Role of fluorine in the transfer of Be and the formation of beryl deposits: a thermodynamic model.

After a thorough study on the tracing of the emerald origin by oxygen data by Zwaan et al. [12], the paper by Moine et al. [4] entitled ‘The role of fluorine in the formation of the Mananjary emerald deposits (eastern Madagascar)' demonstrates through a thermodynamic model that the metasomatic transformation of amphibolites into fluorine-enriched phlogopites was the cause for beryl precipitation. – This paper is important as it shows that fluorine can be a dominant ligand for some metals, like beryllium. As underlined by the authors, the reason for the BeF affinity in solution is that beryllium, despite the fact it is divalent, still displays a high ionic potential due to its small ionic radius. – Moine et al. [4] calculate that a fluid equilibrated with F-phlogopite (XF=0.7) at 500 °C and 2 kbar contains 275 ppm total fluorine, compared to 55 ppm dissolved in fluids buffered by wollastonite–quartz–fluorite (WQF) in the same conditions [11]. This paper therefore contributes to enlighten that fluorine-rich fluids can circulate through rocks in some natural geological settings. More precisely, it shows that rocks dominantly formed of hydrous silicates constitute a remarkable environment where are contradicted previous conclusions in the literature that “fluoride concentrations in natural hydrothermal solutions are restricted by equilibrium constraints involving fluorite, topaz and other fluoride-bearing minerals with low solubilities” (e.g., [2] and references therein). – The numerous local crystal-chemical factors that control (OH–F) exchanges in hydrous silicates (smectites, micas, amphiboles, tourmalines) are far from being understood and modelled for any given composition. However, this paper is a good illustration of the fact that, at least for a limited number of amphibole and biotite end-members with restricted Fe-free Mg-rich compositions, a thermodynamic database is now available that satisfactorily accounts for fluorination reactions. Numerous systematic structural studies of synthetic end-members have shown that some magnesian minerals like talc, phlogopite or tremolite, host the hydroxyl group in a symmetrical trioctahedral 36[Mg3] environment. Fluorination of such minerals is easy in all proportions and controlled by simple local crystal-chemical parameters. Firstly, there is no steric limitation to the complete substitution of OH− by F− in these minerals because the ionic radii of these two anions are very similar. Also, the proton exchanges one charge with the hydroxyl oxygen and is independent of any lattice atom. Such a hydroxyl group, which behaves as a separate entity, can easily be replaced by fluorine [8]

Premarital Education: Participation, Attitudes, and Relation to Marital Adjustment in a Sample from Northern Utah

The purpose of this study was to investigate the attitudes, participation in, and potential effectiveness of premarital education as a vehicle to promote more satisfying marriages. A retrospective survey instrument, including existing measures of religious values, willingness to invest in marriage, and marital satisfaction, was used to gather data to answer research questions related to couples\u27 participation in, and attitudes about premarital education, and their influence on marital adjustment and satisfaction. Information about the amount of Time spent in premarital education, breadth of Topics covered, Training of the provider, and whether or not Testing was performed also was gathered and called Four T\u27s of premarital education. Sample couples were identified by comparing marriage license information to current telephone listings from Cache County, Utah. One hundred forty-five couples returned usable surveys. Statistical analysis revealed that most couples participated in little or no premarital education even though most couples had favorable attitudes towards such marriage preparations. Further, no significant relation was found between participation in any type of premarital education and marital adjustment or satisfaction. Implications for policy and practice are discussed

Accuracy of PIXE analyses using a funny filter

Light and heavy trace elements can be analysed simultaneously by particle-induced X-ray emission (PIXE) using an Al-funny filter (a filter with a hole drilled at its centre, placed in front of the detector window). The treatment of spectra, performed using the GUPIX code, requires the determination of an instrumental constant H. In theory and when using ordinary filters, H is a constant corresponding to the detection solid angle. In contrast, we have observed that H varies with X-ray energy using a funny filter. This is due to an inaccurate description of the geometry of the detection: detector-to-target distance, filter thicknesses and hole diameter of the funny filter. We develop a methodology to determine the effective values of the four geometrical parameters from a calibration of H using standards. In turn, H recalculated using these effective values is a constant equivalent to the effective detection solid angle

Study of pollution in the El Jadida-Safi Atlantic coastal zone (Morocco) by using PIXE and SSNTD methods

