The major- and trace-element chemistry of pyrite and arsenopyrite from the mesothermal Roudný gold deposits was studied by electron microprobe and laser ablation ICP-MS techniques. In total, four generations of pyrite and two of arsenopyrite were distinguished. The pyrite is enriched in As through an Fe (AsxS1–x)2 substitution mechanism. The As-rich zones of pyrite-2 (up to 4.5 wt.% As) are also enriched in gold (up to 20 ppm), lead (commonly up to 220 ppm, exceptionally up to 1500 ppm) and antimony (commonly <600 ppm, rarely up to 1350 ppm). Positive correlation of As and Au in the studied pyrites is not coupled with an Fe deficiency, in contrast to Au-rich As-bearing pyrites in Carlintype gold deposits. The As-rich pyrite-2 coprecipitated with the Sb-rich (1 –4.2 wt.%) and Au-rich (40 –150 ppm) arsenopyrite-1. The younger arsenopyrite-2 is significantly less enriched in these elements (0 –70 ppm of Au).

The chemical zonality of pyrites in the Roudný gold deposits reflects the chemical evolution of orebearing fluids that are not observed in any other mineral phases. The data available suggest relatively high activity of sulphur and low activities of arsenic and gold during crystallization of the older pyrite generation (pyrite-1). Later, after particular dissolution of pyrite-1, Au-rich As-bearing pyrite-2 and arsenopyrite precipitated. These facts suggest a marked increase in the arsenic and gold activities in ore-bearing fluids. The As-content of pyrite-2 decreases in an oscillatory manner from the core to the rim, reflecting changes in the As activity or/and in the P-T conditions. The As-bearing pyrites were formed at temperatures of at least 320–330°C, based on arsenopyrite thermometers and fluid inclusion data.

The study of the materials from these two recently discovered occurrences has added much to the knowledge of meteorite craters. The two present many points in common and they supplement one another. At Henbury there is a much better development of the meteoric iron, while at Wabar the silica-glass predominates.

Well-resolved Mössbauer spectra of several dioctahedral and trioctahedral micas have been obtained and subjected to detailed computer analysis. Most of the spectra can be resolved into two ferrous quadrupole doublets and one ferric quadrupole doublet. In dioctahedral micas, ferrous iron is seen to occupy the larger, more symmetric octahedral site in preference to the smaller, less symmetric site, confirming predictions made on the basis of structure alone. In trioctahedral micas there is still a tendency for ferrous iron to occupy preferentially the more symmetric octahedral site even though the two octahedral sites are no longer distinguished by size. A lithium-rich biotite gives a spectrum typical of that expected from a mica with a zinnwaldite structure, but the spectrum of a more authenticated zinnwaldite could not be resolved sufficiently for detailed structural interpretation. The spectra of pyrophyllite and talc give results that can be related to the corresponding micas by considering their respective structural differences. In none of the micas studied was there evidence of ferric iron in tetrahedral coordination. The ferrous: ferric ratios obtained from the Mössbauer spectra do not always agree with the chemical values. In several cases the spectra show more ferrous iron than found chemically. It is suggested that the spectral values are more accurate, oxidation on chemical analysis being the most likely source of error.

Dykes from four sections across the axis of the Skye regional swarm have been analysed for major elements, Nb, Rb, Sr, Y, Zr, and rare-earth elements. 70 % of the dykes are characterized by relatively high CaO (11–12%), and low abundance of elements such as TiO2 (∼1%), K2O (0·05–0·20 %), Zr (30–60 ppm), with a light-rare-earth depleted chondrite normalized pattern. The remainder of the swarm comprises dykes equivalent in composition to the Skye Main Lava Series and dykes belonging to a further magma type distinguished by a flat chondrite normalized rare-earth pattern. The high-calcium, low-alkali tholeiite dykes are confined to a narrow persistent zone forming the major axis of dilation of the swarm; other basaltic dykes are axially less persistent and have a wider lateral distribution. The more evolved dykes tend to be restricted to central Skye.

The crystal structure of gyrolite from Qarusait, Greenland, was solved and refined with the space group P and cell parameters a = 9.74(1), b = 9.74(1), c = 22.40(2)Å, α = 95.7(1)°, β = 91.5(1)°, γ = 120.0(1)°. The structure is built up by the stacking of the structural units already found in the crystal structure of reyerite (Merlino, 1972, 1988), namely tetrahedral sheets S1 and S2 and octahedral sheets O. The tetrahedral and octahedral sheets are connected by corner sharing to give rise to the complex layer which can be schematically described as 1OS2, where S2 and , as well as O and , are symmetry-related units. Successive complex layers with composition [Ca14Si23AlO60(OH)8]-5 are connected through an interlayer sheet made up by calcium and sodium cations and water molecules.

