The construction of zirconium (Zr) budgets for metamorphic reactions in high-grade rocks provides new insight into zircon growth during metamorphism. In this study we target reactions involving garnet, as they enable zircon growth to be related to known pressure and temperature conditions. Two reactions involving the breakdown of Zr-bearing garnet from Rogaland, SW Norway have been investigated in detail, showing contrasting behaviour of Zr, with zircon formation being subject to the solubility of Zr in product phases. In the decompression reaction garnet + sillimanite + quartz → cordierite, Zr released during garnet breakdown cannot be incorporated into the cordierite structure, resulting in zircon nucleation and growth. In contrast, for the reaction garnet + biotite + sillimanite + quartz → osumilite + orthopyroxene + spinel + magnetite, no new zircon growth takes place, despite the garnet involved containing more than double the Zr concentration of the former reaction. In the latter case, all the Zr released by garnet breakdown can be detected in the product phases osumilite and orthopyroxene, thereby preventing growth of new metamorphic zircon. This study highlights the potential for high resolution geochronology in metamorphic rocks by relating zircon growth to specific metamorphic reactions.

Micas incorporate a wide variety of elements in their crystal structures. Elements occurring in significant concentrations in micas include: Si, IVAl, IVFe3+, B and Be in the tetrahedral sheet; Ti, VIAl, VIFe3+, Mn3+, Cr, V, Fe2+, Mn2+, Mg and Li in the octahedral sheet; K, Na, Rb, Cs, NH4, Ca and Ba in the interlayer; and O, OH, F, Cl and S as anions. Extensive substitutions within these groups of elements form compositionally varied micas as members of different solid-solution series. The most common true K micas (94% of almost 6750 mica analyses) belong to three dominant solid-solution series (phlogopite–annite, siderophyllite–polylithionite and muscovite–celadonite). Theirclassification parameters include: Mg/(Mg+Fetot) [=Mg#] formicas with VIR >2.5 a.p.f.u. and VIAl <0.5 a.p.f.u.; Fetot/(Fetot+Li) [=Fe#] formicas with VIR >2.5 a.p.f.u. and VIAl >0.5 a.p.f.u.; and VIAl/(VIAl+Fetot+Mg) [=Al#] formicas with VIR <2.5 a.p.f.u. The common true K micas plot predominantly within and between these series and have Mg6Li <0.3 a.p.f.u. Tainiolite is a mica with Mg6Li >0.7 a.p.f.u., or, fortr ansitional stages, 0.3–0.7 a.p.f.u. Some true K mica end-members, especially phlogopite, annite and muscovite, form binary solid solutions with non-K true micas and with brittle micas (6% of the micas studied). Graphical presentation of true K micas using the coordinates Mg minus Li (= mgli) and VIFetot+Mn+Ti minus VIAl (= feal) depends on theirclassification according to VIR and VIAl, complemented with the 50/50 rule.

Biominerals are a subset of the mineral kingdom, those created by living creatures. In spite of usually fine grain size and intimate association with organic materials, biominerals are readily identified as common mineral species. Iron hydroxides and oxyhydroxides, calcium carbonates and calcium phosphates from uni- and multi-cellular species are presented as examples of biominerals, and biomineralization processes. Their special morphological, and crystal chemical, characteristics provide unique structural contributions to the life forms that create them. Investigations of novel habitats should present opportunities to expand the number of biominerals and their potential for industrial applications.

A complete mechanism for the transformation goethite to hematite based upon the results of thermogravimetric, transmission electron microscope and X-ray diffraction investigations is presented. A porous microstructure and hematite crystallites in twin orientation are found to develop during transformation. For the main part of the transformation, and at higher temperatures, the reaction is controlled by a two-dimensional phase boundary. Activation energies of 169 ± 8 kJ/mole (for an ore mineral) and 154 ± 15 kJ/mole (for a recent sedimentary goethite) were obtained for this part of the transformation. At early stages and lower temperatures, the mechanism is one of proton/iron transfer across the reaction interface. Important goethite characteristics are grain size, shape, crystallinity and excess water content. The activation energy is found to depend upon temperature and degree of dehydration.

