Calculation of the effect of deprotonation on the Si NMR shielding for the series Si(OH)4 to SiO 4 4−

²⁹Si NMR shieldings have been calculated by ab initio coupled Hartree-Fock perturbation theory for the orthosilicate species Si(OH)₄, Si(OH)₃O^-, Si(OH)₂O ₂ ^2- , Si(OH)O ₃ ^3- and SiO ₄ ^4- using energy optimized geometries from ab initio Hartree-Fock calculations. The shielding of Si(OH)₃O^- is smaller than that of Si(OH)₄ by 2.7 ppm and the shielding trend along the Si(OH)₄ to SiO ₄ ^4- series is decidedly nonlinear. The unprotonated O in Si(OH)₃O^- is more shielded and has a much smaller electric field gradient than do the protonated oxygens. Calculated anisotropies show the largest components of the shielding to lie along or near the short Si-O bonds. Calculations employing point charges in place of H reproduce the shielding trends in T _d and S ₄ symmetry Si(OH)₄ semiquantitatively. The calculated trends in shielding with < si-o-h=" can=" also=" be=" correlated=" with=" the=" energies=" of=" the=" si3p,o2p="> bonding orbitals.     

UNESCO’s role in the rehabilitation of Bamiyan in Afghanistan

This article is complementary to Claudio Margottinis technical article Instability and geotechnical problems of the Buddha niches and surrounding cliff in Bamiyan Valley, central Afghanistan, published in Vol. 1, issue 1 of this journal. The present article provides background information on the framework of UNESCOs strategies for the safeguarding of Afghanistans cultural heritage and, in particular, the Bamiyan site, the mechanisms for the development of operational projects, capacity building of national specialists, UNESCOs partnerships and its fund-raising activities for the successful implementation of projects. The Division of Cultural Heritage is closely involved in ICL, therefore, it was natural to include UNESCOs project for the safeguarding of the Bamiyan site in the framework of IPL. It was approved as IPL project C101-3 titled The geo-morphological instability of the Buddha niches and surroundings cliffs in the Bamiyan Valley.The author is program specialist in charge of Asia at UNESCOs Division of Cultural Heritage and member of ICL     

The role of water resources in the evolution of the Israeli–Lebanese border

The current location of the border between Lebanon and Palestine, today's Israel, is a product of various competing forces. The Zionist Organization aspired to include the entire Galilee region up to the lower reaches of the Litani River (also known as the Kassimiyah River) within Palestine. The river itself was the desired northern border of the country. The Zionists supported their position by employing instrumental arguments that were largely related to the availability of water resources. On the other hand, residents of the upper Galilee, today's southern Lebanon, demanded that they be included with Lebanon. They used their trade links with Beirut, and cultural and familial ties with other parts of Lebanon to support their position. These instrumental and expressive arguments appear to have assisted in the demarcation of the border between Lebanon and Palestine. Currently, access to the water resources, not necessarily control over them, is likely to influence negotiations between Israel and Lebanon over the future of the Israeli-occupied security zone in southern Lebanon.     

A High-Temperature Al–Ca Condensate in the Lunar Regolith

Doklady Earth Sciences - For the first time, a high-temperature condensate in the form of two-component glass beads of about 200–400 nm size, consisting of an Al–Ca oxide core rimmed by...     

Theoretical reaction pathways for the formation of [Si(OH)5]1− and the deprotonation of orthosilicic acid in basic solution

