Odigitriaite, a new Cs, Na, Ca borosilicate mineral, was discovered in moraine adjacent to the Darai-Pioz alkaline massif in the upper reaches of the Darai-Pioz river at the intersection of the Turkestansky, Zeravshansky and Alaisky mountain ridges, Tajikistan. It occurs as irregular thin flakes associated with quartz, pectolite, baratovite, fluorite, pekovite, polylithionite, aegirine, leucosphenite, pyrochlore, neptunite, reedmergnerite, mendeleevite-(Ce), zeravshanite and sokolovaite. It is colourless with a white streak, is translucent and has a vitreous lustre; it does not fluoresce under ultraviolet light. Odigitriaite is brittle with an uneven fracture and a Mohs hardness of 5. The calculated density is 2.80(2) g/cm3. The indices of refraction are α = 1.502, β = 1.564, γ = 1.576; 2Vobs = 46(2)°, dispersion is weak r > v, and there is no pleochroism. The chemical composition is as follows (electron microprobe, H2O calculated from structure): SiO2 55.30, Al2O3 0.09, Y2O3 0.44, MnO 0.94, FeO 0.10, PbO 0.21, K2O 0.01 Cs2O 8.36, B2O3 4.75, H2O 0.37, F 1.74, O = F2 –0.74, total 99.43 wt.%. The empirical formula of odigitriaite is Cs0.90Na5.12Ca4.68Mn0.20Y0.06Fe0.02Pb0.01[Si13.92Al0.03B2.06O38]F1.39(OH)0.62. The end-member formula is CsNa5Ca5[Si14B2O38]F2. The strong reflections in the powder X-ray diffraction pattern are: [(d, Å), (I, %), (hkl)]: 5.45 (25) (1 1 3), 4.66 (33) (3 1 1), 4.40 (26) (0 2 2), 4.10 (36) (3 1 3), 3.95 (25) (3̄ 1 3), 2.85 (31) (2 2 2), 2.68 (40) (0 0 6), 3.62 (45) (0 2 4), 3.35 (100) (2̄ 2 4), 3.31 (30) (3̄ 1 5), 3.25 (35) (4 0 4), 3.04 (60) (4̄ 2 2), 2.925 (22) (4̄ 2 3), 1.813 (23) (9 1 0). Odigitriaite is monoclinic, space group C2/c, a = 16.652(5), b = 9.598 (3), c = 22.120(7) Å, β= 92.875(14)°, V = 3530.9(1.9) Å3, Z = 4. The crystal structure of odigitriaite was solved by direct methods and refined to an R 1 value of 2.75% based on single-crystal X-ray data. It is a double-layer sheet-borosilicate mineral; Cs and Na are intercalated within the double-layer sheet, and the double layers are linked by interstitial Ca and Na atoms.

Several of the Proterozoic natural fission reactors at Oklo, Gabon contain abundant organic matter (bitumen), with which much of the reactor uranium is associated. An understanding of the petrography of the bitumen is important in assessing its role in element retention following fissiogenic reactions. The bitumen is replacive and includes vestiges of detrital grains and clays of the host sandstones. It also contains several generations of mineral phases related to the migration of uranium and daughter lead, and other elements mobilized by hydrothermal activity in the reactor zones. The minerals include (primary) uraninite precipitated after reduction of uranium by organic matter, silicates concentrated in radiation halos around the uraninite, and native lead, galena and further uraninite which migrated from the primary uraninite. The silicates are illitic clays in the immediate vicinity of the reactors, and chloritic more distant from the reactors. Authigenic clays in radiation halos are compositionally distinct from earlier host rock clays. Local migration of uranium and lead is evident as dispersion of the elements through the radiation halos; cross-cutting veinlets of uraninite, native lead and galena, including veinlets extending directly from the primary uraninite crystals; and concentrations of the elements at the margins of bitumen masses. The limit of observed uranium dispersion is within clay immediately beyond the bitumen margins.

The Bondoc Peninsula meteorite appears to be unstable and is disintegrating as the result of terrestrial corrosion. The meteorite is complex with occasional 1 to 3 cm dia. ‘Nodules’ of ‘iron-class’ material, fig. 1, within which are numerous non-metallic inclusions. These range in size from 0·5–1·5 mm and vary in shape from the extremes of angular to globular, shown in figs. 2 and 3. The metallic groundmass of fig. 1 is a polycrystalline array of kamacite grains that are equant in shape and about 3 to 4 mm dia. The boundaries between these kamacite grains are heavily invaded by corrosion product. The films of cracked schreibersite and strips of compositionally zoned taenite that are present at the kamacite boundaries each contribute about 2 % by volume and their average Ni contents are about 45 wt% and 40 wt% respectively. When these figures are combined with the average 6·2 wt% Ni, 0·75 wt% Co, and 0·02 wt% P of the kamacite the resulting bulk composition of the metal is ∼ 7·5 wt% Ni, ∼ 0·7 wt% Co, ∼ 0·3 wt% P. Nital etching reveals partially annealed Neumann bands in the kamacite, indicating a late stage reheating below about 500°C. However, the M profile method of Wood (1967) when applied to the zoned taenite yields a cooling rate of 0·1–0·5°C/Myr before this reheating event.