Most countries intend to dispose of their high-level radioactive wastes by converting them into a solidified wasteform which is to be buried within the earth. SYNROC is a titanate ceramic wasteform which has been designed for this purpose on the basis of geochemical principles. It comprises essentially rutile TiO2, ‘hollandite’ Ba(Al,Ti)Ti6O16, zirconolite CaZrTi2O7, and perovskite CaTiO3. The latter three phases have the capacity to accept the great majority of radioactive elements occurring in high-level wastes into their crystal lattice sites. These minerals (or their close relatives) also occur in nature, where they have demonstrated their capacity to survive for many millions of years in a wide range of geological environments. The properties of SYNROC and the crystal chemistry of its constituent minerals are reviewed in some detail and current formulations of SYNROC are summarized. A notable property of SYNROC it its extremely high resistance to leaching by groundwaters, particularly above 100°C. In addition, it can be shown that the capacity of SYNROC minerals to immobilize high-level waste elements is not markedly impaired by high levels of radiation damage. Current investigations are focused on developing a satisfactory production technology for SYNROC and progress towards this objective is described. The high leach resistance of SYNROC at elevated temperatures increases the range of geological environments in which the waste may be finally interred; in particular, SYNROC is well adapted for disposal in deep drill-holes, both in continental and marine environments. The fact that SYNROC is comprised of minerals which have demonstrated long-term geological stability is significant in establishing public confidence in the ability of the nuclear industry to immobilize high-level wastes for the very long periods required.

Relative to its extremely low abundance in the Earth's crust, tellurium is the most mineralogically diverse chemical element, with over 160 mineral species known that contain essential Te, many of them with unique crystal structures. We review the crystal structures of 703 tellurium oxysalts for which good refinements exist, including 55 that are known to occur as minerals. The dataset is restricted to compounds where oxygen is the only ligand that is strongly bound to Te, but most of the Periodic Table is represented in the compounds that are reviewed. The dataset contains 375 structures that contain only Te4+ cations and 302 with only Te6+, with 26 of the compounds containing Te in both valence states. Te6+ was almost exclusively in rather regular octahedral coordination by oxygen ligands, with only two instances each of 4- and 5-coordination. Conversely, the lone-pair cation Te4+ displayed irregular coordination, with a broad range of coordination numbers and bond distances. A threshold was applied for Te4+–O links of ∼2.45 Å or 0.3 valence units with some flexibility, as a criterion to define strongly bound Te–O polymers and larger structural units. Using this criterion, Te4+ cations display one-sided 3-, 4- or 5-coordination by oxygen (with rare examples of coordination numbers 2 and 6). For both valence states of Te, examples are known of TemOn complexes which are monomeric (m = 1; neso), noncyclic finite oligomers (soro), rings (cyclo), infinite chains (ino), layers (phyllo) and frameworks (tecto tellurates). There is a clear analogy to the polymerization classes that are known for silicate anions, but the behaviour of Te is much richer than that of Si for several reasons: (1) the existence of two cationic valence states for Te; (2) the occurrence of multiple coordination numbers; (3) the possibility of edge-sharing by TeOn polyhedra; (4) the possibility for oxygen ligands to be 3-coordinated by Te; and (5) the occurrence of TemOn polymers that are cationic, as well as neutral or anionic. While most compounds contain only one or two symmetrically distinct types of Te atom, Pauling's Fifth Rule is frequently violated, and stoichiometrically simple compounds such as CaTeO3 can have polymorphs with up to 18 distinct Te sites. There is a tendency for local symmetry features such as the threefold axis of a TeO6 octahedron or the acentric symmetry of a Te4+On polyhedron to be inherited by the host structure; the latter in particular can lead to useful physical properties such as nonlinear optical behaviour. We develop for the first time a hierarchical taxonomy of Te-oxysalt structures, based upon (1) valence state of Te; (2) polymerization state of TemOn complexes; (3) polymerization state of larger strongly-bound structural units that include non-Te cations. Structures are readily located and compared within this classification.

