Elasticity of diopside     

Louise Levien  Donald J. Weidner  Charles T. Prewitt 《Physics and Chemistry of Minerals》1979,4(2):105-113

The thirteen single-crystal elastic moduli for diopside as determined by the acoustic technique based on Brillouin scattering are: c₁₁=2.23, c₂₂=1.71, c₃₃=2.35, c₄₄=0.74, c₅₅=0.67, c₆₆=0.66, c₁₂=0.77, c₁₃=0.81, c₁₅=0.17, c₂₃=0.57, c₂₅=0.07, c₃₅=0.43, c₄₆=0.073. The Reuss bound of the adiabatic bulk and shear moduli calculated from these data are K _s=1.08 Mbar and G=0.651 Mbar. The room-pressure isothermal bulk modulus, K _T , and the pressure derivative of the bulk modulus, K′ _T have also been determined on a four-circle diffractometer, from a single crystal mounted in a gasketed opposed-anvil diamond cell, giving values of K _T =1.13 Mbar and K′ _T =4.8. The principal axes of the strain ellipsoid, calculated from the elastic moduli and observed in the static compression data, are identical, and the linear compressibilities are in reasonable agreement. The single-crystal elastic moduli can be correlated with the structural features of diopside.  相似文献   

In Situ Determination of First‐Row Transition Metal,Ga and Ge Abundances in Geological Materials via Medium‐Resolution LA‐ICP‐MS     

Ricardo Arevalo Jr  William F. McDonough  Philip M. Piccoli 《Geostandards and Geoanalytical Research》2011,35(2):253-273

An in situ, medium‐resolution LA‐ICP‐MS method was developed to measure the abundances of the first‐row transition metals, Ga and Ge in a suite of geological materials, namely the MPI‐DING reference glasses. The analytical protocol established here hinged on maximising the ablation rate of the ultraviolet (UV) laser system and the sensitivity of the ICP‐MS, as well minimising the production of diatomic oxides and argides, which serve as the dominant sources of isobaric interferences. Non‐spectral matrix effects were accounted for by using multiple external calibrators, including NIST SRM 610 and the USGS basaltic glasses BHVO‐2G, BIR‐1G and BCR‐2G, and utilising ⁴³Ca as an internal standard. Analyses of the MPI‐DING reference glasses, which represent geological matrices ranging from basaltic to rhyolitic in composition, included measurements of concentrations as low as < 10⁰ μg g^?1 and as high as > 10⁴ μg g^?1. The new data reported here were found to statistically correlate with the ‘preferred’ reference values for these materials at the 95% confidence level, though with significantly better precision, typically on the order of ≤ 3% (2s_m). This analytical method may be extended to any matrix‐matched geological sample, particularly oceanic basalts, silicate minerals and meteoritic materials.  相似文献   

Refractive index and compressibility of Di64An36 glass over a pressure range of 0–5.0 GPa     

R. G. Kuryaeva  N. V. Surkov 《Geochemistry International》2012,50(12):1026-1031

Data on the refractive index, density, and bulk modulus variations of Di₆₄An₃₆ glass, which is used as a model basalt melt, were obtained with a polarization interference microscope and a high-pressure diamond anvil cell at ambient temperature and pressure up to 5.0 GPa. An anomalous decrease in the bulk modulus, K _t , was observed in the pressure range 0?C1.0 GPa. The values of the zero-pressure isothermal bulk modulus, K _t,0 = 22.2, and variation of the bulk modulus with pressure, ??K _t /??P = 11.35, were derived using a linear equation relating K _t and P over the pressure range with the normal behavior of the compressibility. A comparison of our results with previous data on other glasses and melts showed that the bulk moduli of silicate glasses are similar to those of corresponding melts. The values of the pressure coefficient of the bulk moduli, ??K _t /??P, for glasses derived from linear equations are 2.5 times higher than the pressure derivative of the bulk modulus, K?? _T , derived using the Birch-Murnaghan equation for corresponding melts. The difference in ??K _t /??P and K?? _T has an effect on the compressibility of glasses and melts. The compressibility of glasses up to 5.0 GPa calculated as (d ? d ₀)/d is almost two times lower than that of corresponding melts.  相似文献   

Probing the molecular-level control of aluminosilicate dissolution: A sensitive solid-state NMR proxy for reactive surface area     

Nancy M. Washton  Susan L. Brantley 《Geochimica et cosmochimica acta》2008,72(24):5949-5961

