The Experts below are selected from a list of 270 Experts worldwide ranked by ideXlab platform
Claire J Horwell - One of the best experts on this subject based on the ideXlab platform.
-
The effect of aluminium and sodium impurities on the in vitro toxicity and pro-inflammatory potential of Cristobalite.
Environmental research, 2017Co-Authors: Claire Nattrass, David E Damby, Claire J Horwell, David M. Brown, Vicki StoneAbstract:Abstract Background Exposure to crystalline silica (SiO2), in the form of quartz, tridymite or Cristobalite, can cause respiratory diseases, such as silicosis. However, the observed toxicity and pathogenicity of crystalline silica is highly variable. This has been attributed to a number of inherent and external factors, including the presence of impurities. In Cristobalite-rich dusts, substitutions of aluminium (Al) for silicon (Si) in the Cristobalite structure, and impurities occluding the silica surface, have been hypothesised to decrease its toxicity. This hypothesis is tested here through the characterisation and in vitro toxicological study of synthesised Cristobalite with incremental amounts of Al and sodium (Na) dopants. Methods Samples of synthetic Cristobalite with incremental amounts of Al and Na impurities, and tridymite, were produced through heating of a silica sol-gel. Samples were characterised for mineralogy, Cristobalite purity and abundance, particle size, surface area and surface charge. In vitro assays assessed the ability of the samples to induce cytotoxicity and TNF-α production in J774 macrophages, and haemolysis of red blood cells. Results Al-only doped or Al+Na co-doped Cristobalite contained between 1 and 4 oxide wt% Al and Na within its structure. Co-doped samples also contained Al- and Na-rich phases, such as albite. Doping reduced cytotoxicity to J774 macrophages and haemolytic capacity compared to non-doped samples. Al-only doping was more effective at decreasing Cristobalite reactivity than Al+Na co-doping. The reduction in the reactivity of Cristobalite is attributed to both structural impurities and a lower abundance of crystalline silica in doped samples. Neither non-doped nor doped crystalline silica induced production of the pro-inflammatory cytokine TNF-α in J774 macrophages. Conclusions Impurities can reduce the toxic potential of Cristobalite and may help explain the low reactivity of some Cristobalite-rich dusts. Whilst further work is required to determine if these effects translate to altered pathogenesis, the results have potential implications for the regulation of crystalline silica exposures.
-
The in vitro respiratory toxicity of Cristobalite-bearing volcanic ash
Environmental research, 2015Co-Authors: David E Damby, Claire J Horwell, Fiona Murphy, Jennifer Raftis, Ken DonaldsonAbstract:Ash from dome-forming volcanoes poses a unique hazard to millions of people worldwide due to an abundance of respirable Cristobalite, a crystalline silica polymorph. Crystalline silica is an established respiratory hazard in other mixed dusts, but its toxicity strongly depends on sample provenance. Previous studies suggest that Cristobalite-bearing volcanic ash is not as bio-reactive as may be expected for a dust containing crystalline silica. We systematically address the hazard posed by volcanic Cristobalite by analysing a range of dome-related ash samples, and interpret the crystalline silica hazard according to the mineralogical nature of volcanic Cristobalite. Samples are sourced from five well-characterized dome-forming volcanoes that span a range of magmatic compositions, specifically selecting samples rich in Cristobalite (up to 16wt%). Isolated respirable fractions are used to investigate the in vitro response of THP-1 macrophages and A549 type II epithelial cells in cytotoxicity, cellular stress, and pro-inflammatory assays associated with crystalline silica toxicity. Dome-related ash is minimally reactive in vitro for a range of source compositions and Cristobalite contents. Cristobalite-based toxicity is not evident in the assays employed, supporting the notion that crystalline silica provenance influences reactivity. Macrophages experienced minimal ash-induced cytotoxicity and intracellular reduction of glutathione; however, production of IL-1β, IL-6 and IL-8 were sample-dependent. Lung epithelial cells experienced moderate apoptosis, sample-dependent reduction of glutathione, and minimal cytokine production. We suggest that protracted interaction between particles and epithelial cells may never arise due to effective clearance by macrophages. However, volcanic ash has the propensity to incite a low, but significant, and sample-dependent response; the effect of this response in vivo is unknown and prolonged exposure may yet pose a hazard.