Concentration data are reported for 18 trace elements in chalcopyrite from a suite of 53 samples from 15 different ore deposits obtained by laser-ablation inductively-coupled plasma-mass spectrometry. Chalcopyrite is demonstrated to host a wide range of trace elements including Mn, Co, Zn, Ga, Se, Ag, Cd, In, Sn, Sb, Hg, Tl, Pb and Bi. The concentration of some of these elements can be high (hundreds to thousands of ppm) but most are typically tens to hundreds of ppm. The ability of chalcopyrite to host trace elements generally increases in the absence of other co-crystallizing sulfides. In deposits in which the sulfide assemblage recrystallized during syn-metamorphic deformation, the concentrations of Sn and Ga in chalcopyrite will generally increase in the presence of co-recrystallizing sphalerite and/or galena, suggesting that chalcopyrite is the preferred host at higher temperatures and/or pressures. Trace-element concentrations in chalcopyrite typically show little variation at the sample scale, yet there is potential for significant variation between samples from any individual deposit. The Zn:Cd ratio in chalcopyrite shows some evidence of a systematic variation across the dataset, which depends, at least in part, on temperature of crystallization. Under constant physiochemical conditions the Cd:Zn ratios in co-crystallizing chalcopyrite and sphalerite are typically approximately equal. Any distinct difference in the Cd:Zn ratios in the two minerals, and/or a non-constant Cd:Zn ratio in chalcopyrite, may be an indication of varying physiochemical conditions during crystallization.

Chalcopyrite is generally a poor host for most elements considered harmful or unwanted in the smelting of Cu, suggesting it is rarely a significant contributor to the overall content of such elements in copper concentrates. The exceptions are Se and Hg which may be sufficiently enriched in chalcopyrite to exceed statutory limits and thus incur monetary penalties from a smelter.

The crystal structures of sjögrenite and pyroaurite, two stacking modifications of approximate composition Mg6Fe2(OH)16(CO3).4H2O, have been determined by X-ray diffraction using three-dimensional methods. Sjögrenite is hexagonal, with a 3·13, c 15·66 Å, space group P63/mmc , Z = ¼; pyroaurite is rhombohedral, with aH 3·13, cH 23·49 Å, space group R3̄m or R3m, Z = ⅜. Both structures are based on brucite-like layers, with magnesium and iron distributed among the octahedral positions. The cations appear to be largely disordered, although ordered regions may occur in some crystals. Between the brucite-like layers are the water molecules and carbonate groups. These are statistically arranged, with their oxygen atoms distributed among a larger number of possible sites.

Examples of oscillatory zoning in metamorphic minerals, imaged using a Back-Scattered Electron Detector on the SEM, are described from a series of contrasting environments. These are a prehnite vein sampled by drilling in the Mirvalles geothermal field, Costa Rica, a pyroxene vein developed in a regional metamorphic shear zone in the Yilgarn block, Western Australia, and a bedded metasomatic diopside rock from regionally metamorphosed metasediments in Connemara, Ireland. In each case the formation of oscillatory zoning can be ascribed to mineral growth under supersaturated conditions due to fluid infiltration. Oscillations can be related in the first example to periodic episodes of pressure release and boiling in the geothermal field, but in the regional metamorphic examples actualistic models are harder to define. The development of oscillatory zoning is likely to be a characteristic feature of infiltration metasomatism and can be used as a criterion in the recognition of metasomatic mineral growth in metamorphic rocks outside the vein environment.

We live at the dynamic interface between the solid Earth and its outer fluid envelopes. This interface, extending from the outer vegetation canopy to the base of active groundwater, was recently named the Critical Zone because it supports life and is increasingly impacted by human actions. Understanding the complex interactions between processes that operate in and shape the Critical Zone requires interdisciplinary approaches that span wide spatial and temporal scales. Tectonic processes, weathering, fluid transport, and biological processes control the function and structure of the Critical Zone. Three Critical Zone Observatories recently established by the U.S. National Science Foundation are designed to integrate studies of process interactions up to the watershed scale. A goal of the program is to build the three independently conceived observatories into a network from which broader understanding — larger spatial scales but also deeper insight — can emerge.

