Alkali-rich Glasses Research Articles

Dismantling nuclear waste rich in P2O5, MoO3 and ZrO2: How do these oxides incorporate in aluminoborosilicate glasses?

Dismantling nuclear facilities leads to radioactive waste less active but which may have highly variable compositions compared to the high-level radioactive wastes recovered after the reprocessing of spent nuclear fuel. In this work, we studied the ability of an alkali-rich glass matrix belonging to the SiO2-B2O3-Al2O3-Fe2O3-Na2O-Li2O-CaO system to solubilize P2O5, MoO3, ZrO2 and Cs2O by melting at 1100°C. Phosphorus, molybdenum, zirconium and cesium are present as a mixture of complex compounds in the real radioactive dismantling waste containing 137Cs considered here. To determine the capacity of the matrix to accept a wide range of variations of waste composition and the solubility limits of P2O5, MoO3, and ZrO2, several glass series were prepared by melting mixtures of raw materials (oxides, carbonates, phosphates) and by increasing the total amount of oxides representing the waste and varying their relative proportions. Their incorporation in the melt was studied by analyzing the microstructure of quenched glasses by XRD and SEM-EDS. In addition, the phase separation and crystallization tendencies during cooling were studied by analyzing the microstructure of glasses cooled at 1°C.min-1 from 1100°C (representative of cooling in industrials steel canisters). It is shown that the glass can accept a wide range of waste compositions without exhibiting heterogeneities. For all compositions the melt remained homogeneous (study of quenched samples). However, during slow cooling, P2O5 and MoO3 may lead to phase separation and crystallization of Na2MoO4, CsLiMoO4, NaCaPO4, NaLi2PO4, and Li3PO4. Cs can be partially incorporated into the molybdenum-rich phase CsLiMoO4 when MoO3 content is higher than 1.3wt%. ZrO2 never lead to phase separation or crystallization, possibly because of the existence of strong connections between Zr and Si through Zr-O-Si bonds whereas P and Mo would be present as PO43− and MoO42− mobile entities. The increasing order of oxides solubility in the glass is the following: MoO3<P2O5<ZrO2.

Tephra layers of large explosive eruptions of Baitoushan/Changbaishan Volcano in the Japan Sea sediments

This paper is based on the results of a comprehensive investigations of sediments from seven cores sampled during the International Russian-Chinese Cruise 53 of the R/V “Akademik Lavrentyev” (2010) in the frames of the Russian-Chinese collaboration between the Pacific Oceanological Institute of the Far-Eastern Branch of the Russian Academy of Sciences (POI FEB RAS, Vladivostok, Russia), and the First Institute of Oceanography (FIO, Qingdao, China). Baitoushan (Chanbaishan) Volcano had several powerful explosive eruptions during the Middle Pleistocene-Holocene, which produced widespread tephra layers. The paper reports chemical composition of volcanic glasses and minerals from six tephra layers labeled as B-Og, B-Sado, B-J, B-Un1, B-V, and B-Tm, which belong to Baitoushan Volcano and were identified in sediments of the northwestern part of the Sea of Japan. The tephras were dated using geochronological data for the host sediments. The estimated ages for the Middle Pleistocene tephra is 488 ka; the Late Pleistocene tephras are 71.1–71.9 cal. kа (B-Sado), 50.8 cal. ka (B-J), 38.3 cal. ka (B-Un1), and 29.0–29.4 cal. ka (B-V). The ash layers consist of alkali-rich glass of trachydacitic to alkaline rhyolitic composition and specific assemblage of minerals including Fe-rich augite-hedenbergite, aegirine-augite, aegirine, arfvedsonite, and fayalite. The mineral assemblage is typical for alkalic volcanic rocks from continental rift setting. Aenigmatite, a rare mineral from the group of inosilicates, was firstly identified in distal tephra of Baitoushan Volcano, supplied into marine sediments. The composition of glasses and minerals from all layers are similar. It testifies about steady-state conditions of the magma accumulation under Baitoushan Volcano and about the bimodal character of magmatic chambers during the Late Pleistocene and Holocene (since 100 ka).