-
The α-β phase transition in volcanic Cristobalite.
Journal of Applied Crystallography, 2014Co-Authors: David E Damby, Ben J. Williamson, Edward W. Llewellin, Claire J Horwell, Jens Najorka, Gordon Cressey, Michael A. CarpenterAbstract:Cristobalite is a common mineral in volcanic ash produced from dome-forming eruptions. Assessment of the respiratory hazard posed by volcanic ash requires understanding the nature of the Cristobalite it contains. Volcanic Cristobalite contains coupled substitutions of Al3+ and Na+ for Si4+; similar co-substitutions in synthetic Cristobalite are known to modify the crystal structure, affecting the stability of the α and β forms and the observed transition between them. Here, for the first time, the dynamics and energy changes associated with the α–β phase transition in volcanic Cristobalite are investigated using X-ray powder diffraction with simultaneous in situ heating and differential scanning calorimetry. At ambient temperature, volcanic Cristobalite exists in the α form and has a larger cell volume than synthetic α-Cristobalite; as a result, its diffraction pattern sits between ICDD α- and β-Cristobalite library patterns, which could cause ambiguity in phase identification. On heating from ambient temperature, volcanic Cristobalite exhibits a lower degree of thermal expansion than synthetic Cristobalite, and it also has a lower α–β transition temperature (∼473 K) compared with synthetic Cristobalite (upwards of 543 K); these observations are discussed in relation to the presence of Al3+ and Na+ defects. The transition shows a stable and reproducible hysteresis loop with α and β phases coexisting through the transition, suggesting that discrete crystals in the sample have different transition temperatures.
-
chapter 21 controls on variations in Cristobalite abundance in ash generated by the soufriere hills volcano montserrat in the period 1997 to 2010
Geological Society London Memoirs, 2014Co-Authors: Claire J Horwell, Edward W. Llewellin, David E Damby, S E Hillman, P D Cole, S C Loughlin, Thomas ChristopherAbstract:The Soufriere Hills Volcano (SHV) crystallizes Cristobalite (crystalline silica) in its lava domes, and inhalation of Cristobalite-rich ash may pose a chronic respiratory hazard. We investigate the causes of variation in Cristobalite abundance (measured by X-ray diffraction) in ash from dome collapses, explosions and ash venting from 1997 to 2010. Cristobalite abundance in bulk dome-collapse ash varies between 4 and 23 wt%. During periods of slow lava extrusion ( 5 m3 s−1), Cristobalite abundance is low (4–7 wt%, similar to that associated with Vulcanian explosions), and correlates strongly with DRT. We attribute this correlation to progressive vapour-phase mineralization or devitrification, and the lack of contamination by older lava. Cristobalite abundance is expected to be >7 wt% for collapse of slowly extruded lava, for ash venting through a dome or for incorporation of hydrothermally altered edifice during explosions; Cristobalite abundance is expected to be <7 wt% for collapse of rapidly extruded lava, for ash venting without dome incorporation and from Vulcanian explosions at SHV.
-
The nature and formation of Cristobalite at the Soufrière Hills volcano, Montserrat: implications for the petrology and stability of silicic lava domes
Bulletin of Volcanology, 2013Co-Authors: Claire J Horwell, Ben J. Williamson, Edward W. Llewellin, David E Damby, Jennifer S. BlondAbstract:Cristobalite is commonly found in the dome lava of silicic volcanoes but is not a primary magmatic phase; its presence indicates that the composition and micro-structure of dome lavas evolve during, and after, emplacement. Nine temporally and mineralogically diverse dome samples from the Soufrière Hills volcano (SHV), Montserrat, are analysed to provide the first detailed assessment of the nature and mode of Cristobalite formation in a volcanic dome. The dome rocks contain up to 11 wt.% Cristobalite, as defined by X-ray diffraction. Prismatic and platy forms of Cristobalite, identified by scanning electron microscopy (SEM), are commonly found in pores and fractures, suggesting that they have precipitated from a vapour phase. Feathery crystallites and micro-crystals of Cristobalite and quartz associated with volcanic glass, identified using SEM-Raman, are interpreted to have formed by varying amounts of devitrification. We discuss mechanisms of silica transport and Cristobalite formation, and their implications for petrological interpretations and dome stability. We conclude: (1) that silica may be transported in the vapour phase locally, or from one part of the magmatic system to another; (2) that the potential for transport of silica into the dome should not be neglected in petrological and geochemical studies because the addition of non-magmatic phases may affect whole rock composition; and (3) that the extent of Cristobalite mineralisation in the dome at SHV is sufficient to reduce porosity—hence, permeability—and may impact on the mechanical strength of the dome rock, thereby potentially affecting dome stability.
