The Experts below are selected from a list of 294 Experts worldwide ranked by ideXlab platform
Katsutoshi Tomita - One of the best experts on this subject based on the ideXlab platform.
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TEM-EDX study of weathered layers on the surface of Volcanic Glass, bytownite, and hypersthene in Volcanic ash from Sakurajima volcano, Japan
American Mineralogist, 2001Co-Authors: Motoharu Kawano, Katsutoshi TomitaAbstract:Transmission electron microscopy (TEM) and energy dispersive X-ray (EDX) analysis were used to characterize naturally weathered layers on the surface of Volcanic Glass, bytownite, hypersthene, and secondary precipitates in Volcanic ash erupted from the Sakurajima volcano, Japan. TEM analysis of the Volcanic ash revealed sharply, bounded, leached layers on the surface of the Volcanic Glass and bytownite that were thin structureless coatings mostly ≤0.1 μm thick. EDX analysis showed that the leached layer on the Volcanic Glass surface is preferentially depleted in Si and enriched in Al relative to its parent matrix, whereas the leached layer on the bytownite surface is extremely depleted in Al and enriched in Si relative to the original bytownite matrix. These chemical characteristics of the weathered layers indicate that incipient dissolution of Volcanic Glass and bytownite proceeded by preferential leaching of Si and Al, respectively. On the surface of hypersthene, a noncrystalline weathered layer generally
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tem edx study of weathered layers on the surface of Volcanic Glass bytownite and hypersthene in Volcanic ash from sakurajima volcano japan
American Mineralogist, 2001Co-Authors: Motoharu Kawano, Katsutoshi TomitaAbstract:Transmission electron microscopy (TEM) and energy dispersive X-ray (EDX) analysis were used to characterize naturally weathered layers on the surface of Volcanic Glass, bytownite, hypersthene, and secondary precipitates in Volcanic ash erupted from the Sakurajima volcano, Japan. TEM analysis of the Volcanic ash revealed sharply, bounded, leached layers on the surface of the Volcanic Glass and bytownite that were thin structureless coatings mostly ≤0.1 μm thick. EDX analysis showed that the leached layer on the Volcanic Glass surface is preferentially depleted in Si and enriched in Al relative to its parent matrix, whereas the leached layer on the bytownite surface is extremely depleted in Al and enriched in Si relative to the original bytownite matrix. These chemical characteristics of the weathered layers indicate that incipient dissolution of Volcanic Glass and bytownite proceeded by preferential leaching of Si and Al, respectively. On the surface of hypersthene, a noncrystalline weathered layer generally <0.01 μm in thickness, which has nearly the same composition as that of the parent matrix, was observed. This weathered layer was produced by precipitation of noncrystalline hydrous ferric oxide with partly developed to poorly crystallized Fe-Si-Mg rich phyllosilicate. The Volcanic ash sample contains small amounts of noncrystalline secondary precipitates exhibiting three distinct morphologies: (1) aggregates of very fine fibers, (2) aggregates of fine fibers with crinkled fringes, and (3) spherical forms composed of roughly curled fringes. These noncrystalline precipitates are enriched in Al and Si and contain variable amounts of Fe, depending on their morphology. The Fe content of these materials decreases drastically in the sequence morphology 1 → morphology 2 → morphology 3, which is consistent with the transformation from Al-, Si-, and Fe-rich fine fibers to spherical halloysite by elimination of Fe from the fibers. These alterations of the Volcanic ash took place in the crater of the Sakurajima volcano by interaction with near-neutral to weakly acidic solutions under relatively low-temperature conditions.
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synthesis of smectite from Volcanic Glass at low temperature
Clays and Clay Minerals, 1993Co-Authors: Katsutoshi Tomita, Hisanori Yamane, Motoharu KawanoAbstract:Smectite and zeolites were formed from a Volcanic Glass as the products of reaction with NaOH solution at 90°C and 100°C under atmospheric pressure. Formation conditions of smectite and various zeolites were determined by the ratio of the amounts of Volcanic Glass (g) to NaOH (g) in the solution. Smectite was formed under the condition that the values of weight of Volcanic Glass (g)/(NaOH(g)/40) are between 0.5 and 6. Fe was an important constituent of the octahedral layer of smectite.