Ab initio, molecular orbital calculations at the 6-31G¹ level including second-order Møller-Plesset electron correlation predict that the species [Si(OH)₅]¹⁻ is dynamically stable in a distorted trigonal bipyramid configuration. Reaction pathways for Si(OH)₄ + (OH)⁻ → [Si(OH)₅]¹⁻ → [(OH)₃SiO]¹⁻—H₂O are also calculated. The first reaction represents the formation of pentacoordinate Si from orthosilicic acid and hydroxide. The activation energy for adding a fifth Si-(OH)⁻ bond to the Si(OH)₄ molecule is ≈0.1 eV /molec (≈10kJ/mol). The second reaction is the deprotonation of the Si(OH)₄ which forms as a hydroxyl group leaves the [Si(OH)₅]¹⁻ molecule. Removal of a bond from this complex requires 0.9 eV/molecule (≈85 kJ/mol). Lengthening the Si—OH₂ distance results in the isolated molecules [(OH)₃SiO]¹⁻ + H₂O. This represents dehydration of the deprotonated orthosilicic acid.[Si(OH)₅]¹⁻ and [(OH)₃SiO]¹⁻- H₂O have the same energetic stability within the accuracy of these calculations. The potential energies of the isolated molecular systems [(OH)₃SiO]¹⁻+ H₂O and Si(OH)₄ + (OH)⁻ are considerably higher. These results suggest that [Si(OH)₅]¹⁻ may be a stable species or reaction intermediate in dissolution of silicate minerals in basic aqueous solutions.     

Granitoid massif of the Dal’negorsk borosilicate deposit in the Primorye region of Russia: The role of the intrusion in the formation of the boron mineralization

The granitoids of the Dal’negorsk borosilicate deposit are ascribed mainly to the high-K metaluminous rocks of the calcic and alkali-calcic series. The thermo-baro-geo-chemical studies showed that they originated from melts with low contents of water (H₂O < 3.5% H₂O) and CO₂ at 800–850°C and 65–90 MPa. The data on the average contents of elements in the rock-forming minerals and the estimated initial water content in the magma point to the absence of a genetic relation between the intrusion and boron mineralization. The granitoid magma was responsible for the skarn formation and for the mobilization and remobilization of boron under a favorable environment. The K/Ar dating (51.0 ± 10 Ma), the geochemical typification (signatures of within-plate, subduction, and collisional granitoids), and the low water content in the parental melts of the granitoids, in accordance with the scheme of the geodynamic evolution of the region, indicate their formation in the lithospheric plate sliding environment.     

Evolution of manganese ore genesis in the earth’s geological history and the role of the biosphere

The formation of manganese rocks and ores occurred during the whole geological history of the Earth. Five metallogenic epochs (Early to Middle Proterozoic, Late Proterozoic, Early to Middle Paleozoic, Late Paleozoic, and Meso-Cenozoic) and 7 very important phases (Early, Middle, and Late Proterozoic, Early to Middle Paleozoic, Late Paleozoic, Late Mesozoic, and Meso-Cenozoic) can be distinguished. The phases of manganese ore genesis at many stratigraphic levels are closely related to the global climatic and tectonic reconstructions (the breakup of the continent of Gondwana and periods of glaciations and aridization) and biotic events (mass extinction of organisms). Based on carbon isotopic composition in manganese carbonates, participation of oxidized organic carbon is established.     

The solubility of [4H]Si defects in α-quartz and their role in the formation of molecular water and related weakening on heating

The nature of the solubility of water as [4H]_Si defects in quartz, and their role in providing a source of molecular water on heating, is investigated. Existing ab inito energy calculations on the incorporation of water in quartz are used to show that energetically 4H for Si substitution is likely to constitute the most prevalent mode of water uptake on the atomic scale in quartz under equilibrium conditions, and that the planar defects previously observed by a number of different authors by electron microscopy in wet quartz are likely to be planar rafts of aggregated [4H]_Si defects which are formed on supersaturation. These new conclusions call into question the previous identification of the planar defects as high pressure water clusters and require that their role in the production of molecular water in the context of recent theories of hydrolytic weakening be re-assessed. Accordingly the existing ab initio results have been used to establish the characteristics of the phase diagram for the system quartz-water in the temperature and pressure range of interest in hydrolytic weakening. Additional electron-optical experiments on wet quartz show that, on annealing at temperature in the electron microscope, similar planar defects develop in wet quartz by a diffusion process. In the context of existing theories of hydrolytic weakening it is now proposed that the conversion of [4H]_Si defects to molecular water, where this is dictated by the equilibrium phase diagram, leads to a relatively large increase in volume and to the appearance of the bubbles of free water and the nucleation of associated prismatic dislocation loops of Burgers vector b=1/3 a $\langle 11\bar 20\rangle $ as previously observed. Ultimately the development of these loops leads to dislocation-induced plasticity.     

