ALBERT

Description / Table of Contents: This volume of was prepared in conjunction with the Mineralogical Society of America Short Course on Amphiboles and Other Hydrous Pyriboles, Fall, 1981. Had it not been split into two volumes, 9A and 9B, it would have resembled in some respects the Manhattan telephone directory (it is hoped, however, that the content is more readable and relevant to the geological sciences). The length of this collection of papers appears to result from a combination of phenomena. The amphiboles themselves must accept most of the blame: their structural complexity and resulting chemical variability and diversity of petrologic behavior preclude brief description. In addition, while some of these papers are relatively brief summaries of the published literature that easily and quickly can be consumed by students, others are exhaustive (and lengthy) discourses that may not be digestible in one sitting by even the most dedicated amphibole researcher. Finally, it appears that some geologists, probably with justification, love amphiboles so much that they would never have stopped writing had there been no publication deadline. The extremely short time between the preparation of papers and publication of Reviews in Mineralogy and the authors' intimate knowledge of their fields ensure that the papers reflect the very latest in research results. The rapid production of the "Reviews," however, inevitably results in a few errors that might be caught in a more leisurely publication process; the editors apologize for any such errors that are included in this volume. In addition, the sequence of presentation of papers reflects not only the editors' notions of order in the amphibole universe, but also somewhat the order in which papers were received. Although a collection of reviews of this sort cannot claim to give exhaustive coverage to all aspects of a topic, it is hoped that the papers presented here do review most of the important areas of active amphibole research. The papers have been split in a somewhat arbitrary fashion into Volume 9A, Amphiboles and Other Hydrous Pyriboles - Mineralogy, and Volume 9B, Amphiboles: Petrology and Experimental Phase Relations. Everyone is encouraged to purchase both volumes, however, because there is a hefty dose of petrology in 9A (witness the paper by Thompson, for example) and not a little mineralogy in 9B.

Description / Table of Contents: The development of modern isotope geochemistry is without doubt attributed to the efforts, begun in the 1930's and 1940's, of Harold Urey (Columbia University and the University of Chicago) and Alfred O.C. Nier (University of Minnesota). Urey provided the ideas, theoretical foundation, the drive, and the enthusiasm, but none of this would have made a major impact on Earth Sciences without the marvelous instrument developed by Nier and later modified and improved upon by Urey, Epstein, McKinney, and McCrea at the University of Chicago. Harold Urey's interest in isotope chemistry goes back to the late 1920's when he and I.I. Rabi returned from Europe and established themselves at Columbia to introduce the then brand-new concepts of quantum mechanics to students in the United States. Urey, of course, rapidly made an impact with his discovery of deuterium in 1932, the 'magical' year in which the neutron and positron were also discovered. Urey followed up his initial important discovery with many other experimental and theoretical contributions to isotope chemistry. During this period, Al Nier developed the most sophisticated mass spectrometer then available anywhere in the world, and made a series of surveys of the isotopic ratios of as many elements as he could. Through these studies, which were carried out mainly to obtain accurate atomic weights of the various elements, Nier and his co-workers clearly demonstrated that there were some fairly large variations in the isotopic ratios of the lighter elements. However, the first inkling of a true application to the Earth Sciences didn't come until 1946 when Urey presented his Royal Society of London lecture on 'The Thermodynamic Properties of Isotopic Substances' (now a classic paper referenced in most of the published papers on stable isotope geochemistry). With the information discovered by Nier and his co-workers that limestones were about 3 percent richer in 18O than ocean water, and with his calculations of the temperature coefficient for the