David E Damby - One of the best experts on this subject based on the ideXlab platform.
-
The effect of aluminium and sodium impurities on the in vitro toxicity and pro-inflammatory potential of Cristobalite.
Environmental research, 2017Co-Authors: Claire Nattrass, David E Damby, Claire J Horwell, David M. Brown, Vicki StoneAbstract:Abstract Background Exposure to crystalline silica (SiO2), in the form of quartz, tridymite or Cristobalite, can cause respiratory diseases, such as silicosis. However, the observed toxicity and pathogenicity of crystalline silica is highly variable. This has been attributed to a number of inherent and external factors, including the presence of impurities. In Cristobalite-rich dusts, substitutions of aluminium (Al) for silicon (Si) in the Cristobalite structure, and impurities occluding the silica surface, have been hypothesised to decrease its toxicity. This hypothesis is tested here through the characterisation and in vitro toxicological study of synthesised Cristobalite with incremental amounts of Al and sodium (Na) dopants. Methods Samples of synthetic Cristobalite with incremental amounts of Al and Na impurities, and tridymite, were produced through heating of a silica sol-gel. Samples were characterised for mineralogy, Cristobalite purity and abundance, particle size, surface area and surface charge. In vitro assays assessed the ability of the samples to induce cytotoxicity and TNF-α production in J774 macrophages, and haemolysis of red blood cells. Results Al-only doped or Al+Na co-doped Cristobalite contained between 1 and 4 oxide wt% Al and Na within its structure. Co-doped samples also contained Al- and Na-rich phases, such as albite. Doping reduced cytotoxicity to J774 macrophages and haemolytic capacity compared to non-doped samples. Al-only doping was more effective at decreasing Cristobalite reactivity than Al+Na co-doping. The reduction in the reactivity of Cristobalite is attributed to both structural impurities and a lower abundance of crystalline silica in doped samples. Neither non-doped nor doped crystalline silica induced production of the pro-inflammatory cytokine TNF-α in J774 macrophages. Conclusions Impurities can reduce the toxic potential of Cristobalite and may help explain the low reactivity of some Cristobalite-rich dusts. Whilst further work is required to determine if these effects translate to altered pathogenesis, the results have potential implications for the regulation of crystalline silica exposures.
-
The in vitro respiratory toxicity of Cristobalite-bearing volcanic ash
Environmental research, 2015Co-Authors: David E Damby, Claire J Horwell, Fiona Murphy, Jennifer Raftis, Ken DonaldsonAbstract:Ash from dome-forming volcanoes poses a unique hazard to millions of people worldwide due to an abundance of respirable Cristobalite, a crystalline silica polymorph. Crystalline silica is an established respiratory hazard in other mixed dusts, but its toxicity strongly depends on sample provenance. Previous studies suggest that Cristobalite-bearing volcanic ash is not as bio-reactive as may be expected for a dust containing crystalline silica. We systematically address the hazard posed by volcanic Cristobalite by analysing a range of dome-related ash samples, and interpret the crystalline silica hazard according to the mineralogical nature of volcanic Cristobalite. Samples are sourced from five well-characterized dome-forming volcanoes that span a range of magmatic compositions, specifically selecting samples rich in Cristobalite (up to 16wt%). Isolated respirable fractions are used to investigate the in vitro response of THP-1 macrophages and A549 type II epithelial cells in cytotoxicity, cellular stress, and pro-inflammatory assays associated with crystalline silica toxicity. Dome-related ash is minimally reactive in vitro for a range of source compositions and Cristobalite contents. Cristobalite-based toxicity is not evident in the assays employed, supporting the notion that crystalline silica provenance influences reactivity. Macrophages experienced minimal ash-induced cytotoxicity and intracellular reduction of glutathione; however, production of IL-1β, IL-6 and IL-8 were sample-dependent. Lung epithelial cells experienced moderate apoptosis, sample-dependent reduction of glutathione, and minimal cytokine production. We suggest that protracted interaction between particles and epithelial cells may never arise due to effective clearance by macrophages. However, volcanic ash has the propensity to incite a low, but significant, and sample-dependent response; the effect of this response in vivo is unknown and prolonged exposure may yet pose a hazard.
