The crystal structure of chloroxiphite, Pb3CuO2(OH)2Cl2, from Merehead Quarry (monoclinic, P21/m, a = 6.6972(8), b = 5.7538(5), c = 10.4686(14) Å,β = 97.747(10)°, V = 399.72(8) Å3) has been refined to R1 = 0.041. The structure contains three symmetrically unique Pb sites and one Cu site. The strong distortion of the Pb2+ coordination polyhedra is due to the stereoactivity of the s2 lone electron pairs on the Pb2+ cations. The Cu-site is coordinated by four OH- groups to form an almost planar Cu(OH)4 square that is complemented by two apical Cl– anions, forming an elongated [Cu(OH)4Cl2] octahedron. Because of the large size and variability of coordination polyhedra around Pb2+ cations and the strength of the Me–O bonds in comparison to the Me–Cl bonds (Me = metal), it is convenient to describe the structure of chloroxiphite in terms of oxocentred OPb4 tetrahedra. The O1 atom is tetrahedrally coordinated by four Pb2+ cations forming relatively short and strong O–Pb bonds. The OPb4 tetrahedra link together via common edges to form [O2Pb3]2+ double chains. The difference between chloroxiphite and other natural oxyhalides is the presence of Cu2+ cations which form an independent structural unit that links to units formed by OPb4 tetrahedra. In this sense, chloroxiphite can be considered as a modular structure consisting of both strong cation- and anion-centred units.

Elemental compositions of the <2mm fraction of three sediments sampled along the Kupa River are presented. On plots of log(SiO2/Al2O3) vs. log(CaO+Na2O)/K2O, the sediments plot closest to average sandstone compositions. On plots of weathering indices A vs. B (Kronberg and Nesbitt, 1981) the sediments plot close to basalt, terrestrial crust and granite. X-ray diffraction of the <63 μm fraction suggests chlorite, vermiculite and mica are present as weathering products in the upper, middle and lower stream sediments. Depletion of some elements in the sediments suggests loss of elements from the sediments due to dissolution of minerals.

A multi-methodological investigation of a synthetic Cu/Fe-bearing blue beryl [IV(Be2.86Cu0.14)∑=3.00VI(Al1.83Fe3+0.14Mn2+0.03Mg0.03)∑=2.03IV(Si5.97Al0.03∑=6.00O18.(Li0.12Na0.04.0.40H2O)] has been performed by means of gemmological standard testing, electron microprobe chemical analyses, laser ablation inductively coupled plasma mass spectroscopy, thermo-gravimetric analyses, infrared spectroscopy and single-crystal X-ray diffraction in order to determine the gemmological properties, crystal structure and crystal-chemistry of this material. The increasing production of marketable hydrothermal synthetic beryls with 'exotic' colours and the small number of studies on the accurate location of chromophores in the crystal structure inspired this multi-methodological investigation. The X-ray structural refinements confirm that the space group of the Cu/Fe-bearing blue beryl is P6/mcc, with unit-cell parameters: 9.2483 ≤ a ≤ 9.2502 Å and 9.2184 ≤ c ≤ 9.2211 Å. The analysis of the difference Fourier maps of the electron density suggests that Cu is located at the tetrahedral site (Wyckoff 6fposition) along with Be, whereas Fe shares the octahedral site with Al (4c position). No evidence of extra-framework Cu/Fe-sites (i.e. channel sites) has been found. The Li is probably located at the extra-framework 2b site. Infrared spectra show that the H2O molecules are present with two configurations: one with the H···H vector oriented ‖[0001] and the other with H···H vector oriented ⊥[0001].