In this work PIXE experiments were performed for measuring heavy and light elements (ranging from aluminium to lead) concentrations inside various polluted and unpolluted soils as well as liquid samples collected from different phosphate factory sewers in the El Jadida-Safi Atlantic coastal region (Morocco). In addition, uranium (238U) and thorium (232Th) contents were evaluated in the same samples studied by using CR-39 and LR-115 type II solid state nuclear track detectors (SSNTDs). The influence of the phosphate industry wastes on the concentrations of both radioactive and non-radioactive elements of the samples studied was investigated

Lifetime of superheated water in a micrometric synthetic fluid inclusion

A synthetic pure water fluid inclusion presenting a wide temperature range of metastability (Th - Tn ≈ 50°C; temperature of homogenization Th = 144°C and nucleation temperature of Tn = 89°C) was selected to make a kinetic study of the lifetime of an isolated microvolume of superheated water. The occluded liquid was placed in the metastable field by isochoric cooling and the duration of the metastable state was measured repetitively for 7 fixed temperatures above Tn. Statistically, measured metastability lifetimes for the 7 data sets follow the exponential Reliability distribution, i.e., the probability of non nucleation within time t equals . This enabled us to calculate the half-life periods of metastability τ for each of the selected temperature, and then to predict τ at any temperature T > Tn for the considered inclusion, according to the equation τ(s) = 22.1 × e1.046×ΔT , (ΔT = T - Tn). Hence we conclude that liquid water in water-filled reservoirs with an average pore size ≈ 104 µm3 can remain superheated over geological timelengths (1013s), when placed in the metastable field at 24°C above the average nucleation temperature, which often corresponds to high liquid tensions (≈ -50 MPa)

Lifetime of superheated water in a micrometric synthetic fluid inclusion

International audienceA synthetic pure water fluid inclusion presenting a wide temperature range of metastability (Th - Tn ≈ 50°C; temperature of homogenization Th = 144°C and nucleation temperature of Tn = 89°C) was selected to make a kinetic study of the lifetime of an isolated microvolume of superheated water. The occluded liquid was placed in the metastable field by isochoric cooling and the duration of the metastable state was measured repetitively for 7 fixed temperatures above Tn. Statistically, measured metastability lifetimes for the 7 data sets follow the exponential Reliability distribution, i.e., the probability of non nucleation within time t equals . This enabled us to calculate the half-life periods of metastability Τ for each of the selected temperature, and then to predict Τ at any temperature T > Tn for the considered inclusion, according to the equation Τs , (∃T = T - Tn). Hence we conclude that liquid water in water-filled reservoirs with an average pore size ≈ 104 µm3 can remain superheated over geological timelengths (107s), when placed in the metastable field at 10°C above the average nucleation temperature, which often corresponds to high liquid tensions (≈ -120 -70 MPa)

Experimental superheating of water and aqueous solutions

International audienceThe metastable superheated solutions are liquids in transitory thermodynamic equilibrium inside the stability domain of their vapor (whatever the temperature is). Some natural contexts should allow the superheating of natural aqueous solutions, like the soil capillarity (low T superheating), certain continental and submarine geysers (high T superheating), or even the water state in very arid environments like the Mars subsurface (low T) or the deep crustal rocks (high T). The present paper reports experimental measurements on the superheating range of aqueous solutions contained in quartz as fluid inclusions (Synthetic Fluid Inclusion Technique, SFIT) and brought to superheating state by isochoric cooling. About 40 samples were synthetized at 0.75 GPa and 530-700 °C with internally-heated autoclaves. Nine hundred and sixty-seven inclusions were studied by micro-thermometry, including measuring the temperatures of homogenization (Th: L + V → L) and vapor bubbles nucleation (Tn: L → L + V). The Th-Tn difference corresponds to the intensity of superheating that the trapped liquid can undergo and can be translated into liquid pressure (existing just before nucleation occurs at Tn) by an equation of state. Pure water (840-935 kg m−3), dilute NaOH solutions (0.1 and 0.5 mol kg−1), NaCl, CaCl2 and CsCl solutions (1 and 5 mol kg−1) demonstrated a surprising ability to undergo tensile stress. The highest tension ever recorded to the best of our knowledge (−146 MPa, 100 °C) is attained in a 5 m CaCl2 inclusion trapped in quartz matrix, while CsCl solutions qualitatively show still better superheating efficiency. These observations are discussed with regards to the quality of the inner surface of inclusion surfaces (high P-T synthesis conditions) and to the intrinsic cohesion of liquids (thermodynamic and kinetic spinodal). This study demonstrates that natural solutions can reach high levels of superheating, that are accompanied by strong changes of their physico-chemical properties

