The original description of nickelphosphide from the Butler meteorite [(Ni1.83Fe1.21)Σ3.04P0.96 to (Ni1.71Fe1.28Co0.01)Σ3.00P1.00] lacks detailed and accurate powder data – with only 11 observed reflections down to 1.37 Å. Consequently, no crystal structure information for this phase is available. Here we present the crystal structure for a synthetic analogue of the phase found in the Vicenice IID medium octahedrite (with a mean empirical formula of (Ni1.69Fe1.31)Σ3.00P1.00) and a hypothetical Ni3P end-member. Unit-cell dimensions of the synthetic analogue of Ni1.68Fe1.33P0.99 composition from individual peak profile fitting of XRD data collected with Cu radiation are a= 9.0168(2)Å, c= 4.4491(1)Å, V= 361.72(1)Å3 and those for Ni3P composition are a= 8.9546(1)Å, c= 4.38714(8)Å, V= 351.783(8)Å3. The space group of the mineral is I4¯ and Z= 8. The crystal structure refined from powder data by the Rietveld method is consistent with that refined and published for Fe3P and Ni3P synthetic compounds as well as Fe-dominant schreibersite from single-crystal data. However, because of the similarity of the scattering of iron and nickel, we were not able to refine directly the site occupancies in the synthetic analogue of the nickelphosphide from the Vicenice iron meteorite.

The Assynt Culmination of the Moine Thrust Belt, in the northwest Scottish Highlands, contains a variety of Caledonian alkaline and calc-alkaline intrusions that are mostly of Silurian age. These include a significant but little-studied suite of dykes and sills, the Northwest Highlands Minor Intrusion Suite. We describe the structural relationships of these minor intrusions and suggest a classification into seven swarms. The majority of the minor intrusions can be shown to pre-date movement in the Moine Thrust Belt, but some appear to have been intruded during the period of thrusting. A complex history of magmatism is thus recorded within this part of the Moine Thrust Belt. New geochemical data provide evidence of a subduction-related component in the mantle source of the minor intrusions.

Tacharanite has been re-examined using electron microscopy and diffraction, analytical microscopy, X-ray powder and fibre rotation photographs, and other methods. The composition approximates to Ca12Al2Si18O69H36, and the X-ray diffraction patterns can be referred to an A-centred monoclinic pseudo-cell with a 17·07, b 3·65, c 27·9 Å, β 114·1°, Z = 1. In the true cell b is certainly, and a and c probably, doubled. Small, reversible changes in pseudo-cell parameters occur on heating below 200°C, and parameters found by electron diffraction differ slightly from those found with X-rays, presumably due to shrinkage on dehydration in the high vacuum of the electron microscope. An earlier report that tacharanite changes into a mixture of tobermorite and gyrolite on standing in air is not confirmed. Tacharanite shows some important resemblances to tobermorite, but there are also significant differences.

A gradational increase in concentration of CO2 towards the margins of a very fine-grained basalt dyke has led to the development of a pale marginal facies, enriched in carbonates, particularly siderite. Increases in CO2 from about 3 % in the interior of the dyke to 8 % at the margins are accompanied by decreases in SiO2 and Fe2O3, increases in Al2O3, and less significant changes in the other major components. Cu, Co, and Zn change only slightly, and Cr, Ni, and Li remain constant. Petrographic variation is considerable, even in the superficially homogeneous interior of the dyke, in which it ranges from a type containing a titanaugite (analysed) to one devoid of pyroxene, but containing conspicuous opaque minerals. Microprobe analysis for Fe and Ti shows that these comprise: cotahedral titaniferous magnetite; rodlets, less than 1 µm thick, of rutile partly altered to, or overgrown by, ilmenite; and sub-opaque patches with a very low Ti/Fe ratio. Plagioclase, An55, is the most abundant and constant crystalline phase in the interior of the dyke, but changes to An20 in the marginal facies. Mineral-content of the latter, deduced from optical, chemical, and X-ray data, also includes siderite, serpentine and clay minerals, leucoxene, and apatite. There is no evidence of quartz, sericite, or calcite.

Petrographic evidence shows that variations in concentrations of CO2 and H2O affected phase equilibria from the start of magmatic crystallization. Data on the fO2 required for TiO2 and Fe-oxide phases to co-exist at magmatic temperatures indicate that, initially, the concentrations of CO2 and H2O in the interior of the dyke were higher than the values recorded in analyses of the rocks. From this evidence and the field relationships, it is concluded that the intruding magma was rich in volatiles, which diffused towards the dyke margins and, in part, became trapped as the magma congealed, producing a changed marginal assemblage of minerals. The dyke provides a unique glimpse of influences on a basic magma exerted by what S. J. Shand has aptly termed the ‘fugitive constituents’, the transient effects of which are rarely preserved in the rocks.