The angular inclusions are relatively coarsely crystalline and commonly have massive chromite and tridymite crystals, with pyroxene, anorthite, and whitlockite usually present. Most angular inclusions also contain small particles of metal (10–40 µm dia.) interstitial to the mineral phases in the depth of the inclusion. Small quantities of sulphide and phosphide are similarly located. The metal in the angular inclusions is not detectably zoned and both kamacite and taenite show a range of Ni contents that vary with particle size in the manner previously observed by Powell (1969) for a range of conventional mesosiderites. We have in addition measured the Co and P contents of this metal and find P < 0·1 wt% and the Ni and Co analyses are consistent with equilibration in the ternary Fe-Ni-Co equilibrium diagram at ∼ 450 °C.

Zn-rich staurolite occurs in a pelitic gneiss from the Uvete area, central Kenya. The rock was metamorphosed to staurolite-kyanite grade during the Mozambique metamorphism. Microprobe analyses of the staurolite gave the following values (in wt. %): SiO2 26.2–27.3, Al2O3 52.4–53.5, FeO 8.3–9.2, MgO 2.2–2.6, and ZnO 6.0–7.5. Cell dimensions are a = 7.874(± 0.003), b = 16.620(±0.006), c = 5.656(±0.002) Å and β = 90.00 (± 0.002)°. Optical properties are 2Vz = 82–85°, α = 1.742 (±0.002), β = 1.747(±0.002) and γ = 1.753(±0.002). The optical dispersion is moderate and r > v. Density is 3.83(±0.01) g/cm3. Infra-red absorption spectra were also recorded. The cation correlation suggests that the principal substitutions in the staurolite are Zn ⇆ Fe in the tetrahedral sites in the hydroxide sheet and Al ⇆ Mg in the octahedral sites.

Some twenty kimberlite pipes outcrop along the eastern and western borders of the Kundelungu plateau, Shaba Province, Zaire. They are arranged roughly along two north-south trending alignments. The pipes probably intruded the Bangweulu Block, which stabilized around 1800 Ma. The exceptionally fresh kimberlites contain mantle-derived nodules (peridotites and eclogites), as well as megacrysts which may reach up to several cm in diameter. The most important megacrysts are garnets, ilmenites, clinopyroxenes, orthopyroxenes and olivines. Micas and diamonds are rarely observed. The clinopyroxenes can be subdivided in two groups: (1) a Ca-rich, low-T type, similar to the Cr-rich diopsides found in ‘depleted’ (granular) peridotites; and (2) subcalcic clinopyroxene comparable to the megacrysts and to the clinopyroxenes of ‘fertile’ (sheared) peridotites. The orthopyroxenes are less frequent and are Ca-poor enstatites (0.07–0.42 wt.% CaO) and Ti-bronzites (CaO <1.3 wt.%). All the analysed garnets are Ca-rich (>4.5 wt.% CaO) and all fall in the lherzolite field defined by Sobolev et al., 1973. The low-Ca garnets which appear in many diamond-bearing kimberlites have never been observed in Zaire, neither in the diamond-poor Kundelungu pipes nor in the diamond-rich Mbuji-Mayi pipes. The ilmenites define a trend close to the ‘magmatic Mg-enrichment trend';. The olivine macrocrysts have Fo contents comparable to those of peridotites (Fo90–93). The ultramafic nodules comprise lherzolites, harzburgites, pyroxenites, wehrlites and dunites. The granular textures and P-T equilibrium conditions (770–1380°C and 28–61 kbar) deduced from their mineral compositions, show clearly that they were derived from a mantle zone on the continental geotherm (90–190 km depth). The eclogite nodules, which are less frequent, contain only two mineral phases (pyrope-almandine-grossular and omphacite), and the texture and the mineral compositions are similar to those of Roberts Victor eclogites. Our findings support the conclusion of Nixon and Condliffe (1989) that low-T peridotites, eclogites and pyroxenites derived from ‘depleted’ lithosphere, while Cr-poor garnet, subcalcic diopside and bronzite megacrysts cristallized from fertile asthenosphere.

