ALBERT

Description / Table of Contents: In the two decades since J. Alexander Speer's Zircon chapter in Orthosilicates (Reviews in Mineralogy, Vol. 5), much has been learned about the internal textures, trace-element and isotope geochemistry (both radiogenic and stable) and chemical and mechanical stability of zircon. The application of this knowledge and the use of zircon in geologic studies have become widespread. Today, the study of zircon exists as the pseudo-discipline of "zirconology" that involves materials scientists and geoscientists from across a range of sub-disciplines including stable and radiogenic isotopes, sedimentology, petrology, trace elements and experimental mineralogy. Zirconology has become an important field of research, so much so that coverage of the mineral zircon in a review volume that included zircon as one of many accessory minerals would not meet the needs or interests of the zirconology community in terms of depth or breadth of coverage. The sixteen chapters in this volume cover the most important aspects of zircon-related research over the past twenty-years and highlight possible future research avenues. Finch and Hanchar (Chapter 1) review the structure of zircon and other mineral (and synthetic) phases with the zircon structure. In most rock types where zircon occurs it is a significant host of the rare-earth elements, Th and U. The abundances of these elements and the form of chondrite-normalized rare-earth element patterns may provide significant information on the processes that generate igneous and metamorphic rocks. The minor and trace element compositions of igneous, metamorphic and hydrothermal zircons are reviewed by Hoskin and Schaltegger in Chapter 2. The investigation of melt inclusions in zircon is an exciting line of new research. Trapped melt inclusions can provide direct information of the trace element and isotopic composition of the melt from which the crystal formed as a function of time throughout the growth of the crystal. Thomas et a!. (Chapter 3) review the study of melt inclusions in zircon. Hanchar and Watson (Chapter 4) review experimental and natural studies of zircon saturation and the use of zircon saturation thermometry for natural rocks. Cation diffusion and oxygen diffusion in zircon is discussed by Cherniak and Watson (Chapter 5). Diffusion studies are essential for providing constraints on the quality of trace element and isotope data and for providing estimates of temperature exposure in geological environments. Zircon remains the most widely utilized accessory mineral for U- Th-Pb isotope geochronology. Significant instrumental and analytical developments over the past thirty years mean that zircon has an essential role in early Achaean studies, magma genesis, and astrobiology. Four chapters are devoted to different aspects of zircon geochronology. The first of these four, Chapter 6 by Davis et a!., reviews the historical development of zircon geochronology from the mid-1950s to the present; the following three chapters focus on particular techniques for zircon geochronology, namely ID-TIMS (Parrish and Noble, Chapter 7), SIMS (Ireland and Williams, Chapter 8) and ICP-MS (Kosier and Sylvester, Chapter 9). The application of zircon chronology in constraining sediment provenance.and the calibration ofthe geologic time-scale are reviewed by Fedo et al. (Chapter 10) and Bowring and Schmitz (Chapter 11), respectively. Other isotopic systematics are reviewed for zircon by Kinny and Maas (Chapter 12), who discuss the application of Nd-Sm and Lu-Hf isotopes in zircon to petrogenetic studies, and by Valley (Chapter 13), who discusses the importance of oxygen isotopic studies in traditional and emerging fields of geologic study. As a host of U and Th, zircon is subject to radiation damage. Radiation damage is likely responsible for isotopic disturbance and promotes mechanical instability. There is increasing interest in both the effect of radiation damage on the zircon crystal structure and mechanisms of damage and recrystallization, as well as the structure of the damaged phase. These studies contribute to an overall understanding of how zircon may behave as a waste-form for safe disposal of radioactive waste and are discussed by Ewing et a!. (Chapter 14). The spectroscopy of zircon, both crystalline and metamict is reviewed by Nadsala et a!. (Chapter 15). The final chapter, by Corfu et al. (Chapter 16), is an atlas of internal textures of zircon. The imaging of internal textures in zircon is essential for directing the acquisition of geochemical data and to the integrity of conclusions reached once data has been collected and interpreted. This chapter, for the first time, brings into one place textural images that represent common and not so common textures reported in the literature, along with brief interpretations of their significance. There is presently no comparable atlas. It is intended that this chapter will become a reference point for future workers to compare and contrast their own images against. The chapters in this volume of Reviews in Mineralogy and Geochemistry were prepared for presentation at a Short Course, sponsored by the Mineralogical Society of America (MSA) in Freiburg, Germany, April 3-4, 2003. This preceded a joint meeting of the European Union of Geology, the American Geophysical Union and the European Geophysical Society held in Nice, France, April 6-11, 2003.