Differential thermal analysis of a rapidly reversible transition in carnegieite to 7 kbar shows the transition temperature increases from ⪝ 707°C (on heating) at I bar with initial slope ≈ 8·0 deg kbar−1 and anomalous curvature (d2T/dp2 > o), with hysteresis between heating and cooling signals that decreases with pressure. DTA of rapidly reversible transitions in nepheline shows the very subtle transition near 185°C (on heating) at 1 bar decreases with pressure to ≈ 170°C near 2-3 kbar and hardly varies in temperature up to 6 kbar; and the higher temperature transition increases from ≈ 872°C (on heating) at 1 bar with slope ≈ 25 deg kbar−1, to 5 kbar, with the hysteretic interval remaining essentially unchanged in the investigated range.

Endoskarns formed where a swarm of diorite dykes have intruded calcite marble at Redcap Creek include an inner melilite-dominated, a wollastonite-dominated, and an outer massive tilleyite zone in contact with marble. The massive tilleyite is unusual in that it is coarse-grained (prisms 2–15 cm in length) and its deep grey colour contrasts with the lighter coloured varieties described elsewhere. A chemical analysis gives a formula close to ideal, with only minor substitution of Al, Ti, and Mg. Refined unit cell parameters are in close agreement with those quoted in the literature. The skarns have clearly formed by transport of Si, Mg, Fe, Al, and Ti from the igneous rocks, and Ca in the reverse direction from the marble. Activity diagrams derived from experimental data are most useful in interpreting the zonal sequence of endoskarns, and preliminary results suggest mass transfer at low Xco2 and temperature of the order of 800°C or higher for the formation of the massive tilleyite.

The degree of metamorphism affecting the Devonian-Carboniferous rocks of the Palaeozoic Cinco Villas massif has been studied by (a) petrographic techniques, (b) illite crystallinity, and (c) degree of graphitization of the carbonaceous material. Some mineralogical differences have been found between the Devonian and Carboniferous rocks; paragonite and mixed-layer paragonite/muscovite, typical of anchimetamorphic areas, appear in the Devonian but are not found in the Carboniferous rocks. These are characterized by the local appearance of chloritoid, garnet, amphibole, epidote, andalusite and biotite, and the generalized presence of muscovite/chlorite. Illite crystallinity shows a metamorphic zonation (anchizone epizone) towards the granitic Aya massif, and a concentric pattern around the intrusive body.

The optical analysis shows that the first effects of the regional metamorphism began before the D2 deformation, reaching its paroxysm during this phase and continuing afterwards. The degree of graphitization evolves progressively with metamorphism, and this fact is reflected in an exponential relationship between d(002) and crystallinity Lc(002). The similarity in the degree of graphitization between homologous materials within and outside the Aya aureole suggests a similar kinetic factor for both the thermal and regional metamorphisms, or a similar duration time. This fact, as well as the distribution and relationship between the deformation and recrystallization of the minerals, suggests a syn-plutonic regional metamorphism developed at low pressures, in accordance with the value of the b0 parameter for the white micas, and probably a maximum temperature of about 500°C.

Three types of mafic granulites, namely two pyroxene-plagioclase granutite (MG), two pyroxeneplagioclase-garnet granulite (GMG) and spinel-olivine-plagioclase-two pyroxene granulite (SMG) are exposed at Sunkarimetta, Eastern Ghats belt, India. The marie granulites exhibit a foliation concordant with that in associated granulite facies quartzofeldspathic gneisses. Textural characteristics and mineral chemical data suggest the following mineral reactions: olivine + plagioclase = spinel + orthopyroxene + clinopyroxene (SMG), orthopyroxene + plagioclase = garnet + quartz (GMG), clinopyroxene + plagioclase = garnet + quartz (GMG) and plagioclase + hemoilmenite + quartz = garnet + ilmenite + 02 (GMG). Geothermobarometry indicates maximum P-T conditions of metamorphism at c. 8.5 kbar, 950°C The marie granulites later suffered nearly isobaric cooling to c. 7.5 kbar, 750°C Bulk compositional characteristics suggest that SMG is of cumulate origin. The protoliths of the mafic granulites, emplaced at c. 32 km depth, are probably responsible for thermal perturbation causing granulite facies metamorphism of the enclosing rocks.

