Geochemistry
    Book Description:

    Written expressly for undergraduate and graduate geologists, this book focuses on how geochemical principles can be used to solve practical problems. The attention to problem-solving reflects the authors'belief that showing how theory is useful in solving real-life problems is vital for learning. The book gives students a thorough grasp of the basic principles of the subject, balancing the traditional equilibrium perspective and the kinetic viewpoint.

    The first half of the book considers processes in which temperature and pressure are nearly constant. After introductions to the laws of thermodynamics, to fundamental equations for flow and diffusion, and to solution chemistry, these principles are used to investigate diagenesis, weathering, and natural waters. The second half of the book applies thermodynamics and kinetics to systems undergoing changes in temperature and pressure during magmatism and metamorphism. This revised edition incorporates new geochemical discoveries as examples of processes and pathways, with new chapters on mineral structure and bonding and on organic matter and biomarkers. Each chapter has worked problems, and the authors assume that the student has had a year of college-level chemistry and a year of calculus.

    Praise for the first edition

    "A truly modern geochemistry book.... Very well written and quite enjoyable to read.... An excellent basic text for graduate level instruction in geochemistry." -- Journal of Geological Education

    "An up-to-date, broadly conceived introduction to geochemistry.... Given the recent flowering of geochemistry as an interdisciplinary science, and given the extent to which it now draws upon the fundamentals of thermodynamics and kinetics to understand earth and planetary processes, this timely and rigorous [book] is welcome indeed." -- Geochimica et Cosmochimica Acta

    eISBN: 978-0-231-50903-9
    Subjects: Geology, Chemistry

Table of Contents

  1. Front Matter
    (pp. i-vi)
  2. Table of Contents
    (pp. vii-xiv)
  3. PREFACE TO THE SECOND EDITION
    (pp. xv-xvi)
  4. CHAPTER ONE INTRODUCING CONCEPTS IN GEOCHEMICAL SYSTEMS
    (pp. 1-11)

    In this introductory chapter, our goal is to examine the range of problems that interest geochemists and to compare two fundamental approaches to geochemistry. Thermodynamics and kinetics are complementary ways of viewing chemical changes that may take place in nature. By learning to use both approaches, you will come to appreciate the similarities among geochemical processes and be able to follow the many pathways of change. To develop some skills in using the tools of geochemistry, we also examine the limitations of thermodynamics and kinetics, and discuss practical considerations in problem solving.

    In studying the Earth, geologists use a number...

  5. CHAPTER TWO HOW ELEMENTS BEHAVE
    (pp. 12-34)

    Our goal in this chapter is to refresh concepts that you may have first encountered in a chemistry course and to put them in a geologic context, where they will be useful for the chapters to come. We begin with a review of atomic structure and the periodic properties of the elements, focusing carefully on the electronic structure of the atom. This leads us to consider the nature of chemical bonds and the effects of bond type on the properties of compounds. These should be familiar topics, but they may look different through the lens of geochemistry.

    Long before the...

  6. CHAPTER THREE A FIRST LOOK AT THERMODYNAMIC EQUILIBRIUM
    (pp. 35-55)

    In this chapter, we introduce the foundations of thermodynamics. A major goal is to establish what is meant by the concept of equilibrium, described informally in the context of the party example in chapter 1. The idea of equilibrium is an outgrowth of our understanding of three laws of nature, which describe the relationship between heat and work and identify a sense of direction for change in natural systems. These laws are the heart of the subject of thermodynamics, which we apply to a variety of geochemical problems in later chapters.

    To reach our goal, we need to examine some...

  7. CHAPTER FOUR HOW TO HANDLE SOLUTIONS
    (pp. 56-78)

    This is a chapter about solutions, important to us because most geological materials have variable compositions. They are, in fact, mixtures at the submicroscopic scale between idealized end-member substances such as albite, water, grossular, dolomite, or carbon dioxide, which lose their molecular identities in the mixture. To see how thermodynamics can be used to predict the equilibrium state in a system dominated by phases with variable compositions, we examine first the structure of solutions of solids, liquids, and gases, and discuss ways in which this architecture is reflected in mole fractions of end-member components.