The unit cell content NaCa16Si23AlO60(OH)8·14H2O, determined by the structural study, was confirmed by a chemical analysis, apart from the indication of a somewhat larger water content. The crystal chemistry of gyrolite is discussed on the basis of the present structural results and the chemical data given in the literature for gyrolite from different localities: the crystal chemical formula which accounts for most gyrolite samples is Ca16Si24O60(OH)8·(14+x)H2O, with 0 ⩽ x ⩽ 3.

Stacking disorder, twinning and polytypic variants in gyrolite, as well as the structural relationships of gyrolite with truscottite, reyerite, fedorite and the synthetic phases K and Z are described and discussed.

Electron-microprobe analyses of cumulus olivine, chromite, pyroxene, and plagioclase from layered peridotites and allivalites of the Eastern and Western Layered Series of Rhum demonstrate the presence of cryptic variation. Olivine varies from Fo88-78 within individual units, and there are corresponding changes in the Mg/(Mg+Fe2+) ratios in the pyroxenes and chromites. Plagioclase changes are not so dramatic, but the An-content broadly follows the Mg/(Mg+Fe2+) ratio in the other minerals. The most Fe-(and Na-) rich phases do not occur at the top of lithological units, but some way below. The composition trend above them is reversed. The data are interpreted as the result of periodic infilling of a magma chamber, the new magma mixing with the remains of the previous pulse. Each pulse was followed by a period when fractional crystallization produced the layered rocks. New data on Ni in the olivines suggests that the ratio of the volume of initial magma to volume of layered rocks was about four to one, the initial magma being allied to the high-calcium low-alkali tholeiitic basalts of Skye.

Geiger-counter powder records of soda-rich plagioclases have been carefully measured and indexed. The lattice parameters of the synthetic specimens are almost independent of the lime content, the largest variation (that in β*) amounting to only 0·2°. After strong heating the powder patterns of the natural specimens closely approached those of the synthetic specimens.

Eight out of the nine natural plagioclases gave lattice parameters which fall within experimental error on a continuous line. There is a fairly large variation in lattice parameters, especially for γ*, which changes by 2°. As the lime content increases the lattice parameters of the natural plagioclases approach those for the high-temperature synthetic and heated natural specimens until at An50 the separation is only one-fifth of that at An0. The ninth specimen (from a dacite) gives parameters midway between the curves, thus exhibiting a state of partial inversion.

The partially heated natural plagioclases and the plagioclase from the dacite give parameters indistinguishable within experimental error from the parameters of unheated plagioclases with a higher lime content. There is, therefore, no reliable powder X-ray method for the determination of composition in the region An0-An50. If the composition is known the powder method may be used for the determination of the thermal state. If the plagioclase can be judged to be in the low-temperature state from geological evidence the powder method can be used to estimate the composition with an accuracy of 2 % An.

Calcite and aragonite shell layers of the main classes of Molluscs are composed of monocrystalline units (prisms, tablets, laths or fibres). Scanning electron and atomic force microscopy studies show these units are composed of small round granules with a thin cortex (amorphous calcium carbonate and/or organic matrix). These granules are organo-mineral composites. A comparison of the size and shape of the granules in different taxa (Mollusca, Brachiopoda) suggests a possible relationship with taxonomy and/or phylogeny.

The Grenvillian granulite-facies complex on Holsnøy island, Bergen Arcs, W. Norway, has been metamorphosed at eclogite-facies conditions during the Caledonian orogeny (ca. 425 Ma). The granulite-eclogite facies transition takes place along shear zones and fluid pathways. Mineral thermobarometry indicates PT conditions of 800–900°C and 8–10 kbar for the Proterozoic granulite facies metamorphism and 700–800°C and 16–19 kbar for the eclogite-forming event. Quartz in the granulite facies complex contains CO2 fluid inclusions with less than 2.5 mole percent N2; the molar volumes are compatible with the PT conditions of the Proterozoic granulite metamorphism. Quartz in pegmatitic quartz + omphacite and quartz + phengite/paragonite veins coeval with shear-zone eclogites contain N2 ± CO2 fluid inclusions. Combined laser Raman microanalysis and microthermometry show that the least disturbed inclusions have XCO2 = 0.1–0.3, and molar volumes less than 40 cm3/mole, which may agree with the PT conditions during Caledonian high-pressure metamorphism. Younger, low-density N2 and N2-H2O fluid inclusions are the results of decrepitation and redistribution of early inclusions during the retrograde PT evolution of the eclogites.