The Miocene Monterey Formation constitutes a fracture-controlled petroleum reservoir, with intercalated calcareous and fine-grained siliceous rocks serving as both the source and reservoir for oil accumulations. Petroleum is produced from macroscopic fractures, and numerous tar and asphalt seeps at the surface attest to the present-day movement of hydrocarbons through fractures in the Monterey Formation. Many fractures are filled with carbonate (mostly calcite and dolomite), quartz, baryte and anhydrite. These same fractures often contain tar or oil filling openings, and occasionally a thin layer of oil can be seen coating growth surfaces between two generations of vein-filling minerals.

Evidence for migration of fluids through these fractures in the geological past is provided by aqueous and petroleum fluid inclusions contained within vein-filling minerals. Vein-filling dolomite from Jalama Beach contains three different types of primary petroleum inclusions (based on fluorescence characteristics)—indicating that oils with significantly different API gravities flowed through the fractures. Petrographic and microthermometric analyses of oil and coexisting aqueous inclusions indicate that the fracture-filling minerals precipitated from aqueous solutions of seawater salinity at ∼75–100°C, and that oil was introduced into the fracture system episodically during mineral growth. A sample from the Lion's Head area consists of early calcite and late quartz, both of which contain aqueous inclusions with seawater salinity. Inclusions in quartz homogenize at slightly higher temperatures than those in calcite. These data are consistent with calcite deposition during an early heating event, followed by quartz deposition during cooling. No petroleum inclusions were observed in the Lion's Head sample.

Normal carbonatite magmas are characteristically associated with ijolites and produce extensive fenitization by alkali metasomatism, commonly feldspathization or phlogopitization. The sequence of carbonatites developed from this magma are characterized by igneous isotopic ratios, high contents of incompatible elements, their distinctive pattern of differentiation from sövite to beforsite, and a late-stage rare-earth element, baryte, fluorite mineralization. Carbonatite rock is composed mainly of calcite, but fluid inclusion and related data indicate that the original magma was highly alkaline and chemically similar to that known at Oldoinyo Lengai volcano in Tanzania. It is suggested that this carbonatite magma is secondary magma produced from carbonated nephelinite magma by liquid immiscibility. Carbonatite magma can also occur associated with kimberlites but these carbonatites are alkali-poor and do not produce the characteristic fenitization.

A new synthesis of Mg-Al double hydroxides is described, that gives products relatively low (0.8–1.0%) in CO2. The general formula [Mg1−xAlx (OH)2][(OH)x(H2O)0.81−x] with 0.23 ≤ x ≤ 0.33 is proposed. Cell parameters and thermal data are given. The c-axial length decreases with Al-content; this is attributed to increased electrostatic attraction between layers.

Zircon frequently occurs as a minor mineral in kimberlites, and is recognised as a member of a suite of mantle-derived megacryst minerals. Cathodoluminescence (CL) microscopy and laser ablation ICPMS analysis were used to study the internal structure and chemical composition of zircon crystals from southern African kimberlites. Zoning revealed by CL ranges from fine oscillatory to broad homogeneous cores and overgrowths. The ICPMS data show that kimberlite zircons have distinctive trace element contents, with well defined ranges for REE, Y, U, Th, P and some other trace elements. Both low REE contents (ΣREE < 50 ppm), and distinctive chondrite-normalised REE patterns with low and flat HREE are characteristic of kimberlite zircons. Samples or zones with yellow CL have higher Th, U, Y, and REE than those with blue-violet CL. Variations in the concentrations of a range of trace elements lead to different amounts of lattice defects, creating the possibility for different levels of direct excitation of luminescence centres, and therefore different CL colours. The distinctive CL and compositional features described here can rapidly identify kimberlite zircons in prospecting samples taken during exploration for kimberlite bodies.