isotope exchange reaction between CaCO3 and H2O, Urey realized that it might be possible to apply these concepts to determining the paleotemperatures of the oceans. Urey was never one to overlook important scientific problems, regardless of the field of scientific inquiry involved. In fact, he always admonished his students to 'work only on truly important problems!' Urey, then a Professor at the University of Chicago, decided to take a hard look into the experimental problems of developing an oxygen isotope paleotemperature scale. Although the necessary accuracy had not yet been attained, the design of the Nier instrument seemed to offer a good possibility, with suitable modifications, of making the kinds of precise measurements necessary for a sufficiently accurate determination of the 18O/16O ratios of both CaCO3 (limestone) and ocean water. Enormous efforts would be required to do this, because even if all the mass spectrometric problems could be solved, every analytical and experimental procedure would have to be invented from scratch, including the experimental calibration of the temperature coefficient of the equilibrium fractionation factor between calcite and water at low temperatures. To carry out this formidable study, Urey gathered around himself a remarkable group of students, postdoctoral fellows, and technicians, as well as his paleontologist colleague Heinz Lowenstam. With Sam Epstein at the center of the effort and acting as the principal driving force, the rest, as they say, 'is history.' The marvelous nature of the Nier-Urey mass spectrometer is attested to by the fact that the basic design is still being used, and that there are now hundreds of laboratories throughout the world where this kind of work is being done. For example, the original instrument built by Sam Epstein and Chuck McKinney at Caltech in 1953 is still in use and has to date produced more than 90,000 analyses. University, government, and industrial laboratories have found these instruments to be an indispensable tool. Enormous and widely varying application of the original concepts have been made throughout the whole panoply of Earth, Atmospheric, and Planetary Sciences. In the present volume we concentrate on an important sub-field of this effort. That particular sub-field was inaugurated in Urey's laboratories at Chicago by Peter Baertschi and Sol Silverman, who developed the fluorination technique for extracting oxygen from silicate rocks and minerals. This technique was later refined and improved in the late 1950's by Sam Epstein, Hugh Taylor, Bob Clayton, and Toshiko Mayeda, and has become the prime analytical method for studying the oxygen isotope composition of rocks and minerals. The original concepts and potentialities of high-temperature oxygen isotope geochemistry were developed by Samuel Epstein and his first student, Bob Clayton. Also, Bob Clayton, A.E.J. Engel, and Sam Epstein carried out the first application of these techniques to the study of ore deposits. The first useful experimental calibrations of the high-temperature oxygen isotope geothermometers quartz-calcite-magnetite-H2O were carried out initially by Bob Clayton, and later with his first student Jim O'Neil. In the meantime, Sam Epstein and his second student, Hugh Taylor, had begun a systematic study of 18O/16O variations in igneous and metamorphic rocks, and were the first to point out the regular order of 18O/16O fractionations among coexisting minerals, as well as their potential use as geochemical tracers of petrologic processes. During this period, a parallel development of sulfur isotope geochemistry was being carried out by Harry Thode and his group at McMaster University in Canada. They developed all the mass spectrometric and extraction techniques for this element, and also provided the theoretical and experimental foundation for understanding the equilibrium and kinetic isotope chemistry of sulfur. Starting from these beginnings, most of which took place either at the University of Chicago, Caltech, or McMaster University (but also with important input from Irving Friedman's laboratory at the U.S. Geological Survey, from Athol Rafter's laboratory in New Zealand, and from Columbia, Penn State, and the Vernadsky Institute in Moscow), there followed during the decades of the late 60's, 70's, and early 80's the development and maturing of the sub-field of high-temperature stable isotope geochemistry. This discipline