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Formation of Allophane and Beidellite during Hydrothermal Alteration of Volcanic Glass Below 200°C
Clays and Clay Minerals, 1992Co-Authors: Motoharu Kawano, Katsutoshi TomitaAbstract:Experimental alteration of Volcanic Glass has been carried out in distilled water at 200°C and 150°C. The formation and transformation processes of alteration products have been examined by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray powder diffraction (XRD), infrared absorption analysis, and X-ray photoelectron spectroscopy. SEM and TEM clearly show that amorphous aluminum-silicate coatings with allophane particles precipitate on the surface of Volcanic Glass during the earliest alteration stage. Noncrystalline flaky and/or fibrous materials are formed from the allophane aggregates and from the amorphous coatings as new reaction products. The flaky and/or fibrous materials curl inward and transform into 100–500 nm circular smectite. The Al/Si atomic ratio of 1.09 for allophane decreases progressively to 0.65 for smectite through 0.86 for noncrystalline transitional material. The smectite has d(06) spacing of 1.497 A and consists mainly of Si, Al, and small amounts of Fe, Ca, and Na.
Motoharu Kawano - One of the best experts on this subject based on the ideXlab platform.
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TEM-EDX study of weathered layers on the surface of Volcanic Glass, bytownite, and hypersthene in Volcanic ash from Sakurajima volcano, Japan
American Mineralogist, 2001Co-Authors: Motoharu Kawano, Katsutoshi TomitaAbstract:Transmission electron microscopy (TEM) and energy dispersive X-ray (EDX) analysis were used to characterize naturally weathered layers on the surface of Volcanic Glass, bytownite, hypersthene, and secondary precipitates in Volcanic ash erupted from the Sakurajima volcano, Japan. TEM analysis of the Volcanic ash revealed sharply, bounded, leached layers on the surface of the Volcanic Glass and bytownite that were thin structureless coatings mostly ≤0.1 μm thick. EDX analysis showed that the leached layer on the Volcanic Glass surface is preferentially depleted in Si and enriched in Al relative to its parent matrix, whereas the leached layer on the bytownite surface is extremely depleted in Al and enriched in Si relative to the original bytownite matrix. These chemical characteristics of the weathered layers indicate that incipient dissolution of Volcanic Glass and bytownite proceeded by preferential leaching of Si and Al, respectively. On the surface of hypersthene, a noncrystalline weathered layer generally
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tem edx study of weathered layers on the surface of Volcanic Glass bytownite and hypersthene in Volcanic ash from sakurajima volcano japan
American Mineralogist, 2001Co-Authors: Motoharu Kawano, Katsutoshi TomitaAbstract:Transmission electron microscopy (TEM) and energy dispersive X-ray (EDX) analysis were used to characterize naturally weathered layers on the surface of Volcanic Glass, bytownite, hypersthene, and secondary precipitates in Volcanic ash erupted from the Sakurajima volcano, Japan. TEM analysis of the Volcanic ash revealed sharply, bounded, leached layers on the surface of the Volcanic Glass and bytownite that were thin structureless coatings mostly ≤0.1 μm thick. EDX analysis showed that the leached layer on the Volcanic Glass surface is preferentially depleted in Si and enriched in Al relative to its parent matrix, whereas the leached layer on the bytownite surface is extremely depleted in Al and enriched in Si relative to the original bytownite matrix. These chemical characteristics of the weathered layers indicate that incipient dissolution of Volcanic Glass and bytownite proceeded by preferential leaching of Si and Al, respectively. On the surface of hypersthene, a noncrystalline weathered layer generally <0.01 μm in thickness, which has nearly the same composition as that of the parent matrix, was observed. This weathered layer was produced by precipitation of noncrystalline hydrous ferric oxide with partly developed to poorly crystallized Fe-Si-Mg rich phyllosilicate. The Volcanic ash sample contains small amounts of noncrystalline secondary precipitates exhibiting three distinct morphologies: (1) aggregates of very fine fibers, (2) aggregates of fine fibers with crinkled fringes, and (3) spherical forms composed of roughly curled fringes. These noncrystalline precipitates are enriched in Al and Si and contain variable amounts of Fe, depending on their morphology. The Fe content of these materials decreases drastically in the sequence morphology 1 → morphology 2 → morphology 3, which is consistent with the transformation from Al-, Si-, and Fe-rich fine fibers to spherical halloysite by elimination of Fe from the fibers. These alterations of the Volcanic ash took place in the crater of the Sakurajima volcano by interaction with near-neutral to weakly acidic solutions under relatively low-temperature conditions.
