PASCAL RICHET, GRANT S. HENDERSON, and DANIEL R. NEUVILLE, Guest Editors
Thermodynamics in a Nutshell
Processes in the Moist Atmosphere
Effects of Ocean Acidifi cation
Water–Rock Interaction
Equilibrium in Metamorphic Rocks
Magma Phase Equilibria
Modeling Earth’s Interior
Thermodynamics of Earth Systems
October 2010Volume 6, Number 5
ISSN 1811-5209
Thermodynamics of Earth SystemsGuest Editors: Pascal Richet, Grant S. Henderson, and Daniel R. Neuville
Depar tmentsEditorial – Thanks, Dr. Gibbs . . . . . . . . . . . . . . . . . . . . . . . 275From the Editors – Elements’ Impact Factor 3.569 . . . . . . . . 276Letter to the Editors – Basic Research in U.S. Universities . . 276 The Elements Toolkit – Welcome to the Toolkit . . . . . . . . . 277People in the News – Bau and Koschinsky, “Elements 5” speakers . . . . . . . . . . . . . . . . . . . . . . . . . . . . 278 Meet the Authors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 284Teaching MGP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 326Society News
The Meteoritical Society . . . . . . . . . . . . . . . . . . . . . . . . . . . .327The Clay Minerals Society . . . . . . . . . . . . . . . . . . . . . . . . . .328International Association of Geoanalysts . . . . . . . . . . . . . . .329 Mineralogical Society of Great Britain and Ireland . . . . . . . .330European Mineralogical Union . . . . . . . . . . . . . . . . . . . . . . . 331European Association of Geochemistry . . . . . . . . . . . . . . . .332International Association of GeoChemistry . . . . . . . . . . . . . . 333Deutsche Mineralogische Gesellschaft . . . . . . . . . . . . . . . . .334Sociedad Española de Mineralogía . . . . . . . . . . . . . . . . . . . .335Mineralogical Society of America . . . . . . . . . . . . . . . . . . . . .336 Geochemical Society . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .338 Mineralogical Association of Canada . . . . . . . . . . . . . . . . . .340International Mineralogical Association . . . . . . . . . . . . . . . .342Swiss Society of Mineralogy and Petrology . . . . . . . . . . . . . .343
Meeting Reports – IMA 2010, 11th IPS, AquaTRAIN . . . . . . . 344 Mineral Matters – Census of Mineral Species . . . . . . . . . . . 346Book Reviews – Cosmochemistry, RIMG 71. . . . . . . . . . . . . . 347Calendar . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 349 Parting Shots – Strange Attractors . . . . . . . . . . . . . . . . . . . 351Advertisers in This Issue . . . . . . . . . . . . . . . . . . . . . . . . 352
287
293
299
305
309
315
321
ABOUT THE COVER:
From the atmosphere to the mantle and
core, Earth systems are strictly controlled by
thermodynamic principles. Hurricanes, such as Katrina
shown on the front cover, result from strong interactions between the
ocean and atmosphere and are powered by the
thermal energy stored in warm oceanic waters.
AVHRR (Advanced Very High Resolution Radiometer)
3-channel color composite daytime image showing
the eye of hurricane Katrina on August 28, 2005, just
before it hit New Orleans. COURTESY OF STEVEN BABIN
AND RAY STERNER OF THE JOHNS HOPKINS UNIVERSITY APPLIED
PHYSICS LABORATORY
Thermodynamics: The Oldest Branch of Earth Sciences?Pascal Richet, Grant S. Henderson, and Daniel R. Neuville
Thermodynamic Processes in the Moist AtmosphereAndreas Bott
Use of Thermodynamics in Examining the Effects of Ocean Acidifi cationFrank J. Millero and Benjamin R. DiTrolio
Water–Rock Interaction Processes Seen through ThermodynamicsPierpaolo Zuddas
Using Equilibrium Thermodynamics to Understand Metamorphism and Metamorphic Rocks Roger Powell and Tim Holland
Thermodynamics of Phase Equilibria in MagmaPascal Richet and Giulio Ottonello
Perspective: On Being a Student of ThermodynamicsReid F. Cooper
282
Thermodynamic Modeling of the Earth’s InteriorSurendra K. Saxena
273
Elements is published jointly by the Mineralogical Society of America, the Mineralogical Society of Great Britain and Ireland, the Mineralogical Association of Canada, the Geochemical Society, The Clay Minerals Society, the European Association of Geochemistry, the Inter national Association of GeoChemistry, the Société Française de Minéralogie et de Cristallographie, the Association of Applied Geochemists, the Deutsche Mineralogische Gesellschaft, the Società Italiana di Mineralogia e Petrologia, the International Association of Geoanalysts, the Polskie Towarzystwo Mineralogiczne (Mineralogical Society of Poland), the Sociedad Española de Mineralogía, the Swiss Society of Mineralogy and Petrology, and the Meteoritical Society. It is provided as a benefi t to members of these societies.
Elements is published six times a year. Individuals are encouraged to join any one of the partici-pating societies to receive Elements. Institutional subscribers to any of the following journals —American Mineralogist, Clay Minerals, Clays and Clay Minerals, Mineralogical Magazine, and The Canadian Miner alogist—also receive Elements as part of their 2010 subscription. Institu tional subscriptions are available for US$160 (US$175 non-US addresses) a year in 2010. Contact the managing editor ([email protected]) for information.
Copyright 2010 by the Mineralogical Society of America
All rights reserved. Reproduction in any form, including translation to other languages, or by any means—graphic, electronic or mechanical, including photocopying or information storage and retrieval systems—without written permission from the copyright holder is strictly prohibited.
Publications mail agreement no. 40037944
Return undeliverable Canadian addresses to:PO Box 503 RPO West Beaver Creek Richmond Hill, ON L4B 4R6
Printed in Canada ISSN 1811-5209 (print)ISSN 1811-5217 (online)
www.elementsmagazine.org
Volume 6, Number 5 • October 2010
The Mineralogical Society of America is composed of indivi duals interested in mineralogy, crystallography, petrology, and geochemistry. Founded in 1919, the Society promotes,
through education and research, the under-standing and application of mineralogy by industry, universities, government, and the public. Membership benefi ts include special subscription rates for American Mineralogist as well as other journals, a 25% discount on Reviews in Mineralogy & Geochemistry series and Mono graphs, Elements, reduced registration fees for MSA meetings and short courses, and participation in a society that supports the many facets of mineralogy.
SOCIETY NEWS EDITOR: Andrea Koziol ([email protected])
Mineralogical Society of America 3635 Concorde Pkwy Ste 500Chantilly, VA 20151-1110, USATel.: 703-652-9950; fax: [email protected]
The Mineralogical Society of Great Britain and Ireland is an inter-national society for all those working in the mineral sciences. The Society aims to advance the
knowledge of the science of miner alogy and its application to other subjects, including crystallography, geochemistry, petrology, environmental science and economic geology. The Society furthers its aims through scientifi c meetings and the publica-tion of scientifi c journals, books and mono-graphs. The Society publishes Mineralogical Magazine and Clay Minerals. Students receive the fi rst year of membership free of charge. All members receive Elements.
SOCIETY NEWS EDITOR: Kevin Murphy ([email protected])
The Mineralogical Society12 Baylis Mews, Amyand Park RoadTwickenham, Middlesex TW1 3HQ, UKTel.: +44 (0)20 8891 6600 Fax: +44 (0)20 8891 [email protected]
The Mineralogical Association of Canada was incorpor ated in 1955 to promote and advance the knowledge of miner-alogy and the related disci-plines of crystal lography,
petrol ogy, geochemistry, and economic geology. Any person engaged or inter ested in these fi elds may become a member of the Association. Membership benefi ts include a subscrip tion to Elements, reduced cost for sub scribing to The Canadian Mineralogist, a 20% discount on short course volumes and special publica tions, and a discount on the registration fee for annual meetings.