For two suites of volcanic aluminosilicate glasses, the accessible and reactive sites for covalent attachment of the fluorine-containing (3,3,3-trifluoropropyl)dimethylchlorosilane (TFS) probe molecule were measured by quantitative ¹⁹F nuclear magnetic resonance (NMR) spectroscopy. The first set of samples consists of six rhyolitic and dacitic glasses originating from volcanic activity in Iceland and one rhyolitic glass from the Bishop Tuff, CA. Due to differences in the reactive species present on the surfaces of these glasses, variations in the rate of acid-mediated dissolution (pH 4) for samples in this suite cannot be explained by variations in geometric or BET-measured surface area. In contrast, the rates scale directly with the surface density of TFS-reactive sites as measured by solid-state NMR. These data are consistent with the inference that the TFS-reactive M-OH species on the glass surface, which are known to be non-hydrogen-bonded Q³ groups, represent loci accessible to and affected by proton-mediated dissolution. The second suite of samples, originating from a chronosequence in Kozushima, Japan, is comprised of four rhyolites that have been weathered for 1.1, 1.8, 26, and 52 ka. The number of TFS-reactive sites per gram increases with duration of weathering in the laboratory for the “Icelandic” samples and with duration of field weathering for both “Icelandic” and Japanese samples. One hypothesis is consistent with these and published modeling, laboratory, and field observations: over short timescales, dissolution is controlled by fast-dissolving sites, but over long timescales, dissolution is controlled by slower-dissolving sites, the surface density of which is proportional to the number of TFS-reactive Q³ sites. These latter sites are not part of a hydrogen-bonded network on the surface of the glasses, and measurement of their surface site density allows predictions of trends in reactive surface area. The TFS treatment method, which is easily monitored by quantitative ¹⁹F solid-state NMR, therefore provides a chemically specific and quantifiable proxy to understand the nature of how sites on dissolving silicates control dissolution. Furthermore, ²⁷Al NMR techniques are shown here to be useful in identifying clays on the glass surfaces, and these methods are therefore effective for quantifying concentrations of weathering impurities. Our interpretations offer a testable hypothesis for the mechanism of proton-promoted dissolution for low-iron aluminosilicate minerals and glasses and suggest that future investigations of reactive surfaces with high-sensitivity NMR techniques are warranted.  相似文献   

High-temperature elasticity of magnesioferrite spinel     

Sytle M. Antao  Ian Jackson  Baosheng Li  Jennifer Kung  Jiuhua Chen  Ishmael Hassan  Robert C. Liebermann  John B. Parise 《Physics and Chemistry of Minerals》2007,34(5):345-350

The elastic moduli of magnesioferrite spinel, MgFe₂O₄, and their temperature dependence have been determined for the first time by ultrasonic measurements on a polycrystalline specimen. The measurements were carried out at 300 MPa and to 700°C in a gas-medium high-pressure apparatus. On heating, both the elastic bulk (K _S) and shear (G) moduli decrease linearly to 350°C. By combining with extant thermal-expansion data, the values for the room-temperature K _S and G, and their temperature derivatives are as follows: K ₀ = 176.3(7) GPa, G ₀ = 80.1(2) GPa, (∂K _S/∂T) _P = −0.032(3) GPa K⁻¹ and (∂G/∂T) _P = −0.012(1) GPa K⁻¹. Between 350 and 400°C, there are abrupt increases of 1.4% in both of the elastic moduli; these closely coincide with the magnetic Curie transition that was observed by thermal analyses at about 360°C.  相似文献   

Cation field strength effects on high pressure aluminosilicate glass structure: Multinuclear NMR and La XAFS results     

Kimberly E. Kelsey  Jonathan F. Stebbins  Gordon E. Brown Jr.  Jed L. Mosenfelder 《Geochimica et cosmochimica acta》2009,73(13):3914-2191

We examined aluminosilicate glasses containing a variety of network modifying to intermediate cations (Li, La, Sc, and Fe), quenched from melts at 1 atm to 8 GPa, to further investigate the role of cation field strength in Al coordination changes and densification. ²⁷Al Nuclear Magnetic Resonance Spectroscopy (NMR) reveals that the mean Al coordination increases with increasing pressure in the Li-containing glasses, which can be explained by a linear dependence of fractional change in Al coordination number on cation field strengths in similar K-, Na-, and Ca-containing aluminosilicate glasses (K < Na < Li < Ca). Measured recovered densities follow a similar linear trend. In contrast, the La-containing glasses have significantly lower mean Al coordination numbers at given pressures than the cation field strength of La and glass density would predict. La L₃ X-ray absorption fine structure (XAFS) spectroscopy results indicate a significant increase with pressure in average La-O bond distances, suggesting that La and Al may be “competing” for higher coordinated sites and hence that both play a significant role in the densification of these glasses, especially in the lower pressure range. However, in Na aluminosilicate glasses with small amounts of Sc, ⁴⁵Sc NMR reveals only modest Sc coordination changes, which do not seem to significantly affect the mean Al coordination values. For a Li aluminosilicate glass, ¹⁷O MAS and multiple quantum magic angle spinning (3QMAS) NMR data are consistent with generation of more highly coordinated Al at the expense of non-bridging oxygen (NBO), whereas La aluminosilicate glasses have roughly constant O environments, even up to 8 GPa. Finally, we demonstrate that useful ²³Na and ²⁷Al MAS NMR spectra can be collected for Ca-Na aluminosilicate glasses containing up to 5 wt.% Fe oxide. We discuss the types of structural changes that may accompany density increases with pressure and how these structural changes are affected by the presence of different cations.  相似文献