The kinetics of glauconite dissolution have been determined in the pH range 2—10 (T = 25°C) using flow-batch reactor experiments. Besides the kinetic characteristics, the structural and textural aspects which could influence its long-term reactivity have also been characterized by means of X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), scanning electron microscopy (SEM) and BET surface area measurements. The results from these analyses showed that glauconite follows a dual dissolution pathway which is pH-dependent, being more stable at neutral or slightly alkaline pH values. Under acidic conditions, glauconite is slightly more soluble than other ubiquitous silicates present in the marine sediments. The dissolution mechanism is incongruent at very acid pH values and tends to be congruent for intermediate and neutral ones. In addition, the results from the structural analyses suggest that the dissolution is a two-step process: the first one involves the disorder of the octahedral and tetrahedral layers, probably following a turbostratic mechanism which is evident in the XRD spectra as selective broadening of several reflections. In the second step, the dissolution of the cations from interlayer positions takes place and leads to the formation of an amorphous residue which acts as a passivating layer and reduces the reactive surface considerably. The influence of these aspects on CO2 capture via carbonation reactions is discussed.

Gold mineralization at the Viceroy Mine is hosted in extensional veins in steep shear zones that transect metabasalts of the Archaean Arcturus Formation. The gold mineralization is generally made up of banded or massive quartz carrying abundant coarse arsenopyrite. However, most striking is a distinct suite of Au-Bi-Te-S minerals, namely joseite-A (Bi4TeS2), joseite-B (Bi4Te2S), hedleyite (Bi7Te3), ikunolite (Bi4S3), ‘protojoseite’ (Bi3TeS), an unnamed mineral (Bi6Te2S), bismuthinite (Bi2S3), native Bi, native gold, maldonite (Au2Bi), and jonassonite (AuBi5S4). The majority of the Bi-Te-S phases is characterized by Bi/(Se+Te) ratios of >1. Accordingly, this assemblage formed at reduced conditions at relatively low fS2 and fTe2. Fluid-inclusion thermometry indicates depositional temperatures of the main stage of mineralization of up to 342°C, in the normal range of mesothermal, orogenic gold deposits worldwide. However, melting temperatures of Au-Bi-Te phases down to at least 235°C (assemblage (Au2Bi + Bi + Bi7Te3)) imply that the Au-Bi-Te phases have been present as liquids or melt droplets. Furthermore, the close association of native gold, native bismuth and other Bi-Te-S phases suggests that gold was scavenged from the hydrothermal fluids by Bi-Te-S liquids or melts. It is concluded that a liquid/melt-collecting mechanism was probably active at Viceroy Mine, where the distinct Au-Bi-Te-S assemblage either formed late as part of the main, arsenopyrite-dominated mineralization, or it represents a different mineralization event, related to rejuvenation of the shear system. In either case, some of the gold may have been extracted from pre-existing, gold-bearing arsenopyrite by Bi-Te-S melts, thus leading to an upgrade of the gold ores at Viceroy. The Au-Bi-Te-S assemblage represents an epithermal-style mineralization overprinted on an otherwise mesothermal (orogenic) gold mineralization.

Atomic force microscopy (AFM) and transmission electron microscopy (TEM) were used to investigate the fine structure of the calcite prisms from the pearl-oyster shell Pinctada margaritifera. The AFM analysis shows that the prisms are made of densely packed circular micro-domains (in the 0.1 μm range) surrounded by a dense cortex. The TEM images and diffraction patterns allow the internal structure of the micro-domains to be described. Each of them is enriched in Ca-carbonate. Hosted in distinct regions of each prism, some are fully amorphous, and some others fully crystallized as subunits of a large calcite single crystal. At the border separating the two regions, micro-domains display a crystallized core and an amorphous rim. Such a border probably marks out an arrested crystallization front having propagated through a previously bio-controlled architecture of the piling of amorphous micro-domains. Compared to recent data concerning the stepping mode of growth of the calcite prisms and the resulting layered organization at the μm-scale, these results give unexpected views regarding the modalities of biocrystallization.

