The structure of a natural sample of chondrodite (Mg4.89Fe0.07Si2.04O8F1.54(OH)0.46) was refined using powder neutron diffraction data and the Rietveld technique (P21/b; Z = 2; a = 4.7204(1)Å; b = 10.2360(3)Å; c = 7.8252(2)Å; α = 109.11(1)°; V = 357.26(2)Å3). Hydrogen was found to occupy the H1 site. The significance of hydrogen at this site is discussed in terms of hydrogen-bond stabilization of humite structures containing varying amounts of OH, F and Ti. Arguments are proposed as to why the F and Ti contents of natural humites usually result in only one H per formula unit when there is no crystal-chemical reason why fully hydrated samples should not be favoured.

Amphibolites from the Grampian Moines of Scotland contain clinopyroxene-plagioclase symplectites and plagioclase-hornblende coronas around garnet. The clinopyroxene-plagioclase symplectites are interpreted as former omphacites. It is inferred that an eclogitic garne-tomphacite-quartz assemblage once existed, but has since undergone partial reaction to an amphibolite facies hornblende-plagioclase assemblage. An early high-pressure metamorphic event occurred in parts of the Moine.

Petrographic and mineralogical studies of samples of the Normal (or undisturbed) Merensky Reef from Frank Shaft No.1 at Rustenburg Platinum Mine revealed the presence of a Pt-Fe-alloy, probably isoferroplatinum (58 vol.% of total precious metal minerals), arsenides (21 vol.%), bismuthotellurides (10 vol.%), electrum (9 vol.%) and platinum group element- (PGE-) sulfides and stannides (2 vol.%), associated predominantly with base-metal- and iron-sulfides. A Pt-Fe-alloy-dominated facies has been known for considerable time from potholes and discordant bodies and has been attributed to fluid activity with high fO2 and low fS2. Our petrographic results indicate that the normal thin reef has also undergone hydrothermal alteration. For the first time, the rare mineral troilite (stoichiometric FeS) was found as intergrowths with masses of Pt-Fe-alloy, together with Fe-rich pyrrhotite, secondary hydrous silicates, magnetite and calcite. The observed mineral assemblage and texture is interpreted as the product of partial desulfurization, caused by migrating S-undersaturated fluids, which led to the exsolution of Pt-Fe-alloy from pyrrhotite (Fex–1S) with the latter approaching a stoichiometric composition. Overall our new observations provide convincing support for the importance of metasomatism in the secondary modification of ore mineralogy and textures even in the undisturbed Merensky Reef.

Karroo basaltic lavas of southern Malawi are divided into two groups on the basis of stratigraphy, petrography, and the data from 20 newly analysed rocks. A lower group of porphyritic lavas is notably rich in plagioclase phenocrysts and has contents of K, Ti, P, Ba, and Zr unusually high for tholeiitic basalts. They are overlain by an upper group of aphyric or sparsely microphyric lavas whose chemistry is more normal for tholeiites and is comparable with that of the Karroo dolerite dykes in Malawi. Though they outcrop in the northern part of the Karroo province, the lavas and dykes have chemical characteristics more similar to southern province rocks, adding some complexity to the concept of geochemical provinces established by earlier workers. Inter-suite variations in incompatible trace element contents and ratios indicate that the basalts of each group were derived from heterogeneous mantle sources.

Assessment of available geochronological information, as well as new whole-rock Rb-Sr data from several granitoid rocks of Saskatchewan, shows a close relationship between magmatic-metamorphic events in the Hudsonian orogen and uranium mineralization. Most uranium deposits lie to the west of the Needle Falls Shear Zone and occur as either: (i) vein-type deposits or (ii) unconformity-type deposits close to the contact between the Athabasca sediments and their basement. At least two metamorphisms have affected the pre-Athabasca rocks: the Kenoran at about 2500 Ma ago, and the more pervasive ‘main’ Hudsonian event at 1740 Ma. A much younger thermal event (perhaps associated with uplift and cooling) at 1540 Ma is also indicated. The post-Kenoran K-Ar dates suggest prolonged thermal activity from about 1900 Ma through to about 1500 Ma ago. Granitoid events at 1870 Ma and 1740 Ma ago are outlined by both U-Pb zircon and Rb-Sr whole-rock isochron data. Whole-rock Rb-Sr data from the unmetamorphosed Athabasca sediments suggest an approximate depositional age of 1450±50 Ma, a figure that is consistent with the age of the underlying Hudsonian basement and the truncation of the sediments by the Cree Lake diabase dyke swarm at about 1200–1300 Ma ago. Although several episodes of uranium deposition have been documented, the main ones seem to have occurred at 1860 Ma (syngenetic uraninite in pegmatites), 1740 Ma (the Beaverlodge vein-type deposits) and between 1300 and 800 Ma (the epigenetic uranium of the unconformity-type deposits). Whereas the two earlier episodes can be correlated with periods of either magmatic or metamorphic activity, the late Proterozoic episodes cannot. The close agreement between the age of the Cree Lake dyke swarm and the late Proterozoic mineralization suggests that at about 1300 Ma ago possible hydrothermal activity from relatively deep-seated fractures may have been responsible for the solution and transportation of the uranium of the unconformity-type deposits. The period 1300 Ma to about 900 Ma, in other parts of the Canadian Shield, was a time of crustal rifting, basic magmatism, carbonatite activity, and intense deformation. Prior to the deposition of the Athabasca sediments uranium was concentrated by Hudsonian magmatic and metamorphic processes whereas subsequently, transportation and intermittent deposition of the unconformity-type deposits were related to fairly long-lived, low-temperature hydrothermal activity.