Experimental derivation of nepheline syenite and phonolite liquids by partial melting of upper mantle peridotites

Piston-cylinder experiments were performed to characterize the composition of liquids formed at very low degrees of melting of two fertile lherzolite compositions with 430 ppm and 910 ppm K2O at 1 and 1.3 GPa. We used the microdike technique (Laporte et al., 2004) to extract the liquid phase from the partially molten peridotite, allowing us to analyze liquid compositions at degrees of melting F down to 0.9%. At 1.3 GPa, the liquid is in equilibrium with olivine + orthopyroxene + clinopyroxene + spinel in all the experiments; at 1 GPa, plagioclase is present in addition to these four mineral phases up to about 5% of melting (T≈1240°C). Important variations of liquid compositions are observed with decreasing temperature, including strong increases in SiO2, Na2O, K2O, and Al2O3 concentrations, and decreases in MgO, FeO, and CaO concentrations. The most extreme liquid compositions are phonolites with 57% SiO2, 20–22% Al2O3, Na2O + K2O up to 14%, and concentrations of MgO, FeO, and CaO as low as 2–3%. Reversal experiments confirm that low-degree melts of a fertile lherzolite have phonolitic compositions, and pMELTS calculations show that the amount of phonolite liquid generated at 1.2 GPa increases from 0.3% in a source with 100 ppm K2O to 3% in a source with 2000 ppm K2O. The enrichment in silica and alkalis with decreasing melt fraction is coupled with an increase of the degree of melt polymerization, which has important consequences for the partitioning of minor and trace elements. Thus Ti4+ in our experiments and, by analogy with Ti4+, other highly charged cations, and rare earth elements become less incompatible near the peridotite solidus.Our study brings a strong support to the hypothesis that phonolitic lavas or their plutonic equivalents (nepheline syenites) may be produced directly by partial melting of upper mantle rock-types at moderate pressures (1–1.5 GPa), especially where large domains of the subcontinental lithospheric mantle has been enriched in potassium by metasomatism. The circulation of low-degree partial melts of peridotites into the upper mantle may be responsible for a special kind of metasomatism characterized by Si- and alkali-enrichment. When they are unable to escape by porous flow, low-degree melts will ultimately be trapped inside neighboring olivine grains and give rise to the silica- and alkali-rich glass inclusions found in peridotite xenoliths.

Northwest Africa 4797: A strongly shocked ultramafic poikilitic shergottite related to compositionally intermediate Martian meteorites

Abstract– Northwest Africa (NWA) 4797 is an ultramafic Martian meteorite composed of olivine (40.3 vol%), pigeonite (22.2%), augite (11.9%), plagioclase (9.1%), vesicles (1.6%), and a shock vein (10.3%). Minor phases include chromite (3.4%), merrillite (0.8%), and magmatic inclusions (0.4%). Olivine and pyroxene compositions range from Fo66–72,En58–74Fs19–28Wo6–15, and En46–60Fs14–22Wo34–40, respectively. The rock is texturally similar to “lherzolitic” shergottites. The oxygen fugacity was QFM−2.9 near the liquidus, increasing to QFM−1.7 as crystallization proceeded. Shock effects in olivine and pyroxene include strong mosaicism, grain boundary melting, local recrystallization, and pervasive fracturing. Shock heating has completely melted and vesiculated igneous plagioclase, which upon cooling has quench‐crystallized plagioclase microlites in glass. A mm‐size shock melt vein transects the rock, containing phosphoran olivine (Fo69–79), pyroxene (En44–51Fs14–18Wo30–42), and chromite in a groundmass of alkali‐rich glass containing iron sulfide spheres. Trace element analysis reveals that (1) REE in plagioclase and the shock melt vein mimics the whole rock pattern; and (2) the reconstructed NWA 4797 whole rock is slightly enriched in LREE relative to other intermediate ultramafic shergottites, attributable to local mobilization of melt by shock. The shock melt vein represents bulk melting of NWA 4797 injected during pressure release. Calculated oxygen fugacity for NWA 4797 indicates that oxygen fugacity is decoupled from incompatible element concentrations. This is attributed to subsolidus re‐equilibration. We propose an alternative nomenclature for “lherzolitic” shergottites that removes genetic connotations. NWA 4797 is classified as an ultramafic poikilitic shergottite with intermediate trace element characteristics.