is now recognized as an indispensable adjunct to all studies of igneous and metamorphic rocks and meteorites, particularly in cases where fluid-rock interactions are a major focus of the study. The twin sciences of ore deposits and the study of hydrothermal systems, both largely concerned with such fluid-rock interactions, have been profoundly and completely transformed. Virtually no issue of Economic Geology now appears without 3 or 4 papers dealing with stable isotope variations. No one writes papers on the development of the hydrosphere, hydrothermal alteration, ore deposits, melt-fluid-solid interactions, etc. without taking into account the ideas and concepts of stable isotope geochemistry. Although the present volume represents only a first effort to fill the need for a general survey of this sub-field for students and for workers in other disciplines, and although it is still obviously not completely comprehensive, it should give the interested student an idea of the present 'state-of-the-art' in the field. It should also provide an entry into the pertinent literature, as well as some understanding of the basic concepts and potential applications. Some thought went into the arrangement and choice of chapters for this volume. The first three chapters focus on the theory and experimental data base for equilibrium, disequilibrium, and kinetics of stable isotope exchange reactions among geologically important minerals and fluids. The fourth chapter discusses the primordial oxygen isotope variations in the solar system prior to formation of the Earth, along with a discussion of isotopic anomalies in meteorites. The fifth chapter discusses isotopic variations in the Earth's mantle and the sixth chapter reviews the variations in the isotopic compositions of natural waters on our planet. In Chapters 7, 8, 9 and 10, these isotopic constraints and concepts are applied to various facets of the origin and evolution of igneous rocks, bringing in much material on radiogenic isotopes as well, because these problems require a multi-dimensional attack for their solution. In Chapters 11 and 12, the problems of hydrothermal alteration by meteoric waters and ocean water are considered, together with discussions of the physics and chemistry of hydrothermal systems and the 18O/16O history of ocean water. Finally, in Chapters 13 and 14, these concepts are applied to problems of metamorphic petrology and ore deposits, particularly with respect to the origins of the fluids involved in those processes. It seems clear to us (the editors) that this sub-field of stable isotope geochemistry can only grow and become even more pertinent and dominant in the future. One of the most fruitful areas to pursue is the development of microanalytical techniques so that isotopic analyses can be accurately determined on ever smaller and smaller samples. Such techniques would open up vast new territories for exploitation in every aspect of stable isotope geochemistry. Exciting new methods have recently been developed whereby a few micromoles of CO2 and SO2 can be liberated for isotopic analyses from polished sections of carbonates and sulfides by laser impact. There are also new developments in mass spectrometry like RIMS (resonance ionization mass spectrometry), Fourier transform mass spectrometry and the ion microprobe that offer considerable promise for these purposes. Stable isotope analyses of large-sized samples (even those that must be obtained by reactions of silicates with fluorinating reagents) have now become so routine and so rapid that they represent an 'easy' way to gather a lot of data in a hurry. In fact 'mass production' techniques for rapidly processing samples are starting to become prevalent, so much so that one of the biggest worries in the future may be that a flood of data will overwhelm us and outstrip our abilities to carefully define and carry out sampling strategies, as well as to think carefully and in depth about the data. An organized system of handling the D/H, 13C/12C, 15N/14N, 18O/16O, and 34S/32S data, and/or a computerized data base that could be manipulated and added to would be a useful path to follow in the future, particularly if it were integrated into a larger data base containing radiogenic isotope data, major- and trace-element analyses, electron microprobe data, x-ray crystallographic data, and petrographic data (particularly modal data on mineral abundances in the rocks).