First-principles quantum techniques based on density functional theory (DFT) have made important contributions to the understanding of oxide surfaces over the last four years. Important features of these calculations include: the use of periodic boundary conditions, which avoid the edge effects associated with the cluster approach; plane-wave basis sets, which make the calculation of ionic forces straightforward, so that both static relaxation and dynamical simulation can be done; and the approximate inclusion of electron correlation. A short introduction to DFT techniques is given, and recent work on the structure and energetics of a variety of oxide surfaces is presented. It is shown how the techniques can be used to study molecular and dissociative adsorption of molecules on oxide surfaces, with the emphasis on water and simple organic molecules. The growing importance of dynamical first-principles simulation in the study of surface chemical reactions is illustrated.

A metallographic investigation of macro- and microstructure, supported in some instances by microprobe examination, has been made on a number of nickel-rich iron meteorites from the British Museum Collection. Monahans, Wiley, Cowra, and Deep Springs are considered together as plessitic irons rather than ataxites, whilst Morradal shows an unusual and coarse plessitic structure that has been altered by pre-terrestrial shock and reheating. Cape of Good Hope, Hoba, Tlacotepec, and Chinga show chemical and structural similarities and are discussed together, as are Weaver Mountains, Klondike, and Warburton Range. Meteorites considered separately include Kokomo, Piñon, Shingle Springs, South Byron, San Cristobal, Lime Creek, and Santa Catharina. Particular attention is paid to the presence of sulphides and of phosphorus-containing phases and their influence on the formation of the macro- and microstructure of these meteorites. Patches of oriented sheen form a macroscopic feature of the Cape of Good Hope group of irons and this effect is considered in relation to details of the microstructure. Attention is drawn to the fact that in Cowra, Piñon, Weaver Mountains, South Byron, and Morradal the troilite appears to have been remelted and dispersed by a shock event that operated at a temperature sufficiently high to allow obvious shock damage to anneal out of the metal phases.

Previous investigations have been confined to individual members or to small compositional ranges of the amblygonite-montebrasite series. The present study is a survey based on twenty-two specimens in the range Amb14Mon86 to Amb92Mon8 (1·8–11·8 % fluorine), and indicates that the fluorine content may be related both qualitatively and quantitatively to differences in the X-ray powder patterns. Fully indexed powder data to d = 1·68 Å and derived cell parameters are given for four members of the series. There is no evidence of a break in the continuity of the series. The first British occurrence of both amblygonite and montebrasite is reported from a pegmatite vein in aplite at Meldon, Okehampton, Devonshire.

The X-ray powder diffraction pattern of synthetic anorthite crystallized from a CaO-Al2O3-SiO2 glass having the anorthite (1:1:2) molar ratio is identical with that reported in the literature, and also with that of a natural Japanese anorthite specimen. Increasing the CaO or SiO2 content of the parent glasses used for crystallization studies has no measurable effect on that portion of the powder pattern attributable to anorthite. However, glasses containing an excess of Al2O3 ranging from 5 to 10 mol % gave, after crystallization at temperatures below c. 1150 °C distinctively different powder pattern. Several powder reflections that are normally strong, such as , etc., were found to be virtually absent. Moreover, the chemical excess of Al2O3 did not appear as a separate alumina-bearing phase. Upon reheating these anorthites to temperatures above 1200–50 °C or upon crystallizing a fresh portion of alumina-rich glass above 1200-50 °C, only the normal anorthite powder X-ray pattern was obtained; the pattern also contained some reflections due to corundum (α-Al2O3). Examination of the anomalous low-temperature anorthite by electron diffraction shows that the apparent absence of some powder lines is caused by both albite and Carlsbad twinning, which occur on an intimate scale not exceeding a few unit cell repeats. From the unique manner of its occurrence, the twinning is believed to be associated with the inclusion of an excess of Al3+ in the anorthite.

