| 1. |
- Di Maio, Giovanni, et al.
(författare)
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Mineralogical and geochemical characterization of the concotto artefacts from firing places of Longola protohistoric settlement (Naples)
- 2011
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Ingår i: Periodico di Mineralogia. - 0369-8963. ; 80:3, s. 351-367
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Tidskriftsartikel (refereegranskat)abstract
- A set of concotto samples, a type of fired mixture of various raw materials, coming from firing place of the perifiuvial protohistoric site of Longola (Campania region, southern Italy) was characterized by means of a multi-analytical approach, i.e. polarized light optical microscopy (OM), X-ray powder diffraction (XRD), scanning electron microscopy and energy dispersive spectrometry (SEM-EDS), X-ray fluorescence (XRF), inductively-coupled plasma-mass spectrometry (ICP-MS) and Mossbauer spectroscopy. The specimens generally show a heterogeneous texture, a red-coloured groundmass composed of a mixture of tiny quartz, feldspar, poorly-crystallized goethite, hematite and clay minerals. The crystal fractions show significant amounts of quartz and alkali feldspar and variable percentages of clinopyroxene, leucite, biotite, hematite, magnetite and traces of muscovite. Random secondary phases of calcite, vivianite and gypsum have been identified. The coarser fraction is formed by several types of inclusions, i.e. tephra fragments (pumices, scoriae), volcanic and sedimentary rocks. Illite and very subordinate smectite (montmorillonite) were detected by X-ray diffraction. Trace elements also show a contribution of volcanic raw materials. The Mossbauer analyses at 296 K show the occurrence of paramagnetic Fe(3+) iron (clay minerals) and magnetic Fe(3+) iron (hematite). For the 80 K spectrum, however, two doublets (ferrous and ferric iron in clay minerals) and one sextet (hematite). The concotto samples do not suffer high temperatures, perhaps much lower than 500-600 degrees C in a mainly oxidizing atmosphere. Only sporadically, if any, higher temperatures (> 800 degrees C) might have been reached.
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| 2. |
- Ferrow, Embaie A., et al.
(författare)
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Crystal chemistry and defect structure of ekmanite : New data from transmission electron microscopy and Mossbauer spectroscopy
- 1999
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Ingår i: European Journal of Mineralogy. - 0935-1221. ; 11:2, s. 299-308
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Tidskriftsartikel (refereegranskat)abstract
- Ekmanite is a member of the 2:1 type modulated layer silicates such as ganophyllite and bannisterite. Its chemical composition can be represented by K(M20)[Si32O76](OH)16 (M = Fe2+, Mg2+, Mn2+) where three of eight Si-tetrahedra are inverted across the interlayer sharing an apical oxygen with similarly inverted tetrahedra from the adjacent layers. The arrangement of the regular, D, and inverted, R, tetrahedra has the configuration 4D2R1D1R4D... along the b-axis. In local regions of possibly high Mg/(Mn+Fe) ratio, this configuration is interrupted by the absence of inverted tetrahedra. Ekmanite typically contains a multitude of defects; twinning and both regular and irregular stacking arrangements are the most common ones. Ekmanite is sensitive to oxidation and an unidentified phase, chemically related to it, is always found lining its grain boundaries. This texture results in intergrown rods defining polygons where the central parts do not contain ekmanite. The Mossbauer spectrum consists of Fe2+ and Fe3+ absorption doublets with the Fe2+ absorption composed of two Gaussian line pairs and the Fe3+ absorption of a single but broad line pair.
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| 3. |
- Ferrow, Embaie, et al.