-
The α-β phase transition in volcanic Cristobalite.
Journal of Applied Crystallography, 2014Co-Authors: David E Damby, Ben J. Williamson, Edward W. Llewellin, Claire J Horwell, Jens Najorka, Gordon Cressey, Michael A. CarpenterAbstract:Cristobalite is a common mineral in volcanic ash produced from dome-forming eruptions. Assessment of the respiratory hazard posed by volcanic ash requires understanding the nature of the Cristobalite it contains. Volcanic Cristobalite contains coupled substitutions of Al3+ and Na+ for Si4+; similar co-substitutions in synthetic Cristobalite are known to modify the crystal structure, affecting the stability of the α and β forms and the observed transition between them. Here, for the first time, the dynamics and energy changes associated with the α–β phase transition in volcanic Cristobalite are investigated using X-ray powder diffraction with simultaneous in situ heating and differential scanning calorimetry. At ambient temperature, volcanic Cristobalite exists in the α form and has a larger cell volume than synthetic α-Cristobalite; as a result, its diffraction pattern sits between ICDD α- and β-Cristobalite library patterns, which could cause ambiguity in phase identification. On heating from ambient temperature, volcanic Cristobalite exhibits a lower degree of thermal expansion than synthetic Cristobalite, and it also has a lower α–β transition temperature (∼473 K) compared with synthetic Cristobalite (upwards of 543 K); these observations are discussed in relation to the presence of Al3+ and Na+ defects. The transition shows a stable and reproducible hysteresis loop with α and β phases coexisting through the transition, suggesting that discrete crystals in the sample have different transition temperatures.
-
chapter 21 controls on variations in Cristobalite abundance in ash generated by the soufriere hills volcano montserrat in the period 1997 to 2010
Geological Society London Memoirs, 2014Co-Authors: Claire J Horwell, Edward W. Llewellin, David E Damby, S E Hillman, P D Cole, S C Loughlin, Thomas ChristopherAbstract:The Soufriere Hills Volcano (SHV) crystallizes Cristobalite (crystalline silica) in its lava domes, and inhalation of Cristobalite-rich ash may pose a chronic respiratory hazard. We investigate the causes of variation in Cristobalite abundance (measured by X-ray diffraction) in ash from dome collapses, explosions and ash venting from 1997 to 2010. Cristobalite abundance in bulk dome-collapse ash varies between 4 and 23 wt%. During periods of slow lava extrusion ( 5 m3 s−1), Cristobalite abundance is low (4–7 wt%, similar to that associated with Vulcanian explosions), and correlates strongly with DRT. We attribute this correlation to progressive vapour-phase mineralization or devitrification, and the lack of contamination by older lava. Cristobalite abundance is expected to be >7 wt% for collapse of slowly extruded lava, for ash venting through a dome or for incorporation of hydrothermally altered edifice during explosions; Cristobalite abundance is expected to be <7 wt% for collapse of rapidly extruded lava, for ash venting without dome incorporation and from Vulcanian explosions at SHV.