New milarite/osumilite-type phase formed during ancient glazing of an Egyptian scarab

A scarab found in grave 25 of the Monte Prama necropolis, near Cabras, Oristano, Sardinia, is of special importance for the archaeological interpretation and dating of this important archaeological site. The object has been misinterpreted in the past as composed by bone: recent archaeometric analyses showed that it is a glazed steatite of Egyptian origin and that the altered surface contains interesting phases crystallized during the high-temperature interaction of the Mg-rich talc core with the alkali-rich glass used for glazing. A novel single crystal X-ray diffraction analysis of one of the phases indicates that it is a new compound having the milarite-osumilite structure type, with a peculiar composition close to (Na1.52K0.12□0.36)(Mg3)(Mg1.72Cu0.16Fe0.12)(Si11.4Al0.6)O30, not reported for naturally occurring minerals. The structural and crystal chemical features of the compound, together with the known high-temperature stability of the series, allow a complete interpretation of the glazing process and conditions, based on direct application of the glaze on the steatite core with subsequent treatment at temperatures above 1000 °C.

Mixed electrical conduction in a hydrous pantellerite glass

Electrical conductivity measurements were carried out on pantelleritic trachyte glasses containing up to 3.5wt.% dissolved H2O. At temperatures below about 700K, we find evidence for small polaron conduction due to the presence of both ferrous and ferric iron in the glass. At the higher temperatures of the investigation (up to 973K), a marked change in the conductivity–temperature relation is observed, which suggests that an ionic conduction mechanism becomes the dominant means of charge transport. In the ionic conduction regime, conductivity increases with increasing H2O concentration. Activation energies are similar for both the anhydrous and hydrous glasses, indicating that the conductivity is controlled by sodium diffusion even for the highest H2O concentration examined. A slight variation in activation energy is observed depending on the H2O concentration, which is most likely associated with the depolymerising effect of dissolved water on the silicate network structure. At low temperatures, we find a dramatic effect of fO2 on the conductivity that supports an electronic conduction mechanism based on small polaron hopping between Fe3+ and Fe2+ sites. This electronic pathway controls the overall electrical conductivity in these alkali-rich glasses at temperatures exceeding 500°C if conditions remain anhydrous at an oxygen fugacity of 0.2atm.

Anodic bonding of activated tin solder alloys in the liquid state: A novel large-area hermetic glass sealing method

A new variant of the anodic bonding technique (ALTSAB: Activated Liquid Tin Solder Anodic Bonding) is described, which offers a number of advantages for direct glass to metal sealing over conventional methods. It employs a tin solder alloy containing an activating metal which is anodically bonded to alkali rich glass substrates in the liquid state. Two different test specimens were fabricated and characterized under vacuum at a pressure of 5×10 −4 mbar and a bonding temperature of 300 °C and compared with standard Al/glass anodic bonds. The ability to fabricate dual interface bonds of good quality and high shear strength >16 MPa by the ALTSAB method was demonstrated. With the sealant metal in the liquid state, this methodology promises superior surface adaptation and therefore joint performance when compared with the standard anodic bonding. More importantly, there is no need for premetallization or surface pretreatment of the glass substrates, and unlike in conventional anodic bonding, there is no need for mechanically loading the joining assembly. Wetting of the float glass substrates by the activated solder alloy SnAl0.6 after successful anodic bonding was confirmed by optical microscopy. The enrichment of the activating element Al at the bonding interface was confirmed by SEM and EDS element mapping. The methodology presented here shows great promise for various large-area sealing applications, particularly vacuum glazing, thin film and organic PV and OLED technology.