SOCIETY NEWS EDITOR: Pierrette Tremblay ([email protected])
Mineralogical Association of Canada490, de la Couronne Québec, QC G1K 9A9, Canada Tel.: 418-653-0333; fax: 418-653-0777offi [email protected]
The Clay Minerals Society (CMS) began as the Clay Minerals Committee of the US National Academy of Sciences – National Research Council in 1952. In 1962, the CMS was
incorporated with the primary purpose of stimu lating research and disseminating information relating to all aspects of clay science and technology. The CMS holds an annual meeting, workshop, and fi eld trips, and publishes Clays and Clay Minerals and the CMS Workshop Lectures series. Member-ship benefi ts include reduced registration fees to the annual meeting, discounts on the CMS Workshop Lectures, and Elements.
SOCIETY NEWS EDITOR: Jeffery Greathouse ([email protected])
The Clay Minerals Society 3635 Concorde Pkwy Ste 500Chantilly, VA 20151-1125, USATel.: 703-652-9960; fax: [email protected] www.clays.org
The Geochemical Society (GS) is an international organization founded in 1955 for students and scientists involved in the practice, study and teaching of geochemistry. Our
programs include co-hosting the annual Goldschmidt ConferenceTM, editorial over-sight of Geochimica et Cosmochimica Acta (GCA), supporting geochemical symposia through our Meeting Assistance Program, and supporting student development through our Student Travel Grant Program. GS annually recognizes excellence in geochemistry through its medals, lectures and awards. Members receive a subscription to Elements, special member rates for GCA and G-cubed, and publication and confer-ence discounts.
SOCIETY NEWS EDITOR: Seth Davis ([email protected])
Geochemical SocietyWashington UniversityEarth & Planetary SciencesOne Brookings Drive, Campus Box #1169 St. Louis, MO 63130-4899, USATel.: 314-935-4131; fax: 314-935-4121 gsoffi [email protected] GS online at www.geochemsoc.org
The European Association of Geochemistry was founded in 1985 to promote geochemical research and study in Europe. It is now recognized as the premiere geochemical organi zation
in Europe encouraging interaction between geoche mists and researchers in asso cia ted fi elds, and promoting research and teaching in the public and private sectors.
SOCIETY NEWS EDITOR: Liane G. Benning ([email protected])
Membership information: www.eag.eu.com/membership
The International Association of GeoChemistry (IAGC) has been a pre-eminent inter na-tional geo chemical organi-zation for over 40 years. Its principal objectives are to
foster cooperation in the advancement of applied geochemistry by sponsoring specialist scientifi c symposia and the activities organized by its working groups and by support ing its journal, Applied Geochemistry. The adminis tra-tion and activities of IAGC are conducted by its Council, comprising an Executive and ten ordinary members. Day-to-day administration is performed through the IAGC business offi ce.
SOCIETY NEWS EDITOR: Chris Gardner ([email protected])
IAGC Business Offi ce275 Mendenhall Laboratory125 South Oval Mall Columbus, OH 43210, USATel.: 614-688-7400; fax: 614-292-7688www.iagc.ca
The Société Française de Minéralogie et de Cristallographie, the French Mineralogy and Crystallography Society, was founded on March 21, 1878. The purpose of the
Society is to promote mineralogy and crystallography. Member ship benefi ts include the “bulletin de liaison” (in French), the European Journal of Miner alogy, Elements, and reduced registration fees for SFMC meetings.
SOCIETY NEWS EDITOR: Anne-Line Auzende ([email protected])
SFMCCampus Boucicaut, Bâtiment 7 140 rue de Lourmel75015 Paris, Francewww.sfmc-fr.org
The Association of Applied Geochemists is an international organiza-tion founded in 1970 that specializes in the fi eld of applied geochemistry. It aims to advance the science
of geochem istry as it relates to exploration and the environment, further the common interests of exploration geochemists, facili-tate the acquisition and distribution of scientifi c knowledge, promote the exchange of information, and encourage research and development. AAG membership includes the AAG journal, Geochemistry: Exploration, Environment, Analysis; the AAG newsletter, EXPLORE; and Elements.
SOCIETY NEWS EDITOR: David Lentz ([email protected])
Association of Applied Geochemists P.O. Box 26099 Nepean, ON K2H 9R0, Canada Tel.: 613-828-0199; fax: 613-828-9288 offi [email protected] www.appliedgeochemists.org
The Deutsche Mineralogische Gesellschaft (German Mineralogical Society) was founded in 1908 to “promote miner alogy and all its subdisciplines in
teaching and research as well as the personal relationships among all members.” Its great tradition is refl ected in the list of honorary fellows, who include M. v. Laue, G. v. Tschermak, P. Eskola, C.W. Correns, P. Ramdohr, and H. Strunz. Today, the Society especially tries to support young researchers, e.g. to attend conferences and short courses. Membership benefi ts include the European Journal of Mineralogy, the DMG Forum, GMit, and Elements.
SOCIETY NEWS EDITOR: Michael Burchard ([email protected])
Deutsche Mineralogische Gesellschaft [email protected]
The Società Italiana di Mineralogia e Petrologia (Italian Society of Mineralogy and Petro-logy), established in 1940, is the national body repre-senting all researchers deal-
ing with mineralogy, petrology, and related disciplines. Membership benefi ts include receiving the European Journal of Mineralogy, Plinius, and Elements, and a reduced registra-tion fee for the annual meeting.
SOCIETY NEWS EDITOR: Marco Pasero ([email protected])
Società Italiana di Mineralogia e Petrologia Dip. di Scienze della TerraUniversità di Pisa, Via S. Maria 53I-56126 Pisa, ItalyTel.: +39 050 2215704 Fax: +39 050 [email protected]
The International Asso-ciation of Geoanalysts is a worldwide organization supporting the profes sional interests of those involved in the analysis of geological and environmental mate-
rials. Activities include the management of profi ciency testing programmes for bulk rock and micro-analytical methods, the production and certifi cation of reference materials and the publication of the Association’s journal, Geostandards and Geoanalytical Research.
SOCIETY NEWS EDITOR: Michael Wiedenbeck ([email protected])
International Association of Geoanalysts 13 Belvedere CloseKeyworth, Nottingham NG12 5JFUnited Kingdomhttp://geoanalyst.org
The Polskie Towarzystwo Mineral-ogiczne (Mineralogical Society of Poland), founded in 1969, draws together professionals and amateurs interested in mineralogy,
crystal lography, petrology, geochemistry, and economic geology. The Society promotes links between mineralogical science and education and technology through annual conferences, fi eld trips, invited lectures, and publish ing. Membership benefi ts include subscriptions to Mineralogia and Elements.
SOCIETY NEWS EDITOR: Zbigniew Sawłowicz ([email protected])
Mineralogical Society of PolandAl. Mickiewicza 30, 30-059 Kraków, PolandTel./fax: +48 12 [email protected] www.ptmin.agh.edu.pl
The Sociedad Española de Mineralogía (Spanish Mineralogical Society) was founded in 1975 to promote research in mineralogy, petrology, and geochem-istry. The Society organizes
annual conferences and furthers the training of young researchers via seminars and special publications. The SEM Bulletin published scientifi c papers from 1978 to 2003, the year the Society joined the Euro-pean Journal of Mineralogy and launched Macla, a new journal containing scientifi c news, abstracts, and reviews. Membership benefi ts include receiving the European Journal of Mineralogy, Macla, and Elements.