-
The nature and formation of Cristobalite at the Soufrière Hills volcano, Montserrat: implications for the petrology and stability of silicic lava domes
Bulletin of Volcanology, 2013Co-Authors: Claire J Horwell, Ben J. Williamson, Edward W. Llewellin, David E Damby, Jennifer S. BlondAbstract:Cristobalite is commonly found in the dome lava of silicic volcanoes but is not a primary magmatic phase; its presence indicates that the composition and micro-structure of dome lavas evolve during, and after, emplacement. Nine temporally and mineralogically diverse dome samples from the Soufrière Hills volcano (SHV), Montserrat, are analysed to provide the first detailed assessment of the nature and mode of Cristobalite formation in a volcanic dome. The dome rocks contain up to 11 wt.% Cristobalite, as defined by X-ray diffraction. Prismatic and platy forms of Cristobalite, identified by scanning electron microscopy (SEM), are commonly found in pores and fractures, suggesting that they have precipitated from a vapour phase. Feathery crystallites and micro-crystals of Cristobalite and quartz associated with volcanic glass, identified using SEM-Raman, are interpreted to have formed by varying amounts of devitrification. We discuss mechanisms of silica transport and Cristobalite formation, and their implications for petrological interpretations and dome stability. We conclude: (1) that silica may be transported in the vapour phase locally, or from one part of the magmatic system to another; (2) that the potential for transport of silica into the dome should not be neglected in petrological and geochemical studies because the addition of non-magmatic phases may affect whole rock composition; and (3) that the extent of Cristobalite mineralisation in the dome at SHV is sufficient to reduce porosity—hence, permeability—and may impact on the mechanical strength of the dome rock, thereby potentially affecting dome stability.
Jennifer Le S Blond - One of the best experts on this subject based on the ideXlab platform.
-
the nature and formation of Cristobalite at the soufriere hills volcano montserrat implications for the petrology and stability of silicic lava domes
Bulletin of Volcanology, 2013Co-Authors: Claire J Horwell, Ben J. Williamson, Edward W. Llewellin, David E Damby, Jennifer Le S BlondAbstract:Cristobalite is commonly found in the dome lava of silicic volcanoes but is not a primary magmatic phase; its presence indicates that the composition and micro-structure of dome lavas evolve during, and after, emplacement. Nine temporally and mineralogically diverse dome samples from the Soufriere Hills volcano (SHV), Montserrat, are analysed to provide the first detailed assessment of the nature and mode of Cristobalite formation in a volcanic dome. The dome rocks contain up to 11 wt.% Cristobalite, as defined by X-ray dif- fraction. Prismatic and platy forms of Cristobalite, identified by scanning electron microscopy (SEM), are commonly found in pores and fractures, suggesting that they have precipitated from a vapour phase. Feathery crystallites and micro-crystals of Cristobalite and quartz associated with vol- canic glass, identified using SEM-Raman, are interpreted to have formed by varying amounts of devitrification. We dis- cussmechanismsof silicatransport and Cristobaliteformation, and their implications for petrological interpretations and domestability. We conclude: (1) that silica maybetransported in the vapour phase locally, or from one part of the magmatic system to another; (2) that the potential for transport of silica into the dome should not be neglected in petrological and geochemical studies because the addition of non-magmatic phases may affect whole rock composition; and (3) that the extent of Cristobalite mineralisation in the dome at SHV is sufficient to reduce porosity—hence, permeability—and may impact on the mechanical strength of the dome rock, thereby potentially affecting dome stability.
-
the structure of volcanic Cristobalite in relation to its toxicity relevance for the variable crystalline silica hazard
Particle and Fibre Toxicology, 2012Co-Authors: Claire J Horwell, David E Damby, Benedict J Williamson, Ken Donaldson, Jennifer Le S Blond, Leon BowenAbstract:Background Respirable crystalline silica (RCS) continues to pose a risk to human health worldwide. Its variable toxicity depends on inherent characteristics and external factors which influence surface chemistry. Significant population exposure to RCS occurs during volcanic eruptions, where ashfall may cover hundreds of square km and exposure may last years. Occupational exposure also occurs through mining of volcanic deposits. The primary source of RCS from volcanoes is through collapse and fragmentation of lava domes within which Cristobalite is mass produced. After 30 years of research, it is still not clear if volcanic ash is a chronic respiratory health hazard. Toxicological assays have shown that Cristobalite-rich ash is less toxic than expected. We investigate the reasons for this by determining the physicochemical/structural characteristics which may modify the pathogenicity of volcanic RCS. Four theories are considered: 1) the reactivity of particle surfaces is reduced due to co-substitutions of Al and Na for Si in the Cristobalite structure; 2) particles consist of aggregates of Cristobalite and other phases, restricting the surface area of Cristobalite available for reactions in the lung; 3) the Cristobalite surface is occluded by an annealed rim; 4) dissolution of other volcanic particles affects the surfaces of RCS in the lung.
