Single crystal raman studies of pyrite-type RuS2, RuSe2, OsS2, OsSe2, PtP2, and PtAs2

Single crystal Raman spectra of pyrite-type RuS₂, RuSe₂, OsS₂, OsSe₂, PtP₂, and PtAs₂ are presented and discussed with reference to the energies of the X-X stretching modes _x-x (A _g, F _g) and the X₂ librations (E, 2F_g). The main results obtained are (i) strong Raman resonance effects, (ii) different sequences for _x-x (A _g) and (E _g), i.e., R_{x_2 } $$ " align="middle" border="0"> for PtP₂ and PtAs₂ and R_{x_2 } $$ " align="middle" border="0"> for OsS₂, owing to the interplay of intraionic and interionic lattice forces, (iii) greater strengths for the intraionic P-P and As-As bonds compared to the S-S and Se-Se bonds, respectively, and (iv) a strong influe_gnce of the metal ions on the strength of the X-X bonds.This is contribution LXI of a series of papers on lattice vibration spectra     

Isotope Dilution MC-ICP-MS Rare Earth Element Analysis of Geochemical Reference Materials NIST SRM 610, NIST SRM 612, NIST SRM 614, BHVO-2G, BHVO-2, BCR-2G, JB-2, WS-E, W-2, AGV-1 and AGV-2

We present data for the concentrations of eleven rare earth elements (La, Ce, Pr, Nd, Sm, Eu, Gd, Dy, Er, Yb, Lu) in eleven international geochemical reference materials obtained by isotope dilution multi-collector inductively coupled plasma-mass spectrometry (MC-ICP-MS). We have analysed both rock powders and synthetic silicate glasses, and the latter provide precise data to support the use of these as reference materials for in situ trace element determination techniques. Our data also provide precise measurements of the abundance of mono-isotopic Pr in both glasses and powders, which allows more accurate constraints on the anomalous redox-related behaviour of Ce during geochemical processes. All materials were analysed in replicate providing data that typically reproduce to better than one percent. Sm/Nd ratios in all these materials also reproduce to better than 0.2% and are accurate to < 0.2% and can thus be used as calibrants for Sm-Nd geochronology. Our analyses agree well with existing data on these reference materials. In particular, for NIST SRM 610, USGS BHVO-2, AGV-1 and AGV-2, our measured REE abundances are typically within < 2% (and mostly 1%) of REE concentrations previously determined by isotope dilution analysis and thermal ionisation mass spectrometry, consistent with the higher degree of precision and accuracy obtained from isotope dilution techniques. Close agreement of results between basaltic glass reference materials USGS BHVO-2G and BCR-2G and the BHVO-2 and BCR-2 powders from which they were created suggests that little fractionation, concentration or dilution of REE contents occurred during glass manufacture.     

High-Precision Trace Element Data for the USGS Reference Materials BCR-1, BCR-2, BHVO-1, BHVO-2, AGV-1, AGV-2, DTS-1, DTS-2, GSP-1 and GSP-2 by ID-TIMS and MIC-SSMS

Different batches of the new US Geological Survey (USGS) reference materials (RMs) BCR-2, BHVO-2, AGV-2, DTS-2 and GSP-2 and the original USGS RMs BCR-1, BHVO-1, AGV-1, DTS-1 and GSP-1 have been analysed by isotope dilution using thermal ionisation mass spectrometry (ID-TIMS) and by multi-ion counting spark source mass spectrometry (MIC-SSMS). The concentrations of K, Rb, Sr, Ba and the rare earth elements were determined with overall analytical uncertainties of better than 1% (ID-TIMS) and 3% (MIC-SSMS). The analyses of different aliquots and batches of BCR-2, BHVO-2, AGV-2 and GSP-2, respectively, agree within 1%, i.e. approximately the analytical uncertainties of the data. This indicates an homogeneous distribution of the trace elements in these RMs. Differences in element concentrations of up to 17% in different aliquots of the depleted RM DTS-2 are outside the analytical uncertainty of our data. They may be attributed to a slightly heterogeneous distribution of trace elements in this dunite sample. Our trace element data for BCR-2, BHVO-2, AGV-2 and GSP-2 agree within about 3% with preliminary reference values published by the USGS. They also agree within 1-6% with those of the original RMs BCR-1, BHVO-1, AGV-1 and GSP-1. Large compositional differences are found between DTS-2 and DTS-1, where the concentrations of K, Rb, Sr and the light REE differ by factors of 2 to 24.     