The sizes, distributions and shapes of zircon grains within variably deformed granite gneiss from the western Alps have been studied. Zircon shows numerous indicators of a metamorphic response in both the host gneiss and a 5 cm wide continuous ductile shear zone, within which the zircon grain sizes range from <1 urn to >50 μm. However, the very fine grain sizes are virtually absent from grain boundaries. Within this zone, zircons consistently have more rounded and embayed margins, which are interpreted as evidence of dissolution in response to fluid influx during shearing. Zircons are preferentially located near metamorphic muscovite in both the host gneiss and the shear zone and tend to show the poorest crystal shape, indicating that fluids linked to the formation and presence of muscovite may enhance both the crystallization of zircon and its subsequent dissolution. Larger zircon crystals typically show a brittle response to deformation when adjacent to phyllosilicates, with fractures consistently perpendicular to the (001) mica cleavage. The variety of metamorphic behaviour observed for zircon indicates that it may be highly reactive in sub-solidus mid-crustal metamorphic environments.

Irinarassite, Ca3Sn2SiAl2O12, a new mineral species of the garnet supergroup was discovered in metasomatically altered carbonate-silicate xenoliths in ignimbrites of the Upper Chegem Caldera, Northern Caucasus, Kabardino-Balkaria, Russia. It occurs as small zones and irregular spots in kimzeyite-kerimasite or rarely as single crystals not exceeding 10 μm in size, within complex pseudomorphs after zircon. Lakargiite, tazheranite, baddeleyite, kerimasite, kimzeyite, baghdadite and rarely magnesioferrite are associated with irinarassite in the pseudomorphs which are confined to larnite-cuspidine zones immediately adjoining the ignimbrite. Larnite, cuspidine, rondorfite, fluor- and hydroxylellestadite, fluorite and secondary minerals such as ettringite, hillebrandite and bultfonteinite are associated with irinarassite. Irinarassite is pale brown to yellow colour. The mineral is characterized by the absence of cleavage and by an irregular fracture. The calculated density is 4.3 g cm–1. The mineral is isotropic with a calculated refractive index of 1.9. The empirical crystal chemical formula of irinarassite from the holotype specimen is as follows (Ca2.965Fe2+0.035)Σ3(Sn1.016Zr0.410Ti0.262Sb5+0.237Fe2+0.035U6+0.017Sc0.014Hf0.006Nb0.004)Σ2.001(Al1.386Fe3+0.804Si0.446Ti4+0.364)Σ3O12. Electron backscatter diffraction patterns of irinarassite are fitted to the garnet model with a = 12.50(3) Å with excellent MAD (mean angular deviation) = 0.16°. The Raman spectrum of irinarassite is analogous to those of kerimasite and other Zr-Sn-garnets of the schorlomite and bitikleite groups.

The crystal structure and chemical composition of two samples of fettelite from the type locality, including a portion of the holotype material, was investigated to verify if a previously proposed revision of the chemical formula was applicable, and to study the role of cation substitution for Hg that would suggest new members of the fettelite family. The crystal structure of fettelite from the type locality was found to be equivalent to that reported previously for the Chilean occurrence, and consists of an alternation of two kinds of layers along c: layer A with general composition [Ag6As2S7]2– and layer B with general composition [Ag10HgAs2S8]2+. In this structure, the Ag atoms occur in various coordination configurations, varying from quasi-linear to quasi-tetrahedral, the AsS3 groups form pyramids as are typically observed in sulfosalts, and Hg links two sulfur atoms in a linear coordination. The refined compositions for the crystals in this study, [Ag6As2S7][Ag10(Fe0.53Hg0.47)As2S8] (R100124) and [Ag6As2S7][Ag10(Hg0.79Cu0.21)As2S8] (R110042), clearly indicate that new mineral species related to fettelite are likely to be found in nature.

Perovskite compositions are used to investigate the relationship between the minor components (i.e. LREE, Fe3+ and Nb) and the oxygen fugacity (fo2) of perovskite in four different kimberlite lithofacies from the Dutoitspan pipe, Kimberley, South Africa, which range from diamondiferous to barren. The perovskite textures and chemical variations provide insight into magmatic and eruptive processes. Some crystals display cores with rims separated by a sharp boundary. The cores contain larger Na and LREE contents relative to the rims, which show a large increase in Fe3+ and Al. The mid-grade and barren kimberlites have bi-modal cores, reflected in the mineral chemistry, signifying multiple batches of magma and magma mixing. The fo2 of the magma is determined by an Fe-Nb oxygen barometer. The most diamondiferous kimberlite has the greatest Fe3+ content and highest fo2 (NNO –3.6 to –1.1). The kimberlite containing large diamonds has the smallest Fe3+ content and lowest fo2 (NNO –5.2 to –3.0). The barren and mid-grade kimberlites display a wide range of fo2,(NNO –5.3 to –1.5) as a result of perovskites forming in different melts and subsequently mixing together. Chemical and petrological evidence suggests that the volatile content, degassing, decompression and rate of crystallization can influence the rate at which the magma is erupted. One possibility is that the most oxidized magma, containing the highest volatile content, is therefore erupted much more rapidly, preserving diamond as a consequence.