A petrological and geochemical study has been made of the late Precambrian St. David's granophyre (SDG) and the Cwm Bach rhyolites (CBR). The SDG is trondhjemitic, peraluminous, and chemically zoned with lower Na/K ratios in its interior portions. Although the SDG contains only minor amounts of K, the Rb content is relatively high and ratios of immobile versus mobile elements indicate that K has been removed. The CBR are flow-banded and autobrecciated subaerial rhyolite flows which are more K-rich and less altered than the SDG, lying close to the ternary minimum composition of the system Q-Or-Ab-(H2O). K mobility is considered to result from the reaction K-feldspar→ K-mica which released excess K ions, imparting peraluminous compositions to the rocks. On the basis of this reaction the original K content of the rocks has been estimated, the values for which are more compatible with immobile element abundances and with normal igneous trends. Similar abundances of the relatively immobile elements Ti, Zr, Sr, Y and Nb, together with K-corrected K/Rb ratios, suggest that the SDG and CBR may be comagmatic volcanic-arc-collision-type granite and rhyolite.

Intracellular crystals of aragonite have been identified by selected area electron diffraction (SAED) in the freshwater filamentous alga Spirogyra sp. which grows sporadically as carpets in the Thames river, Ontario, Canada. The crystals are 2 to 24 µm in length, and characterized by a unique cross-shaped morphology, in which needle-like, or prismatic outgrowths develop from a common axis. Crystals may be dispersed through filaments, but tend to cluster as aggregates towards the centre.

This paper presents new data on the metasomatic development of zoned ultramafic balls from Fiskenaesset, West Greenland. Field and petrographic evidence indicate retrogression of original ultrabasic inclusions in acid country rock gneisses to serpentinemagnesite assemblages, followed by regional metamorphism and consequent development of the zonal structure upon metasomatic re-equilibration via a supercritical aqueous fluid phase confined to grain boundaries. The balls show varying degrees of deviation from an ideal sequence (antigorite-talc-tremolite-hornblende-chlorite-country rock) intimated by non-equilibrium thermo-dynamics, the currently accepted conceptual framework for the discussion of diffusion metasomatism.

Major and trace-element variations behave in a similar manner to those reported from other zoned ultramafic balls but fail to define the original country rock ultrabasic discontinuity unambiguously. It is tentatively suggested that application of the apparently systematic deviations from ideality may provide additional evidence.

The presence of a hornblende zone and absence of a continuous biotite zone are two significant differences from other zoned ultramafic bodies. The former may suggest increased mobility of the aluminium species at Fiskenaesset, the latter a lower temperature of formation or smaller K2O content of the gneissic hosts.

Zircon from two types of orthogneisses (inheritance-rich and inheritance-poor) from Sierra Nevada (Betic Cordillera, Spain) was investigated by integrating U–Pb geochronology, cathodoluminescence and back-scattered SEM imaging, laser-ablation inductively coupled plasma mass spectrometry analyses and Raman spectroscopy to examine the conditions of magmatic zircon growth and the variable extent and mechanisms of the Alpine modifications. Zircon from inheritance-rich gneiss consists of two main domains: inherited (Neoproterozoic-to-Early Paleozoic and Devonian) cores and magmatic overgrowths, which provided 206Pb/238U concordant ages of 286 ± 3 Ma. In inheritance-poor gneiss, zircons consist of magmatic cores and very altered rims defining a discordia with an upper intercept with the Concordia at 287 + 21 –22 Ma and a lower intercept at 20.8 + 48.6 –20.8 Ma. Magmatic domains of zircon from inheritance-rich gneiss have lower rare-earth element (REE) contents than magmatic domains from inheritance-poor gneiss, reflecting the less evolved nature of the melt. Altered domains in zircon from inheritance-poor gneisss how greater U concentrations, lower REE concentrations and lower Th/U ratios relative to the cores, interpreted as representing Pb loss from the U-rich magmatic domains during the Alpine event. Morphological changes within single grains and between populations reflects the evolution during magmatic cooling. We show that, whereas classic methods allow two different interpretations for the geodynamic setting of the two types of gneisses, a complete study of composition, morphology and structure of zircon can help to decide that a model based on a common source for the granitic melt better fits the zircon characteristics than a model based on melts generated in two different geotectonic settings.

