This issue of Mineralogical Magazine – Journal of Mineral Sciences contains nine articles by distinguished mineralogists which were delivered as plenary lectures to the 18th General Meeting of the International Mineralogical Association held in Edinburgh in early September 2002. The IMA is the only truly international organization representing mineralogy, and is supported by subscriptions from 37 mineralogical societies world-wide. Its main activity is to hold a General Meeting every four years in one of the subscribing countries, and in 2002 the organization was handled jointly by a group based in Edinburgh and by the Mineralogical Society of Great Britain & Ireland. The organizers invited lecturers who we believed would provide an authoritative and exciting overview of the most vigorous areas of the science of mineralogy as we enter a new millennium. In this the lecturers have unquestionably succeeded and we are very grateful for the scholarship, time and effort that they have put into these presentations. Each article was checked by an expert, and I thank Ross Angel, Derek Bain, Bill Brown, Martin Lee, David Manning, Bryne Ngwenya and Alison Pawley for their help.

Sustaining Earth, in the face of both technology thrusts and population dynamics, depends on our ability to maintain a delicate balance between human-promoted planetary modification and decline thresholds for land (soils), water, atmosphere, and biological systems. Mineralogy, as much as any other single science, will be central to this process. A set of links between Earth sustainability issues and the science of mineralogy are formulated and discussed in this discourse. The strongest ties exist in the areas of mineral-water and mineral-atmosphere interactions. Minerals are also particularly important in human disease generation. In addition, due to the role of minerals as invaluable economic resources, the environmental consequences of mining also come into play. New subdisciplines have recently emerged to bring mineralogy even closer to Earth sustainability issues, particularly mineral-microbe interaction science and nanomineralogy

Aspects of the (bio)geochemical cycling of metals (including Fe, Cu, Pb, Zn, Hg, As, Sb, U, Tc, Np) at or near the Earth's surface are discussed with reference to the recent work of the authors. Key stages of the breakdown of metalliferous minerals, transport of metals as solution complexes or colloidal precipitates, and interaction of metals in solution with the surfaces of minerals are considered. Emphasis is on molecular-scale observations using techniques such as scanning probe microscopy, photoelectron and (synchrotron) X-ray spectroscopies. The importance of the biological/mineralogical interface is also emphasized with reference to the bacterial colonization of mineral surfaces and formation of biofilms, and their influence on mineral surface reactivity and flow of fluids through rocks and sediments. Also noted is the importance of relating molecular and micro-scale observations to macroscopic phenomena. Molecular-scale understanding is central to attempts to model many processes of relevance in mineral exploration and exploitation, and in the containment of hazardous wastes and remediation of polluted areas. Mineralogists have a central role to play in the relevant environmental sciences and technologies.

Clays are the most complicated objects in quantitative mineral analysis of sedimentary rocks. Complex quantitative analysis of clays comprises four major steps: measuring bulk quantities, quantifying the mixed layering, determining the three-dimensional organization, and measuring the particle size. Computerization has resulted in major progress in all four areas during the last decade. X-ray diffraction remains the major tool of the quantitative studies of clays, supported by Fourier Transform Infrared Spectroscopy (bulk quantities), chemical analysis (bulk quantities) and electron microscopy (particle size). This contribution reviews recent developments in the techniques used for quantifying clays and their properties, and looks at the use of these quantification techniques in K-Ar dating of geological processes.

Mineral replacement reactions take place primarily by dissolution-reprecipitation processes. Processes such as cation exchange, chemical weathering, deuteric alteration, leaching, pseudomorphism, metasomatism, diagenesis and metamorphism are all linked by common features in which one mineral or mineral assemblage is replaced by a more stable assemblage. The aim of this paper is to review some of these aspects of mineral replacement and to demonstrate the textural features they have in common, in order to emphasize the similarities in the underlying microscopic mechanisms. The role of volume change and evolution of porosity is explored both from natural microtextures and new experiments on model replacement reactions in simple salts. It is shown that the development of porosity is often a consequence of mineral replacement processes, irrespective of the relative molar volumes of parent and product solid phases. The key issue is the relative solubility of the phases in the fluid phase. Concepts such as coupled dissolution-precipitation, and autocatalysis are important in understanding these processes. Some consequences of porosity generation for metamorphic fluid flow as well as subsequent crystal growth are also discussed.

From a few examples, the first part of this paper discusses the use of transmission electron microscopy in characterizing arrested silicate reaction mechanisms in coherent rocks, including nucleation, crystal growth, and resorption events. Some attention is given to the role of reaction sites and strain. The second part of the paper addresses the wealth of mutual arrangement of serpentine tubules (chrysotile sl) found recently in serpentinite cracks, the result of hydration reactions. It is suggested that their great flexibility of association as fascinating mesostructures may indicate how veins formed and how they were filled. Micro- to nano-cracks might potentially serve as markers of brittle deformation in the submicron range, and therefore might document nanostructural geology. When possible the topological and self-assembly features observed for chrysotile are compared with those reported for graphene nanotubes.