Description / Table of Contents: Fourteen years ago the American Geological Institute (AGI) sponsored a Short Course on Chain Silicates. At that time, a substantial amount was known about the crystal chemistry and phase equilibria of pyroxenes, and this knowledge has been of fundamental importance in guiding research on pyroxenes in the years following the AGI Short Course. In 1966, single-crystal x-ray diffractometry was well advanced and good crystal structure refinements were available for jadeite, spodumene, hypersthene, c1inoferrosi1ite, orthoferrosi1ite, and omphacite; the distinction between the c1inoenstatite (pigeonite) and diopside (augite) structures had been established, and the structure of protoenstatite was known, although some doubt existed about the space group of protoenstatite. Phase diagrams for several joins in the pyroxene quadrilateral had been published, but often equilibrium had not been established in the experiments and not enough was known about the effects of pressure, oxygen fugacity, and non-quad elements such as aluminum on the phase equilibria. Also, inversion relations of Ca-poor pyroxenes were not well understood, and petrologists had just become aware of the effect of stress on orthoto-clinopyroxene transitions. In 1966 few of us would have guessed how-much new data and new analytical results would become available in the next fourteen years. Although most, if not all, of the important instrumental techniques we use today were available in 1966, the truly spectacular development and application of these techniques did not take place until the Apollo 11 samples and the attendant funding from NASA became available. Pyroxene research has profited immensely from the application of Mossbauer, optical, and infrared spectroscopy, x-ray and electron diffraction, transmission electron microscopy, automated electron microprobes, and digital computers. During these years experimentalists extended the capabilities of their equipment to examine the behavior of pyroxenes under conditions of controlled oxygen fugacity, pressure, and temperature, conditions more nearly like those under which pyroxenes crystallize in natural systems. Looking back, one remembers the excitement of seeing the first lunar samples. We were surprised at the large amounts of pigeonite and the quality of crystals unaffected by water or the presence of sodium. The influence of the lunar program on pyroxene research was extraordinary, and our understanding of pyroxene relationships in terrestrial occurrences benefited tremendously because the lunar pyroxenes provided a basis for comparison with the more complex chemical and structural behavior of terrestrial environments. Probably the most impressive development in the early lunar sample studies was the application of transmission electron microscopy to mineralogy. We were able to see exsolution and other textural features in crystals that looked homogeneous in the optical microscope, thus opening up a wide range of research possibilities that had not existed previously. Advanced crystal growth experiments, detailed phase equilibria, x-ray diffraction at high temperatures, and statistical analyses of microprobe data were all applied to lunar pyroxenes and then extended to terrestrial and meteorite investigations, making this period one of the most productive in history. In the compilation of this volume, an attempt has been made to review the essential aspects of pyroxene research, primarily those of the last ten or fifteen years. Although the largest fraction of pyroxene research has been performed in the U.S.A., significant advances have been made in other countries, particularly in Europe, Japan, Canada, and Australia, with interest and activity in these countries probably growing at a faster rate than in the United States. Recently, Deer, Howie and Zussman (DHZ) published a second edition of their volume in the Rock-Forming Minerals series, Single-Chain Silicates, Vol. 2A (John Wiley, New York, 1978). The present volume is intended to be complementary to DHZ and to provide material covered lightly or not at all in DHZ, such as electron microscopy, spectroscopy, and detailed thermodynamic treatments. However, because the range of pyroxene research has grown so much in recent years, there still are important areas not covered comprehensively in either of these volumes. Some of these areas are kinetics, diffusion, crystal defects, deformation, and nonsilicate pyroxene crystal chemistry. Because of these omissions and because this volume is intended for use with the MSA Short Course on Pyroxenes to be held at Emory University in conjunction with the November, 1980 meeting of the Society, a Symposium on Pyroxenes was organized by J. Stephen Huebner for the meeting that is designed to present the latest research results on several different topics, including those above. With DHZ, this volume, and publications from the Symposium, the student of pyroxenes should be well-equipped to advance our knowledge of pyroxenes in the decades ahead.