SOCIETY NEWS EDITOR: Jordi Delgado ([email protected])
Sociedad Española de Mineralogí[email protected]/sem
The Swiss Society of Mineralogy and Petrology was founded in 1924 by professionals from academia and industry and by amateurs to promote knowledge in the fi elds of
mineralogy, petrology and geochemistry and to disseminate it to the scientifi c and public communities. The Society coorganizes the annual Swiss Geoscience Meeting and publishes the Swiss Journal of Geosciences jointly with the national geological and paleontological societies.
SOCIETY NEWS EDITOR: Urs Schaltegger ([email protected])
Swiss Society of Mineralogy and PetrologyUniversité de GenèveSection des Sciences de la Terre et de l’Environnement13, rue des Maraîchers1205 Genève, SwitzerlandTel.: +41 22 379 66 24; fax: +41 22 379 32 10http://ssmp.scnatweb.ch
The Meteoritical Society is an international organi-zation founded in 1933 for scientists, collectors, and educators to advance the study of meteorites and other extraterrestrial mate-
rials and their parent asteroids, comets, and planets. Members receive our journal, Mete-oritics and Planetary Science, reduced rates for Geochimica et Cosmochimica Acta, which we cosponsor, the Meteoritical Bulletin, and Elements. We organize annual meetings, workshops, and fi eld trips, and support young planetary scientists worldwide. Through our medals and awards, we recog-nize excellence in meteoritics and allied fi elds.
SOCIETY NEWS EDITOR: Cari Corrigan ([email protected])
http://meteoriticalsociety.org
Affi liated Societies The International Mineralogical Association, the European Mineralogical Union, and the International Association for the Study of Clays are
affi liated societies of Elements. The affi liated status is reserved for those organizations that serve as an “umbrella” for other groups in the fi elds of min er alogy, geochemistry, and petrology, but that do not themselves have a membership base.
ELEMENTS AUGUST 2010274
PARTICIPATING SOCIETIES
When I was fi rst exposed to thermodynamics as an undergraduate, I felt like the kid who opened the balloon to see how it works: I wasn’t left with much. It seemed like smoke and mirrors. Why would anyone envision such an intangible and non-intuitive way to understand chemical reac-tions? And, who came up with this approach in the fi rst place?
I’ve since learned to appreciate, even delight in, the elegance of thermodynamics. We all have J. Willard Gibbs to thank. Nowadays, his name is almost uni-versally recognized by scientists and engineers. Even the fi rst letter of his surname is forever memorial-ized as the symbol for Gibbs free energy (the U.S. National Bureau of Standards uses F rather than G, but the latter is recommended by the International Union of Pure and Applied Chemistry). His visage even graces a U.S. postage stamp, a rare honor for a scientist. During his lifetime, though, Gibbs’s genius mostly went unacknowledged, especially in his native America.
Gibbs was educated at Yale University, and in 1863 received the fi rst PhD in engineering awarded in the United States. After spending a year each in Paris, Berlin, and Heidelberg, he returned to Yale as Professor of Mathematical Physics, a position that initially carried no salary. In 1880 Johns Hopkins University offered Gibbs a faculty posi-tion paying $3000. Yale countered with a $2000 salary, which proved to be enough to retain him.
Several years before he started getting a regular paycheck, Gibbs wrote a series of papers that were eventually published together in a monograph entitled On the Equilibrium of Heterogeneous Substances. In hindsight, this work is viewed as one of the greatest scientifi c achievements of the nineteenth century, and it has garnered Gibbs the title of founder of chemical thermodynamics. Despite publication of this book, some time elapsed before the signifi cance of Gibbs’s work was recognized, because its mathematical rigor made it diffi cult reading for experimental chem-ists, who could most readily use its approach. A few leading European chemists noticed, notably James Clerk Maxwell, Wilhelm Ostwald, and Henry Louis le Chatelier, but Gibbs’s revolu-tionary contribution was not widely appreciated until two decades after his death, with the 1923
THANKS, DR. GIBBS
publication of Lewis and Randall’s classic chem-istry text, Thermodynamics and the Free Energy of Chemical Substances.
Gibbs’ thermodynamics fi rst found application in physics, then chemistry, and later engineering. Its utility in geology had to wait until enough data on the thermodynamic properties of com-positionally complex minerals, melts, and fl uids
became available. The phase equi-libria experiments of Norman Bowen, carried out between 1912 and 1956, constituted an impor-tant part of that data set. Bowen was educated in both geology and chemistry, and he surely was familiar with Gibbs’s work. Surprisingly, though, in leafi ng through Bowen’s The Evolution of the Igneous Rocks (1928), I could fi nd no mention of Gibbs or even of any thermodynamic functions. Victor Goldschmidt’s Geochemistry, published posthumously in 1956,
explains the chemical affi nities of elements for oxide, silicate, sulfi de, and metal phases in terms of their free energies of formation, but again Gibbs’s name is nowhere to be found. The fi rst textbooks that really showed mineralogists, petrologists, and geochemists how to apply ther-modynamic principles were authored by Robert Garrels in 1960 (Mineral Equilibria at Low Temperatures and Pressures) and by Raymond Kern and Alain Weisbrod in 1964 (Thermodynamique de Base pour Minéralogistes, Pétrographes et Géologues). After a slow start, Gibbs’s concepts have become indispensable parts of our science.
I’ve heard it said that the sincerest form of fl attery for scientists is to have their contributions become so ingrained that they need no reference. Gibbs should truly be fl attered. I looked through my extensive collection of modern mineralogy, petrology, and geochemistry texts, and not a single one references his published work. Any reference to him (if there is one at all) only acknowledges his derivation of the phase rule, although our community did christen a mineral (gibbsite) in his honor. Thermodynamics is man-ifestly one of those areas where we stand on the shoulders of a giant. Thanks, Dr. Gibbs, on behalf of geoscientists everywhere.
Hap McSween, University of Tennessee ([email protected])
* Hap McSween was the principal editor in charge of this issue.
Hap McSween
Thermodynamics is manifestly one of
those areas where we stand on the
shoulders of a giant. Thanks Dr. Gibbs,
on behalf of geoscientists everywhere.
