Glasses Tech - Prescription Glasses, Prescription Eyeglasses » Glasses 1999

Rose-Colored Glasses

admin — Mon, 08 Mar 2010 02:02:33 +0000

The social information-processing (SIP) model has generated significant knowledge concerning the social cognitions of rejected and aggressive children. However, the model rarely has been applied to the cognitions and behavior of prosocial children or adolescents. This study examined SIP patterns of prosocial young adolescents (10 through 12 years of age). Hypothetical situation instruments were used to assess the intent attributions, feelings of distress, and response-ecision processes (for relational and instrumental provocation situations) of fourth- through sixth-grade young adoles-cents (N = 675). Results revealed that, in contrast to their comparison group peers, pro-social young adolescents (a) were less likely to attribute hostile intent or feel distressed in provocation situations (i.e., a benign attributional bias), (b) gave relatively more negative evaluations of aggressive responses and relatively more positive evaluations of prosocial responses to provocation, and (c) were more likely to endorse relational rather than instrumental goals in dealing with provocation. Implications for prosocial development and intervention are discussed.

David A. Nelson
University of Minnesota

Nicki R. Crick

University of Minnesota

The Journal of Early Adolescence, Vol. 19, No. 1, 17-38 (1999)
DOI: 10.1177/0272431699019001002

Carbonatite Metasomatism of the Oceanic Upper Mantle: Evidence from Clinopyroxenes and Glasses in Ultramafic Xenoliths of Grande Comore, Indian Ocean

admin — Mon, 08 Mar 2010 02:01:28 +0000

Petrological and geochemical data are presented for a suite of ultramafic xenoliths (lherzolites and wehrlites) from La Grille volcano, Grande Comore island. These xenoliths have peculiar textural features characterized by reaction rims or glassy patches, where clinopyroxene grows at the expense of orthopyroxene. The glasses vary from very strongly silica-oversaturated to strongly undersaturated varieties. They are generally homogeneous within a single xenolith, are extremely alkali rich, with Na2O contents (up to 14 wt %) higher than any previously encountered, and are highly evolved (mg-number 34–37). The major element (especially Na) and trace element abundances, together with some remarkable Ti and Zr negative anomalies in chondrite-normalized diagrams, suggest that the metasomatizing agent was an ephemeral alkali-rich carbonatite. These metasomatic reactions appear to have involved an increase in oxygen fugacity from lherzolites (–0.56 to 1.29log units) to wehrlites (up to 2.68log units), with a concomitant decrease in temperature (lherzolites: 908–993°C; wehrlites: 816–893°C). Geobarometric indicators point to equilibration in the range of 7–12 kbar, above the carbonate stability field. An experimentally determined carbonatite composition reacting with a harzburgitic–lherzolitic protolith was successfully balanced with the observed secondary paragenesis allowing calculation of the trace element content of the metasomatizing carbonatitic fluid/s. These modelling procedures were subsequently used to estimate a set of Kd cpx/carb values for mantle depths, which compare well with (scarce) data from both natural occurrences and experimental runs. The origin of the CO2 and H2O in the metasomatizing melts or fluids is problematic. The melts or fluids may have originated from recycled material in or, most probably, below the asthenospheric mantle, brought down in a subducting slab at a former convergent plate margin.

KEY WORDS: carbonatite; mantle; metasomatism; partition coefficients

M. Coltorti1,*, C. Bonadiman1, R. W. Hinton2, F. Siena1 and B. G. J. Upton2
1 Istituto Di Mineralogia, Università Di Ferrara C.So E. 1° D’;Este, 32, 44100 Ferrara, ITALY
2 Department of Geology and Geophysics, University of Edinburgh Edinburgh Eh9 3Jw, UK