The origin of reaction textures in mantle peridotite xenoliths from Sal Island, Cape Verde: the case for “metasomatism” by the host lava

Reaction zones around minerals in mantle xenoliths have been reported from many localities worldwide. Interpretations of the origins of these textures fall into two groups: mantle metasomatic reaction or reaction during transport of the xenoliths to the surface. A suite of harzburgitic mantle xenoliths from Sal, Cape Verde show clear evidence of reaction during transport. The reactions resulted in the formation of olivine–clinopyroxene and Si- and alkali-rich glass reaction zones around orthopyroxene and sieve-textured clinopyroxene and sieve textured spinel, both of which are associated with a Si- and alkali-rich glass similar to that in the orthopyroxene reaction zones. Reaction occurred at pressures less than the mantle equilibration pressure and at temperatures close to the liquidus temperature of the host magma. In addition, there is a clear spatial relation of reaction with the host lava: reaction is most intense near the lava/xenolith contact. The residence time of the xenoliths in the host magma, determined from Fe–Mg interdiffusion profiles in olivine, was approximately 4 years. Our results cannot be reconciled with a recent model for the evolution of the mantle below the Cape Verde Archipelago involving mantle metasomatism by kimberlitic melt. We contend that alkali-rich glasses in the Sal xenoliths are not remnants of a kimberlitic melt, but rather they are the result of reaction between the host lava or a similar magma and xenolith minerals, in particular orthopyroxene. The formation of a Si- and alkali-rich glass by host magma–orthopyroxene reaction appears to be a necessary precursor to formation of sieve textured spinel and clinopyroxene.

Inhomogeneous glass surfaces resulting from rapid forming operations – evidence from differential corrosion

A chemical compositional heterogeneity develops on glass surfaces which have experienced rapid expansion/stretching – as during the press or press/blow process used in forming. A differential etching technique using HF and HBF 4 is developed to demonstrate that such heterogeneities occur on the surface of commercial articles such as soda-lime silicate tumblers. Comparison with articles exposed to aggressive conditions in a well-characterized dishwasher reveals that similar corrosion patterns appear in both cases – as alternatively corroded/non-corroded regions arranged as striations running vertically along the tumbler. Analysis of these striae by imaging ellipsometry and interferometry indicates that they consist of ridges 50–150 nm high in relief with a width and repeat distance of 0.05–0.15 mm. This pattern is in qualitative agreement with a recent physical modeling study and suggests that the ridges arise from durable low alkali glass which is at the surface of the gob/parison before the press/blow and which has been striated by less durable, high alkali glass from the interior of the gob. Under corrosive conditions, the alkali-rich glass dissolves away to leave behind the durable ridge.

The Lithospheric Mantle beneath Continental Margins: Melting and Melt-Rock Reaction in Canadian Cordillera Xenoliths