ELEMENTS OCTOBER 2010275
EDITORIAL
PRINCIPAL EDITORSDAVID J. VAUGHAN, The University of
Manchester, UK ([email protected])
HARRY Y. (Hap) McSWEEN, University of Tennessee, USA ([email protected])
JAMES I. DREVER, University of Wyoming, USA ([email protected])
ADVISORY BOARD 2010JOHN BRODHOLT, University College London, UKNORBERT CLAUER, CNRS/UdS, Université de
Strasbourg, FranceWILL P. GATES, SmecTech Research
Consulting, AustraliaGEORGE E. HARLOW, American Museum
of Natural History, USAJANUSZ JANECZEK, University of Silesia, PolandHANS KEPPLER, Bayerisches Geoinstitut,
Germany DAVID R. LENTZ, University of New Brunswick,
Canada ANHUAI LU, Peking University, China ROBERT W. LUTH, University of Alberta, CanadaDAVID W. MOGK, Montana State University, USATAKASHI MURAKAMI, University of Tokyo, Japan ROBERTA OBERTI, CNR Istituto di Geoscienze
e Georisorse, Pavia, ItalyTERRY PLANK, Lamont-Doherty Earth
Observatory, USAXAVIER QUEROL, Spanish Research Council, SpainMAURO ROSI, University of Pisa, ItalyBARBARA SHERWOOD LOLLAR, University of
Toronto, CanadaTORSTEN VENNEMANN, Université de
Lausanne, SwitzerlandOLIVIER VIDAL, Université J. Fourier, FranceMEENAKSHI WADHWA, Arizona State
University, USABERNARD WOOD, University of Oxford, UKJON WOODHEAD, University of Melbourne,
Australia
EXECUTIVE COMMITTEELIANE BENNING, European Association
of GeochemistryPETER C. BURNS, Mineralogical Association
of Canada GIUSEPPE CRUCIANI, Società Italiana di
Mineralogia e Petrologia BARBARA L. DUTROW, Mineralogical
Society of America, ChairW. CRAWFORD ELLIOTT, The Clay Minerals SocietyRODNEY C. EWING, FounderJEFFREY N. GROSSMAN, The Meteoritical SocietyGUY LIBOUREL, Société Française
de Minéralogie et de CristallographieMAREK MICHALIK, Mineralogical Society
of PolandMANUEL PRIETO, Sociedad Española
de Mineralogía CLEMENS REIMANN, International Association
of GeoChemistryURS SCHALTEGGER, Swiss Society of
Mineralogy and Petrology CLIFFORD R. STANLEY, Association
of Applied GeochemistsNEIL C. STURCHIO, Geochemical SocietyPETER TRELOAR, Mineralogical
Society of Great Britain and IrelandFRIEDHELM VON BLANCKENBURG,
Deutsche Mineralogische GesellschaftMICHAEL WIEDENBECK, International
Association of Geoanalysts
MANAGING EDITORPIERRETTE TREMBLAY, [email protected]
EDITORIAL OFFICE
490, rue de la Couronne Québec (Québec) G1K 9A9 CanadaTel.: 418-654-2606Fax: 418-653-0777
Layout: POULIOT GUAY GRAPHISTESCopy editor: THOMAS CLARKProofreaders: THOMAS CLARK
and DOLORES DURANTPrinter: SOLISCO
The publishers assume no responsibility for any statement of fact or opinion expressed in the published material. The appearance of advertising in this magazine does not constitute endorsement or approval of the quality or value of the products or of claims made for them.
www.elementsmagazine.org
THIS ISSUEGuest editors Richet, Henderson, and Neuville take us from the atmo-sphere to the deep Earth with the seven papers they have assembled for this issue. In each of the illustrated Earth systems, thermodynamic principles can be applied to get a better understanding of the processes shaping them. Thermodynamics is more needed than ever: as is elo-quently demonstrated, it can give insight into real global problems. As for me, I gained a new respect for clouds and raindrops after reading Andreas Bott’s paper. I wish you all some interesting discoveries.
Two new features make their debut in this issue. The Elements Toolkit (page 277) will present new technological developments of interest to our readers. The plan is to publish it every other issue. You can send your ideas and suggestions for coverage to Michael Wiedenbeck ([email protected]), the feature editor.
David Mogk will coordinate our new Teaching MGP feature. In it, he or an invited contributor will present resources that are available for teaching the topic of the issue. In his fi rst contribution, David illustrates the wealth of information available to teachers of thermodynamics (page 326).
THE OTHER SIDE OF THE COIN: BASIC RESEARCH IN U.S. UNIVERSITIES Passionate identifi cation with basic research is often expressed in the U.S. scientifi c community. Peer-reviewed publications in basic-research disciplines dominate criteria for academic appointment, promotion, and tenure in American academic science departments. The U.S. National Science Foundation, whose policies since its founding in 1950 have largely excluded applied research, received an additional $3 billion through the Obama Admistration’s Recovery Act budget in 2009.
Thus, I did a double take when I read in Susan Stipp’s parting editorial (Elements, June 2010) that “in the last 20 years basic research has become unpopular.” The contradiction was clarifi ed when background research revealed that Stipp is head of the University of Copenhagen’s NanoGeoScience Centre, whose purpose is to foster applied research and train students whose employment would largely be in private industry. Denmark’s strong emphasis on applied research is mirrored in all other leading EU nations except the UK.
My recent comparisons between American and German institutions for chemistry and engineering offered wake-up calls. Distinguished American chemistry departments’ websites call attention to cutting-edge research and lists of peer-reviewed publications by faculty. Their German counterparts cite no publications (although they certainly have them). Instead, they emphasize research and curricula that relate to the needs of society and prepare students to take up meaningful and challenging work.
The Technical University of Munich’s main divisions resemble those of the Georgia Institute of Technology (highly rated by NSF). But there the similarity stops. Georgia Tech’s schools have a strong independent research focus, and half the buildings on campus are devoted to lan-guages, arts, humanities, sports facilities, and other functions. In con-trast TUM is focused on research and teaching that directly serves German social needs and industry. Specialized master’s programs, including administration and management, as well as doctoral pro-grams, are closely coordinated with internship programs sponsored by German engineering and industrial fi rms. This system allows graduates to move smoothly into industrial jobs upon graduation.
These and other purposeful features let me understand why the U.S. has only 13% of its university students majoring in science and engi-neering, while Germany has 30–40%. And those graduates have rewarding and more stable futures ahead of them. In 2007 Germany had a trade surplus of $250 billion, whereas the U.S. had a defi cit of nearly $900 billion. Germany’s rebound is now bringing it closer to precrash conditions. The U.S. anticipates no foreseeable break in the ongoing retrenchment of its research universities.
Germany’s industries are now world leaders in both renewable energy development and conventional manufacturing. Relegating applied research in U.S. universities to second-class status has helped create a stigma on American industry (including the minerals industry). Now there is no longer the “Golden Age of Research” that blossomed in the 1960s and 1970s.
There is much more to this story, the history of which I trace in a chapter of a book published in my new specialty of public policy research* (in my former career I concentrated on marine geochemistry and hydrochemistry). I suggest that if the U.S. scientifi c community takes voluntary initiatives and broadens its goals, it will be in a better position to aid economic recovery and retain the independence it now enjoys. If, on the other hand, the economy continues to sour, at some point Congress may discover that other nations are making better use of their scientifi c talent than the U.S., and then changes may be drastic.
Frank T. Manheim School of Public Policy
George Mason University, Fairfax, VA 22030, USA E-mail: [email protected]
* The Confl ict over Environmental Regulation in the United States: Origins, Outcomes and Comparison with the EU, Springer 2009, 321 pp
Readers can contribute to many other features:
Letters to the Editors: Has an editorial spurred some thoughts? Have you a short news item of interest to the membership of Elements? Consider submitting a letter to the editor ([email protected]).
Triple Point raises issues of broad interest. Since volume 1, this feature has explored dif-ferent aspects of our science (teaching, publishing, historical aspects, etc.), our societies, funding, policy, and political issues. Contact Bruce Yardley (B.W.D. [email protected]) or Marty Goldhaber ([email protected]) if you have an idea for a future topic.
People in the News highlights the accomplishments of mem-bers of our communities: awards they have received or exciting new projects in which they are engaged.
Travelogue: Have you done fi eld work in or traveled to an exotic location? Consider writing an account of your expe-riences (send ideas to [email protected]).
Parting Shots: Ian Parsons has provided many fascinating con-tributions, but he would wel-come other contributors. Beautiful, unusual rock and mineral textures are welcome.
ELEMENTS’ IMPACT FACTOR CLIMBS TO 3.569We are pleased to report that Elements’ impact factor is con-tinuing the climb it started in 2006. Elements, launched in 2005, received its fi rst impact factor from the Institute of Scientifi c Information for 2006 (1.562). The following year, its impact factor rose to 2.23. And from 3.069 in 2008, it climbed to 3.569 in 2009.