Description / Table of Contents: Since the dawn of life on earth, organisms have played roles in mineral formation in processes broadly known as biomineralization. This biologically-mediated organization of aqueous ions into amorphous and crystalline materials results in materials that are as simple as adventitious precipitates or as complex as exquisitely fabricated structures that meet specialized functionalities. The purpose of this volume of Reviews in Mineralogy and Geochemistry is to provide students and professionals in the earth sciences with a review that focuses upon the various processes by which organisms direct the formation of minerals. Our framework of examining biominerals from the viewpoints of major mineralization strategies distinguishes this volume from most previous reviews. The review begins by introducing the reader to over-arching principles that are needed to investigate biomineralization phenomena and shows the current state of knowledge regarding the major approaches to mineralization that organisms have developed over the course of Earth history. By exploring the complexities that underlie the "synthesis" of biogenic materials, and therefore the basis for how compositions and structures of biominerals are mediated (or not), we believe this volume will be instrumental in propelling studies of biomineralization to a new level of research questions that are grounded in an understanding of the underlying biological phenomena.

Description / Table of Contents: Exactly 100 years before the publication of this volume, the first paper which calculated the half-life for the newly discovered radioactive substance U-X (now called 234Th), was published. Now, in this volume, the editors Bernard Bourdon, Gideon Henderson, Craig Lundstrom and Simon Turner have integrated a group of contributors who update our knowledge of U-series geochemistry, offer an opportunity for non-specialists to understand its basic principles, and give us a view of the future of this active field of research. In this volume, for the first time, all the methods for determining the uranium and thorium decay chain nuclides in Earth materials are discussed. It was prepared in advance of a two-day short course (April 3-4, 2003) on U-series geochemistry, jointly sponsored by GS and MSA and presented in Paris, France prior to the joint EGS/AGU/EUG meeting in Nice. The discovery of the 238U decay chain, of course, started with the seminal work of Marie Curie in identifying and separating 226Ra. Through the work of the Curies and others, all the members of the 238U decay chain were identified. An important milestone for geochronometrists was the discovery of 230Th (called Ionium) by Bertram Boltwood, the Yale scientist who also made the first age determinations on minerals using the U-Pb dating method (Boltwood in 1906 established the antiquity of rocks and even identified a mineral from Sri Lanka-then Ceylon as having an age of 2.1 billion years!) The application of the 238U decay chain to the dating of deep sea sediments was by Piggott and Urry in 1942 using the "Ionium" method of dating. Actually they measured 222Ra (itself through 222Rn) assuming secular equilibrium had been established between 230Th and 226Ra. Although 230Th was measured in deep sea sediments by Picciotto and Gilvain in 1954 using photographic emulsions, it was not until alpha spectrometry was developed in the late 1950's that 20Th was routinely measured in marine deposits. Alpha spectrometry and gamma spectrometry became the work horses for the study of the uranium and thorium decay chains in a variety of Earth materials. These ranged from 222Rn and its daughters in the atmosphere, to the uranium decay chain nuclides in the oceanic water column, and volcanic rocks and many other systems in which either chronometry or element partitioning, were explored. Much of what we learned about the 238U, 235U and 232Th decay chain nuclides as chronometers and process indicators we owe to these seminal studies based on the measurement of radioactivity. The discovery that mass spectrometry would soon usurp many of the tasks performed by radioactive counting was in itself serendipitous. It came about because a fundamental issue in cosmochemistry was at stake. Although variation in 235U/238U had been reported for meteorites the results were easily discredited as due to analytical difficulties. One set of results, however, was published by a credible laboratory long involved in quality measurements of high mass isotopes such as the lead isotopes. The purported discovery of 235U/238U variations in meteorites, if true, would have consequences in defining the early history of the formation of the elements and the development of inhomogeneity of uranium isotopes in the accumulation of the protoplanetary materials of the Solar System. Clearly the result was too important to escape the scrutiny of falsification implicit in the way we do science. The Lunatic Asylum at Caltech under the leadership of Jerry Wasserburg took on that task. Jerry Wasserburg and Jim Chen clearly established the constancy and Earth-likeness of 235U/238U in the samplable universe. In the hands of another member of the Lunatic Asylum, Larry Edwards, the methodology was transformed into a tool for the study of the 238U decay chain in marine systems. Thus the mass spectrometric techniques developed provided an approach to measuring the U and Th isotopes in geological materials as well as cosmic materials with the same refinement and accommodation for small sample size. Soon after this discovery the harnessing of the technique to the measurement of all the U isotopes and all the Th isotopes with great precision immediately opened up the entire field of uranium and thorium decay chain studies. This area of study was formerly the poaching ground for radioactive measurements alone but now became part of the wonderful world of mass spectrometric measurements. (The same transformation took place for radiocarbon from the various radioactive counting schemes to accelerator mass spectrometry.) No Earth material was protected from this assault. The refinement of dating corals, analyzing volcanic rocks for partitioning and chronometer studies and extensions far and wide into ground waters and ocean bottom dwelling organisms has been the consequence of this innovation. Although Ra isotopes, 210Pb and 210Po remain an active pursuit of those doing radioactive measurements, many of these nuclides have also become subject to the mass spectrometric approach. In this volume, for the first time, all the methods for determining the uranium and thorium decay chain nuclides in Earth materials are discussed. The range of problems solvable with this approach is remarkable-a fitting, tribute to the Curies and the early workers who discovered them for us to use.