The macroscopic behaviour of minerals is not always directly related to their crystalline structure at the atomic scale but often depends explicitly on mesoscopic (nanometer–micrometer) features. This paper reviews various cases where the macroscopic phenomena differ from those of the bulk, with structural and chemical variations related to: domain walls, leading to enhanced or reduced transport properties; surfaces controlling growth morphologies; and radiation-damaged minerals where the interface between the amorphous and crystalline phase is believed to play a key role in hydrothermal leaching behaviour. Minerals explicitly discussed are: quartz, agate, hydroxylapatite, cordierite and metamict zircon.

The importance of impact cratering on terrestrial planets is obvious from the abundance of craters on their surfaces. On Earth, active geological processes rapidly obliterate the cratering record. To date only about 170 impact structures have been recognized on the Earth's surface. Mineralogical, petrographic, and geochemical criteria are used to identify the impact origin of such structures or related ejecta layers. The two most important criteria are the presence of shock metamorphic effects in mineral and rock inclusions in breccias and melt rocks, as well as the demonstration, by geochemical techniques, that these rocks contain a minor extraterrestrial component. There is a variety of macroscopic and microscopic shock metamorphic effects. The most important ones include the presence of planar deformation features in rock-forming minerals, high-pressure polymorphs (e.g. of coesite and stishovite from quartz, or diamond from graphite), diaplectic glass, and rock and mineral melts. These features have been studied by traditional methods involving the petrographic microscope, and more recently with a variety of instrumental techniques, including transmission electron microscopy, Raman spectroscopy, cathodoluminescence imaging and spectroscopy, and high-resolution X-ray computed tomography. Geochemical methods to detect an extraterrestrial component include measurements of the concentrations of siderophile elements, mainly of the platinum-group elements (PGEs), and, more recently, chromium and osmium isotopic studies. The latter two methods can provide confirmation that these elements are actually of meteoritic origin. The Cr isotopic method is also capable of providing information on the meteorite type. In impact studies there is now a trend towards the use of interdisciplinary and multi-technique approaches to solve open questions.

A combination of Kawai-type multianvil apparatus and highly brilliant X-rays at the third generation synchrotron radiation facility (SPring-8) in Japan has been successfully applied to various studies in high-pressure mineral sciences such as determinations of phase transition boundaries, P–V–T relations of high-pressure phases, kinetics of phase transitions, structure and viscosity of melts. These studies are now comfortably made at pressures of ˜25 GPa and at temperatures to 2300°C, using the intense X-ray beam and the large capacity of the high-pressure apparatus at SPring-8. Moreover, efforts have been made to further extend the pressure limit using large sintered diamond anvils. Thus in situ X-ray observations are now possible at pressures to 50 GPa with the Kawai-type apparatus, which may be doubled in the near future when the potential of sintered diamond anvils is fully utilized. On the other hand, some problems, such as those related to pressure and temperature measurement, have been manifested in these studies. These should be overcome for further quantitative studies of the mineralogy of the Earth's deep interior based on these techniques.

Recent diamond-anvil cell experiments are providing windows of unprecedented clarity on the interiors of the Earth, other planets, and their moons from high P-T studies of the materials that comprise these bodies. With recent advances in techniques, the component minerals can be examined with a growing array of in situ methods over an expanding range of conditions that extend to hundreds of gigaspascals in pressure and thousands of degrees in temperature. Such investigations reveal that major, if not profound, changes in physical and chemical properties of these materials occur with depth. This information is crucial for understanding the materials basis of regional to global structure and processes documented by a wealth of recent observational and geophysical data. This paper reviews selected recent studies of major planet-forming minerals, focusing on key examples that illustrate different microscopic origins of macroscopic behaviour. This comparative mineralogical approach provides insight into phenomena occurring over a wide range of length scales. For terrestrial planets, the high-pressure behaviour of representative silicates, oxides and sulphides is examined. This includes the silicate perovskite assemblages that form the bulk of the Earth's lower mantle, for which a number of new findings concerning effects of non-stoichiometry and defect properties, pressure-induced electronic and magnetic transitions, and rheology have been obtained. High P-T studies of Fe-Ni alloys, together with various light elements, provide constraints on the composition, structure and dynamics of terrestrial planet cores. Water is a key component of many planetary bodies; as ice it undergoes numerous high-pressure transformations and as a volatile component it is involved in potentially important high P-T mineral reactions and is incorporated in dense mineral phases. Striking behaviour is observed in other molecular systems, including CO2 and CH4 and their mixtures with H2O; these form new phases, some relevant at the relatively modest conditions of deep marine sediments, others at the extreme states found in the deepest planetary interiors. Additional high P-T interactions between rare gases and ices and silicates are also documented. For the large planets, the most abundant ‘mineral’ is hydrogen, which has been shown to undergo novel mineral/gas reactions, possibly in cloud decks deep within the dense atmospheres of these bodies.