Received March 8, 1997; Revised typescript accepted April 30, 1998

Empirical calibration of the sulphur valence oxygen barometer from natural and experimental glasses; method and applications

admin — Mon, 08 Mar 2010 01:38:44 +0000

New data on sulphur valence and magmatic oxidation state for Central Andean volcanic rocks, in combination with published data for experimental and natural samples, allow derivation of a simple relationship between magma oxidation state and sulphur speciation. For a number of highly oxidized Central Andean volcanic rocks f O2 has been calculated using magnetite-ilmenite or olivine-spinel pairs and the sulphur valence in glasses has been measured using the peak shift of S-Kalpha radiation relative to a pyrite standard. Previously published experimental and natural data have been incorporated with a wider range in f O2 and S valence. The variation in sulphur speciation (as S (super 2-) or SO (super 2-) 4 ) as a function of log f O2 is described by an empirical polynomial fit which reproduces the data to within + or -0.5 log units and allows use of electron microprobe measurements of the S-Kalpha wavelength shift for estimation of magmatic oxygen fugacities. This approach is applicable for f O2 between FMQ-2 and FMQ+6, encompassing most terrestrial magmas. The method has been used to calculate the f O2 conditions under which melt inclusions were trapped in andesitic magmas before magma mixing in two Central Andean volcanoes, and to calculate the oxygen fugacity of a slowly-cooled pyroclastic flow in which the Fe-Ti oxide phases have subsequently re-equilibrated. In combination with Fe-Ti oxide data, two distinct trends emerge for Lascar volcano. Basaltic andesite-andesitic magma chambers follow T-f O2 trends which parallel the FMQ buffer curve, indicating ferrous-ferric iron buffering of oxygen fugacity. Dacitic anhydrite-bearing magmas with admixed basaltic andesite and andesite follow trends of increasing f O2 with decreasing temperature, indicative of buffering of f O2 by SO 2 -H 2 S in a co-magmatic gas phase. This trend continues into the metamorphic aureole of the magma chamber, resulting in highly oxidized (close to magnetite-hematite) conditions.

This record provided courtesy of AGI/GeoRef.

S. J. Matthews, D. H. S. Moncrieff, and M. R. Carroll
University of Bristol, Department of Earth Sciences, Bristol, United Kingdom

Al-O-Al oxygen sites in crystalline aluminates and aluminosilicate glasses; high-resolution oxygen-17 NMR results

admin — Mon, 08 Mar 2010 01:22:13 +0000

We report 17 O magic-angle spinning (MAS) NMR data for crystalline NaAlO 2 and CaAl 2 O 4 at external magnetic fields of 9.4 and 14.1 T, as model compounds for Al-O-Al sites in tetrahedral networks. The former contains one peak with isotropic chemical shift (delta iso ) = 30.9 ppm and quadrupolar coupling constant (C Q ) nearly equal 1.8 MHz. The latter contains several peaks with delta iso ranging from 39 to 87 ppm and C Q nearly equal 1.5 to 2.4 MHz. Triple-quantum MAS (3QMAS) spectra of sodium and calcium aluminosilicate glasses with Si/Al<1 show clearly resolved peaks for Al-O-Al sites, removing ambiguity in the use of such spectra to explore the extent of aluminum avoidance in both glassy and crystalline materials. We also report 23 Na and 27 Al NMR data for the crystalline phases.

This record provided courtesy of AGI/GeoRef.
Jonathan F. Stebbins, Sung Keun Lee, and Jane V. Oglesby
Stanford University, Department of Geological and Environmental Sciences, Stanford, CA, United States