The 10 most cited articles from the time of publication to July 2010 were: • Harley SL, Kelly NM, Moller A (2007) Zircon behaviour and the thermal histories of mountain chains. Elements 3: 25-30 (49 citations)• Charlet L, Polya DA (2006) Arsenic in shallow, reducing ground-waters in southern Asia: An environ-mental health disaster. Elements 2: 91-96 (49)• Geisler T, Schaltegger U, Tomaschek (2007) Re-equilibration of zircon in aqueous fl uids and melts. Elements 3: 43-50 (48)
• Cartigny P (2005) Stable isotopes and the origin of diamond. Elements 1: 79-84 (38) • Morin G, Calas G (2006) Arsenic in soils, mine tailings, and former industrial sites. Elements 2: 97-101 (29)• Self S, Thordarson T, Widdowson M (2005) Gas fl uxes from fl ood basalt eruptions. Elements 1: 283-287 (28)• Vaughan DJ (2006) Arsenic. Elements 2: 71-75 (27)• Ohtani E (2005) Water in the mantle. Elements 1: 25-30 (26)• O’Day PA (2006) Chemistry and mineralogy of arsenic. Elements 2: 77-83 (24)• Rubatto D, Hermann J (2007) Zircon behaviour in deeply sub-ducted rocks. Elements 3: 31-36 (23)
The issues that have garnered the most citations are: Zircon (2007, v3n1, 174 citations); Arsenic (2006, v2n2, 163); Large Igneous Provinces (2005, v1n5, 105); Diamonds (2005, v1n2, 90); The Nuclear Fuel Cycle (2006, v2n6, 84); and Supervolcanoes (2008, v4n1, 65).
Pierrette TremblayManaging Editor
ELEMENTS OCTOBER 2010276
FROM THE EDITORS LETTER TO THE EDITORS
ELEMENTS OCTOBER 2010277
WELCOME TO THE TOOLKIT
From my laboratory per-spective, I see scientifi c progress as a dynamic a nd eve r- evolv i ng human endeavor. This is certainly true for the Earth sciences, where lengthy periods of fi lling in the puzzle pieces are punctuated with break-throughs in our under-
standing of how our planet works. But how are such leaps in knowledge achieved? Three aspects appear to interact to bring a sudden surge in our comprehension of nature:
A steady fl ow of seemingly unrelated observations suddenly crosses a threshold where some new “truth” becomes apparent: the “long, hard toil route.”
Discovery resulting from a new research strategy leads to a fully unanticipated conclusion: the “serendipitous route.”
Finally, progress frequently can be attributed to “breakthrough technologies,” which fl ow into the hands of the broad research community.
An example of this last route to discovery is the explosion in data resulting from the intro-duction of laser ablation sampling technology in conjunction with ever-improving mass spec-trometric methods. Over the past decade or two, this cost-effective and rapid analytical method has become an essential tool for many colleagues. Certainly, some of the resulting data are of questionable signifi cance or dubious quality—as always, the value of the data rests in the hands of the individual practitioner. Nonetheless, it would be diffi cult for me to imagine modern-day geochemistry without the existence of laser ablation technology.
“The Elements Toolkit” is a feature that the editors of this magazine have asked me to pro-vide at regular intervals, roughly every second issue. My goal is to present new technologies that seem to offer great potential to the research community. I will also highlight instrumentation or software that I see as pow-erful but underutilized tools of our trade. Perhaps my musings will give the broader com-munity a picture of key strategies being applied in other disciplines. Of course, I would only be too happy if the dissemination of such ideas into the hands of the adventurous were to lead to serendipity…
I hope that you will fi nd this and the upcoming Toolkit articles of interest. Perhaps some of the resources that I present will actually prove useful in your own research. And now, as a first contribution, I would like to briefly
present a web resource that provides a glimpse of what might become in a few years “standard methodology” for Earth science researchers.
The Global Registration of Geologic Sampling Have you ever felt that it would be really useful to have a list of all samples that have been collected in or near your fi eld area? Of course, such a database would ideally provide both a basic description of the material and informa-tion about where one should look to obtain part of said sample. Better still, wouldn’t it be great if the sample numbers were linked to all literature citations in which the material is mentioned? And wouldn’t it also be a big advantage if all sample designators were unique and unambiguous? Well, such a web resource has been under construction for the past couple of years. The International Geo Sample Number (IGSN) registry, managed by the System for Earth Sample Registration (SESAR), addresses these issues. An IGSN is a unique and persistent identifi er for geomate-rials, and such an identifi er can easily be assigned by registering sample properties with SESAR via the Internet. If data in a publication are referenced to an IGSN, then key informa-tion about the sample can rapidly be retrieved from the SESAR database. Have a look at http://www.geosamples.org/.
As an example of what one might learn from this database, my search of all records from South Africa reports a total, as of mid- September 2010, of 603 registered samples.
This is certainly not a comprehensive record of geologists’ activities in the country, but nonetheless it is a useful starting point. In addition to using this database with a geo-graphic fi lter, it is also possible to conduct a search based on rock type. As a test, I randomly selected a fi lter based on intermediate plutonic rocks, the net result being only three entries, a rather meagre yield for fans of monzonite. This low result is despite the fact that some 4 million records are registered in the system. Looking at individual records, one fi nds many
characteristics reported as “not provided,” meaning extra time at the computer will be necessary to determine if a given sample is relevant for the topic of study. Nonetheless, despite these shortcomings, this tool might already prove valuable to many, and one can hope that such a system will win ubiquitous support from the fi eld geologists and lab ana-lysts of the future. Interested in fi nding out a bit more? Have a look at “Facilitating Research in Mantle Petrology with Geoinformatics,” by K. Lehnert and J. Klump (2008) (www.cosis.net/abstracts/9IKC/00250/9IKC-A-00250-1.pdf).
Michael Wiedenbeck([email protected])
ABOUT THE AUTHOR
Michael Wiedenbeck is in charge of the Potsdam Secondary Ion Mass
Spectrometry facility, a position he has held since December 1998. He began his career as an isotope geochemist at the ETH-Zürich, being trained in the art of K–Ar and Rb–Sr age determinations. Having discovered that wet chemical isotope work can involve a Herculean struggle against the laboratory blank, he decided to move to Australia to become one of the early practitioners in the then emerging fi eld of ion probe geo-chronology. His work on the Archean of Western Australia brought with it the epiphany that data quality in analytical geo-chemistry is critically dependent on access to high-quality calibration materials. Leaving Canberra, his next move was back to Europe, to the CRPG in Nancy, France, where he devoted a year’s effort to fi nding and characterizing homogeneous zircon crystals for calibrating U–Th–Pb age deter-minations. Subsequent career stops included Ahmedabad, India (more Archean SIMS geochronology); Oak Ridge, Tennessee (building a new type of SIMS instrument); and Albuquerque, New Mexico (running a multi-user SIMS facility).
Michael’s position as a senior scientist at the Helmholtz Center Potsdam has allowed him to invest a signifi cant effort toward his pas-sion for improving metrology in analytical geochemistry. Through his involvement with the International Association of Geoanalysts, of which he has been president since 2006, Michael has been involved with the ISO-based certifi cation of fi ve whole-rock Reference Materials; these remain some of the best-characterized Earth materials ever produced. With this experience in the production of highest-quality reference materials for bulk analytical methods, he is now turning his attention towards the needs of the microanalytical community.
GEOCHEMICAL JOURNAL AWARD FOR 2010 TO BAU AND KOSCHINSKY
The Geochemical Society of Japan, publisher of the Geochemical Journal, is proud to announce that the paper entitled “Oxidative scavenging of cerium on hydrous Fe oxide: Evidence from the distribution of rare earth elements and yttrium between Fe oxides and Mn oxides in hydro-genetic ferromanganese crusts” (Geochemical Journal 43: 37-47, 2009), co-authored by Prof. Michel Bau and Prof. Andrea Koschinsky of Bremen University, has been selected for the 2010 Geochemical Journal Award.