A re-examination of petrogenesis and 40Ar/39Ar systematics in the Chain of Ponds K-feldspar: “diffusion domain” archetype versus polyphase hygrochronology

K-feldspar (Kfs) from the Chain of Ponds Pluton (CPP) is the archetypal reference material, upon which thermochronological modeling of Ar diffusion in discrete “domains” was founded. We re-examine the CPP Kfs using cathodoluminescence and back-scattered electron imaging, transmission electron microscopy, and electron probe microanalysis. ⁴⁰Ar/³⁹Ar stepwise heating experiments on different sieve fractions, and on handpicked and unpicked aliquots, are compared. Our results reproduce the staircase-shaped age spectrum and the Arrhenius trajectory of the literature sample, confirming that samples collected from the same locality have an identical Ar isotope record. Even the most pristine-looking Kfs from the CPP contains successive generations of secondary, metasomatic/retrograde mineral replacements that post-date magmatic crystallization. These chemically and chronologically distinct phases are responsible for its staircase-shaped age spectra, which are modified by handpicking. While genuine within-grain diffusion gradients are not ruled out by these data, this study demonstrates that the most important control on staircase-shaped age spectra is the simultaneous presence of heterochemical, diachronous post-magmatic mineral growth. At least five distinct mineral species were identified in the Kfs separate, three of which can be traced to external fluids interacting with the CPP in a chemically open system. Sieve fractions have size-shifted Arrhenius trajectories, negating the existence of the smallest “diffusion domains.” Heterochemical phases also play an important role in producing nonlinear trajectories. In vacuo degassing rates recovered from Arrhenius plots are neither related to true Fick’s Law diffusion nor to the staircase shape of the age spectra. The CPP Kfs used to define the “diffusion domain” model demonstrates the predominance of metasomatic alteration by hydrothermal fluids and recrystallization in establishing the natural Ar distribution among different coexisting phases that gives rise to the staircase-shaped age spectrum. Microbeam imaging of textures is as essential for ⁴⁰Ar/³⁹Ar hygrochronology as it is for U–Pb geochronology.     

Effect of the Si/Al ordering on structural parameters and the energetic stabilization of vermiculites – a theoretical study

The effect of the Si/Al distribution in the tetrahedral sheets of the vermiculite mineral has been investigated employing density functional theory. The structures of six models for vermiculite with the structural formula (Mg₄)(Mg₁₂)(Si₈Al₈)O₄₀(OH)₈·24(H₂O) per unit cell were fully optimized. The models differ by the T···Mg²⁺···T coordination of the interlayer Mg²⁺ cations by two central cations from the adjacent tetrahedral sheets of the 2:1 vermiculite layers (T,T=Si,Al). We observed the formation of very strong hydrogen bonds between water molecules solvating the interlayer Mg²⁺ cations and the surface basal oxygen atoms of the 2:1 layers. The directionality of hydrogen bonds is the major factor determining the layer stacking in the vermiculite structure. Results showed that the most stable model is that where only silicon atoms in the tetrahedral sheets coordinate all interlayer Mg²⁺ cations.     

Influence of hydrogen on Fe–Mg interdiffusion in (Mg,Fe)O and implications for Earth’s lower mantle

Interdiffusion of Fe and Mg in (Mg,Fe)O has been investigated experimentally under hydrous conditions. Single crystals of MgO in contact with (Mg_0.73Fe_0.27)O were annealed hydrothermally at 300 MPa between 1,000 and 1,250°C and using a Ni–NiO buffer. After electron microprobe analyses, the dependence of the interdiffusivity on Fe concentration was determined using a Boltzmann–Matano analysis. For a water fugacity of ∼300 MPa, the Fe–Mg interdiffusion coefficient in Fe _x Mg_1−x O with 0.01 ≤ x ≤ 0.25 can be described by with and C = −80 ± 10 kJ mol⁻¹. For x = 0.1 and at 1,000°C, Fe–Mg interdiffusion is a factor of ∼4 faster under hydrous than under anhydrous conditions. This enhanced rate of interdiffusion is attributed to an increased concentration of metal vacancies resulting from the incorporation of hydrogen. Such water-induced enhancement of kinetics may have important implications for the rheological properties of the lower mantle.