Synchrotron X-ray topography was the principal perfection-assessment method employed. X-ray wavelengths were chosen that gave optimum penetration and diffraction contrast characteristics for the size of crystals examined. Two colourles transparent specimens were selected for comprehensive study. Both were of simple habit consisting of the prism {101̄0} terminated at each end by major and minor rhombohedral facets only. The larger specimen, volume ≈250 mm3, contained a moderately high but non-uniformly distributed dislocation population, totalling ≈103, all emanating from a roughly centrally located small nuclear volume. One apical region was dislocation-free. Optical microscopic observations including Nomarski interference contrast of features on one major rhombohedral facet in this region are described. The smaller specimen, volume ≈30 mm3, was remarkable for its low dislocation content, ≈20 in total, all radiating from a central point. Enhancement of dislocation image visibility relative to diffraction contrast images of severe surface damage on this crystal was demonstrated using higher-order X-ray reflections. Neither of the specimens studied in detail contained twinning or evident diffraction contrast from impurity zoning. Their lack of a microscopically visible or X-ray topographically detectable nucleating body favours a homogenous nucleation origin of these crystals.

Uranoan thorite crystals have been found occurring as a sparse constituent in lithophysae in 6.1 to 6.8 Ma alkali rhyolite flows at Thomas Mountain, Utah, USA. The crystals are associated with sandidine, quartz, topaz, hematite, magnetite, and calcite; they are leek to dark grass green, transparent, well-formed, euhedral prisms, showing development of forms {100}, {101}, and {111}. The mineral is both optically isotropic, with a refractive index of 1.86(1), and X-ray amorphous, indicating its metamict state. Electron microprobe analysis yields: SiO2 17.3, ThO2 56.8, UO2 25.4, total 99.5%, and a structural formula of (Th0.72U0.31)Σ1.03Si0.97O4.

This appears to be the first reported occurrence of thorite in volcanic rocks of rhyolitic composition, and may account for part or all of the Th reported in alkali rhyolites and so-called ‘topaz-rhyolites’ of the western USA.

A group of ultrabasic dykes occurring in south-west Skye is typified by often abundant and diverse ultrabasic xenoliths composed of essentially the same minerals as the dykes. The xenoliths, which vary considerably in shape and size, are in sharp contact with the host rocks and exhibit no evidence of remelting by, or reaction with, the dykes. Although extensive axial concentration of olivine occurred in the dykes during intrusion, the xenoliths appear to be randomly distributed throughout all but the extreme margins of the dykes and often exhibit a preferred orientation. The orientation and distribution of the xenoliths are attributed to the suppression of rotation and axial migration of the xenoliths during the emplacement of the dykes because of the relatively high viscosity of the suspending medium.

The ultrabasic xenoliths, unlike many of those occurring in basalts, kimberlites, etc., are considered unlikely to represent primary upper mantle material and it is suggested that they were probably derived by the disintegration of layered ultrabasic rocks genetically related to the dykes and hence are of cognate origin.

Andychristyite, PbCu2+Te6+O5(H2O), is a new tellurate mineral from Otto Mountain near Baker, California, USA. It occurs in vugs in quartz in association with timroseite. It is interpreted as having formed from the partial oxidation of primary sulfides and tellurides during or following brecciation of quartz veins. Andychristyite is triclinic, space group P1̄, with unit-cell dimensions a = 5.322(3), b= 7.098(4), c = 7.511 (4) Å, α = 83.486(7), β = 76.279(5), γ = 70.742(5)°, V = 260.0(2) Å3 and Z = 2. It forms as small tabular crystals up to ∼50 μm across, in sub-parallel aggregates. The colour is bluish green and the streak is very pale bluish green. Crystals are transparent with adamantine lustre. The Mohs hardness is estimated at between 2 and 3. Andychristyite is brittle with an irregular fracture and one perfect cleavage on {001}. The calculated density based on the empirical formula is 6.304 g/cm3. The mineral is optically biaxial, with large 2V, strong dispersion, and moderate very pale blue-green to medium blue-green pleochroism. The electron microprobe analyses (average of five) provided: PbO 43.21, CuO 15.38, TeO3 35.29, H2O 3.49 (structure), total 97.37 wt.%. The empirical formula (based on 6 O apfu) is: Pb0.98Cu2+0.98Te6+1.02O6H 1.96. The Raman spectrum exhibits prominent features consistent with the mineral being a tellurate, as well as an OH stretching feature confirming a hydrous component. The eight strongest powder X-ray diffraction lines are [dobs in Å(I)(hkl)]: 6.71(16)(010), 4.76(17)(110), 3.274(100)(120,102,012), 2.641(27)(102, 211, 112), 2.434(23)(multiple), 1.6736(17)(multiple), 1.5882(21)(multiple) and 1.5133(15)(multiple). The crystal structure of andychristyite (R1 = 0.0165 for 1511 reflections with Fo > 4σF) consists of stair-step-like hcp polyhedral layers of Te6+O6 and Cu2+O6 octahedra parallel to {001}, which are linked in the [001] direction by bonds to interlayer Pb atoms. The structures of eckhardite, bairdite, timroseite and paratimroseite also contain stair-step-like hcp polyhedral layers.