This award was created in 2003 to commemorate the 50th anniversary of the Geochemical Journal and was fi rst awarded at the Goldschmidt Conference in Kurashiki. Every year, the Geochemical Journal Award honors the authors of outstanding research articles published during the previous year in the Geochemical Journal.
In their paper, Drs. Bau and Koschinsky present and discuss experi-mental data on the partitioning of redox-sensitive rare elements, such as cerium, between Fe and Mn oxides. The strongest point in this paper is that both the Mn oxides and the Fe oxides display pronounced pos-itive Ce anomalies of almost identical size. This suggests that in the natural marine system oxidative scavenging of Ce from seawater is not restricted to Mn oxides but also occurs on hydrous Fe oxides, a phe-nomenon that was not previously well documented. Furthermore, pref-erential Ce removal from seawater does not result from the oxidation of dissolved Ce(III) within the marine water column; rather, Ce(III) is oxidized after its sorption at the metal (hydr)oxide surface.
This paper contributes to the understanding of the behavior of rare elements in ocean water, a fi eld in which Dr. Bau is one of the leading geochemists. Understanding the behavior of peculiar rare elements, such as cerium, is fundamental for using them as paleoredox proxies.
It is therefore vital to correctly interpret Ce variations in ancient, chemically precipitated (or biogenic?) rocks such as Archean banded iron formations, for determining when and how oxygen fi rst accumu-lated in the atmosphere–ocean system.
The conclusions in this paper go well beyond the fi eld of REE geo-chemistry and have broad implications in the fi elds of astrobiology and Precambrian geology, as well as in the diffi cult but exciting search for pristine proxies of the environmental conditions of the young Earth.
For these reasons, the Geochemical Society of Japan has selected this remarkable work for the Geochemical Journal Award for the year 2010.
Andrea Koschinsky and Michel Bau, Bremen University
As part of Elements’ 5th anniversary celebra-
tions, IMA 2010 presented a series of plenary
lectures by guest editors and authors of pre-
vious issues of the magazine. We extend our
thanks to these contributors for having
enthusiastically responded to Ian Parsons’
and David Vaughan’s invitation to join in
this celebration. We also thank the orga-
nizers of IMA 2010 for having given
prominence to these lectures.
Éva Valsami-Jones (Natural History Museum, UK), co–guest editor of volume 4, number 2 (Phosphates and Global Sustainability), in the opening “Elements 5” lecture, summarized the
different aspects of the global phosphorus cycle and presented results of the study of apatite at the nanoscale.
Rod Ewing (University of Michigan, USA), founder of Elements and guest editor of volume 2, number 6 (The Nuclear Fuel Cycle), high-lighted the role of miner-alogy and geochemistry in the treatment of nuclear waste.
Nigel Kelly (Colorado School of Mines, USA) was a co–guest editor of volume 3, number 1 (Zircon). The zircon issue has the distinc-tion of being the most heavily cited of all issues we have published so far. In his
presentation, Nigel showed how research is helping to improve the interpretation of
zircon ages and gave an overview of the processes that can be traced with indi-vidual grains.
Mihály Pósfai (University of Pannonia, Hungary), an author in the Mineral Magnetism issue (volume 5, number 4), presented a talk on magnets in organisms and how they can help us understand the mechanisms of magnetic sensing by organisms.
Nita Sahai (University of Wisconsin–Madison, USA), guest editor of the Medical Mineralogy and Geo-chemistry issue (volume 3, number 6), gave a talk on mineral interactions with the human body—some medically benefi cial and some harmful.
Glenn Waychunas (Berkeley Nanogeoscience Center, USA) spoke about mineral–water interfaces and nanoparticles. He was an author in the Nanogeoscience issue (volume 4, number 6).
“ELEMENTS 5” SPEAKERS AT IMA 2010
ELEMENTS OCTOBER 2010278
PEOPLE IN THE NEWS
PHOTO: BARB DUTROW
I am a student of thermodynamics. Yes, I have been teaching the subject to baccalaureate and graduate students in petrology and materials science for about 25 years. But in
every course, almost every lecture, I perceive something new: some new (to me) subtlety in the ideas that facilitates deeper appreciation and understanding of some of the experimental data generated in my research group and that fosters a profound admiration for the many scholars who brought forth these ideas in the nineteenth century and refi ned them in the twentieth. In this process, I have identifi ed and shared with my fellow learners two pieces of advice that are particularly valuable in applying thermodynamics to the analysis of textures in rocks, which is so very often the center of our interest in thermodynamics: trust your eyes; use your imagination. Let me explain, or at least try…
The textures of rocks—that is, the spatial dis-tribution of minerals, the morphologies of the interfaces between grains (grain and hetero-phase boundaries), and the spatial differences of oxide composition (including compositional gradients)—are a result of a convolution of ther-modynamics and kinetics. Beginning petrology students frequently struggle to under-stand that there is no textural information in an equilibrium
phase diagram (indeed, there is no time in equilibrium thermodynamics). The amount of creative synthesis involved in the thought experiment of logically stepping through a time (t)–temperature (T)–pressure (P) protocol with an equilibrium phase diagram so as to predict a texture is profound. I might add that learning to teach this synthesis is simultaneously humbling and rewarding. For many students of petrology, this is the fi rst example and practice of “trusting your eyes” in doing predictive science: we (the community) construe that the texture observed is a result of a chemical system subjected to a time-varying set of thermodynamic potentials, and so we apply equilibrium thermodynamic arguments—like phase dia-grams—step-wise in time to develop an interpretation that is extrapo-lative.
One can learn to trust one’s eyes at a fi ner scale, too, which is particu-larly important in studying mineral reactions. As a simple, practical, and provocative illustration, consider the oxidation of solid-solution, ferromagnesian olivine beyond its stability limit. For the fayalite end-member, the chemical reaction is straightforward:
3Fe2SiO4 + O2 = 2Fe3O4 + 3SiO2 ; ΔrGoFMQ ,
fayalite + oxygen gas = magnetite + α-quartz
where ΔrGoFMQ is the standard Gibbs free energy of this reaction. If we
were considering the oxidation breakdown of pure fayalite, this reaction would describe the FMQ (fayalite–magnetite–quartz) oxygen buffer. In the actual case of ferromagnesian olivine, though, the fayalite compo-
Reid F. Cooper*
* Reid F. Cooper is Professor of Geological Sciences at Brown University, Providence, RI, USA. His research emphases are experimental chemical and mechanical kinetics in upper-mantle minerals and rocks and reaction dynamics in silicate melts and glasses.
Department of Geological SciencesBrown University, 324 Brook StreetProvidence, RI 02612, USAE-mail: [email protected]
nent is dissolved into forsterite; as a consequence, the reaction (at a given P and T) would occur only at an oxygen activity (fugacity) that is greater than FMQ. The reaction texture is illustrated schematically in FIGURE 1. When exposed to an oxygen activity exceeding the stability of the fayalite component (e.g. annealing at ~900 °C and 1 atm in air), one discovers that the texture of the incomplete reaction includes (1) a specular, polycrystalline thin fi lm of periclase (MgO) and magnesio-ferrite (MgFe2O4) covering the original surface (between ξ = 0, the original surface, and ξ = ξʹ); (2) fi ne (nanometer-scale) precipitates of pure magnetite (Fe3O4) and amorphous silica precipitated on lattice dislocations in the olivine and existing in a “matrix” of pure forsterite between ξ = 0 and an internal reaction interface ξ = ξʺ; and (3) yet-to-be-reacted olivine solid solution at ξ > ξʺ (Wu and Kohlstedt 1988). This process is “dislocation decoration”; deformation-effected dislocations in olivine can be studied with standard petrographic techniques fol-lowing such oxidation (Kohlstedt et al. 1976); see FIGURE 2.
