Search

In this paper, we review 10 years of research on high-temperature oxidation process on amphiboles with variable composition. One notable feature that has emerged from our experiments is that iron oxidation is reversible over a relatively large thermal range before the kinetic energy of delocalized electrons and H+ ions becomes high enough to allow their ejection from the crystal. Experiments under different oxidation conditions showed that the sodic amphibole riebeckite follows two distinct paths: under oxidizing conditions, it undergoes both Fe oxidation and dehydrogenation and the resulting oxo-riebeckite is stable up to ~ 900 °C; under vacuum conditions, neither Fe oxidation nor dehydrogenations occur, and the amphibole is stable up to 800 °C, via a rearrangement of the octahedral cations. In situ HT Raman measurements on grunerite provided the first atomic-scale proof for the thermal activation of polarons in Fe-amphiboles; further studies showed that this process is a general feature of Fe2+-bearing amphiboles. For riebeckite, it starts at 227 °C and is complete at 377 °C under both reducing and oxidizing conditions. Above 377 °C, external oxygen triggers the expulsion of H+ and e− from the crystal. The temperature range observed for the development of charge carriers accurately fits the temperatures for the development of high-conductivity layers in warm and cold subduction zones and provides the atomic-scale picture for large-scale processes such as the development of anomalous conductivity layers at convergent-plate margins. Our work shows that Raman spectroscopy may provide relatively straightforward access to the properties of rock-forming minerals of geophysical interest. [ABSTRACT FROM AUTHOR]

The study of volatile constituents in minerals has potential applications ranging from environmental studies to ore research to volcanic hazards. In this paper we present new data on the volatile (particularly CO2) content of a series of feldspathoids belonging to the cancrinite-sodalite group of minerals, in combination with other data collected over the last few years. The work has been essentially done using FTIR microspectroscopy to detect and characterize the speciation of H and C in the micropores of these minerals. We show that most cancrinite-sodalite group of minerals are able to trap CO2 in their structure in addition to other molecular and anionic species such as H2O, OH, F, Cl, SO4, SO3 etc. A combination of in situ and annealing heat-treatments shows that the different species in the cancrinite-sodalite group release CO2 at different temperatures, due to the different connectivity of their pores. Detailed FTIR microspectrometry mappings typically show non-homogeneous distributions of hydrogen and carbon across the samples, and suggest a possible use of these minerals as a tool for geothermometric modelling. The finding that most cancrinite-sodalite group minerals are able to trap carbon dioxide opens a new frontier in the design of materials having potential for carbon sequestration from the atmosphere. [ABSTRACT FROM AUTHOR]

Copyright of Rendiconti Lincei: Scienze Fisiche e Naturali is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Rendiconti Lincei: Scienze Fisiche e Naturali is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Rendiconti Lincei: Scienze Fisiche e Naturali is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Rendiconti Lincei: Scienze Fisiche e Naturali is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)