Edward W. Llewellin - One of the best experts on this subject based on the ideXlab platform.
-
The α-β phase transition in volcanic Cristobalite.
Journal of Applied Crystallography, 2014Co-Authors: David E Damby, Ben J. Williamson, Edward W. Llewellin, Claire J Horwell, Jens Najorka, Gordon Cressey, Michael A. CarpenterAbstract:Cristobalite is a common mineral in volcanic ash produced from dome-forming eruptions. Assessment of the respiratory hazard posed by volcanic ash requires understanding the nature of the Cristobalite it contains. Volcanic Cristobalite contains coupled substitutions of Al3+ and Na+ for Si4+; similar co-substitutions in synthetic Cristobalite are known to modify the crystal structure, affecting the stability of the α and β forms and the observed transition between them. Here, for the first time, the dynamics and energy changes associated with the α–β phase transition in volcanic Cristobalite are investigated using X-ray powder diffraction with simultaneous in situ heating and differential scanning calorimetry. At ambient temperature, volcanic Cristobalite exists in the α form and has a larger cell volume than synthetic α-Cristobalite; as a result, its diffraction pattern sits between ICDD α- and β-Cristobalite library patterns, which could cause ambiguity in phase identification. On heating from ambient temperature, volcanic Cristobalite exhibits a lower degree of thermal expansion than synthetic Cristobalite, and it also has a lower α–β transition temperature (∼473 K) compared with synthetic Cristobalite (upwards of 543 K); these observations are discussed in relation to the presence of Al3+ and Na+ defects. The transition shows a stable and reproducible hysteresis loop with α and β phases coexisting through the transition, suggesting that discrete crystals in the sample have different transition temperatures.
-
chapter 21 controls on variations in Cristobalite abundance in ash generated by the soufriere hills volcano montserrat in the period 1997 to 2010
Geological Society London Memoirs, 2014Co-Authors: Claire J Horwell, Edward W. Llewellin, David E Damby, S E Hillman, P D Cole, S C Loughlin, Thomas ChristopherAbstract:The Soufriere Hills Volcano (SHV) crystallizes Cristobalite (crystalline silica) in its lava domes, and inhalation of Cristobalite-rich ash may pose a chronic respiratory hazard. We investigate the causes of variation in Cristobalite abundance (measured by X-ray diffraction) in ash from dome collapses, explosions and ash venting from 1997 to 2010. Cristobalite abundance in bulk dome-collapse ash varies between 4 and 23 wt%. During periods of slow lava extrusion ( 5 m3 s−1), Cristobalite abundance is low (4–7 wt%, similar to that associated with Vulcanian explosions), and correlates strongly with DRT. We attribute this correlation to progressive vapour-phase mineralization or devitrification, and the lack of contamination by older lava. Cristobalite abundance is expected to be >7 wt% for collapse of slowly extruded lava, for ash venting through a dome or for incorporation of hydrothermally altered edifice during explosions; Cristobalite abundance is expected to be <7 wt% for collapse of rapidly extruded lava, for ash venting without dome incorporation and from Vulcanian explosions at SHV.