Neodymium and Strontium Isotope Data for USGS Reference Materials BCR-1, BCR-2, BHVO-1, BHVO-2, AGV-1, AGV-2, GSP-1, GSP-2 and Eight MPI-DING Reference Glasses

We have measured ⁸⁷Sr/⁸⁶Sr and ¹⁴³ Nd/¹⁴⁴ Nd isotope ratios in different batches and aliquots of the new US Geological Survey (USGS) reference materials (RMs) BCR-2, BHVO-2, AGV-2 and GSP-2 and the original USGS RMs BCR-1, BHVO-1, AGV-1 and GSP-1 by thermal ionisation mass spectrometry. In addition, we also analysed the eight Max-Planck-Institut-Dingwell (MPI-DING) reference glasses. Nearly all isotope ratios obtained in the different aliquots and batches agree within uncertainty limits indicating excellent homogeneity of the USGS powders and the MPI-DING glasses. With the exception of GSP-2, the new USGS RMs are also indistinguishable from the ratios found in the original USGS RMs (⁸⁷Sr/⁸⁶Sr: 0.704960, 0.704958 (BCR-1, -2), 0.703436, 0.703435 (BHVO-1, -2), 0.703931, 0.703931 (AGV-1, -2); ¹⁴³ Nd/¹⁴⁴ Nd: 0.512629, 0.512633 (BCR-1, -2), 0.512957, 0.512957 (BHVO-1, -2); 0.512758, 0.512755 (AGV-1, -2)). This means that for normalisation purposes in Sr and Nd isotope geochemistry BCR-2, BHVO-2 and AGV-2 can well replace BCR-1, BHVO-1 and AGV-1 respectively.     

Production of Bauxite Certified Reference Material (BARC-B1201) for Nine Property Values (Al2O3, Fe2O3, SiO2, TiO2, V2O5, MnO,Cr2O3, MgO and LOI) Traceable to SI Units

The National Centre for Compositional Characterisation of Materials (NCCCM) / Bhabha Atomic Research Centre (BARC) and National Aluminium Company Limited (NALCO), India have produced an Indian origin bauxite certified reference material (CRM), referred to as BARC-B1201, certified for major (Al₂O₃, Fe₂O₃, SiO₂, TiO₂, loss on ignition - LOI) and trace contents (V₂O₅, MnO, Cr₂O₃, MgO). Characterisation was undertaken by strict adherence to ISO Guides. A method previously developed and validated in our laboratory, using single step bauxite dissolution and subsequent quantitation (of Al₂O₃, Fe₂O₃, SiO₂, TiO₂, V₂O_5, MnO, Cr₂O₃ and MgO) by ICP-AES (SSBD ICP-AES) was used for homogeneity studies and an inter-laboratory comparison exercise (ILCE) of the candidate CRM. LOI was determined by thermo-gravimetric analysis. Property values were assigned after an ILCE with participation from seventeen reputed government and private sector laboratories in India. The CRM was certified for nine property values: Al₂O₃, Fe₂O₃, SiO₂, TiO₂, V₂O_5, MnO, Cr₂O₃, MgO and LOI, which are traceable to SI units.     