The effect of pressure on the naturally occurring hydroxide-perovskite stottite, FeGe(OH)6, has been studied in situ by micro-Raman spectroscopy to 21 GPa at 300 K. The ambient spectrum contains six OH-stretching bands in the range 3064 3352 cm–1. The presence of six non-equivalent OH groups is inconsistent with space group P42/n. In view of this inconsistency a new ambient structure determination of stottite from Tsumeb was carried out, but this did not allow the clear rejection of P42/n symmetry. However, a successful refinement was also carried out in space group P2/n, a subgroup of P42/n, which allows for six non-equivalent O atoms. The two refinements are of comparable quality and do not allow a choice to be made based purely on the X-ray data. However, taken with the ambient and 150 K Raman spectra, a good case can be made for stottite having P2/n symmetry at ambient conditions. On this basis, the pressure induced spectroscopic changes are interpreted in terms of a reversible phase transition P2/n ↔ P42/n.

Transmission X-ray diffraction is demonstrated as a new tool for examining daughter minerals within sub-micrometre-size fluid inclusions in fibrous diamond. In transmission geometry, the X-ray beam passes through the sample, interacting with a volume of material. Fibrous diamonds from Mbuji-Mayi. Democratic Republic of Congo; the Wawa area, Ontario, Canada; and the Panda kimberlite, Ekati Mine, Northwest Territories and the Jericho kimberlite, Nunavut, Canada were analysed using X-rays from a high-brilliance lab source and a synchrotron source. Daughter minerals present include the mica-group mineral celadonite, sylvite, halite, dolomite and other carbonates. This represents the first positive identification of halide minerals in fibrous diamond. Mineral inclusions such as forsteritic olivine and pyrope garnet were also found. Unexpectedly, daughter minerals were identified in only ten of the 38 diamonds analysed, despite their concentrations being greater than experimentally proven detection limits. The presence of significant amounts of amorphous or dissolved material appears unlikely, but cannot be ruled out. Alternatively, the results may indicate a wide variety of related daughter minerals, such that most phases fall below the detection limits. Transmission X-ray diffraction should be applied cautiously to the study of fibrous diamond, as it provides an incomplete account of the fluid-inclusion mineralogy.

The thermal diffusivity of diopside, jadeite and enstatite were measured at simultaneous pressures and temperatures of up to 7 GPa and 1200 K using the X-radiographic Ångström method. The measurements herein show that the pressure dependency of thermal diffusivity in pyroxenes is significantly greater than in olivine or garnet and that in the MORB-layer of a subducting slab the thermal diffusivity of pyroxenes are a factor of 1.5 greater than that of olivine. The temperature dependence of all the data sets is well described by a low-order polynomial fit to 1/K and the pressure dependence is exponential in 1/K, formulations which are consistent with the damped harmonic oscillator model for thermal properties.

Solution calorimetry and phase equilibrium data for the diopside–jadeite system are assessed using a combination of the cluster variation method (CVM) and Redlich-Kister (RK) polynomial expansion. The CVM is used to model part of the free energy of mixing which depends on short-range order (SRO) and long-range order (LRO) effects. The SRO/LRO independent part of the free energy is modelled using an RK polynomial. The parameters of the RK and CVM models are obtained through the fit to the experimental data. The best-fit parameters are used to calculate activity-composition relations and a temperature-composition phase diagram of the diopside–jadeite system.

A quantitative determination of Fe3+/ΣFe ratios using the electron microprobe is presented for glasses. The measurements are based on the shift of the Fe-Lα peak position between Fe3+ and Fe2+, resulting from differences in self-absorption. We present new calibration curves for glasses with Fe contents as low as 2 wt.% Fe.

This method was used for glasses from a metasomatized spinel Iherzolite (Massif Central, France) in which highly vesicular glass associated with secondary minerals occurs in reaction pockets around corroded Cr-spinels. The glass was found to be oxidized homogeneously with Fe3+/ΣFe ≈ 0.70 (measured with an uncertainty of ±0.06), in contrast with the value of ∼0.15 that would correspond to the former melt under fo2 conditions inferred from secondary minerals. The glass oxidation probably results from the dissociation of the melt-water content under degassing, prior to local hematite depositions (spinel rims and crack fillings).