-
The nature and formation of Cristobalite at the Soufrière Hills volcano, Montserrat: implications for the petrology and stability of silicic lava domes
Bulletin of Volcanology, 2013Co-Authors: Claire J Horwell, Ben J. Williamson, Edward W. Llewellin, David E Damby, Jennifer S. BlondAbstract:Cristobalite is commonly found in the dome lava of silicic volcanoes but is not a primary magmatic phase; its presence indicates that the composition and micro-structure of dome lavas evolve during, and after, emplacement. Nine temporally and mineralogically diverse dome samples from the Soufrière Hills volcano (SHV), Montserrat, are analysed to provide the first detailed assessment of the nature and mode of Cristobalite formation in a volcanic dome. The dome rocks contain up to 11 wt.% Cristobalite, as defined by X-ray diffraction. Prismatic and platy forms of Cristobalite, identified by scanning electron microscopy (SEM), are commonly found in pores and fractures, suggesting that they have precipitated from a vapour phase. Feathery crystallites and micro-crystals of Cristobalite and quartz associated with volcanic glass, identified using SEM-Raman, are interpreted to have formed by varying amounts of devitrification. We discuss mechanisms of silica transport and Cristobalite formation, and their implications for petrological interpretations and dome stability. We conclude: (1) that silica may be transported in the vapour phase locally, or from one part of the magmatic system to another; (2) that the potential for transport of silica into the dome should not be neglected in petrological and geochemical studies because the addition of non-magmatic phases may affect whole rock composition; and (3) that the extent of Cristobalite mineralisation in the dome at SHV is sufficient to reduce porosity—hence, permeability—and may impact on the mechanical strength of the dome rock, thereby potentially affecting dome stability.
-
the nature and formation of Cristobalite at the soufriere hills volcano montserrat implications for the petrology and stability of silicic lava domes
Bulletin of Volcanology, 2013Co-Authors: Claire J Horwell, Ben J. Williamson, Edward W. Llewellin, David E Damby, Jennifer Le S BlondAbstract:Cristobalite is commonly found in the dome lava of silicic volcanoes but is not a primary magmatic phase; its presence indicates that the composition and micro-structure of dome lavas evolve during, and after, emplacement. Nine temporally and mineralogically diverse dome samples from the Soufriere Hills volcano (SHV), Montserrat, are analysed to provide the first detailed assessment of the nature and mode of Cristobalite formation in a volcanic dome. The dome rocks contain up to 11 wt.% Cristobalite, as defined by X-ray dif- fraction. Prismatic and platy forms of Cristobalite, identified by scanning electron microscopy (SEM), are commonly found in pores and fractures, suggesting that they have precipitated from a vapour phase. Feathery crystallites and micro-crystals of Cristobalite and quartz associated with vol- canic glass, identified using SEM-Raman, are interpreted to have formed by varying amounts of devitrification. We dis- cussmechanismsof silicatransport and Cristobaliteformation, and their implications for petrological interpretations and domestability. We conclude: (1) that silica maybetransported in the vapour phase locally, or from one part of the magmatic system to another; (2) that the potential for transport of silica into the dome should not be neglected in petrological and geochemical studies because the addition of non-magmatic phases may affect whole rock composition; and (3) that the extent of Cristobalite mineralisation in the dome at SHV is sufficient to reduce porosity—hence, permeability—and may impact on the mechanical strength of the dome rock, thereby potentially affecting dome stability.
Ben J. Williamson - One of the best experts on this subject based on the ideXlab platform.
-
The α-β phase transition in volcanic Cristobalite.
Journal of Applied Crystallography, 2014Co-Authors: David E Damby, Ben J. Williamson, Edward W. Llewellin, Claire J Horwell, Jens Najorka, Gordon Cressey, Michael A. CarpenterAbstract:Cristobalite is a common mineral in volcanic ash produced from dome-forming eruptions. Assessment of the respiratory hazard posed by volcanic ash requires understanding the nature of the Cristobalite it contains. Volcanic Cristobalite contains coupled substitutions of Al3+ and Na+ for Si4+; similar co-substitutions in synthetic Cristobalite are known to modify the crystal structure, affecting the stability of the α and β forms and the observed transition between them. Here, for the first time, the dynamics and energy changes associated with the α–β phase transition in volcanic Cristobalite are investigated using X-ray powder diffraction with simultaneous in situ heating and differential scanning calorimetry. At ambient temperature, volcanic Cristobalite exists in the α form and has a larger cell volume than synthetic α-Cristobalite; as a result, its diffraction pattern sits between ICDD α- and β-Cristobalite library patterns, which could cause ambiguity in phase identification. On heating from ambient temperature, volcanic Cristobalite exhibits a lower degree of thermal expansion than synthetic Cristobalite, and it also has a lower α–β transition temperature (∼473 K) compared with synthetic Cristobalite (upwards of 543 K); these observations are discussed in relation to the presence of Al3+ and Na+ defects. The transition shows a stable and reproducible hysteresis loop with α and β phases coexisting through the transition, suggesting that discrete crystals in the sample have different transition temperatures.