P CO2 in low-grade metamorphism; zeolite,carbonate, clay mineral,prehnite relations in the system CaO-Al2O3-SiO2-CO2-H2O

Equilibria for several reactions in the system CaO-Al₂O₃-SiO₂-CO₂-H₂O have been calculated from the reactions calcite+quartz=wollastonite+CO₂ (5) and calcite+Al₂SiO₅+quartz=anorthite+CO₂ (19) and other published experimental studies of equilibria in the systems Al₂O₃-SiO₂-H₂O and CaO-Al₂O₃-SiO₂-H₂O.The calculations indicate that the reactions laumontite+CO₂=calcite+kaolinite+2 quartz+2H₂O (1) and laumontite+calcite=prehnite+quartz+3H₂O+CO₂ (3) in the system CaO-Al₂O₃-SiO₂-CO₂-H₂O, are in equilibrium with an H₂O-CO₂ fluid phase having -0.0075 for P _fluid=P _total=2000 bars.These calculations limit the stability of zeolite assemblages to low p CO₂.Using the above reactions as model equilibria, several probelms of p CO₂ in low grade metamorphism are discussed. (a) the problem of producing zeolitic minerals from metasedimentary assemblages of carbonate, clay mineral, quartz. (b) the significance of calcite (or aragonite) associated with zeolite (or lawsonite) in low grade metamorphism and hydrothermal alteration. (c) the reaction of zeolites (or lawsonite) with calcite (or aragonite) to produce dense Ca-Al-hydrosilicates (eg. prehnite, zoisite, grossular).     

P--T Stabilities of Laumontite, Wairakite, Lawsonite, and Related Minerals in the System CaAl2Si2O8-SiO2-H2O

Hydrothermal investigation of the bulk composition CaO.Al₂O₃.4SiO₂+excessH₂O has been conducted using conventional techniques over thetemperature ranges 200–450 °C and 500–6000 barsP_fluid. A number of reactions have been studied by employingmineral mixtures consisting of reactants and products in about9: 1 and 1: 9 ratios. The phase relations were deduced fromrelatively long experiments by observing which seeded assemblagedisappeared or decreased markedly in one of the paired run charges. Laumontite was synthesized in the laboratory, probably for thefirst time. Laumontite was grown from seeded wairakite to over99 per cent using a weak NaCl solution. The refractive indicesof the synthetic material are about = 1.504 and = 1.514. Theaverage unit cell dimensions are a₀ = 14.761±0.005 Å;b₀ = 13.077±0.005 Å; c₀ = 7.561±0.003 Å;and ß = 112.02°±0.04°. Within the errorof measurement, the optical properties and cell parameters arein good agreement with those of natural laumontite. The equilibriumdehydration of laumontite involves two reactions: (1) laumontite= wairakite+2H₂O, passing through about 230 °C at 0.5 kb,255±5 °C at 1 kb, 282±5 °C at 2 kb, 297±5°C at 3 kb and 325±5 °C at 6 kb; and (2) laumontite= lawsonite+2 quartz+2H₂O, taking place at about 210 °Cat 3 kb and 275 °C at 3.2 kb. Above 300 °C, the equilibriumcurve for the solid-solid reaction (3) lawsonite+2 quartz =wairakite passes through 305 °C, 3.4 kb and 390 °C,4.4 kb. Equilibrium has been demonstrated unambiguously forthe above three reactions. The hydrothermal decomposition ofnatural laumontite above its own stability limit appears tobe a very slow process. Combined with previously published equilibria determined hydrothermallyfor wairakite, the phase relations are further investigatedby chemographic analysis interrelating the phases, laumontite,wairakite, lawsonite, anorthite, prehnite+kaolinite, and 2 pumpellyite+kaolinitein the system CaAl₂Si₂O₈-SiO₂-H₂O. This synthesis allowed theconstruction of a semiquantitative petrogenetic grid applicableto natural parageneses and the delineation of the physical conditionsfor the various low-grade metamorphic facies in low µCO₂environments. The similar stratigraphic zonations, consistentlyfound in a variety of environments, are recognized to be a functionof burial depth, geothermal gradient, and mineralogical andchemical composition of the parental rocks. Departures fromthe normal sequences are believed to be due to the combinationsof mineralogical variations, availability of H₂O, differencesin the ratio µCO₂/µH₂O, and the rate of reaction.The possible P-T boundaries for diagenesis, the zeolite facies,the lawsonite-albite facies, the prehnite-pumpellyite facies,and the adjacent metamorphic facies are illustrated diagrammatically.     