A unique hybrid natrocarbonatite, collected from the new ash cone of the volcano Oldoinyo Lengai. Tanzania in July 2008, consists of phenocrysts of nyerereite and gregoryite together with xenocrysts of clinopyroxene, nepheline and Ti-andradite set in a groundmass of cuspidine, sodalite, ferroan manganoan monticellite, K-Fe sulphide and manganoan titanian magnetite and gregoryite. The xenocrysts were not in equilibrium with the melt which formed their current host, as clinopyroxenes and Ti-andradite are mantled by cuspidine, and nepheline by sodalite and phlogopite—potassian kinoshitalite solid solutions. A microxenolith of ijolite exhibits similar reaction phenomena. The minerals of the xenocryst suite have similar compositions to plutonic ijolites found at Oldoinyo Lengai, and are thus considered to be derived by the fragmentation of such material in a previously contaminated natrocarbonatite melt. The latter, which has cuspidine, sodalite and monticellite as primary liquidus phases, is considered to have been formed by the complete assimilation of ijolitic material in a natrocarbonatite magma at depth in the volcano conduit. The occurrence of trace amounts of cuspidine, Fe-Mn-monticellite, K-Fe sulphide and Mn-Ti-spinel in recently erupted natrocarbonatites is ascribed to similar, but less extensive, assimilation of silicate material prior to their eruption.

Coiraite, ideally (Pb,Sn2+)12.5As3Fe2+Sn4+S28, occurs as an economically important tin ore in the large Ag-Sn-Zn polymetallic Pirquitas deposit, Jujuy Province, NW-Argentina. The new mineral species is the As derivative of franckeite and belongs to the cylindrite group of complex Pb sulphosalts with incommensurate composite-layered structures. It is a primary mineral, frequently found in colloform textures, and formed from hydrothermal solutions at low temperature. Associated minerals are franckeite, cylindrite, pyrite-marcasite, as well as minor amounts of hocartite, Ag-rich rhodostannite. arsenopyrite and galena. Laminae of coiraite consist of extremely thin bent platy crystals up to 50 urn long. Electron microprobe analysis (n = 31) gave an empirical formula Pb11.21As2.99Ag0.13Fe1.10Sn6.13S28.0 close to the ideal formula (Pb11.3Sn2+1.2)Σ=12.5As3Fe2+Sn4+S28. Coiraite has two monoclinic sub-cells, Q (pseudotetragonal) and H (pseudohexagonal). Q: a 5.84(1) Å, b 5.86(1) Å, c 17.32(1) Å, β 94.14(1)°, F 590.05(3) Å3, Z = 4, a:b:c = 0.997:1:2.955; H (orthogonal setting): a 6.28(1) Å, b 3.66(1) Å, c 17.33(1) Å, β 91.46(1)°, V398.01(6) Å3, Z = 2, a∶b∶c = 1.716∶1∶4.735. The strongest Debye-Scherrer camera X-ray powder-diffraction lines [d in Å, (I), (hkl)] are: 5.78, (20), (Q and H 003); 4.34, (40), (Q 004); 3.46, (30), (Q and H 005); 3.339, (20), (Q 104); 2.876, (100), (Q and H 006); 2.068, (60), (Q 220).

The crystal structure of a clinopyroxene with composition (Na0.75Ca0.25)(Cr0.75Mg0.25)Si2O6 was refined at 100, 150, 200, 250 and 298 K. The work was performed in the context of an investigation on the low-temperature behaviour of A+M3+Si2O6 (with A dominant in Na and M = transition elements) pyroxenes in order to provide new insights concerning the phase transition and anomalies recently found in the low-temperature behaviour of NaTiSi2O6 and NaGaSi2O6 compounds. The refinements were done in the C2/c space group (wR2 between 0.048 and 0.068), and no change of symmetry was observed down to 100 K. Highly-anisotropic axial thermal expansion occurs with the scheme αb ≥ αb > αc.

The M2, M1 and T polyhedra expand with αM2 > αM1 αT as generally observed in pyroxenes. A discontinuity in the M1 polyhedral volume is observed between 200 and 250 K, similar to the one observed in NaGaSi2O6 between 190 and 235 K.