Seven alkali basalt centers in the southern Canadian Cordillera INTRODUCTION contain mantle xenolith suites that comprise spinel Cr-diopside Spinel peridotite xenoliths occur in many alkali basalt peridotites, spinel augite-bearing wehrlites and orthopyroxene-poor centers of the Canadian Cordillera, a Phanerozoic conlherzolites, and minor pyroxenites. The Cr-diopside peridotites vergent orogen bordering the western edge of the Caappear to be residues of the extraction of Mg-rich basalts by up to nadian craton. The Cordillera formed during the late 15% partial melting (median 5–10%) of a pyrolite-like source in Jurassic and Cretaceous through the successive accretion the spinel stability field. The xenoliths are similar to other mantle of tectonic terranes of various lithologies (mainly arc xenolith suites derived from beneath convergent continental margins, related) to the stable margin of ancestral North America but are less depleted, less oxidized, and have lower spinel mg(e.g. Monger et al., 1982; Gabrielse & Yorath, 1991). number than peridotites found in fore-arc settings. Their dominant However, the nature of the lithospheric mantle beneath high field strength element depleted character, however, is typical of these terranes and its tectonic origin are poorly conarc lavas, and may suggest that fluids or melts circulating through strained. Moreover, the southern part of this continental the Canadian Cordillera lithosphere were subduction related. Modmargin is bordered by an active subduction zone (Gaeling using MELTS is consistent with the augite-bearing xenoliths brielse et al., 1991), and thus the lithosphere may have being formed by interaction between crystallizing alkaline melts and been modified by subduction-related melts or fluids. The peridotite. Assimilation–fractional crystallization modeling suggests mantle xenoliths thus represent samples of the lithospheric that the trace element patterns of liquids in equilibrium with the mantle at the transition between cratonic continental augite xenoliths may represent the initial melts that reacted with the lithosphere and oceanic mantle. The major element peridotite. Moreover, the compositions of these melts are similar to composition of the mantle lithosphere is of interest as a those of some glasses observed in the mantle xenoliths. Melt–rock potential source of magmas and also because it may react interaction may thus be a viable mechanism for the formation of with magmas migrating through it on their way to the Siand alkali-rich glass in peridotites. surface.

In situ origin for glass in mantle xenoliths from southeastern Australia: insights from trace element compositions of glasses and metasomatic phases

Siliceous, aluminous and alkali-rich glasses, commonly found in patches and veins in spinel peridotite xenoliths, have been attributed to a number of different origins. These include low-degree primary melts of the mantle, exotic metasomatic melts influxing into the lithosphere, or breakdown of amphibole, and other phases during high-temperature transport of the xenoliths to the surface in their host magmas. We present new laser ablation inductively coupled plasma-mass spectrometry (LA-ICP-MS) analyses of trace element abundances in glasses, and in metasomatically introduced phases (clinopyrox-ene, amphibole, phlogopite, apatite) from a suite of spinel wehrlite, lherzolite and harzburgite xenoliths from southeastern Australia. The majority of glass compositions are best explained by melting of amphibole (usually complete, as amphibole is now absent from most samples) with varying but significant contributions from partial melting of clinopyroxene. However, some glasses require additional components derived from partial or complete modal melting of phlogopite, or apatite. The data confirm our earlier model, that the glass present in patches in these samples derives from high-temperature, transport-related breakdown of a metasomatic phase assemblage (amphibole + clinopyroxene ± phlogopite =b apatite) present in the xenoliths prior to their entrainment in the host magmas.

Glasses in mantle xenoliths from western Victoria, Australia, and their relevance to mantle processes

Mantle-derived xenoliths from western Victoria, Australia, contain glass in patches and veinlets, and as secondary inclusions within xenolith minerals. Glass patches are commonly associated with primary clinopyroxene, spinel and in some cases relict pargasitic amphibole, phlogopite, apatite or calcitic carbonate. The patches and veins are filled with secondary microphenocrysts of olivine, clinopyroxene and spinel. The siliceous, aluminous, alkali-rich glasses display ranges in major element compositions which are similar to those of glasses in mantle xenoliths worldwide. Textures and compositions of glass and associated phases in the Victorian xenolith suite argue strongly against origins involving equilibrium partial melting of spinel peridotite, or migration of exotic metasomatic melts. Metasomatism of the southeastern Australian lithosphere is expressed by formation of amphibole, phlogopite, and apatite, and increased abundances of clinopyroxene at the expense of orthopyroxene, in lherzolite or harzburgite. Partial or complete melting of this metasomatic assemblage occurred immediately prior to, or during, entrainment of the xenolith in the host magmas, and locally produced disequilibrium liquids, now preserved as glass. Melting in the xenoliths was caused by the thermal and decompressional effects of transport in the host magma, or by thermal and metasomatic effects in the lithosphere associated with adjacent intrusion of magmas. Large inter-xenolithic variation in glass compositions was caused by variations in the nature and proportions of the precursor metasomatic assemblage, by reaction of the melts with primary orthopyroxene in the lherzolites and harzburgites, and by rapid, disequilibrium crystallization from the melts of an assemblage of olivine, clinopyroxene and spinel in all samples.