The role of conjugate crenulation cleavage in the development of ‘millipede’ microstructures

Millipede microstructures are described from Archean metaturbidites surrounding the Back River volcanic complex, eastern Slave Structural Province. They are locally developed within andalusite porphyroblasts that grew in response to the intrusion of late syn-kinematic granitoids. The porphyroblasts acted as a mechanical heterogeneity and resulted in the nucleation of conjugate crenulations, which were then helicitically overgrown by the porphyroblasts. This process produced the millipede morphology through a simple, consistent mechanism. The model presented here for the development of millipede microstructures represents an alternative to other models requiring complex deformation partitioning and restricted porphyroblast growth.     

Evaluation of the origin and fate of nitrate in the Abbotsford Aquifer using the isotopes of15N and18O in NO3−

Extensive NO₃⁻ contamination of groundwater in the Abbotsford aquifer to levels above drinking water limits is a major problem in the Fraser Lowlands of southwestern British Columbia, Canada. Nitrate concentrations in the aquifer ranged from 0 to 151 mg/l NO₃⁻, with a median concentration of 46 mg/l NO₃⁻. Of 117 wells sampled, 54% had NO₃⁻ concentrations exceeding the drinking water limit of 45 mg/1. Approximately 80% of the study area had groundwater NO₃⁻ concentrations exceeding 40 mg/1 NO₃⁻. Potential NO₃⁻ source materials were poultry manure N and synthetic NH₄ based fertilizers. Theδ¹⁵N of solid poultry manure samples ranged between + 7.9 and + 8.6‰ (AIR). Four brands of synthetic fertilizers commonly used hadδ¹⁵N values between −1.5 and −0.6‰. Ammonia volatilization caused theδ¹⁵N of groundwater NO₃⁻ produced from poultry manure N to range between +8 and +16‰. Theδ¹⁸O values of groundwater NO₃⁻, by contrast, mostly ranged between +2 and +5‰ (SMOW). This narrow range ofδ¹⁸O values fell within the expected range of NO₃⁻ produced by nitrification of reduced N forms such as poultry manure N and NH₄ fertilizers, and had a similar range ofδ¹⁸O values as NO₃⁻ in the upper part of the unsaturated zone below raspberry fields and beneath former manure piles. Theδ¹⁵N-NO₃⁻ andδ¹⁸O-NO₃⁻ data confirmed that NO₃⁻ in the aquifer was predominantly derived from poultry manure and to a lesser extent from synthetic fertilizers. Theδ¹⁸O-NO₃⁻ data further suggested the nitrification process occurred mainly in the summer months, with the soil NO₃⁻ produced subsequently flushed into the aquifer during fall recharge. Theδ¹⁵N-NO₃⁻andδ¹⁸O-NO₃⁻ data conclusively indicated that no significant bacterial denitrification is taking place in the Abbotsford aquifer.     

Mineralogical note petrogenetic significance of the state of K‐feldspars from spatially related granitic intrusives in West Herberton,North Queensland

This short note presents the results of triclinicity determination of purified K‐feldspars from three spatially related granitic bodies (Kalunga Granodiorite, Watsonville granite, and Elizabeth Creek granite, ECG) in west Herberton, Queensland. The systematic decrease of triclinicity values (as 5 index) with increasing weight percent K₂O and differentiation indices, decreasing colour indices, and K/Rb ratios is considered to provide an additional line of evidence for a possible co‐genetic relationship of the intrusives. The second phase of the Elizabeth Creek Granite (ECG II) is a late stage intrusive and its emplacement may explain the close spatial association of ECG members and the economic mineralization in the district.     