The atomic displacement parameters are scaled according to the following pattern: UM2 > UO2 > UO3 ≥ U01 > UT ≥ UM1 Comparison with previous data along the CaMgSi2O-NaCrSi2O6 join suggests significant positional disorder for the O1 oxygen, due to repulsion of the 2p orbitals of O1 and the non-bondine 3d electrons of Cr.

Minerals are an important component of the soil environment (Dixon et al., 1977). They provide a structural framework which supports plants and contribute to the physical heterogeneity of soil. Minerals also contribute to the fertility of soils. Primary minerals are a source of essential plant nutrients (Harley and Gilkes, 2000). Clay minerals impact on the water-holding capacity of soils, affect the cation exchange capacity of soils (Brown, 1977) and are able to sequester nutrients and contaminants within the soil (Dubbin, 2001).

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.

Felsic volcanic rocks exposed in the Frasnian Gafo Formation, in the Azinhalinho area of Portugal, display very similar geochemical signatures to volcanic rocks from the Iberian Pyrite Belt (IPB). located immediately to the south. The similarities include anomalously low high field-strength elements (HFSE) concentrations, possibly caused by low-temperature crustal melting, which translate into classification problems.

A geochronological study, using laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) analyses of zircon grains from these rocks, has provided concordia ages of 356±1.5 Ma and 355±2.5 Ma for two samples of rhyodacite porphyry, and 356±1.4 Ma for a granular rhyodacite. These results show that volcanism at Azinhalinho was broadly contemporaneous with IPB volcanism, widely interpreted as being of Famennian to Visean age. Considering that the host rocks of the Azinhalinho volcanic rocks are Frasnian, and therefore deposited synchronously with the Upper Devonian Phyllite-Quartzite Group sedimentation in the IPB basin, the radiometric ages imply that the Azinhalinho felsic rocks are intrusive and likely represent conduits or feeders to the volcanism of the IPB.

This paper highlights new research on the biomineralization of otoliths and uses a mineralogical approach to understand mechanisms of crystal growth and metal incorporation into otoliths. Petrographic observations of the nucleation of otolith growth in the core for several fish species reveals that sagittal otoliths appear to nucleate around a few or many nucleation sites (primordia) and that these sites vary in size (ranging in diameter from 1 to 20 μm), depending on the species. Spectroscopic data show a large Mn-enrichment in the primordia within the core but the reasons for this enrichment are still unclear (e.g. organic matter or possibly another material other than CaCO3). This study also provides the first multi trace-element data for endolymph fluid and the growing otolith; we found large enrichments (Ca and Sr) and depletions (Na, K, Zn and Rb) of elements in the otolith relative to the endolymph. The last part of this paper examines the effect of crystal structure on the microchemistry ofotoliths. Our investigation helps understand how the chemical characteristics of the metal ions (i.e. ionic radii) and the crystalline structure interact to cause differential trace-metal uptake between the CaCO3 polymorphs, aragonite and vaterite.

Vernadite is a nanocrystalline turbostratic phyllomanganate containing Ni, and is widespread in surface environments and oceanic sediments. To improve our understanding of Ni uptake in this mineral, two series of analogues of vernadite (δ-MnO2) were prepared with Ni/Mn atomic ratios of 0.002—0.105 at pH4 and 0.002—0.177 at pH 7. Their structures were characterized using X-ray powder diffraction (XRD). The δ-MnO2 nano-crystals are essentially monolayers with coherent scattering domains sizes of ∼10 Å perpendicular to the layering and ∼55 Å within the layer plane. For Ni/Mn < 0.01, the layer charge deficit is apparently balanced entirely by interlayer Mn, Na and protons. At higher Ni/Mn, Ni occupies the same site as interlayer Mn above and below vacant sites within the MnO2 layer and at sites along the edges of the layer. However, the layer charge is balanced differently at the two pH values. At pH 4, Ni uptake is accompanied by a reduction in structural Na and protons, whereas interlayer Mn remains strongly bound to the layers. At pH 7, interlayer Mn is less strongly bound and is partially replaced by Ni. The results of this study also suggest that the number of vacant octahedral sites and multi-valent charge-copmpensating interlayer species are underestimated by the currently used structure models of δ-MnO2.