The degree of aluminum avoidance in aluminosilicate glasses

admin — Mon, 08 Mar 2010 01:20:35 +0000

For two series of aluminosilicate glasses on the SiO 2 -NaAlO 2 and SiO 2 -CaAl 2 O 4 joins, 29 Si magic-angle-spinning (MAS) NMR spectra were measured. Systematic variations in peak positions and widths with composition are closely related to the extent of ordering of Si and Al cations. A statistical thermodynamic model based on the quasi-chemical approximation was formulated to calculate the proportions of SiO 4 groups with varying numbers of Al neighbors and thus to quantify the extent of ordering. Multiple spectra in each compositional series were fitted simultaneously with several peaks representing each of these structural species and with area constraints generated by the model. The extent of aluminum avoidance (Q), which was defined using the relative lattice energy differences among the linkages Si-O-Si, Si-O-Al, and Al-O-Al, was optimized for each series. For the calcium aluminosilicates, the best fit is with 0.8< or =Q< or =0.875, where Q = 1 represents perfect Al-avoidance. For the sodium series, Q was found to be larger (0.93< or =Q< or =0.99), as expected from energetic considerations and from known variations in ordering in minerals. The contributions to the overall configurational entropy and heat capacity from Si-Al disorder can be calculated, and are significant fractions of experimentally estimated values. However, major contributions must also come from other sources of disorder, such as “topological” disorder of bond angles and length.

This record provided courtesy of AGI/GeoRef.
Sung Keun Lee, and Jonathan F. Stebbins
Stanford University, Department of Geological and Environmental Sciences, Stanford, CT, United States

Structural investigation of platinum solubility in silicate glasses

admin — Mon, 08 Mar 2010 01:17:20 +0000

The coordination environment of 20-200 ppm Pt in yellowish glasses from the CaO-Al 2 O 3 -SiO 2 (CAS) ternary was studied using X-ray absorption fine structure spectroscopy at the Pt-L III edge. Analysis of the Pt-L III edge region suggests that Pt in these glasses is mainly tetravalent and sixfold-coordinated by O (with a mean Pt-O distance of 2.08+ or -0.02 Aa). No evidence for Pt (super 2+) or Pt (super 6+) was found in any of the glasses studied, suggesting that one can not derive valence information easily from solubility data. No second-neighbor contribution was observed around Pt (super 4+) O 6 polyhedra. However, bond-valence modeling suggest that these polyhedra are likely to bond mostly to (super [VI]) Ca (super 2+) , which should promote high positional disorder of second-neighbor cations around Pt. This particular bonding arrangement may explain the relatively high solubility of Pt in these relatively depolymerized melts, as CaPtO 3 -type units.

This record provided courtesy of AGI/GeoRef
Francois Farges, Daniel R. Neuville, and Gordon E. Brown
Universite de Marne-la-Vallee, Marne-la-Vallee, France
Institute de Physique du Globe de Paris, France
Stanford University, United States

Hydrothermal conversion of trachytic glass to zeolite; 3, Monocationic model glasses

admin — Mon, 08 Mar 2010 01:14:59 +0000

Experiments on zeolitization were conducted on four synthetic monocationic glasses (Na, K, Ca, or Mg-rich glass) with Si/Al molar ratios of 2.67, similar in acidity to many volcanic glasses of partially zeolitized Italian tuffs. The products of the hydrothermal treatment at 100, 150, and 200 degrees C of single glasses or glass mixtures with deionized H 2 O or monosaline solutions (NaCl, KCl, CaCl 2 ) were characterized by X-ray diffraction, thermal, microscopic and chemical analyses. Chemical analyses of mother liquors were also performed. Mineral assemblages, containing chabazite, phillipsite, analcime, and K-feldspar, very similar to those found in altered, volcaniclastic alkali-trachytic or trachytic glass deposits were produced. Potassium was essential to chabazite and phillipsite crystallization, although phillipsite was obtained also in Ca-Na mixed systems. Sodium was necessary for analcime formation. Calcium plays only a secondary role in zeolitization, and magnesium does not favor zeolite crystallization but promotes the formation of smectite. Glass composition determines the mineral assemblages obtained and hence in those commonly found in nature.

This record provided courtesy of AGI/GeoRef.
Maurizio de Gennaro, Alessio Langella, Piergiulio Cappelletti, and Carmine Colella
Universita Federico II, Dipartimento di Scienze della Terra, Naples, Italy