Zektzerite and its isotypes with Zr4+ replaced by Ti4+ or Sn4+ are readily synthesized by fusion of the constituent oxides at 1550 °C followed by recrystallization of the melt or quenched glass at 750–850 °C and I bar pressure. Indexed powder X-ray data for synthetic zektzerites are presented in miniprint Table I. The powder patterns are consistent with an A-centred orthorhombic symmetry. Refined cell dimensions are given in Table III.

The Ti, Zr, and Sn zektzerites melt incongruently. Table IV records melting-point data. The coefficients of thermal expansion of Zr and Ti zektzerite have been determined by X-ray dilatometry. Both have moderately low coefficients of expansion: numerical values are given in miniprint Table II.

Zektzerites contain a six-repeat unit doublechain silicate anion. Although they are chemically similar to milarites, the latter contain double-ring Si12O30 anions. Despite the difference in anion constitution both have structures in which many chemically similar atoms occupy similar positions. The effect of this similarity on the physical properties (e.g. X-ray powder pattern) is enhanced by the similar size and shape of their orthorhombic unit cells. The presence of vacant sites in zektzerite that are potentially available for cation occupancy suggests that chemically complex substitutions may occur; for example LiNa2ScSi6O15 has been synthesized and is believed to be isostructural with zektzerite and emeleusite, LiNa2FeSi6O15.

Ammoniovoltaite, (NH4)2Fe2+5Fe3+3Al(SO4)12(H2O)18, is a new voltaite-group mineral. The mineral was discovered at the Severo-Kambalny (North-Kambalny) geothermal field, Kambalny volcanic ridge, Southern Kamchatka, Russia. Ammoniovoltaite forms at ~100°C around geothermal gas/steam vents in association with alunogen, tschermigite and pyrite. Crystals of ammoniovoltaite have euhedral habit, are up to 50 µm in size and grow on alunogen plates. Ammoniovoltaite is black with vitreous lustre, opaque, brittle and water-soluble. Neither cleavage nor parting is found, the fracture is conchoidal. The mineral is isotropic, with the refractive index n = 1.602(2) (589 nm). Infrared spectra contain an absorption band at 1433 cm–1 distinctive for the ammonium ion. The chemical composition is (iron content is given in accordance with Mössbauer data, H2O calculated from a crystal-structure refinement, wt.%): FeO 13.26, Fe2O3 11.58, MgO 2.33, ZnO 0.04, Al2O3 2.74, SO3 47.46, K2O 0.19, CaO 0.11, (NH4)2O 2.96, H2O 16.03, total 96.70. The empirical formula based on S = 12 atoms per formula unit is [(NH4)1.88K0.08Ca0.04]Σ2.00(Fe2+3.74Mg1.17Fe3+0.05Zn0.01)Σ4.97(Fe3+2.89Al0.09)Σ2.98Al1.00(SO4)12.00(H2O)18.00. The crystal structure has been refined to R1 = 0.031 and 0.030 on the basis of 1217 and 1462 unique reflections with I >2σ(I) collected at 100 K and room temperature, respectively. Ammoniovoltaite is the ammonium analogue of voltaite. The mineral is cubic, Fd$\bar{3}$c, a = 27.250(1) Å and V = 20234(3) Å3 (at 100 K); and a = 27.322(1) Å and V = 20396(3) Å3 (at RT), with Z = 16. The strongest lines of the powder X-ray diffraction pattern [d, Å (I, %) (hkl)] are: 9.67 (74) (022), 7.90 (56) (222), 5.58 (84) (422), 3.560 (100) (731), 3.418 (100) (008) and 2.8660 (37) (931). A brief review of ammonium minerals from various volcanically active geological environments is given.