The work on liquid immiscibility in carbonate-silicate systems of Freestone and Hamilton (1980) has been extended to include alkali-poor and alkali-free compositions. Immiscibility is shown to occur on the joins albite-calcite and anorthite-calcite at 5 kbar. These results make it possible to interpret ocellar structure between calcite-rich spheroids in lamproite or kimberlite host rock as products of liquid immiscibility. The common sequence of rock types found in carbonatite complexes of melilitite-ijolite-urtite-phonolite is interpreted as being the result of both fractional crystallization and liquid fractionation, the corresponding carbonatite composition changing from nearly pure CaCO3 (±MgCO3) progressively to natrocarbonate. A carbonate melt cooling in isolation will suffer crystal fractionation, the residual liquid producing the rarer ferrocarbonatites, etc., whilst the crystal accumulate of calcite (dolomite) plus other phases such as magnetite, apatite, baryte, pyrochlore, etc., are the raw material for the coarse-grained intrusive carbonatites commonly found in ring complexes.

The origin in rocks of the common iron sulphides, pyrrhotine, Fe1-xS and pyrite, FeS2 and their behaviour during geochemical processes is best considered using the simplified redox reaction: 2FeS ⇌ FeS2 + Fe2+ + 2e−.

Thus pyrrhotine is more reduced than pyrite and is the stable iron sulphide formed from magmas except where relatively high oxygen fugacities result from falling pressure or hydrothermal alteration. Pyrite, on the other hand, is the stable iron sulphide in even the most reduced sedimentary rocks where it usually forms during diagenesis through bacteriogenic reduction of sulphate; it is stable throughout the pressure/temperature range endured by normal sedimentary rocks. Pyrrhotine after pyrite or sulphate in metasediments of regional metamorphic origin results mainly from progressive reduction on metamorphism due to the presence of graphite-buffered fluids. Pyrrhotine and/or pyrite may be precipitated from hydrothermal solutions on epigenetic or syngenetic mineralization but pyrrhotine will only be preserved if protected from oxidation to pyrite or to more oxidized species. Exhalative pyrrhotine appears to have been more common in Precambrian times and/or in depositional environments destined to become regionally metamorphosed. FeS can be considered to be the soluble iron sulphide, rather than FeS2, in reduced aqueous systems although pyrite may precipitate from solution as a result of redox reactions. The relatively soluble nature of FeS explains the observed mobility of iron sulphides in all rock types.

Total neutron scattering measurements, analysed using a modification of the reverse Monte Carlo modelling method to account for long-range crystallographic order, have been used to describe the temperature-dependent behaviour of the structure of quartz. Two key observations are reported. First, the symmetry change associated with the displacive α–β phase transition is observed in both the long-range and short-range structural correlations. Secondly, some aspects of the structure, such as the Si–O bond length and the thermally-induced dynamic disorder, the latter of which sets in significantly below the transition, are relatively insensitive to the phase transition. These results are used to show that the α-domain model of the β-phase disorder is inappropriate and that the classical soft-mode picture of the phase transition is too simplistic. Instead, it is argued that the structural behaviour is best described in terms of its ability to respond to low-frequency, high-amplitude vibrational modes. This view is supported by additional single-crystal diffuse neutron scattering measurements.

Equilibrium thermodynamic methods are used to develop an independent iron-titanium oxide geothermometer and oxygen barometer from the experimental data of Buddington and Lindsley (1964). The geothermometer and oxygen barometer are presented graphically for coexisting ilmenite solid solution and magnetite solid solution in the system FeO-Fe2O3-TiO2. Equations are also given for calculating temperature and oxygen activity for natural coexisting iron-titanium oxides containing other components. Large departures in composition from the system FeO-Fe2O3-TiO3 result in large uncertainties in the calculated temperature and activity of oxygen.

It is now generally agreed that the term ‘agpaitic’ should be restricted to peralkaline nepheline syenites (and phonolites) containing minerals such as eudialyte and rinkite, that is complex silicates of Zr, Ti, the rare earth elements (REE), and F and other volatiles. There are, however, cases of transition into more common types of nepheline syenites containing zircon, titanite, ilmenite, etc.