A strange texture! The reaction has not produced an equilibrium assem-blage within the olivine: forsterite and silica should react to form enstatite (MgSiO3); the chemical potential of MgO in the forsterite is suffi ciently high that magnesioferrite should form instead of magnetite. The assemblage is metastable: if the specimen is annealed at high tem-
perature for a time very, very long compared to that required for the reaction front at ξ = ξʺ to march through, say, a millimeter-scale experimental specimen, enstatite and magnesioferrite will form. Not evident in the sche-matic, but important in the texture nevertheless, is the fact that microprobe analyses of the forsterite matrix between 0 and ξʺ and ion-backscattering spectrometry analyses of the (new) surface thin fi lm reveal no concen-tration gradients whatsoever of the component ions.
What, then, can be said? Trust your eyes! The magnetite (Mt) and silica (Sil) precipitated on the dislocations are pure; the activity of each is unity, to fi rst order (the Gibbs free energy of α-quartz and vitreous silica being quite similar). Thermodynamically, then, the reaction is easily analyzed. Using the mass-action equation,
,
where Keq is the equilibrium constant and ai is the activity of species i, one can substitute unity for aMt and aSil and so discern the trade-off between the activity of fayalite (aFa) in the olivine solid solution and the oxygen activity (aO2) at which the fayalite component is no longer stable.
FIGURE 1 Schematic diagram of the (incomplete) oxidation of ferromagnesian olivine beyond its limit of stability. The original surface is at location 0.
The reaction sees both external and internal reaction fronts, ξʹ and ξʺ, respectively. Reaction products include phase-pure magnetite and vitreous silica in a matrix of pure forsterite (Wu and Kohlstedt 1988).
On Being a Student of Thermodynamics: Trust Your Eyes; Use Your Imagination
“Thermodynamics smells more of its human origin than other branches of
physics.”
—Percy W. Bridgman, USA physicist, Nobel laureate (1882–1961)
Reid Cooper
ELEMENTS OCTOBER 2010282
PERSPECTIVE
282
[As an exercise, students can take experimental data of the breakdown oxygen activity for various olivine compositions and so calculate a solution model—aFa as a function of XFa—for olivine (cf. Nitzan 1974).]
The texture and context reveal more. In this example, the oxygen activity at the free surface, ξ ,́ is that of air (i.e. aξʹ
O2 = 0.21). The oxygen activity at ξʺ is that at which the olivine solid solution is no longer stable (as discerned from Keq). So, clearly, there is a gradient in the chemical potential of oxygen (µO2) within the reacting specimen, i.e. dµO2 / dξ = RT(dlnaO2 / dξ) . And yet, as already noted, one cannot iden-tify concentration gradients of ion species between ξʹ and 0 and between 0 and ξ .̋ The thin fi lm at the surface is a mixture of magnesium and ferric-iron oxides: there is no SiO2 component in this two-phase fi lm. The silica-free, surface thin fi lm is critical in interpreting the dynamics of the reaction.
And so the second exhortation: use your imagination. Interpreting the texture to comprehend the dynamics in this case involves identifying the physical manifestation of the oxygen activity in olivine. Now, the ther-modynamics we teach in petrology classes is typically that of Clausius, Joule, and Gibbs, which is based on state variables, that is, enthalpy, entropy, Gibbs free energy, and activity. These are ensemble or average values representative of the bonding and the vibrational/translational “chaos” of ions and molecules making up a system: “black-box” vari-ables masking an atomic reality. The activity of a component in a mineral has as its physical manifestation a collection of point defects on the lattice. Point defects in minerals are atomic vacancies, substi-tutionals, and interstitials; they are equilibrium defects: there is suf-fi cient entropy associated with their deployment on the lattice to “over-come” the enthalpy of their formation. The concentration of these defects rarely reaches 0.1 atomic percent, making their quantitative characterization beyond the capabilities of, for example, X-ray spec-trometry on a microprobe. One employs imagination in the sense of contemplating the variations of concentrations of defects at different locations within a reaction microstructure: if there are activity gradients, there must be, physically, gradients in the concentrations of point defects.
The physical manifestation of the oxygen activity in olivine is a charge-compensating pair of point defects—vacancies on the divalent-cation (Me2+ ≡ Mg2+ and Fe2+) sublattice (octahedral sites in the O2– array) and ferric-iron ions (Fe3+) on the octahedral sites. It ends up that point defects in minerals have actual charges, that is, their presence in the lattice locally distorts the electronic structure of the mineral. Vacancies on the divalent cation sites in olivine have a 2– charge. Fe3+ occupying a site where an Fe2+ is “normally” present has an additional 1+ charge. Creating this latter defect requires only the removal of an electron from the Fe2+ present originally; the “lost” electron—called an electron “hole”—is highly mobile and easily “hops” from one iron ion to another nearby in the crystal.
Equilibrium thermodynamics is enforced for point defects: one can articulate defect-formation reactions, but these have requirements not only of conservation of matter but also of conservation of charge and, in minerals, conservation of lattice sites (that is, conservation of the mineral structure proper). So, relating oxygen activity to defect con-centration in olivine can be written as:
3FexMe + ½O2 = 2Fe•
Me + V”Me + FeO = 2h• + V”Me + FeO ; ΔrGo .
In this (Kröger-Vink) notation, the subscripts refer to lattice sites and the superscripts refer to charge on that site relative to whatever species occupies the site in the perfect crystal (e.g. Schmalzried 1981, p. 39). Thus, Fex
Me is an Fe2+ occupying an appropriate Me2+ octahedral site; it is electrically neutral (“x”) as a divalent cation normally occupies the site. A “dot” superscript denotes relative positive charge; a “prime” superscript denotes relative negative charge. Thus, Fe•
Me is an Fe3+ occu-pying a Me2+ site (because of the high mobility of charge transfer, it is identifi ed alternatively as an electron hole, h•), and V”Me is an octahe-dral-site vacancy with a 2– charge. Note the balances: beyond mass conservation, charge neutrality is maintained on both sides of the equation, as is site conservation (three octahedral sites accounted for on each side). Mass-action applies:
.
In the equation, the activities of FexMe and FeO are essentially fi xed
(constant), set by the situation, that is, by the fayalite composition of the olivine and by the fact that olivine (in its natural context) is also in equilibrium with orthopyroxene. Thus, one sees in the equation that an increase in oxygen activity results in an increase in the activities—and so the concentrations—of the defect species h• and V”Me.
One realizes, then (trust your eyes!), that in the olivine the equilibrium concentrations of vacancies and holes are much higher at ξ = 0 than at ξ = ξʺ: fl ux of the defects “inward” (jV”Me
and jh• and attendant arrows in FIGURE 1) and the physically required counterfl ux of Me2+ “outward” (j
Me2+) is how the external oxygen activity is transferred into the reacting crystal. The loss of the cations from the olivine to the free surface—where they react with environmental oxygen to produce the silica-free, oxide thin fi lm (plus h•)—means that the divalent cation/oxygen anion ratio within the olivine is decreasing. The olivine oxidizes internally not by adding oxygen but rather by losing cations; too, one sees that oxidation occurs not by diffusion of an oxygen species but rather by the diffusive motion of the divalent cations in response to a gradient in µO2 (and proceeds at the rate of the cation fl ux). The high mobility of the electron holes “decouples” the fl uxes of anions and cations, which is critical in facilitating the dynamics and so the texture. All minerals containing even low concentrations of transition-metal cat-ions can anticipate similar decoupling.