(författare)
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Characterization of pyrrhotite in Cu-Ni-ore bodies from mines in Botswana by Mossbauer spectroscopy, X-ray diffraction, and thermomagnetometry
- 2006
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Ingår i: European Journal of Mineralogy. - : Schweizerbart. - 1617-4011 .- 0935-1221. ; 18:5, s. 653-664
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Tidskriftsartikel (refereegranskat)abstract
- Cu-Ni ore bodies from five Botswana mines were investigated, using a combination of X-ray diffraction, thermomagnetic measurements, Mossbauer spectroscopy, and Inductively Coupled Plasma-Atomic Absorption Electro-optic Spectroscopy (ICP-AES). The four dominant phases in the ores were found to be pyrrhotite, magnetite, pentlandite, and chalcopyrite. Mossbauer spectroscopy shows that pyrrhotite is the dominant Fe-bearing phase in the samples with 75 % in B-S1, 84 % in B-S2, and 80 % in B-S4 and was selected for detailed characterization. Our results show that the three first techniques provide an excellent approach to estimate the degree of polytype intermixing in pyrrhotite. Accordingly, the ores can be grouped into three types: A hexagonal (or peak-type), with a 5c stacking arrangement; a monoclinic (or Weiss-type), with a 4c stacking arrangement; and a mixture of monoclinic and hexagonal types. A low-temperature study of the monoclinic form shows that the low-temperature magnetic transition close to 35 K has features similar to the Verwey transition in magnetite induced by Jahn-Teller distortion due to orbital order-disorder transition.
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| 4. |
- Ferrow, Embaie
(författare)
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Experimental weathering of biotite, muscovite and vermiculite: a Mossbauer spectroscopy study
- 2002
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Ingår i: European Journal of Mineralogy. - : Schweizerbart. - 1617-4011 .- 0935-1221. ; 14:1, s. 85-95
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Tidskriftsartikel (refereegranskat)abstract
- Biotite, muscovite and vermiculite were treated in HCl and H2SO4 solutions at pH ranging between 7 and 1. The solid residue was studied using Mossbauer spectroscopy at room temperature. The spectra of the untreated samples, D0Bio, D0Mus and DOVer were fitted assuming quadrupole splitting distribution, QSD. Different fitting models with different combinations of Gaussian components for the Fe sites were tested and the models with chi(2) near 1.0+/-0.1237 and with the least number of free parameters were adopted as working models. The models were then used to fit the experimental products of each group. If a model fails to describe a spectrum of a sample in the group then this is taken to signal a significant crystal chemical change induced by weathering. All three minerals are oxidized during weathering and the correlation between oxidation ratio and pH is modeled using a Weibull function. The rate of oxidation in biotite is higher than that in muscovite and vermiculite, The average CS and QS of the Fe sites in a group remain more or less constant during the experiment. However, the position of the peak QS of Fe-[6](2+) in biotite is shifted to low energies with decreasing pH, a measure of the decreasing covalence character of the Fe/Mg-O bonds. In muscovite the major feature observed is the enhancement of the bi-modal distribution of the QSD of Fe-[6](2+) with decreasing pH.
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| 5. |
- Ferrow, Embaie
(författare)
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Fe-57 Mossbauer effect study of bannisterite: a modulated 2 : 1-type phyllosilicate
- 2006
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Ingår i: Mineralogical Magazine. - : Mineralogical Society. - 0026-461X .- 1471-8022. ; 70:2, s. 187-199
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Tidskriftsartikel (refereegranskat)abstract
- Bannisterite is a modulated 2:1-type phyllosilicate having ten octahedral sites with hydroxyl groups in trans, cis and combined trans-cis configurations. Each octahedral site, depending on its proximity to the layer modulation, is exposed to a different degree of distortion. The electric field gradient at the Fe site and the site distortion are used to propose a model for the site assignment and oxidation mechanism in bannisterite. The results show that two models are compatible with the experimental results of fitting the spectrum of bannisterite. However, the model which allows for site distortion accounts better for the observed line overlap of the Fe-[6](2+) sites. Accordingly, the octahedral sites with a greater degree of distortion are assigned to the Fe-[6](2+) with lower electric quadrupole splitting, and the octahedral sites with lower site distortion are assigned to the Fe-[6](2+) with higher electric quadrupole splitting. Moreover, the ease of oxidation decreases in the order trans > trans-cis > cis.
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| 6. |
- Ferrow, Embaie, et al.