Monazite is a light rare-earth element (LREE)-bearing accessory phase common in felsic granitic rocks, and strongly influences LREE concentrations in granites and the chemistry of melts and residues formed during partial melting. Cheralite-rich (high-Th) monazite-(Ce) has been recorded as rims on partially dissolved cores in a suite of granulite-facies migmatites generated by disequilibrium melting. High-Th monazite has previously been recorded only in granitic-pegmatite occurrences. Subidiomorphic monazite-(Ce) from leucosome, melanosome and mesosome consists of complexly zoned cores (up to 300 µm in diameter) containing 5.17–9.87 wt.% ThO2, overgrown by essentially unzoned rims (containing up to 21.4 wt.% ThO2). Uranium contents are average for Th-rich monazite-(Ce) (0.22–3.17 wt.% UO2). Th enrichment (relative to LREE) in monazite-(Ce) rims is ascribed to the presence of fluorine-bearing melts (formed during the incongruent breakdown of biotite to produce a water-undersaturated melt), allowing the formation of REE-fluoride complexes in the melt, coupled with the increased charge balanced substitutions Th4+ + Si4+ ⇌ REE3+ + P5+ and Th4+ + Ca2+ ⇌ 2REE3+ into monazite-(Ce). Fractionation of Th and U (reflected by an increased in Th/U in rims relative to cores) may have occurred due to the removal by a CO2-rich fluid phase in the melt. These interpretations are consistent with elevated CO2 and F contents of granitic liquids produced during the water-undersaturated breakdown of biotite under granulite-facies conditions. Evidence for restricted monazite-(Ce)-melt equilibration and rapid melt removal is provided by the ubiquitous presence of partially embayed cores and unzoned rims.

Understanding the environmental and biogeochemical behaviour of radionuclides is essential for managing our nuclear legacy safely. Remediation efforts and the concept of geological disposal of nuclear waste focus on immobilizing radionuclides within the subsurface. Here we review recent developments in the understanding of solid-phase capture processes of Cs, Sr, Tc, U, Pu and Np. Abiotic interactions between minerals and these radionuclides (including sorption, reductive precipitation and co-precipitation) have been studied in various conditions. Microbially driven processes are much less well characterized, for example the effects of microbial reduction on the structure and reactivity of existing minerals, or their role in the formation of new minerals. Metabolites released by bacteria can play a role in both mineral dissolution and formation, and better understanding their release and role in mineralization has great potential in the development of solid-phase capture processes for radionuclides.

With the aid of a map of the research landscape covered by this review (created using a cluster-analysis tool, a self-organizing map), we highlight the most promising sequestration processes for specific radionuclides. However, radionuclides exhibit highly species-specific behaviour in their interactions with minerals and microorganisms. More research is required to characterize the role mineral surfaces play in bioreductive immobilization of Pu and Np, the reduction products formed, and their relative stability. Further studies should concentrate on more environmentally relevant experiments that include bacteria, minerals and radionuclides.

This paper presents the results of an experimental study of muscovite solid solutions in the system K2O-M2+O-Al2O3-SiO2-H2O-(HF), with M2+ = Mg2+ or Fe2+ in the temperature range 300-700°C under 2 kbar PH2O. Muscovite solid solutions can be described, in this system, as the result of two substitutions. One is the phengitic substitution (x), which preserves the pure dioctahedral character of the mica; the second is the biotitic substitution (y), which leads to trioctahedral micas and does not change the composition of the tetrahedral layer Si3Al. The general formula of muscovite in this system is K(Al2−x−2y∕3M2+x+y□1−y∕3)(Si3+xAl1−x)O10(OH,F)2. Both substitutions x and y are more extensive at lower temperatures. The extent of solid solution decreases drastically with increasing temperature.

For T > 600°C, the phengitic substitution (x) becomes negligible, but some biotitic substitution (y) persists. This unsymmetrical decrease of the solid solution of muscovite with increasing temperature is similar to that previously observed in phlogopite, the micas with a tetrahedral layer composition of Si3Al being the most stable. The behaviour of muscovite solid solutions in the ferrous system is qualitatively identical to that observed in the magnesian one, but the extent of solid solution is smaller than with Mg2+. Fluorine neither changes the size nor the shape of the solid solution fields but increases their stability by about 50°C.