Synthetic Eu-anorthite of the alkali feldspar structure type has been refined to Rw = 4.7% using 3-D counter diffractometer data and full-matrix least-squares methods. The chemical composition of the feldspar is Eu0.92Al1.76Si2.24O8, based on both occupancy refinement of the Eu atom site and estimation of the Al/Si distribution calculated from the mean T-O bond length. The unit cell parameters are a = 8.373(1), b = 12.959(1), c = 7.124(1) Å, and β = 115.51(1)° and the symmetry is enhanced to C2/m. Mean bond lengths are T(1)-O = 1.677 Å, T(2)-O = 1.668 Å, and Eu-O = 2.721 Å. The average Al/Si distribution over the T(1) and T(2) sites calculated from the mean T-O bond length is in fairly good agreement with an estimate of the Al content from the bond strength calculation; the Al partition is calculated as t1 = 0.47 and t2 = 0.41 respectively. Summing the bond strengths of these Eu and partially disordered Al/Si cations approximates to electrostatic neutrality for the anion content of the feldspar structure, indicating that this synthetic Eu feldspar can be non-stoichiometric, signifying vacancies on the alkali cation site.

Plagioclase and melilite generally show a positive Eu anomaly. A fair insight into the driving force of this anomaly can be afforded by the crystallo-chemical affinities of Eu2+ and Eu3+ cations to the crystal structures of their host minerals; (1) ioinic radius, (2) electrostatic charge balance and (3) tolerance for non-stoichiometry of the crystal structure.

Phase transitions in the BaAl2O4–SrAl2O4 solid solution have been analysed as a function of temperature and composition using infrared (IR) powder absorption spectroscopy. The improper ferroelectric phase transition P6322 → P63 (2A superstructure) in the BaAl2O4 end-member can be detected through a change in slope of the wavenumbers of hard modes at ∽450 K. A change in line widths at ∽520 K appears to correlate with the development of diffuse intensity in a*-b* planes of electron diffraction patterns reported elsewhere in the literature. The same shift in wavenumber of hard modes is not observed in spectra from samples with compositions corresponding to 60, 80 and 90% of BaAl2O4 component, but a change in line widths at ∽500 K has been tentatively explained in terms of a different phase transition, from a P6322 parent structure to a P63 (√3A superstructure) product. Strain analysis of published high-temperature lattice parameter data suggests that the hexagonal → monoclinic transition in Sr-rich members of the solid solution may consist of two discrete transitions, and a sequence P6322 → C2 → P21 is suggested. The second transition could be related to instabilities in the hexagonal solid solution. Autocorrelation analysis of the IR spectra reveals a large positive deviation from linear behaviour across the solid solution, which is interpreted in terms of microscopic strain effects. These microscopic strains are probably responsible for the different transformation behaviour shown by samples with different compositions across the solid solution.

Separated stocks of UK civil plutonium are currently held as a zero value asset in storage, as there is no final decision about whether they should be treated as a resource for future use as nuclear fuel or as waste. Irrespective of future UK government strategies regarding plutonium, at least a portion of the UK civil plutonium inventory will be designated for geological disposal. In this context, we performed a high-level review of the performance of potential wasteforms for the disposal of separated civil plutonium. The key issues considered were the durability and chemical reactivity of the wasteforms in aqueous environments and the long-term radionuclide release under conditions relevant to geological disposal. The major findings of the review, relevant not only to the situation in the UK but to plutonium disposal in general, are summarized in this paper. The review showed that, in the event of a decision being taken to declare plutonium as a waste for disposal, more systematic studies would be required to constrain the wasteform performance under repository conditions in order to derive realistic source terms for a safety case.

Calcium carbonate forms three polymorphic minerals that are found in a variety of environments at the Earth’s surface. Other compounds in the aqueous system can inhibit or enhance the probability of one phase or another, favour growth of specific crystal faces, and change the rate of recrystallization. Control of crystal systems requires understanding of the relationships between the foreign agent and the CaCO3 mineral surface. This work, which examines the transformation of vaterite to calcite, is part of a larger project that aims to define some of the parameters that control calcite recrystallization and grain coarsening.