    At the end of chapter 3,...

  8. CHAPTER FIVE DIAGENESIS: A Study in Kinetics
    (pp. 79-93)

    Diagenesis embraces all of the changes that may take place in a sediment following deposition, except for those due to metamorphism or to weathering at the Earth’s surface. Intellectual battles have been waged over these two environmental limits to diagenesis. Rather than join these battles, we focus on some of the geochemical processes that affect sediments after burial and consider some of the pathways along which they may change.

    Diagenetic changes take place slowly at low temperature. The assemblages we see in sediment, therefore, usually represent some transition between stable states. In previous chapters, we began to study thermodynamic principles...

  9. CHAPTER SIX ORGANIC MATTER AND BIOMARKERS: A Different Perspective
    (pp. 94-110)

    Organic geochemistry is built on the application of organic chemical principles and analytical techniques to sedimentary geology. Carbon, nitrogen, oxygen, sulfur, hydrogen, calcium, and iron are the primary elements that living organisms utilize in their structural tissues, for energy harvesting, and for replication. Accumulation of organic matter in recent and ancient sediments is the most important link between the biosphere and geology. Not only are the organic materials in sedimentary rocks an economically important resource (coal and petroleum) but, as we shall see, they also provide a molecular record of life. The sedimentary burial of organic matter is also important...

  10. CHAPTER SEVEN CHEMICAL WEATHERING: Dissolution and Redox Processes
    (pp. 111-136)

    The geochemical processes that most profoundly affect the surface of continents—the environment with which we have the closest personal familiarity—can be classed together as chemical weathering processes. These include a variety of reactions involving water and either acids or oxygen in the decomposition of rocks. In chapter 5, we referred to these implicitly as the source of sediments and ionic species for diagenetic processes. In this chapter, we examine them explicitly. Our focus is on the weathering of silicates, which constitute the bulk of continental rocks.

    We begin the chapter by considering simple reactions that dominate the low-temperature...

  11. CHAPTER EIGHT THE OCEANS AND ATMOSPHERE AS A GEOCHEMICAL SYSTEM
    (pp. 137-168)

    In this chapter, we introduce three broad problems that have occupied much of the attention of geochemists who deal with the ocean-atmosphere system. The first of these concerns the composition of the oceans and the development of what has been called a “chemical model” for seawater. This is a comprehensive description of dissolved species, constrained by mass and charge balance and the principles of electrolyte solution behavior we discussed in chapter 4.

    Closely linked to this problem are questions about the dynamics of chemical cycling between the ocean-atmosphere and the solid Earth. Aside from the geologically rapid processes that control...

  12. CHAPTER NINE TEMPERATURE AND PRESSURE CHANGES: Thermodynamics Again
    (pp. 169-187)

    This chapter expands on the thermodynamic principles introduced in chapter 3 and provides the preparation for the next chapter on phase diagrams. We first give a thermodynamic definition for equilibrium. We also derive the phase rule and explore its use as a test for equilibrium. The effects of changing temperature and pressure on the free energy of a system at equilibrium are analyzed, and a general equation for dḠ at P and T is formulated. P-T and Ḡ-T diagrams for one-component systems are introduced. The utility of the Clapeyron equation in constructing or interpreting phase diagrams is explored. We then...

  13. CHAPTER TEN PICTURING EQUILIBRIA: Phase Diagrams
    (pp. 188-205)

    Even after years of experience, many geologists find thermodynamics difficult to understand unless they can draw pictures that relate their equations to tangible systems. Phase diagrams provide a convenient and powerful way to picture equilibria. In this chapter, we introduce the principles of Ḡ-X2 diagrams for binary systems and illustrate graphically the minimization of free energy. We then construct T-X2 diagrams by stacking Ḡ-X2 sections atop one another, using examples of real geochemical systems. These diagrams illustrate simple crystallization, the formation of chemical compounds, solid solution, and exsolution. We review equilibrium crystallization paths and show how binary phase diagrams can...