The agpaitic rocks are characterized by extremely high contents of rare elements such as Li, Be, Nb, Ta, REE, Zr, Th, etc. and of volatiles, first of all F and Cl. This gives rise to a wealth of mineral species, more than 500 in the Lovozero and Khibina complexes of the Kola peninsula, about 250 in Mont Saint-Hilaire, Quebec, Canada, and about 200 in the type locality, the Ilímaussaq complex, South Greenland.

These rocks have very long melting intervals and solidus temperatures as low as 500 to 400°C. They are accompanied by a gas phase rich in methane and other hydrocarbons and most probably also by sodium-rich fluids as indicated by the presence of minerals such as ussingite (NaAlSi3O8·NaOH) and villiaumite (NaF) and of pegmatites and hydrothermal veins rich in sodium and rare and volatile elements.

Agpaitic nepheline syenites are considered to have been formed by consolidation of melts oversaturated in alkalis, especially sodium, under conditions preventing the volatiles from escaping. These melts have been derived by extreme fractionation processes in alkali basaltic or nephelinitic magmas. The main stage of crystallization of the melts is characterized by minerals such as nepheline (sometimes also sodalite), alkali feldspars, arfvedsonite, aegirine and eudialyte, but the most highly developed, hyperagpaitic lujavrites of the Ilímaussaq complex have been formed from melts with extreme concentrations of sodium and volatiles resulting in the formation of naujakasite instead of nepheline, ussingite instead of sodalite and alkali feldspars, and steenstrupine instead of eudialyte. During the late stages of crystallization, sodium-rich fluids are the cause of late- and postmagmatic alteration and of the formation of hydrothermal mineralizations. The late stages are characterized by water-soluble sodium-rich minerals of which more than 80 have been found in the Khibina and Lovozero complexes.

Homogeneous and heterogeneous phase relationships in the alkali feldspars are reviewed, and behaviour diagrams developed. Al,Si ordering is almost certainly continuous and higher order in both albite and potassium feldspar and has been established reversibly or nearly so down to below 500°C in albite and possibly to ∼ 200°C in potassium feldspar. The degree of order in intermediate albite changes strongly over a range of ∼ 75–150°C depending on pressure, low albite being stable up to about 620–650°C and high albite above about 725°C at low pressure. Symmetry is broken at ∼ 980°C mainly by a cooperative shearing of the whole framework and not by Al,Si ordering alone; there is a thermal crossover near 700°C shearing being dominant above (high albite) and ordering dominant below (intermediate albite).

In potassium feldspar symmetry is broken by Al,Si ordering at a temperature of about 500°C The change in degree of order with respect to temperature has been followed easily and reversibly in sanidine from ∼ 1075 to ∼ 550°C and to a lesser extent in microcline from 450 to 200°C. Ordering rates in sanidine down to 500°C and ordering rates in microcline between 450 and 200°C are almost as fast as in albite. Ordering in sanidine at 500°C and below slows and then stops with the development of the tweed orthoclase domain texture. The tweed texture acts as a barrier to further order because the strain energy associated with the (incipient) twin domain texture balances or nearly balances the free energy decrease resulting from ordering. Ordering stops not because of the kinetics of Al,Si diffusion, but because the total driving force is very small or nil. Ordering can readily proceed to completion, with the formation of low microcline, only if the domain-texture barrier is overcome by processes involving fluids or strong external stresses. There is no barrier in albite.

The symmetry-breaking process in alkali feldspar changes with composition from mainly shearing in albite to ordering in potassium feldspar. Symmetry is broken equally at a compositional crossover (metastable with respect to exsolution) near Ab80-75 at low pressure and progressively displaced towards Or at higher pressures. Ordering in pure albite occurs by a (nearly) one-step path which progressively becomes two-step with substitution of Or. Diagrams showing the near-equilibrium variation of the order parameters at low pressure with composition and T are given, as well as two extreme phase and behaviour diagrams for complete coherent and complete incoherent (strain-free) relationships. These diagrams can be used to understand feldspar relationships and microtextures in hypersolvus and subsolvus rocks, the occurrence of orthoclase, and of intermediate and low microcline.