Description / Table of Contents: In 1978 the Short Course Committee decided to forego activities because the annual meeting of the M.S.A. was held together with the Mineralogical Association of Canada, who sponsored a Short Course in Uranium Deposits and published a book by the same title. A number of mineralogists expressed regret at the potential loss of momentum in MSA's production of this series and encouraged several authors of this book to press on with their idea of publishing Volume 5 -- Orthosilicates. Work was begun in 1978; however, without the pressure of a deadline associated with presenting the material to students of a short course at the annual meeting, procrastination set in and the first edition of this volume was not completed until September 1980 (with the exception of Chapters 1 and 2 which were submitted in their present form in 1978). In the meantime Volume 6, Marine Minerals, appeared in time for the annual meeting of the Society and a Short Course in San Diego in November 1979. In 1980 the Council of the MSA changed the name of the published volumes from SHORT COURSE NOTES to REVIEWS in MINERALOGY in order to more aptly describe the material contained in this now highly successful series. The First Edition of Orthosilicates was the first volume to appear under the REVIEWS banner. This is the Second Edition of Orthosilicates. It contains an updating and minor revisions of Chapters 3 through 10 (only) and two new chapters originally intended for the First Edition. The intent of this volume is to emphasize the crystal chemistry and related physical properties of the major rock-forming orthosilicates. Though in some chapters more attention is given to phase equilibria and paragenesis than in others, these are for the most part cursorily treated with references to the more important papers and to review articles (also see Deer, Howie and Zussman, 1962, Rock-forming Minerals, Vol. 1, Ortho- and Ring Silicates). Some confusion will inevitably result from the definition of the term used as the title for this volume. In Chapter 1 Liebau (p. 14) says that "silicates containing (SiO4) groups should be called monosilicates rather than orthosilicates or nesosilicates." The editor chose not to adopt Liebau's terminology for the title, because monosilicate is not yet widely accepted (although it might well be). To set manageable boundaries for the scope of the First Edition of Orthosilicates, an editorial option was exercised in rejecting as "orthosilicates" those minerals with both (SiO4) tetrahedra and (Si2O7) groups (zoisite, epidote, vesuvianite, etc.), as well as those with (SiO4) tetrahedra that are polymerized to other tetrahedra by sharing corners with (BeO4), (BO4), (A1O4), (ZnO4), etc. However, as mentioned in the Foreword, Chapter 13 has been added to the Second Edition to correct for the latter omission. Chapter 12 contains very brief descriptions of the paragenesis and crystal chemistry of many orthosilicates that fit the description stated in the Preface (p. iv). It may be used as an index, because all orthosilicates are listed alphabetically, including those discussed in Chapters 2 through 11.

Description / Table of Contents: Geochemistry is a science that is based on an understanding of chemical processes in the earth. One of the principal tools available to the chemist for understanding systems at equilibrium is thermodynamics. The awareness and application of thermodynamic techniques has increased at a very fast pace in geosciences; in fact, one may be so bold as to say that thermodynamics in geology has reached the "mature" stage, although much future thermodynamic research is certainly needed. However, the natural processes in the earth are often sluggish enough that a particular system may not reach equilibrium. This observation is being supported constantly by new experimental and field data available to the geochemist e.g. the non-applicability of the phase rule in some assemblages, the compositional inhomogeneities of mineral grains, the partial reaction rims surrounding original minerals, the lack of isotopic equilibration or the absence of minerals (e.g. dolomite), which should be present according to thermodynamics. The need to apply kinetics has produced a large number of papers dealing with kinetics in geochemistry. As an initial response to this growing field, a conference on geochemical transport and kinetics was conducted at Airlie House, VA, in 1973, sponsored by the Carnegie Institution of Washington. The papers there dealt with several kinetic topics including diffusion, exsolution, metasomatism and metamorphic layering. Since 1973 the number of kinetic papers has continued to increase greatly. Therefore, the time is ripe for a Short Course in Kinetics, which brings together the fundamentals needed to explain field observations using kinetic data. It is hoped that this book may serve, not only as a reference for researchers dealing with the rates of geochemical processes, but also as a text in courses on geochemical kinetics. One of us has found this need of a text in teaching a graduate course on geochemical kinetics at Harvard and at Penn State during the past several years. Finally, it is our hope that the book may itself further even more research into the rates of geochemical processes and into the quantification