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Application of an improved TEM-EDS protocol based on charge balance for accurate chemical analysis of sub-micrometric phyllosilicates in low-grade metamorphic rocks

Published online by Cambridge University Press:  06 December 2024

Edoardo Sanità Open the ORCID record for Edoardo Sanità [Opens in a new window] ,
Roberto Conconi Open the ORCID record for Roberto Conconi [Opens in a new window] ,
Sofia Lorenzon Open the ORCID record for Sofia Lorenzon [Opens in a new window] ,
Maria Di Rosa Open the ORCID record for Maria Di Rosa [Opens in a new window] ,
Giancarlo Capitani Open the ORCID record for Giancarlo Capitani [Opens in a new window]  and
Enrico Mugnaioli Open the ORCID record for Enrico Mugnaioli [Opens in a new window]
Edoardo Sanità*
Affiliation:
Università di Pisa, Dipartimento di Scienze della Terra, Via Santa Maria, 53, Pisa, Italy
Roberto Conconi
Affiliation:
Università degli Studi di Milano-Bicocca, Dipartimento di Scienze dell’Ambiente e della Terra, Piazza della Scienza 4, Milano, Italy
Sofia Lorenzon
Affiliation:
Università di Pisa, Dipartimento di Scienze della Terra, Via Santa Maria, 53, Pisa, Italy
Maria Di Rosa
Affiliation:
Università di Pisa, Dipartimento di Scienze della Terra, Via Santa Maria, 53, Pisa, Italy
Giancarlo Capitani
Affiliation:
Università degli Studi di Milano-Bicocca, Dipartimento di Scienze dell’Ambiente e della Terra, Piazza della Scienza 4, Milano, Italy
Enrico Mugnaioli
Affiliation:
Università di Pisa, Dipartimento di Scienze della Terra, Via Santa Maria, 53, Pisa, Italy
*
Corresponding author: Edoardo Sanità; Email: [email protected]
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Abstract

Determining the chemical composition of sub-micrometer rock-forming minerals is still a challenging task. The electron probe micro-analyzer (EPMA) is considered the most accurate analytical way to obtain chemical data on amorphous and crystalline materials. However, performing EPMA analyses on sub-micrometer-sized grains is uncertain not recommended as the risk of obtaining analyses contaminated from the surrounding phases. A transmission electron microscope (TEM) equipped with an energy dispersive X-ray spectrometer (EDS) provides a greater spatial resolution, making it possible to obtain trustworthy chemical information on sub-micrometer-sized material. In this work, we present a fast and cheap data-reduction protocol for TEM-EDS chemical analysis, where k-factors derived experimentally for each element of interest and absorption correction are implemented. The results are compared with those determined using standardless and non-corrected TEM-EDS protocols. The k-factor for oxygen plays a fundamental role and its value should be calculated from compounds similar to the phase of interest. For absorption correction, the contribution of hydrogen during structural formula recalculation is taken into account, like a lower net valence of oxygen. The robustness of this protocol was tested by performing TEM-EDS analyses on white mica grains from metapelites, belonging to the Internal Ligurian Units exposed in the Northern Apennines, the chemical composition of which is well constrained. Such a protocol has proven to provide high-quality results from both statistical and crystallo-chemical perspectives. Remarkably, the tested data-reduction protocol for TEM-EDS analysis provided chemical compositions consistent with the EPMA results previously obtained from the same samples.

Keywords

charge balanceEDSmetapelitesphyllosilicateTEM
Type
Original Paper
Information
Clays and Clay Minerals , Volume 72 , 2024 , e31
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Copyright
© The Author(s), 2024. Published by Cambridge University Press on behalf of The Clay Minerals Society

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