  14. CHAPTER ELEVEN KINETICS AND CRYSTALLIZATION
    (pp. 206-226)

    Not all geochemical processes make the final adjustment to equilibrium conditions. Even those processes that eventually go to completion, such as crystallization of magmas and recrystallization of metamorphic rocks, are sometimes controlled by kinetic factors. In this chapter, we discover what these factors are and how they can be understood. We first examine the effect of temperature on rate processes, which leads to the concept of activation energy. We then consider three specific rate processes: diffusion, nucleation, and growth. Differences between volume diffusion and grain boundary diffusion are explained, and the importance of crystal defects is considered. We introduce nucleation...

  15. CHAPTER 12 THE SOLID EARTH AS A GEOCHEMICAL SYSTEM
    (pp. 227-262)

    In this chapter, we explore how the various parts of the Earth’s interior can be integrated into a grand geochemical system. First, we estimate the compositions of the reservoirs—that is, crust, mantle, and core—in terms of both chemistry and phase assemblages. We then investigate how these reservoirs interact through the exchange of heat and matter. The continental crust was extracted from the upper mantle, which appears to be geochemically isolated from the lower mantle. Generally, convection within the upper mantle and crust is manifested in plate tectonics. During certain episodes, however, whole-mantle convection may occur, resulting in sinking...

  16. CHAPTER 13 USING STABLE ISOTOPES
    (pp. 263-285)

    This is the first of two chapters on isotope geochemistry. In it, we discuss how geochemists use stable isotopes of hydrogen, carbon, nitrogen, oxygen, and sulfur to interpret geologic processes and environments. You may want to review portions of chapter 2 to refresh your familiarity with the language and some of the basic concepts in nuclear chemistry. With the aid of several case studies, we show how those and other concepts can be applied to problems of practical interest. In each case study, the common principle is mass fractionation. We explain how the different stable isotopes of a single element...

  17. CHAPTER 14 USING RADIOACTIVE ISOTOPES
    (pp. 286-312)

    In the geochemist’s arsenal of techniques for unraveling geological problems, the study of radioactive isotopes and their decay products has become very prominent. This chapter begins with a discussion of nuclide stability and decay mechanisms. After equations that describe radioactive decay are derived, we examine the utility of certain naturally occurring radionuclide systems (K-Ar, Rb-Sr, Sm-Nd, and U-Th-Pb) in geochronology. The concept of extinct radionuclides that were present in the early solar system is also discussed. The principles behind both mass spectrometry and fission track techniques are introduced. We discuss how induced radioactivity can be used to solve geochemical problems....

  18. CHAPTER 15 STRETCHING OUR HORIZONS: Cosmochemistry
    (pp. 313-342)

    In this chapter, we explore the rapidly emerging field of cosmochemistry. This subject involves the geochemical aspects of systems of planetary or solar system scale. We first consider nucleosynthesis processes in stars and use this foundation to understand the abundances of elements in the Sun and the solar system. Chondritic meteorites are discussed next, as samples of average solar system material stripped only of the lightest elements. Analyses of these meteorites provide information on the behavior of various elements in the early solar nebula; from these, we learn that elements were fractionated according to both geochemical affinity and volatility. Chondritic...

  19. APPENDIX A: MATHEMATICAL METHODS
    (pp. 343-348)
  20. APPENDIX B: FINDING AND EVALUATING GEOCHEMICAL DATA
    (pp. 348-351)
  21. APPENDIX C: NUMERICAL VALUES OF GEOCHEMICAL INTEREST
    (pp. 351-352)
  22. GLOSSARY
    (pp. 353-358)
  23. INDEX
    (pp. 359-364)