Advances in multi-elementary analysis of fluid or solid micro-crystalline inclusions (12

International audienceX-Ray-based analytical methods can be applied in an absolute fashion, provided that matrix effects are calculated and that parameters related to instrumental factors are controlled (Newbury, 1986). When EPMA (Electron Probe Micro Analysis) was conceived at the end of the 60's, this potentiality was abandoned, as the instrument works in a relative fashion, by comparison with standards. At the end of the 70's and in the 80's, PIXE (Proton Induced X-Ray Emission) by contrast was applied in a way that preserved the possibility of an absolute application: the computer programs developed to interpret PIXE spectra calculate matrix effects and also integrate instrumental factors (e.g., Maxwell et al., 1989). In spite of this advantage, and also despite the fact that PIXE application extends to trace element analysis, the development of PIXE in the scientific community was sluggish, in deep contrast with the widespread applications of EPMA. In the field of Earth Sciences particularly, EPMA was recognized by the Mineralogical Society of America to have had 'a revolutionary, profound impact on mineralogy and petrology'. In the same time, PIXE applications remained mainly restricted to trace element analysis, and the potential accuracy of the method was never clearly realized. A first aim of this presentation is to show that, using a simple standardization procedure, the multi-elementary absolute capability of PIXE can be revealed. This in turn changes PIXE into a tool of quantitative mineralogy and trace element geochemistry. We then show that, by coupling PIXE to PIGE (Proton Induced Gamma Ray Emission) and RBS (Rutherford Back Scattering) spectrometries, the Nuclear Microprobe becomes a tool for quantitative mineralogy s.l. and geochemistry, i.e., an instrument to analyze all major to trace elements from Li to U in minerals and their inclusions. In the second part of the presentation, we illustrate the capability of µ-PIXE to analyze in situ individual fluid inclusions that have been carefully localized in space and time. The Hercynian French Massif Central and its sedimentary eastern margin are part of a large European Carbonic Province, which hosts numerous deep CO2 reservoirs and carbonic springs (Blavoux, Dazy, 1990). Carbonic fluids are present at all stages of the long-lived evolution of this crustal segment, from deep metamorphic fluids involved in a thrusting event at 340 M.a to mantle-derived volcanic CO2 related to Neogene volcanism. In order to characterize the main aquo-carbonic fluid reservoirs through time in this crustal segment, we present preliminary data on the trace element content of aquo-carbonic inclusions trapped in the schists at peak and retrograde metamorphic conditions, and compare them to contemporaneous granite-related fluid inclusion

Micro-crystalline inclusions analysis by PIXE and RBS

A characteristic feature of the nuclear microprobe using a 3 MeV proton beam is the long range of particles (around 70 \mu m in light matrices). The PIXE method, with EDS analysis and using the multilayer approach for treating the X-ray spectrum allows the chemistry of an intra-crystalline inclusion to be measured, provided the inclusion roof and thickness at the impact point of the beam (Z and e, respectively) are known (the depth of the inclusion floor is Z + e). The parameter Z of an inclusion in a mineral can be measured with a precision of around 1 \mu m using a motorized microscope. However, this value may significantly depart from Z if the analyzed inclusion has a complex shape. The parameter e can hardly be measured optically. By using combined RBS and PIXE measurements, it is possible to obtain the geometrical information needed for quantitative elemental analysis. This paper will present measurements on synthetic samples to investigate the advantages of the technique, and also on natural solid and fluid inclusions in quartz. The influence of the geometrical parameters will be discussed with regard to the concentration determination by PIXE. In particular, accuracy of monazite micro-inclusion dating by coupled PIXE-RBS will be presented

The European Space Analogue Rock Collection (ESAR) at the OSUC-Orleans for in situ planetary missions

International audienceThe ESAR is a collection of well-characterised planetary analogue rocks and minerals that can be used for testing in situ instrumentation for planetary exploration. An online database of all relevant structural, compositional and geotechnics information is also available to the instrument teams and to aid data interpretation during missions