(författare)
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Multiproxy analysis of a new terrestrial and a marine Cretaceous-Paleogene (K-Pg) boundary site from New Zealand
- 2011
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Ingår i: Geochimica et Cosmochimica Acta. - : Elsevier BV. - 0016-7037. ; 75:2, s. 657-672
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Tidskriftsartikel (refereegranskat)abstract
- An integrated study of palynology, Mossbauer spectroscopy, mineralogy and osmium isotopes has led to the detection of the first K-Pg boundary clay layer in a Southern Hemisphere terrestrial setting. The K-Pg boundary layer was independently identified at centimetre resolution by all the above mentioned methods at the marine K-Pg boundary site of mid-Waipara and the terrestrial site of Compressor Creek (Greymouth coal field), New Zealand. Mossbauer spectroscopy shows an anomaly of Fe-containing particles in both K-Pg boundary sections: jarosite at mid-Waipara and goethite at Compressor Creek. This anomaly coincides with a turnover in vegetation indicated by an interval dominated by fern spores and extinction of key pollen species in both sections. In addition to the terrestrial floristic changes, the mid-Waipara section reveals a turnover in the dinoflagellate assemblages and the appearance of global earliest Danian index species. Geochemical data reveal relatively small iridium enrichments in the boundary layers of 321 pg/g at mid-Waipara and 176 pg/g at Compressor Creek. Unradiogenic Os-187/Os-188 values of the boundary clay reveal the presence of a significant extraterrestrial component. We interpret the accumulation of Fe nano-phases at the boundary as originating from both the impactor and the crystalline basement target rock. The goethite and jarosite are interpreted as secondary phases formed by weathering and diagenesis. The primary phases were probably controlled by the initial composition of the vapor plume and condensation kinetics rather than condensation thermodynamics. This investigation indicates that identification of Fe in nano-phases by Mossbauer spectroscopy is an accurate and cost-effective method for identifying impact event horizons and it efficiently complements widely used biostratigraphic and geochemical methods. (C) 2010 Elsevier Ltd. All rights reserved.
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| 7. |
- Ferrow, Embaie
(författare)
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Non-integral hybrid ions in tourmaline: buffering and geo-thermometry
- 2009
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Ingår i: European Journal of Mineralogy. - : Schweizerbart. - 1617-4011 .- 0935-1221. ; 21:1, s. 241-250
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Tidskriftsartikel (refereegranskat)abstract
- The tourmaline group of minerals is indeed an enigma. Experimental data from optical spectroscopy, electron microscopy, and Mossbauer spectroscopy reveal a host of physical properties that lack a common structural clarification. For example, tourmaline samples change colour when irradiated with X-ray and gamma-ray radiations some reverting back when heated in air; exhibit simultaneous oxidation and reduction on annealing in an atmosphere of H-2; display different plane group symmetries under TEM; possess the most complicated Mossbauer spectra of all Fe-bearing silicates. In this study, four Brazilian samples were chosen for detailed study by Mossbauer spectroscopy to find out a common structural factor to the physical anomalies reported in the literature. It was found out that the tourmaline group of minerals contain multi-valence elements that are involved in electron exchange between the edge-sharing asymmetric Y and Z crystallographic sites. It is conceivable that the host of physical properties recorded in the literature could be due to the inherent structural misfit between the Y and Z sites and the mechanisms adopted to reduce the strain associated along the shared edges. The complexity of non-integral oxidation states possible - due to electron sharing among the different multi-valence elements present in the structure - further enhances the diverse physical properties observed. Moreover, on heating in air, no net oxidation or reduction takes place in the tourmaline group of minerals over a temperature range as long as there are electron donors and acceptors left in the structure, serving simultaneously as potential single-phase buffers and geo-thermometers.
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| 8. |
- Ferrow, Embaie, et al.