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synthesis of smectite from Volcanic Glass at low temperature
Clays and Clay Minerals, 1993Co-Authors: Katsutoshi Tomita, Hisanori Yamane, Motoharu KawanoAbstract:Smectite and zeolites were formed from a Volcanic Glass as the products of reaction with NaOH solution at 90°C and 100°C under atmospheric pressure. Formation conditions of smectite and various zeolites were determined by the ratio of the amounts of Volcanic Glass (g) to NaOH (g) in the solution. Smectite was formed under the condition that the values of weight of Volcanic Glass (g)/(NaOH(g)/40) are between 0.5 and 6. Fe was an important constituent of the octahedral layer of smectite.
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Formation of Allophane and Beidellite during Hydrothermal Alteration of Volcanic Glass Below 200°C
Clays and Clay Minerals, 1992Co-Authors: Motoharu Kawano, Katsutoshi TomitaAbstract:Experimental alteration of Volcanic Glass has been carried out in distilled water at 200°C and 150°C. The formation and transformation processes of alteration products have been examined by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray powder diffraction (XRD), infrared absorption analysis, and X-ray photoelectron spectroscopy. SEM and TEM clearly show that amorphous aluminum-silicate coatings with allophane particles precipitate on the surface of Volcanic Glass during the earliest alteration stage. Noncrystalline flaky and/or fibrous materials are formed from the allophane aggregates and from the amorphous coatings as new reaction products. The flaky and/or fibrous materials curl inward and transform into 100–500 nm circular smectite. The Al/Si atomic ratio of 1.09 for allophane decreases progressively to 0.65 for smectite through 0.86 for noncrystalline transitional material. The smectite has d(06) spacing of 1.497 A and consists mainly of Si, Al, and small amounts of Fe, Ca, and Na.
Tohru Danhara - One of the best experts on this subject based on the ideXlab platform.
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a proposed methodology for analyses of wide ranged elements in Volcanic Glass shards in widespread quaternary tephras
Quaternary International, 2016Co-Authors: Seiji Maruyama, Kentaro Hattori, Takafumi Hirata, Tohru DanharaAbstract:The abundances of 58 elements from lithium to uranium of Volcanic Glass shards in 11 Quaternary widespread tephras of Japan and those of 4 tephras of North America have been analyzed using the laser ablation inductively-coupled plasma mass spectrometry (LA-ICP-MS) technique. The analytical values of the major components (SiO2, TiO2, Al2O3, FeO, MnO, MgO, CaO, and K2O) were systematically lower (<10%) than those of analyzed using electron microanalysis techniques in previous researches, whereas that Na2O tend to be ∼20% higher than those of previous researches using the electron-beam microanalysis technique. The higher values of Na2O obtained by LA-ICP-MS may result from the absence of the Na-loss phenomenon associated with the electron-beam analytical techniques. Most elements were analyzed with less than 20% of the relative standard deviations (RSDs), whereas some trace elements such as beryllium and some transition metals exhibit higher RSDs (up to ∼120%) in 5-repeated analyses on the single Glass shard. The LA-ICP-MS technique can be reasonably available for quantitative analyses of the major elements in Volcanic Glass shards, in addition to the trace elements. The Volcanic Glass can be clearly distinguished from each other by the patterns of the element abundances. The element abundances and the patterns of the elements of the Volcanic Glass shards are helpful to more precise identification and correlation of tephra samples.
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A proposed methodology for analyses of wide-ranged elements in Volcanic Glass shards in widespread Quaternary tephras
Quaternary International, 2016Co-Authors: Seiji Maruyama, Kentaro Hattori, Takafumi Hirata, Tohru DanharaAbstract:The abundances of 58 elements from lithium to uranium of Volcanic Glass shards in 11 Quaternary widespread tephras of Japan and those of 4 tephras of North America have been analyzed using the laser ablation inductively-coupled plasma mass spectrometry (LA-ICP-MS) technique. The analytical values of the major components (SiO2, TiO2, Al2O3, FeO, MnO, MgO, CaO, and K2O) were systematically lower (
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A method for determination of Volcanic Glass concentrations in sedimentary sequences and its application to quaternary studies
Geoarchaeology-an International Journal, 1994Co-Authors: Keiji Takemura, Tohru DanharaAbstract:A method for determination of Volcanic Glass concentration in sedimentary sequences is presented. This method consists of two steps: (1) systematic extraction of Volcanic Glass particles from samples taken at close intervals in a sedimentary section, and the determination of their concentration; (2) precise measurement of the refractive indices of the separated Glass particles. A recently developed measuring system (RIMS 86) based on the thermal immersion method permits quick and accurate measurement of the refractive index of a large number of grains within samples. Based on these kinds of data, we typically recognize five types of concentration of Volcanic Glass shards in sedimentary sequences. The method proposed here enables the simultaneous determination of the refractive index of Glass shards and the proportion of Glass shards in a sample, which makes it possible to recognize certain ash-fall-horizons, even those undetectable through visual observation of a sedimentary column. © 1994 John Wiley & Sons, Inc.