A comparison of these experimental results with data on natural muscovites is presented. Most natural primary (magmatic) granitic muscovites lie very close to the muscovite end member, in agreement with their high-temperature origin. Low-temperature muscovites (300–400°C), typically muscovites from hydrothermally altered granitic rocks, can have high x and y values. The rate of the biotitic substitution y can reach 0.6, which corresponds to an octahedral occupancy of 2.2 atoms per formula unit (based on 11 oxygens), consistent with the experimental data.

In a thin specimen X-ray absorption and fluorescence can, to a first approximation, be ignored and the observed X-ray intensity ratios, IA/IB, can be converted into weight fraction ratios, , can be converted into weight fraction ratios, CA/CB, by multiplying by a constant , by multiplying by a constant kAB;

kAB values can be calculated or determined experimentally. The major correction which may have to be made to the calculated weight fraction ratio is for X-ray absorption within the specimen. The activated volume for analysis in a thin specimen is approximately 100 000 × less than in a bulk sample. Beam spreading within the specimen can be estimated using a simple formula based on a single elastic scattering event at the centre of the specimen. Examples are given of the application of the technique to obtain both qualitative and quantitative analyses from thin mineral specimens. The minimum detectable mass and the minimum mass fraction which can be measured using the technique are estimated.

In a preliminary note on the dolomite contaet-skarns of the Broadford area, Skye (Tilley, 1948, a), a brief account was given of the constitution and environment of these multizoned assemblages at the contact of the Durness limestone succession with the Tertiary Beinn an Dubhaich granite.1 No detailed survey of the numerous parageneses was then attempted, and it is the purpose of the present paper to fill this gap and to discuss the genetic problems of these skarn assemblages.

Forearc peridotite is generally characterized by low Mg# (= Mg/[Mg + Fe2+] atomic ratio) at a given Cr# (= Cr/[Cr + Al] atomic ratio) of chromian spinel compared to common abyssal peridotite. This may be due to (1) smaller modal abundance of spinel and/or (2) lower equilibrium temperature, for the forearc peridotite. Forearc peridotite has the same amount of spinel as abyssal peridotite, eliminating the first possibility. Spinel in harzburgite and dunite from the Hahajima Seamount at the Izu-Bonin forearc, has a large Cr#, >0.57, and the Mg# is slightly variable towards low values at a given Cr#. The Mg# of spinel cores decreases strongly with a decrease in size. This is due to cooling along with hydration, which gave rise to a compositional variation of Ca-amphibole, from edenitic hornblende (high-temperature) to tremolite (low-temperature) in the Hahajima peridotite. The average two- pyroxene temperature of the Hahajima peridotite, 921°C, is less than that of the abyssal peridotite (1138°C), which is not consistent with a size-dependent Mg# of spinel for the latter. Forearc peridotite has been cooled effectively by H2O released from the subducted slab, causing a small Mg# of their spinels.

Micas of the muscovite–lepidolite series are main constituents of the evolved pegmatites from the Okatjimukuju-Kaliombo portion of the Karibib belt, Namibia. The compositional variations shown by the micas from the intermediate zones are mainly controlled by the Li3Al-1□-2 and SiLi2Al-2□-1 substitution schemes, whereas for the micas from the core margins and the replacement bodies, only the first of these two exchange vectors seems to operate. The chemical composition of the micas not only depends on the degree of pegmatite evolution, but also on the position in the internal zonation of the pegmatite. Micas from the core margins and the replacement units are generally richer in F, Li, Rb, Cs and Zn than those from the intermediate zones. In general, the contents of these elements increase with decreasing K/Rb ratio. However, some data departing from this general trend are also observed, which could be related to subsolidus processes. Some pegmatite bodies show a complete internal evolution, developed from the margins to the core zone, which is reflected in the chemical composition of the micas. The regional distribution of pegmatites does not define a zonation, because an overlapping of pegmatites with different degrees of evolution occurs. This could be due to the high level of evolution attained by most of the rare-element pegmatites, and to their topography with respect to a dome structure of the basement.