of geochemical observations. The book is organized with a rough temperature gradient in mind, i.e. low temperature kinetics at the beginning and igneous kinetics at the end (no prejudices are intended with this scheme!). However, the topics in each chapter are general enough that they can be applied often to any geochemical domain: sedimentary, metamorphic or igneous. The theory of kinetics operates at two complementary levels: the phenomenological and the atomistic. The former relies on macroscopic variables (e.g. temperature or concentrations) to describe the rates of reactions or the rates of transport; the latter relates the rates to the basic forces operating between the particular atomic or molecular species of any system. This book deals with both descriptions of the kinetics of geochemical processes. Chapter one sets the framework for the phenomenological theory of reaction rates. If any geochemical reaction is to be described quantitatively, the rate law must be experimentally obtained in a kinetically sound manner and the reaction mechanism must be understood. This applies to heterogeneous fluid-rock reactions such as those occurring during metamorphism, hydrothermal alteration or weathering as well as to homogeneous reactions. Chapter 2 extends the theory to the global kinetics of geochemical cycles. This enables the kinetic concepts of stability and feedback to be applied to the cycling of elements in the many reservoirs of the earth. Chapter 3 applies the phenomenological treatment of chapter 1 to diagenesis and weathering. The rate of dissolution of minerals as well as the chemical evolution of pore waters are discussed. The atomistic basis of rates of reaction, transition state theory, is introduced in Chapter 4. Transition state theory can be applied to relate the rate constants of geochemical reactions to the atomic processes taking place. This includes not only homogeneous reactions but also reactions that occur at the surface of minerals. Chapter 5 discusses the theory of irreversible thermodynamics and its application to petrology. The use of the second law of thermodynamics along with the expressions for the rate of entropy production in a system have been used successfully since 1935 to describe kinetic phenomena. The chapter applies the concepts to the growth of minerals during metamorphism as well as to the formation of differentiated layers (banding) in petrology. Chapter 6 describes the phenomenological theory of diffusion both in aqueous solutions and in minerals. In particular, the multicomponent nature of diffusion and its consequence in natural systems is elaborated. Chapter 7 provides the atomistic basis for the rates of reactions in minerals. Understanding of the rates of diffusion, conduction, order-disorder reactions or exsolution in minerals depends on proper description of the defects in the various mineral structures. Chapter 8 provides the kinetic theory of crystal nucleation and growth. While many of the concepts in the chapter can be applied to aqueous systems, the emphasis is on igneous processes occurring during crystallization of a melt. To fully understand both the mineral composition as well as the texture of igneous rocks, the processes whereby new crystals form and grow must be quantified by using kinetic theory. Due to space and time limitations (kinetics!) some topics have not been covered in detail. In particular, the mathematical solution of diffusion or conduction equations is discussed very well by Crank in his book, Mathematics of Diffusion, and so is not covered to a great extent here. The treatment of fluid flow (e.g. convection) is also not covered in the text.

Description / Table of Contents: Although it includes some discussion of chemically complex reactions and the chemographic relationships among amphiboles and other rockforming minerals, most of Volume 9A of Reviews in Mineralogy treats amphiboles and other hydrous pyriboles as isolated systems. In contrast, Volume 9B is dedicated more to an exploration of the social life of amphiboles and the amphibole personality in real rocks and in the experimental petrology laboratory. The chemical complexity of amphibole, which Robinson et al., refer to as "a mineralogical shark in a sea of unsuspecting elements," permits amphiboles to occur in a very wide variety of rock types, under a large range of pressure and temperature conditions, and in association with an impressive number of other minerals. The description of amphibole petrology and of petrologists' attempts to understand amphibole phase relations are therefore not simple matters, as the length of this volume suggests. Although they do not cover every type of amphibole occurrence, it is hoped that the papers in this volume will provide the amphibole student and researcher with an up-to-date summary of the most important aspects of amphibole petrology. Volume 9B, Amphiboles: Petrology and Experimental Phase Relations, was begun in 1981 in preparation for the Short Course on Amphiboles and Other Hydrous Pyriboles presented at Erlanger, Kentucky, October 29 - November 1, 1981, prior to the annual meetings of the Geological Society of America and associated societies. Unfortunately, only the first chapter was in manuscript form at the time of the short course, and publication was delayed by one year.