Graeme T Swindles - One of the best experts on this subject based on the ideXlab platform.
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standard chemical based tephra extraction methods significantly alter the geochemistry of Volcanic Glass shards
Journal of Quaternary Science, 2019Co-Authors: Claire L Cooper, Ivan P Savov, Graeme T SwindlesAbstract:The chemical compositions of tephra shards are widely utilised in a myriad of disciplines, including volcanology, petrology, tephrochronology, palaeoecology and climate studies. Previous research has raised concerns over the possible chemical alteration of microscopic (<100 µm) Volcanic Glass shards through standard extraction procedures, such as the widely used acid digestion method. This study subjects 10 samples of well-characterised Volcanic Glasses ranging from basalt to rhyolite to three common methods used in the extraction of Volcanic material from lake sediments and peats. The major element geochemistry of each sample was analysed and compared with a control group. The results of this test indicate that basaltic and andesitic Glasses are highly susceptible to chemical alteration, particularly to the concentrated corrosive materials used in acid and base digestion techniques. PERMANOVA analysis of the variation within groups suggests that the oxides most susceptible to variation are alkalis from groups I and II (K2O, Na2O, CaO, MgO) and SiO2, and the most stable oxides are Al2O3 and FeO. Felsic Glasses are considerably less susceptible to alteration by both acidic (HCl, HNO3, H2SO4) and alkaline (KOH) digestions. Our findings have important implications for interpreting the geochemistry of Volcanic Glasses.
Rowan Gard - One of the best experts on this subject based on the ideXlab platform.
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A cost surface model of Volcanic Glass quarrying and exchange in Hawai‘i
Journal of Archaeological Science, 2011Co-Authors: Mark D. Mccoy, Peter R. Mills, Steven P. Lundblad, Tim Rieth, Jennifer G. Kahn, Rowan GardAbstract:Abstract The spatial distribution of artifacts from the Pu‘u Wa‘awa‘a Volcanic Glass source (North Kona District, Hawai‘i Island) shows a pattern of direct access by those living in the immediately vicinity of the source with subsequent down-the-line exchange. Most quarrying and exchanges likely occurred within a single day’s travel from sites where artifacts were deposited. The exception to this is the discovery of non-local direct access evident in assemblages from the extreme southern end of Hawai‘i Island; these visits may have involved voyages by canoe. While people did not often travel far for Volcanic Glass they nonetheless appear to have had unfettered accessed to source material and freely conducted inter-community exchanges. This implies Volcanic Glass was treated as a common pooled resource and the existence of informal exchange relationships.
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a cost surface model of Volcanic Glass quarrying and exchange in hawai i
Journal of Archaeological Science, 2011Co-Authors: Mark D. Mccoy, Peter R. Mills, Steven P. Lundblad, Tim Rieth, Jennifer G. Kahn, Rowan GardAbstract:Abstract The spatial distribution of artifacts from the Pu‘u Wa‘awa‘a Volcanic Glass source (North Kona District, Hawai‘i Island) shows a pattern of direct access by those living in the immediately vicinity of the source with subsequent down-the-line exchange. Most quarrying and exchanges likely occurred within a single day’s travel from sites where artifacts were deposited. The exception to this is the discovery of non-local direct access evident in assemblages from the extreme southern end of Hawai‘i Island; these visits may have involved voyages by canoe. While people did not often travel far for Volcanic Glass they nonetheless appear to have had unfettered accessed to source material and freely conducted inter-community exchanges. This implies Volcanic Glass was treated as a common pooled resource and the existence of informal exchange relationships.