New Sr-Nd isotope data were obtained from Late Pleistocene carbonatite-kamafugite associations from the Umbria-Latium Ultra-Alkaline District of Italy (ULUD) with the aim of constraining their origin and possible mantle source(s). This is relevant to the origin and evolution of ultrapotassic (K/Na ≫2) and associated rocks generally, notably the occurrences from Ugandan kamafugites,Western Australian lamproites and South African orangeites. The selected ULUD samples yielded 87Sr/86Sr and 143Nd/144Nd ranging from 0.7100 to 0.7112 and from 0.5119 to 0.5121 respectively, similar to cratonic potassic volcanic rocks with higher Rb/Sr and lower Sm/Nd ratios than Bulk Earth. Silicate and carbonate fractions separated from melilitite are in isotopic equilibrium, supporting the view that they are cogenetic. The ULUD carbonatites yielded the highest radiogenic Sr so far reported for carbonatites. In contrast, sedimentary limestones from ULUD basement formations are lower in radiogenic Sr, i.e. 87Sr/86Sr = 0.70745–0.70735. The variation trend of ULUD isotopic compositions is similar to that reported for Ugandan kamafugites and Western Australian lamproites and overlaps the values for South African orangeites in the εSr-εNd diagram. A poor correlation between Sr/Nd and 87Sr/86Sr ratios in ULUD rocks is inconsistent with a mantle source generated by subduction-driven processes, while the negligible Sr and LREE in sedimentary limestones from the ULUD region fail to account for a hypothetical limestone assimilation process. The Nd model ages of 1.5–1.9 Ga have been inferred for a possible metasomatic event, allowing further radiogenic evolution of the source, a process which may have occurred in isolation until eruption time. While the origin of this component remains speculative, the Sr-Nd isotope trend is consistent with a simple mixing process involving an OIB-type mantle and a component with low εNd and high εSr.

The crystal structure of kilchoanite, Ca6(SiO4)(Si3O10), has been determined from three- dimensional X-ray methods (r = 0·089 on 348 independent reflections). It is closely related to that of γ-Ca2SiO4, which is olivine-like. In kilchoanite, slabs of γ-Ca2SiO4 structure alternate with ones composed of Ca ions and finite chains of three tetrahedra; these have the composition Si3O108− and have rarely been observed previously. A related, synthetic phase, 8CaO. 5SIO2, probably has a similar structure but with a higher proportion of γ-Ca2SiO4 regions, and should thus be formulated as Ca8(SiO4)2(Si3O10). Disordered synthetic phases also occur that appear to have similar structures with still higher proportions of γ-Ca2SiO4 regions. These phases collectively form an interesting contrast to the chondrodite minerals.

The results of measurements of diffuse reflectance over the wavelength range 200 < λ < 2500 nm are reported for sphalerite, cinnabar, alabandite, chalcopyrite, bornite, orpiment, stibnite, bismuthinite, enargite, and pyrargyrite, and for eight pyrite-type and four NiAs-type compounds. Some spectral assignments have been made.

Optical properties are related to the absorption spectrum (and through this to composition and structure) in a rational way. Absolute reflectances tend to increase with mean atomic number (z) through the operation of the ‘z-sum rule’, and at constant z they decrease as the band gap increases. Bireflectance is structurally controlled, being weak in derivatives of the cubic sphalerite and pyrite structures, moderate in derivatives of wurtzite and NiAs, and strong in anisodesmic structures such as that of stibnite. Extreme bireflectance occurs in anisodesmic structures with strong dichroic absorption bands in the visible (molybdenite, covelline).

The dispersion of reflectance (dR/dλ) depends on the position of the centre of the main absorption envelope in relation to the visible spectrum. For λ > , dispersion is normal (Rblue > Rred, dR/dλ negative), the streak is light or coloured, and polished surfaces tend to be bluish. For λ < , dispersion is reversed (Rred > Rblue), the streak is dark, and polished surfaces are yellowish. Polished surfaces are white or grey if absorption varies little through the visible or strongly coloured if it varies rapidly (covelline, chalcopyrite).

Chemical data are given for four rocks from the Scourie dyke, Sutherland, and for the constituent minerals. Three of the specimens are unsheared and represent stages in a continuous variation from a one-pyroxene (subcalcic ferroaugite) dolerits through partially amphibolized two-pyroxene dolerite to garnet-plagioclase amphibolite. These changes are not accompanied by conspicuous changes in bulk composition. The garnetiferous varieties represent a border facies of the dyke, which is in contact with little-altered pyroxene-bearing gneisses of the Lewisian complex. The fourth specimen is a hornblende schist formed from the dolerite by shearing. This change also involves little change in bulk composition, and affects impartially the three types of dolerite referred to above. Mineral relations are discussed and a hypothesis advanced to account for the garnetiferous border facies of the intrusion, invoking intrusion while the country rock was at relatively high temperature and pressure.