-
The nature and formation of Cristobalite at the Soufrière Hills volcano, Montserrat: implications for the petrology and stability of silicic lava domes
Bulletin of Volcanology, 2013Co-Authors: Claire J Horwell, Ben J. Williamson, Edward W. Llewellin, David E Damby, Jennifer S. BlondAbstract:Cristobalite is commonly found in the dome lava of silicic volcanoes but is not a primary magmatic phase; its presence indicates that the composition and micro-structure of dome lavas evolve during, and after, emplacement. Nine temporally and mineralogically diverse dome samples from the Soufrière Hills volcano (SHV), Montserrat, are analysed to provide the first detailed assessment of the nature and mode of Cristobalite formation in a volcanic dome. The dome rocks contain up to 11 wt.% Cristobalite, as defined by X-ray diffraction. Prismatic and platy forms of Cristobalite, identified by scanning electron microscopy (SEM), are commonly found in pores and fractures, suggesting that they have precipitated from a vapour phase. Feathery crystallites and micro-crystals of Cristobalite and quartz associated with volcanic glass, identified using SEM-Raman, are interpreted to have formed by varying amounts of devitrification. We discuss mechanisms of silica transport and Cristobalite formation, and their implications for petrological interpretations and dome stability. We conclude: (1) that silica may be transported in the vapour phase locally, or from one part of the magmatic system to another; (2) that the potential for transport of silica into the dome should not be neglected in petrological and geochemical studies because the addition of non-magmatic phases may affect whole rock composition; and (3) that the extent of Cristobalite mineralisation in the dome at SHV is sufficient to reduce porosity—hence, permeability—and may impact on the mechanical strength of the dome rock, thereby potentially affecting dome stability.
-
the nature and formation of Cristobalite at the soufriere hills volcano montserrat implications for the petrology and stability of silicic lava domes
Bulletin of Volcanology, 2013Co-Authors: Claire J Horwell, Ben J. Williamson, Edward W. Llewellin, David E Damby, Jennifer Le S BlondAbstract:Cristobalite is commonly found in the dome lava of silicic volcanoes but is not a primary magmatic phase; its presence indicates that the composition and micro-structure of dome lavas evolve during, and after, emplacement. Nine temporally and mineralogically diverse dome samples from the Soufriere Hills volcano (SHV), Montserrat, are analysed to provide the first detailed assessment of the nature and mode of Cristobalite formation in a volcanic dome. The dome rocks contain up to 11 wt.% Cristobalite, as defined by X-ray dif- fraction. Prismatic and platy forms of Cristobalite, identified by scanning electron microscopy (SEM), are commonly found in pores and fractures, suggesting that they have precipitated from a vapour phase. Feathery crystallites and micro-crystals of Cristobalite and quartz associated with vol- canic glass, identified using SEM-Raman, are interpreted to have formed by varying amounts of devitrification. We dis- cussmechanismsof silicatransport and Cristobaliteformation, and their implications for petrological interpretations and domestability. We conclude: (1) that silica maybetransported in the vapour phase locally, or from one part of the magmatic system to another; (2) that the potential for transport of silica into the dome should not be neglected in petrological and geochemical studies because the addition of non-magmatic phases may affect whole rock composition; and (3) that the extent of Cristobalite mineralisation in the dome at SHV is sufficient to reduce porosity—hence, permeability—and may impact on the mechanical strength of the dome rock, thereby potentially affecting dome stability.