Sorption of uranyl and arsenate on SiO2, Al2O3, TiO2 and FeOOH

Migration of uranium and arsenic in aquatic environments is often controlled by sorption on minerals present along the water flow path. To investigate the sorption behaviour, batch experiments were conducted for uranium and arsenic as single components and also solutions containing both uranium and arsenic in the presence of SiO₂, Al₂O₃, TiO₂ and FeOOH at a pH ranging from 3 to 9. In solutions containing only U(VI) or As(V) with the minerals, the sorption of U(VI) was low at acidic pH range and increases with increasing pH, whereas As(V) showed opposite sorption behaviour to Al₂O₃, TiO₂ and FeOOH from acidic pH range to alkaline condition. For the As(V)–SiO₂ system, the sorption was low for almost all pH. Sorption of U(VI) and As(V) on SiO₂ and FeOOH is almost similar in solutions containing either U(VI) or As(V) separately, or both together. In the U(VI)–As(V)–Al₂O₃ system, a significant retardation in uranyl sorption and an enhancement in arsenate sorption on Al₂O₃ were observed for a wide range of pH. The sorption behaviour of U(VI) and As(V) was changed when Al₂O₃ was replaced by TiO₂, where an increase in sorption was observed for both elements. The sorption behaviour of uranyl and arsenate in the U(VI)–As(V)–TiO₂ system gives evidence for the formation of uranyl–arsenate complexes. The change in sorption retardation/enhancement of U(VI) and As(V) could be explained by the formation of uranyl–arsenate complexes or due to the competitive sorption between uranyl and arsenate species.     

Zur Bildung und Stabilität von Forsterit,Talk, Serpentin,Quarz und Magnesit im System MgO-SiO2-H2O-CO2

The equilibrium data (temperatures and CO₂ content of the fluid phase) were de termined under a total pressurePf = 2 kb for the following bivariant reactions in the four components system MgO-SiO₂ H₂O-CO₂:

1. a)
   2 forsterite + 2 H₂O + 1 CO₂ ? 1 serpentine + 1 magnesite     
   
   

High-pressure Raman spectroscopic study of Mn2GeO4, Ca2GeO4, Ca2SiO4, and CaMgGeO4 olivines

We present a Raman spectroscopic study of the structural modifications of several olivines at high pressures and ambient temperature. At high pressures, the following modifications in the Raman spectra are observed: 1)?in Mn₂GeO₄, between 6.7 and 8.6?GPa the appearance of weak bands at 560 and 860?cm^?1; between 10.6 and 23?GPa, the progressive replacement of the olivine spectrum by the spectrum of a crystalline high pressure phase; upon decompression, the inverse sequence of transformations is observed with some hysteresis in the transformation pressures; this sequence may be interpreted as the progressive transformation of the olivine to a spinelloid where Ge tetrahedra are polymerized, and then to a partially inverse spinel; 2)?in Ca₂SiO₄, the olivine transforms to larnite between 1.9 and 2.1?GPa; larnite is observed up to the maximum pressure of 24?GPa and it can partially back-transform to olivine during decompression; 3)?in Ca₂GeO₄, the olivine transforms to a new structure between 6.8 and 8?GPa; the vibrational frequencies of the new phase suggest that the phase transition involves an increase of the Ca coordination number and that Ge tetrahedra are isolated; this high pressure phase is observed up to the maximum pressure of 11?GPa; during decompression, it transforms to a disordered phase below 5?GPa; 4)?in CaMgGeO₄, no significant modification of the olivine spectrum is observed up to 15?GPa; between 16 and 26?GPa, broadening of some peaks and the appearance of a weak broad feature at 700–900?cm^?1 suggests a progressive amorphization of the structure; near 27?GPa, amorphization is complete and an amorphous phase is quenched down to ambient pressure; this unique behaviour is interpreted as the result of the incompatibilities in the high pressure behaviour of the Ca and Mg sublattices in the olivine structure.