Thermally stimulated currents in pyrex and soda-lime glasses

Thermally stimulated current studies of commercially available soda-lime and pyrex glasses were made within the temperature range 170–700 K. Three different polarization peaks were found and compared with the peaks for alkali-rich glasses. The data were interpreted in terms of the heterogeneous distribution of alkali ions and structural rearrangement of the silicon network near the electrodes.

Concordant 3,676 Myr U–Pb formation age for the Kodaikanal iron meteorite

The Kodaikanal iron meteorite contains evidence of intensive chemical activity which, according to Rb–Sr studies1, occurred ∼800 Myr after the formation of the Solar System. Here we report the results of U–Pb isotope analyses on a silicate inclusion from Kodaikanal. Leaching experiments on the two major phases, clinopyroxene (CPX) and alkali-rich glass, indicate a contamination by terrestrial Pb attributable to previous curatorial cutting of this iron meteorite. The leached minerals define concordant U–Pb ages that validate the precise Pb–Pb age of 3,676±3 Myr. These data are consistant with Rb–Sr age determinations1. The absence of initial Pb indicates a fast cooling of the silicate material. This has already been established for the metal phase, and a collisional origin for Kodaikanal is favoured.

Glasses in Mantle Xenoliths from Olmani, Tanzania

Nineteen mantle xenoliths from Olmani, Tanzania, have deformation textures and fluid inclusions like those in olivine-rich peridotites from Hawaii. Group A comprises 7 barren harzburgites (spinel, TiO2 <. 1 wt %) and group B (spinel, TiO2.8–2.6 wt %) contains 6 clinopyroxene-dunites, 2 lherzolites, 1 wehrlite, 1 two-pyroxene-dunite, and 1 olivine-orthopyroxenite. Both groups lack garnet and porphyroclastic textures and display fingerprint intergrowths of spinel with ortho-or clinopyroxene. Many secondary inclusions of several generations within olivine are rich in Co2. Alkali-rich glasses (Na2O.4–7.3 wt %, K2O 3.3–5.1, P2O5 ∼1) in B xenoliths are unrelated chemically to the olivine-augite-phyric ankaramite host. Aphyric inter-granular glass occurs along with larger patches of residual glasses associated with euhedral olivine, clinopyroxene and spinel. Clinopyroxenes of B xenoliths show decreasing Na2O (2.1–.3 wt %) and Cr2O3 from olivine-brown cores to clear margins of larger grains, and to finer grains associated with residual glass. These properties of the xenoliths are consistent with establishment of a coarse texture during prolonged metamorphism in the mantle (∼28 kb, 1100 K?), partial melting in the presence of a CO2-rich fluid (∼26 kb, 1400 K?), transport by ankaramite magma to the Earth's surface, and rapid crystallization of some of the melts at 1300–1200 K.