The Bonser vein, one of the most productive sources of copper in the English Lake District, contains a mineral assemblage comprising quartz, chlorite, calcite, dolomite, stilpnomelane, magnetite, pyrrhotine, pyrite, marcasite, native bismuth, bismuthinite, laitakarite, joseite, arsenopyrite, chalcopyrite, sphalerite, galena, and cosalite. The phases pyrrhotine, sphalerite, arsenopyrite, laitakarite, joseite, and cosalite were analysed by electron microprobe. The occurrence of laitakarite is the first reported in the British Isles. Textures of the ore and gangue minerals show that the vein minerals were deposited successively in open voids. The sequence of deposition was of quartz forming throughout, early chlorite and stilpnomelane with some dolomite and calcite, magnetite as the earliest opaque phase, followed by arsenopyrite, pyrrhotine, sphalerite, chalcopyrite, pyrite, and marcasite; the bismuth- and lead-bearing minerals were the last to form.

The data on the coexisting phases and their compositions have been used to estimate the temperatures of mineralization and the activities of sulphur and oxygen. Magnetite and arsenopyrite appear to have formed at 350–400% with aS2 reaching 10−12 to 10−14 atm. and aO2 around 10−24 to 10−29 atm. The assemblage of quartz, chlorite, stilpnomelane, calcite, dolomite, pyrrhoine, chalcopyrite, sphalerite, and (late) arsenopyrite was probably deposited at ∼ 240°C, with aS2 decreasing to 10−15 to 10−16 atm and aO2 to 10−38) to 10{su−44 atm. The later minerals probably formed at temperatures as low as 200°C and under similar conditions of sulphur and oxygen activity.

We report a single-crystal Fourier-transform infrared (FTIR) study of a sample of pollucite from Maine, USA. Prior to our work, the sample had been characterized by single-crystal X-ray diffraction, neutron diffraction and electron-probe microanalysis. It is cubic Ia3d, with a crystal-chemical formula Na1.93(Cs10.48Rb0.31K0.04)Σ=10.83(Al14.45Si33.97)Σ=48.42O96·3.92H2O, and an H2O content, determined by thermogravimetric analysis, of 1.6 wt.%. The single-crystal FTIR spectrum has a doublet of intense bands at 3670 and 3589 cm–1, which are assigned to the ν3 and ν1 stretching modes of the H2O molecule, respectively. A very intense and sharp peak at 1620 cm–1 is assigned to the ν2 bending vibration. In the near-infrared region there is a relatively intense peak at 5270 cm–1, which is assigned to a combination (ν2 + ν3) mode of H2O, and a weak but well defined doublet at 7118 and 6831 cm–1, which is assigned to the first overtones of the fundamental stretching modes. A relatively weak but extremely sharp peak at 2348 cm–1 shows that the pollucite contains CO2 molecules in structural cavities. Mapping the sample using FTIR indicates that both H2O and CO2 are homogeneously distributed. Secondary ion mass spectrometry yielded an average CO2 content of 0.09±0.02 wt.%. On the basis of this value, we determined the integrated molar absorption coefficient for the spectroscopic analysis of CO2 in pollucite to be εiCO2 = 11,000±3000 l mol–1 cm–2; the linear molar absorption coefficient for the same integration range is εlCO2 = 1600±500 l mol–1 cm–1.

The crystal structure of mattheddleite (Pb5(Si1.5S1.5)O12(Cl0.57OH0.43), P63/m, a = 10.0056(6), c = 7.4960(9) Å) from Leadhills, Scotland has been determined to R = 0.065. The structure is that of apatite where Pb replaces Ca, equal amounts of S and Si replace P and the X anion is OH + Cl. The composition deduced from the structural refinement differs from that of microprobe analyses by giving full occupancy of the tetrahedral site and equal Si and S to preserve charge balance. We conclude that the microprobe analysis is incorrect possibly due to large and inaccurate absorption corrections. For the crystal analysed, the X anion position is zoned from an OH-rich interior to a Cl-rich exterior. The Pb(2) atom is disordered which may be analogous to the disordering of the Ca(2) site in Cl-rich, Ca apatites.