Soils are the dominant terrestrial sink for carbon, containing three times as much C as above-ground plant biomass, and acting as a host for both organic and inorganic C, as soil organic matter and pedogenic carbonates, respectively. This article reviews evidence for the generation within the soil solution of dissolved C derived from plants and recognition of its precipitation as carbonates. It then considers the potential value of this process for artificially-mediated CO2 sequestration within soils. The ability of crops such as wheat to produce organic acid anions as root exudates is substantial, generating 70 mol/(y kg) of exuded C, equivalent to the plant's own ‘body weight’. This is still an order of magnitude less than measured C production from Icelandic woodlands (Moulton et al., 2000), which have no other possible source of C. Thus, there is apparently no shortage of available dissolved C, as bicarbonate in solution, and so the formation of pedogenic carbonates will be controlled by the availability of Ca. This is derived from mineral weathering, primarily of silicate minerals (natural plagioclase feldspars and pyroxenes; artificial cement and slag minerals). Within the UK, existing industrial arisings of calcium silicate minerals from quarrying, demolition and steel manufacture that are fine-grained and suitable for incorporation into soils are sufficient to account for 3 MT CO2 per year, compensating for half of the emissions from UK cement manufacture. Pursuing these arguments, it is shown that soils have a role to play as passive agents in the removal of atmospheric CO2, analogous to the use of reed beds to clean contaminated waters.

Euhedral crystals of complexly zoned niobian titanite (up to 0.3 mm) are enclosed in hedenbergite (Hd53—81Di15—43Jh3-5) and quartz from a hedenbergite vein skarn at Kamenne doly near Pisek, Czech Republic. They are associated with minor clinozoisite-epidote (Ps3—22), calcite, plagioclase (An95). scapolite (Me80—82), scheelite, pyrrhotite, fluorapatite, arsenopyrite, native bismuth and Bi,Te-minerals. The following textural and compositional subtypes were recognized: (I) Nb-rich titanite, (II) Nb-moderate titanite in the central zone, (III) Nb-poor, Sn-enriched titanite and (IV) Nb-poor, Al,F-rich titanite in the outer zone. The substitution Al(Nb,Ta)Ti—2 is dominant in subtypes I and II, the titanite subtype I being characterized by elevated contents of Al ≤ 0.257 atoms per formula unit (a.p.f.u.), Nb (≤ 0.161 a.p.f.u.) and Ta (≤ 0.037 a.p.f.u.). Amounts of Al, Nb and Ta in subtype II are smaller and more variable. The minor substitution SnTi—1 occurs chiefly in titanite subtype III with a content of Sn ≤ 0.039 a.p.f.u.. The substitution Al(F,OH)(TiO)_i is typical for titanite subtype IV exhibiting elevated contents of Al (s£ 0.221 a.p.f.u.), F (≤ 0.196 a.p.f.u.) and Fe (≤ 0.039 a.p.f.u.).

The negative relationship of substitutions Al(F,OH)(TiO)_i vs. SnTi—1 and Al(Nb,Ta)Ti—1 is constrained chiefly by crystal structure rather than by the composition of parent medium alone. Textural relations suggest that the Nb-moderate titanite in the core zone and entire outer zone are products of fluids-induced dissolution-reprecipitation processes. The studied niobian titanite represents a new F-enriched type from a medium-grade, calc-silicate rock.