Experimental Leaching of Volcanic Glass: ABSTRACT

Thoroughly analyzed samples of natural glass were subjected to experimental open-system leaching by aerated alkaline solutions at controlled temperature, pressure, and flow rate. The concentrations of dissolved U, Si, K, and Li were monitored and the amounts dissolved during a fixed time were expressed as percentages of the amounts contained in the unaltered glass. The results serve to identify likely mechanisms for U removal to evaluate the relative influence of some environmental parameters affecting the rate of leaching of U from volcanic glass. Of the measured variables, temperature had the greatest influence on the removal of U and Si. Percentages of U and Si increased two to three times over the range from 90 to 120°C. In all experiments, the percentage of uranium that was removed was similar to the percentage of Si that was removed, implying that U removal proceeds by a mechanism of glass-matrix destruction. As the pH of the solutions increased from 8.5 to 10, the percentages of U and Si that were removed increased by a factor of three to four. In most experiments, Li and K were in greater percentages than Si and U, reflecting additional diffusional transport of these elements across a proposed surficial leached layer. Hydrated glass (perlite) produced two times more dissolved Si and U than equivalently treated obsidian of similar composition, a result of the increased effective surface area produced by perlitic fracturing. An increase of dissolved carbonate from 0.005 to 0.2M (pH ± 8.5) caused preferential removal of U 40% increase) relative to Si (20% increase). Rhyolite glasses of different alkali content showed no apparent difference in the percentage of U removed when by identical alkaline solutions. The apparent greater reactivity of alkali-rich glasses in nature is caused by increased exchange of alkalis for H+, which promotes more rapid evolution of interstitial solution to the pH favorable for glass dissolution. End_of_Article - Last_Page 772------------

The Kenna ureilite: an ultramafic rock with evidence for igneous, metamorphic, and shock origin

The Kenna ureilite was found in February, 1972 near the town of Kenna, Roosevelt County, New Mexico U.S.A., weighed 10.9 kg, and measured 26.7 × 14.7 × 14.2 cm; it is the seventh known ureilite. The meteorite is composed of xenoblastic olivine (Fo 79.2), commonly rimmed by forsterite (Fo 99), and pigeonite (En 73Wo 9Fs 18), in a volumetric ratio of 3:1, set in a matrix of three carbon polymorphs (graphite, lonsdaleite, and diamond) plus nickel-iron metal and troilite. Some thin metalliferous veins penetrating silicate grains contain secondary inclusions of melt with high-calcium clinopyroxene (high-Ca, Mg-rich augite to augite), andesine, K-feldspar, chromite, and siliceous CaO- and alkali-rich glasses of variable compositions. Textural, mineralogical and fabric information suggest a complex history for Kenna, involving igneous, metamorphic and shock processes. The rock appears to have originated as an ultramafic cumulate whose texture and structure was modified by adcumulus processes and by solution and redeposition in a weak deviatoric stress field. A strong mineral elongation lineation was produced during this high-temperature phase accompanied by mild plastic deformation of olivine on the system 0kl[100]. Superimposed on this original texture and fabric are processes resulting from light to moderate (50–250 kbar) shock deformation, as manifested by fracturing of the silicates, slip parallel to (001) in olivine, and twin and translation gliding parallel to (100) in the clinopyroxene. Lonsdaleite and diamond probably formed during this shock phase, which may be associated with the break-up of the parent body, but the relative time of introduction of the carbon-rich matrix is still unresolved.

Optical absorption of nickel (II) in Na2O-NaCl-B2O3 and Na2O-NaBr-B2O3 glasses

The optical absorption spectra of nickel(II) have been studied in Na2O-NaX-B2O3 glasses X = Cl or Br); the absorption bands have been interpreted in terms of Ligand Field Theory. In halide-free B2O3-rich glasses nickel(II) is octahedral, and halide substitution is accompanied by the formation of a tetrahedral nickel(II)-oxide-halide complex. In alkali-rich glasses nickel(II) is square planar and/or tetrahedral and no halide substitution can be observed. It is suggested that the halide ions are unable to substitute for oxygen in the predominantly covalent nickel(II)-oxygen bonds of the complex formed in basic glasses.

The effects of inkomogeneous center structure on the shape of the ESR spectra of alkali-rich glasses

The paper considers the effect of nonuniform structure in the centers on the ESR spectrum for the case of axial anisotropy in the g factor; it is shown that if (σ2⊥ >σ2∥, γ¦ >γ⊥), the model enables one to describe fairly completely the spectrum of a glass containing 33% Na2O and 67% SiO2. Good agreement with all experimental evidence is not obtained for potassium silicate glasses.