(författare)
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Oxidation of pyrite grains: A Mossbauer spectroscopy and mineral magnetism study
- 2005
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Ingår i: Hyperfine Interactions. - : Springer Science and Business Media LLC. - 1572-9540 .- 0304-3843. ; 163:1-4, s. 95-108
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Tidskriftsartikel (refereegranskat)abstract
- Fe2+ in pyrite is found in a low-spin d(6) configuration, a necessary condition for diamagnetic and semi-conducting properties of material. The semi-conducting property of pyrite has been studied since the time when pyrite was used as a rectifier in early radios. Pyrite posses the highest possible crystal field stabilisation energy and offers a better altemative as solar material compared to Si- based materials. Unfortunately, pyrite is difficult to study due to its inherent deviation from stoichiometry and its ease of oxidation. Since pyrite and its oxidation products are all Fe-bearing phases, combining Mossbauer spectroscopy with mineral magnetic methods provides enough information to monitor the oxidation of pyrite in air and identify the different phases produced and their relation to different experimental parameters. For mm-sized grain samples, heating FeS2 at temperatures between 450 degrees C and 650 degrees C five different mineral assemblages are identified. FeS2 is oxidized to alpha-Fe2O3 along two separate routes: FeS2 -> FeSO4 -> epsilon-Fe2O3 -> alpha-Fe2O3; and FeS2 -> FeSO4 -> Fe-2 (SO4)(3) -> ss-Fe2O3 -> alpha-Fe2O3.
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| 9. |
- Ferrow, Embaie, et al.
(författare)
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Pyrite: Linking Mossbauer spectroscopy to mineral magnetism
- 2003
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Ingår i: Material Research in Atomic Scale by Mössbauer Spectroscopy. - 1402011962 ; 94, s. 251-259
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Konferensbidrag (refereegranskat)abstract
- Gold-bearing pyrite ores are refractory and must be pre-treated to break down the sulphides by oxidation. This is done usually by roasting, bacterial oxidation and smelting. Moreover, ores with high sulphur content require pre-treatment to prevent excessive chlorine consumption, an important source of pollution. The pyrite waste created in mining operation presents serious problems on the environmental impact of acid mine drainage. In order to improve separation of pyrite from other metals as well as for the development of new strategies to inhibit oxidation of pyrite, it is necessary to understand the thermal, chemical, magnetic and biological implications during alteration of pyrite. The oxidation of pyrite in air was studied using Mossbauer spectroscopy and mineral magnetic methods. A pyrite concretion from biogenic limestone shows a very weak natural remanent magnetization. Heating of the pyrite produced alpha-hematite as the end product. Intermediate mineral phases created during heating depend mainly on temperature, heating rate, grain size and the atmosphere in the oven. The most magnetic phases occur about 500 T as determined from magnetic susceptibility and hysteresis measurements. The components of the compound hysteresis were iron sulphates and polymorphs of hematite as determined by Mossbauer spectroscopy. Heating of powder of pyrite produced higher concentration of pyrrhotite than grains of mm size as a result of more thorough oxidation as a result of increased ratio of iron to sulphur produced by degassing during heating. Since pyrite and its oxidation products are all Fe-bearing phases, combining Mossbauer spectroscopy with rock magnetic methods provides information to monitor the oxidation of pyrite in air and identify the different phases produced and their relation to different experimental parameters.
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| 10. |
- Ferrow, Embaie, et al.
(författare)
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Reaction kinetics and oxidation mechanisms of the conversion of pyrite to ferrous sulphate: A Mossbauer spectroscopy study
- 2005
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Ingår i: Hyperfine Interactions. - : Springer Science and Business Media LLC. - 1572-9540 .- 0304-3843. ; 163:1-4, s. 109-119
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Tidskriftsartikel (refereegranskat)abstract
- Pyrite undergoes a series of exothermic reactions during mine roasting to porous hematite. At low temperatures, the first non-refractive phase to form is ferrous sulphate and could be a cheaper alternative to hematite roasting for the mining industry. In this study, pyrite powder is heated in air at temperatures between 200 and 370 degrees C for 1 to 256 h in a temperature and time series. The rate of oxidation of pyrite to ferrous sulphate is modelled by combining the Arrhenius equation with the Weibull function to extract reliable thermodynamic data, including the energy of activation, the frequency factor and the overall order of reaction. From the thermodynamic data obtained, two possible oxidation mechanisms are recognized, depending on the bond dissociation energies of the S-S and Fe-S bonds in pyrite.
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