Three natural crystals of the wulfenite (PbMoO4)—stolzite (PbWO4) series were investigated by single-crystal X-ray diffraction. The results indicate that the symmetry is I41/a from nearly pure wulfenite to intermediate compositions, in contrast to previous work which claimed a symmetry change to 74 symmetry (acentric) for intermediate compositions compared with I41/a (centric space group) for the end-members. The results reported here show that the reflections violating I41/a symmetry observed in this work and in a previous study are related primarily to λ/2 effects, even if Renninger effects are not excluded. Consequently, we find that the I41/a symmetry is retained throughout the wulfenite— stolzite.

Earth scientists currently use changes in major and minor elements as an indication of rock alteration. Work on spheroidal weathering has shown an increase in the rare earth element (REE) whole-rock abundancescan accompany minor changes in major elementsand highlights the need for new, more sensitive, geochemical techniques of detecting incipient alteration. Augites from the core and rind of a corestone system from the Tecuamburro complex in SE Guatemala are examined to determine their role in the whole-rock REE increases.

Lizardite-1T crystals from Gew-graze at the Lizard, Cornwall, of an apparent composition (Mg2.94Fe0.03Al0.03)(Si1.97Al0.03)05(OH)4, have been observed to contain 2–5% of thin interstratifications of clinochlore when investigated by analytical transmission electron microscopy (TEM). The clinochlore is usually only a few unit layers thick but has an extensive lateral dimension parallel to the lizardite layers. Analytical TEM confirms the existence of very low-Al lizardite with a planar structure interstratified with occasional thin units of clinochlore containing substantial Al. Compositionally, such clinochlore (invisible by X-ray diffraction) interstratified throughout the lizardite crystals, could account for most of the Al present. We suggest that an occasional influx of Al causes the nucleation and growth of clinochlore at the expense of lizardite. The possibility of clinochlore contributing to the measured Al content in lizardite samples highlights the need for future investigations of Al-bearing serpentines to include careful examination and interpretation using imaging and analysis by TEM.

It has crept into serpentine discussions that lizardite cannot form without the coupled substitution of Al to relieve the misfit between the sheets of octahedra and tetrahedra. The lizardite at Gew-graze is almost Al-free, forms well-crystallized planar crystals and demonstrates that Al is not an essential element for lizardite crystallization.

The Silbergrube Aplite (SA) in the Hagendorf-Pleystein Pegmatite District, near Waidhaus, Germany, is a mildly peraluminous NW-SE directed leucogranite dyke. It occurs in association with quartz dykes and aplitic metamorphic mobilizates in the NE Bavarian crystalline basement. The SA differs from other aplitic mobilizates in the region in having a less well developed strain-related mineral orientation and in containing only minor amounts of garnet and tourmaline. The aplitic metamorphic mobilizates and the SA are chemically and mmeralogically almost identical and yield the same age of formation of ∼302 Ma (stage I). The age of formation of the Hagendorf pegmatites seemingly post-dates the emplacement of the SA. The SA was emplaced at the boundary between fine-grained biotite granites and metamorphic country rocks within a zone of structural weakness, favouring the formation of disseminated late magmatic to hydrothermal mineralization of Li-bearing Fe-Mn phosphates (stages II and III). Brittle deformation along this zone was conducive to the faultbound Fe-Mn-Ca phosphates. Mineral telescoping is evident from the presence of Fe2+, Fe3+ and Mn2+ phosphates in fissures and vugs in a texturally highly variable host-rock environment (stage IV). This intimate intergrowth of phosphate minerals reflects contrasting physical and chemical conditions prevailing in a near-surface/ shallow epithermal S-deficient phosphate system (stage IV), similar to what is known from Cu-Au epithermal systems. The most recent mineral assemblages that formed under predominantly oxidizing conditions are correlated with the subtropical weathering during the Neogene which resulted in the formation of a peneplain truncating the SA and its country rocks (stage V). The SA is the root zone of the felsic aplitic-pegmatitic mobilizates in this region and is overprinted by an epithermal phosphate system.