Tennantite-(Cd), Cu10Cd2As4S13, was approved as a new mineral species from the Berenguela mining district, Pacajes Province, La Paz, Bolivia. It occurs as black metallic anhedral grains, up to 1 mm across, associated with baryte, montmorillonite and secondary Cd-sulfates (aldridgeite, niedermayrite and voudourisite). In reflected light, tennantite-(Cd) is isotropic and grey with brownish tints. Reflectance data for the four COM wavelengths in air are [λ (nm): R (%)]: 470: 30.0; 546: 30.1; 589: 28.2; and 650: 25.8. Electron microprobe analysis gave (in wt.% – average of 11 spot analyses): Cu 40.56(32), Ag 0.05(5), Fe 0.04(1), Zn 1.91(63), Cd 11.32(1.09), Hg 0.04(7), As 19.04(43), S 26.78(30), total 99.74(53). On the basis of ΣMe = 16 atoms per formula unit (apfu), the empirical formula of tennantite-(Cd) is Cu9.98Ag0.01Cd1.57Zn0.46Fe0.01As3.97S13.05. Tennantite-(Cd) is cubic, I$\bar{4}$3m, with unit-cell parameters a = 10.3088(2) Å, V = 1095.53(6) Å3 and Z = 2. Its crystal structure was refined by single-crystal X-ray diffraction data to a final R1 = 0.0152 on the basis of 359 unique reflections with Fo > 4σ(Fo) and 22 refined parameters. Tennantite-(Cd) is isotypic with other tetrahedrite-group minerals. Its crystal-chemistry is discussed and previous findings of Cd-rich tetrahedrite-group minerals are briefly reviewed.

Dobrovolskyite, Na4Ca(SO4)3, is a new sulfate mineral from the Great Tolbachik fissure eruption, Kamchatka peninsula, Russia. It occurs as aggregates of tabular crystals up to 1–2 mm in maximum dimension, with abundant gas inclusions. The empirical formula calculated on the basis of O = 12 is (Na3.90K0.10)Σ4(Ca0.45Mg0.16Cu0.12Na0.10)Σ0.83S3.08O12. The crystal structure of dobrovolskyite was determined using single-crystal X-ray diffraction data as: trigonal, R3, a = 15.7223(2), c = 22.0160(5) Å, V = 4713.1(2) Å3, Z = 18 and R1 = 0.072. The Mohs’ hardness is 3.5. The mineral is uniaxial (+), with ω = 1.489(2) and ɛ = 1.491(2) (λ = 589 nm). The seven strongest lines of the powder X-ray diffraction pattern [d, Å (I, %)(hkl)] are: 11.58(40)(101); 5.79(22)(202); 4.54(18)(030); 3.86(88)(033); 3.67(32)(006); 2.855(50)(306); and 2.682(100)(330). The mineral is named in honour of Prof. Dr. Vladimir Vitalievich Dolivo-Dobrovolsky (1927–2009), one of the leading Russian scientists in the field of petrology, crystal optics and crystal chemistry. The crystal structure of dobrovolskyite can be described as composed of three symmetrically independent rods running parallel to the c axis. The rods consist of six octahedral–tetrahedral [Na(SO4)6]11– or [Ca(SO4)6]10– clusters of central octahedra sharing common corners with six adjacent SO4 tetrahedra. Alternatively, the crystal structure of the mineral can be described as a 12-layer ABACABACABAC eutactic array of Na+ and Ca2+ cations, and vacancies with disordered (SO4) tetrahedra in interstices. Dobrovolskyite and similar minerals probably formed upon cooling of a high-temperature phase with disordered cation and anion arrangements.

Four new isotopic U/Pb ages from Cornwall are reported. The Pb206/U238 and Pb207/U235 ages for each specimen are concordant. The Pb206/U238 ages are : South Terras mine 225 ± 5 million years (Myr.), Redruth Area 124 ± 4 Myr., Wheal Owles mine 58 ± 3 Myr., and South Terras Area 62 ± 3 Myr. Cell sizes, calculated from X-ray powder photographs, decrease with decreasing ages of the specimens, indicating a progressive increase in the oxidation states of the uranium present. It is concluded tentatively that at least two periods of mineralization affected south-west England at about 290 Myr. and 225 Myr., and that a final event occurred at about 60 Myr. Whether this final event involved the remobilization of older uranium with loss of lead, or the introduction of additional uranium, or a combination of both effects cannot be established from this evidence. No unique explanation has been made for the 124 Myr. age.

The existence in the British Isles of a rock essentially composed of garnet and omphacite, and answering therefore to Hauy's' definition of eclogite, does not appear to have been hitherto recorded.

The following description of such a rock from Totig Ferry, Loch Dutch, is therefore of some interest. The specimen was collected by the Director General, who informs me that he believes it to be a part of the Archæan gneiss which in the region of Loch Alsh and Loch Carron has been thrust bodily from the east over the Torridon sandstone.

The rock is of a dull green eolour, and contains numerous reddishbrown garnets. Under the microscope the principal constituents are seen to be garnet and omphacite—a pale green pyroxene without any definite crystalline form. Green hornblende, plagioclase, rutile, ironores, quartz, and epidote occur as accessories.