An optical transform and Monte Carlo study of the diffuse X-ray scattering in mullite,Al2(Al2+2xSi2−2x)O10−x

Diffuse X-ray scattering distributions have been recorded for reciprocal layers normal to c ^* of a synthetic mullite with composition Al₂(Al_2+2xSi_2–2x) O_10–xx, where represents an oxygen vacancy and x is close to 0.4. The effect on the diffuse scattering pattern of different schemes for ordering of the oxygen vacancies and the accompanying cation shifts within a single ab-layer of mullite has been investigated using optical diffraction analogue experiments in conjunction with Monte Carlo simulation.A simple scheme in which the only driving force for the ordering is that the O_c oxygens are precluded from being bonded to four T/T^* cations, results in a 2D diffuse intensity distribution which displays many of the features that are observed in the x-ray scattering patterns. An alternative scheme in which bonding to four T/T^* cations was favoured, resulted in a domain structure consisting of islands of the -alumina structure within a matrix of sillimanite. This gave diffraction patterns bearing no resemblance to the observed x-ray patterns and can, we believe, be discounted completely.     

The Al (Nb,Ta) Ti(in−2) substitution in titanite: the emergence of a new species?

Summary The highest (Nb, Ta) content ever encountered in titanite is reported from the Maríkov 11 pegmatite in northern Moravia, Czech Republic. This dike is a member of a pegmatite swarm of the beryl-columbite subtype, metamorphosed under conditions of the amphibolite facies. The pegmatite carries, i.a., rare tantalian rutile intergrown with titanian ixiolite, titanian columbite-tantalite, fersmite and microlite. Fissures generated in the Nb, Ta oxide minerals during deformation are filled with titanite, formed by reaction of the oxide minerals with metamorphic pore fluids. The titanite displays limited degrees of substitutions Na(Ta > Nb)(CaTi)_–1, (Ta > Nb)₄Ti_–4Si_–1 and AI(OH, F)(TiO)_–1, but an extensive (and occasionally the sole significant) substitution (Al > Fe³⁺)(Ta > Nb)Ti_–2, responsible for widespread oscillatory zoning. This substitution reduces the proportion of the titanite componentsensu stricto, CaTiSiO₄,O, to less than 50 mole % in many analyzed spots. The extreme composition corresponds to (Ca_0.994Na_0.011)(Ti_0.436Sn_0.007Al_0.280Fe³⁺ _0.006Ta_0.199Nb_0.079)Si_0.988O₄(O_0.974F_0.026). However, so far this substitution fails to generate compositions that would define a new species.

---

Zusammenfassung Die AI(Nb, Ta)Ti_–2 Substitution im Titanit: Auftauchen einer neuen Mineralspecies? Die höchsten (Nb, Ta) Gehalte, die jemals für Titanit gefunden wurden, werden für den Maríkov II Pegmatit in Nordmähren, Tschechei, berichtet. Der Intrusivgang ist Teil eines Amphibolit-faziell überprägten Pegmatitschwarms vom Beryll-Columbit Subtypus Der Pegmatit führt u.a. seltene tantalbetonte Rutile verwachsen mit titanbetontem Ixiolith, titanbetontem Columbit-Tantalit, Fersmit and Mikrolith. Deformationsbedingte Frakturen in den (Nb, Ta) Oxiden sind mit Titanit, als Folge der Reaktion der metamorphen Porenlösungen mit den Oxidmineralen, verkittet. Titanit zeigt begrenzte Substitutionen Na(Ta > Nb)(CaTi)_–1,(Ta > Nb)₄Ti_–4Si_–1 and Al(OH, F)(TiO)_–1, aber extensive (und gelegentlich einzig bedeutsame) Substitution (Al >> Fe³⁺)(Ta > Nb)Ti_–2, die eine weitverbreitete, oszillierende Zonierung hervorruft. Diese Substitution verringert den Anteil der Titanit-Komponentesensu stricto, CaTiSiO,O, auf weniger als 50 Mol% in vielen Analysen. Die Extremzusammensetzung entspricht Ca_0.994Na_0.11) (T_10.436Sn_0.007Al_0.280Fe³⁺ _0.006Ta_0.199Nb_0.079)Si_0.988O₄(O_0.974F_0.026). Das AusmaB dieser Substitution ist unzureichend, um eine neue Mineralspecies zu definieren.