This is a rather simple example of a thermodynamic approach to appre-hending the development of a complex texture. As a fellow student, what I recommend is identifying points in a reaction texture where one can identify unequivocally (eyes!) values of certain chemical poten-tials (activities) and ask how those points “communicate” via defects (imagination!). Dealing similarly with more complex textures, for example, the development of a metamorphic symplectite, involves additional thought and information regarding, for instance, interface stability. Nevertheless, the eyes/imagination approach still applies, and is quite powerful.
REFERENCESKohlstedt DL, Goetze C, Durham WB, Vander Sande J (1976) New technique
for decorating dislocations in olivine. Science 191: 1045-1046
Nitzan U (1974) Oxidation and reduction of olivine. Journal of Geophysical Research 79: 706-711
Schmalzried H (1981) Solid State Reactions. Verlag Chemie, Weinheim, FRG, 254 pp
Wu T, Kohlstedt DL (1988) Rutherford backscattering spectroscopy study of the kinetics of oxidation of (Mg,Fe)2SiO4. Journal of the American Ceramic Society 71: 540-545
FIGURE 2 Dislocations in experimentally deformed San Carlos (AZ) peridot (transmitted, plane-polarized light). The ubiquitous dark dots are
dislocation lines viewed end-on. The dislocations are visible because the crystal has been oxidized subsequent to deformation. This is the structure imaged between 0 and ξʺ in FIGURE 1.
ELEMENTS OCTOBER 2010283
PERSPECTIVE
Andreas Bott obtained his PhD at the Max-Planck-Institute for Chemistry in Mainz under Prof. Paul Crutzen. He is currently University Professor for Theoretical Meteorology at the Rheinische Friedrich-Wilhelms-University Bonn. His main research interests are in the thermodynamics of clouds and precipitation. His current research activities are in the fi elds of cloud microphysics and radiation fogs, as well as in the development
of new physical parameterizations for use in numerical models of the atmosphere.
Benjamin R. DiTrolio is a PhD candidate in the Rosenstiel School of Marine and Atmospheric Science, University of Miami. He attended the University of Massachusetts, Amherst, where he graduated summa cum laude in 2008 with a BS in chemistry. Currently he is working under Dr. Frank Millero to characterize the effect of pH on the spe-ciation of metals with organic matter in the marine environment.
Grant S. Henderson is a professor in the Department of Geology at the University of Toronto. He studied geology and chemistry at the University of Auckland, New Zealand, and the University of Western Ontario, Canada. He has been interested in the structure of glasses as it applies to geological melts since the early 1980s. His current research emphasizes the use of syn-chrotron-based spectroscopic and diffraction tech-
niques to elucidate the structure of silicate and germanate glasses. He is particularly interested in the coordination and medium-range struc-ture changes responsible for variation in physical properties.
Tim Holland is a Reader in the Department of Earth Sciences at the University of Cambridge. He did an undergraduate degree in geology at Oxford from 1971 to 1974, and then a DPhil on eclogites in the Tauern Window, Austria, at Oxford from 1974 to 1977. After spending two years at Chicago doing high-pressure experiments with Bob Newton, he returned to Britain in 1979 for a teaching/research post at Cambridge. He has con-
tinued to work on high-pressure metamorphism and the thermody-namics of minerals there. Work with Roger Powell started after a chance meeting at a conference in London in 1981, and their friendship and collaboration continue to this day.
Frank J. Millero, professor of marine and physical chemistry at the Rosenstiel School of Marine and Atmospheric Science, University of Miami, received his BS (1961) from Ohio State University and his MS (1964) and PhD (1965) from Carnegie Mellon University in physical chemistry. After a brief interval in industry, he moved to the University of Miami in 1966. From 1986 to 2006 he was Associate Dean of Academic Studies at the School.
He serves as an associate editor for a number of journals, and since 1993 has been editor-in-chief of Marine Chemistry. Millero’s research includes studies of the global carbon dioxide cycle in the world’s oceans, ionic interactions in seawater, trace metals in natural waters, and ocean acidifi cation.
Daniel R. Neuville is a CNRS research director at the IPGP in Paris. He received his PhD in geochem-istry at the University of Paris 7 in 1992 and then moved to a postdoctoral position at the Geophysical Laboratory, Carnegie Institution of Washington, where he conducted research on the structure and properties of crystals, glasses, and melts in relation
to volcanology and the glass-making industry. He has used various thermodynamics and rheological tools in his work, and he has carried out in situ investigations of melts and crystals at high temperature using Raman, NMR, and X-ray diffraction and absorption.
Giulio Ottonello holds the Chair of Geochemistry at the University of Genoa (Italy). His main inter-ests concern theoretical aspects of the reactivity of Earth materials in various aggregation states, especially aqueous solutions and silicate melts, to which he applies methods ranging from classical thermodynamics to ab initio quantum chemical calculations. Among his various publications, he is the author of the scholarly book Principles of
Geochemistry (Columbia University Press, New York, 1997).
Roger Powell is an ARC Australian Professorial Fellow in the School of Earth Sciences at the University of Melbourne. Following his fi rst degree at the University of Durham, he did a DPhil at Oxford from 1970 to 1973. Following short stints elsewhere, he taught at the University of Leeds from 1975 to 1984. He then moved to the antipodes where he remains. He works on the application of mathematics, statistics, and thermodynamics to
metamorphic rocks, and also provides software implementations of solutions to problems. The core of his work continues to be carried out in collaboration with Tim Holland.
Pascal Richet is a senior geophysicist at the Institut de Physique du Globe de Paris. He works mainly on the physics of minerals and melts under wide temperature and pressure ranges. In addition, he is involved in transferring fundamental research to problems of industrial interest and writes arti-cles and books to promote the popularization, his-tory, and philosophy of science. Examples are the Guide to the Volcanoes of France and the Guide to the
Volcanoes of French Overseas Territories (Editions Belin, Paris, 2003 and 2007, both in French).
Surendra Saxena is the director of the Center of Study of Matter at Extreme Conditions at Florida International University, Miami, Florida. He grad-uated from the Institute of Mineralogy and Geology, Uppsala University, Sweden, in 1967. He was a professor at Brooklyn College, City University of New York, until 1991 and then a professorat Uppsala University (1989–1999). He was elected as a member of the Royal Swedish Academy of
Sciences in 1994. He is the recipient of La Laurea Ad Honorem in Scienze Geologiche, Padova University, Italy, 2001, and of the Rudbeck Medal of Excellence in Science, Uppsala University, Sweden, 2007.
Pierpaolo Zuddas is Professor of Environmental Geochemistry at the Université de Lyon, France. His research is aimed at understanding the kinetics and thermodynamics of water and mineral inter-faces using fi eld and theoretical approaches. He also works on the human environmental impacts in urban areas and at mining sites, on the reac-tivity of naturally occurring nanoparticles, and on
the environmental risks of waste deposits in geological media. He received the Italian laurea degree in geological sciences from the University of Cagliari and a PhD from the University of Paris for his work on trace element behavior in geothermal fl uids. He has also worked at McGill University in Canada on the kinetics of calcite formation in seawater.
ELEMENTS OCTOBER 2010284
RARE MINERALS FOR RESEARCH
FROM our inventory of over 200,000 specimens, we can supply your research specimen
needs with reliably identifi ed samples from worldwide localities, drawing on old,
historic pieces as well as recently discovered exotic species. We and our predecessor
companies have been serving the research and museum communities since 1950. Inquiries
by email recommended.
Red ber yl f rom the Violet Claims, Wah Wah Mt s., Utah.
Jef f Scovil image f rom the Photographic Guide to Mineral Species CD
Excalibur Mineral Corp.1000 North Division St. Peekskill, NY 10566 USA
Telephone: 914-739-1134; Fax: 914-739-1257www.excaliburmineral.com | email: [email protected]
ELEMENTS OCTOBER 2010285