Description / Table of Contents: In October 1975 a Short Course on Feldspar Mineralogy was held at the Hotel Utah, Salt Lake City, in conjunction with the annual meetings of the Mineralogical Society of America. Richard A. Yund, David B. Stewart, Joseph V. Smith and Paul R. Ribbe presented workshops on x-ray single-crystal and powder diffraction methods and electron optical techniques as applied to the study of feldspars and presented eight lectures, the substance of which became the nine chapters of the first edition of Feldspar Mineralogy. That book was published by the Mineralogical Society as the second volume of its series entitled Short Course Notes. In 1980 the MSA renamed the series Reviews in Mineralogy to more accurately reflect the scope and contents of the volumes, some of which -- including Volume 5 (1st and 2nd editions), this volume and a forthcoming one on fluid inclusions --were written without presentation at a short course. It will be noted by readers experienced with feldspars that there are many new ideas appearing in Chapters 3, 4 and 5 that have neither received scrutiny by review (other than ourselves) nor survived practical tests of time in the research community. There is some danger in this, but the editor decided the greater risk was to produce a review volume soon to be outdated. Inevitably, given the different goals of individual authors in their assigned topics, some repetition of material has occurred, although usually with quite different emphases. Chapters 1, 2, 9 and 10, in which plagioclase structures and diffraction patterns and their Al,Si distributions, phase equilibria and exsolution textures are featured, are notable in this regard. The editor has attempted to cross-reference these and as many other subjects throughout the volume as feasible. This is a luxury not afforded in other books of this series produced with a short course deadline, and it, together with the detailed Table of Contents, compensates to some degree for the lack of an index. Throughout this book repeated references are made to Smith (1974a,b); these are Volumes 1 and 2 of Feldspar Minerals, an encyclopedic work written by Joseph V. Smith and published by Springer-Verlag. We are particularly indebted to Drs. Konrad Springer and H. Wiebking for permission to reproduce many figures free of charge. The editor (and hopefully this volume) benefitted greatly from numerous stimulating discussions with David B. Stewart, some of which reached a high pitch, none of which came to blows, and several of which produced some palpable scientific progress. Stewart read and criticized many of the chapters. The authors are grateful to numerous individual scientists for figures, for data in advance of publication, and for encouragement and correction.

Description / Table of Contents: When Van't Hoff calculated the effect of solution composition on the gypsum-anhydrite transition a century ago, he solved a significant geochemical problem (Hardie, 1967). Other well known examples of the early use of chemical thermodynamics in geology are Bowen's calculations of the plagioclase melting loop and the diopside-anorthite eutectic (Bowen, 1913, 1928). Except for a few specialists, however, these techniques were largely ignored by earth scientists during the first half of the 20th century. The situation changed dramatically by the 1950's when more and better thermodynamic data on geologic materials became available, and when thermodynamic arguments of increasing sophistication began to permeate the petrologic and geochemical literature. This rejuvenation was spearheaded by D.S. Korzhinskii, H. Ramberg, J.B. Thompson, J. Verhoogen and others. Today a graduating petrologist or geochemist can be expected to have a thorough grounding in geological thermodynamics. Rapid intellectual growth in a field brings with it the difficulty of keeping abreast of parallel and diverging specialties. In order to alleviate this problem, we asked a group of active researchers to contribute up-to-date summaries relating to their specialties in the thermodynamic modeling of geological materials, in particular minerals, fluids and melts. Whereas each of these topics could fill a book, by covering the whole range we hope to emphasize similarities as much as differences in the treatment of various materials. For instance, there are useful parallels to be noted between Margules parameters and Pitzer coefficients. The emphasis here is on modeling, after the required data have been collected, and the approach ranges form theoretical to empirical. We deliberately imposed few restrictions on the authors. Some chose to interpret modeling in the rigorous thermodynamic sense, while others approached their topics from more general geochemical viewpoints. We hope that any lack of unity and balance is compensated for by a collection of lively and idiosyncratic essays in which students and professionals will find new ideas and helpful hints. If the selection appears tilted towards fluids, it is because other recent summaries have emphasized minerals and melts. The editors and authors of this volume presented a short course, entitled "Thermodynamic Modeling of Geological Materials: Minerals, Fluids amd Melts," October 22-25, 1987, at the Wickenburg Inn near Phoenix, Arizona.