Non-destructive determination of the biotite crystal chemistry using Raman spectroscopy: how far we can go?
<p>Raman spectroscopy combined with electron microprobe analysis as well as Mössbauer spectroscopy was applied to a series of 18 samples along the phlogopite (KMg<span class="inline-formula"><sub>3</sub></span>AlSi<span class="inline-formula">&...
| Main Authors: | , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2022-12-01
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| Series: | European Journal of Mineralogy |
| Online Access: | https://ejm.copernicus.org/articles/34/573/2022/ejm-34-573-2022.pdf |
| Summary: | <p>Raman spectroscopy combined with electron microprobe analysis as well as
Mössbauer spectroscopy was applied to a series of 18 samples along the
phlogopite (KMg<span class="inline-formula"><sub>3</sub></span>AlSi<span class="inline-formula"><sub>3</sub></span>O<span class="inline-formula"><sub>10</sub></span>(OH)<span class="inline-formula"><sub>2</sub></span>)–annite
(KFe<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M5" display="inline" overflow="scroll" dspmath="mathml"><mrow><msubsup><mi/><mn mathvariant="normal">3</mn><mrow><mn mathvariant="normal">2</mn><mo>+</mo></mrow></msubsup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="12pt" height="17pt" class="svg-formula" dspmath="mathimg" md5hash="5b2612ce1172c0a300921cfd96af72d6"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="ejm-34-573-2022-ie00001.svg" width="12pt" height="17pt" src="ejm-34-573-2022-ie00001.png"/></svg:svg></span></span>AlSi<span class="inline-formula"><sub>3</sub></span>O<span class="inline-formula"><sub>10</sub></span>(OH)<span class="inline-formula"><sub>2</sub></span>) join to establish a truly
non-destructive method for crystallochemical characterization of biotite
(A<span class="inline-formula"><sub>1</sub></span>M<span class="inline-formula"><sub>3</sub></span>T<span class="inline-formula"><sub>4</sub></span>O<span class="inline-formula"><sub>10</sub></span>X<span class="inline-formula"><sub>2</sub></span>, M<span class="inline-formula"><sub>3</sub></span> <span class="inline-formula">=</span> M1M2M2). The Raman
scattering arising from the framework (15–1215 cm<span class="inline-formula"><sup>−1</sup></span>) and OH-stretching
phonon modes (3000–3900 cm<span class="inline-formula"><sup>−1</sup></span>) was used to build up correlation trends
between the Raman spectral features and crystal chemistry of biotite. We
show that (a) the contents of <span class="inline-formula"><sup>M</sup></span>Mg, <span class="inline-formula"><sup>M</sup></span>Fe<span class="inline-formula"><sup>2+</sup></span>, and
<span class="inline-formula"><sup>M</sup></span>Fe<span class="inline-formula"><sup>3+</sup></span> contents can be quantified with a relative error of
<span class="inline-formula">∼</span> 6 %, <span class="inline-formula">∼</span> 6 %, and <span class="inline-formula">∼</span> 8 %,
respectively, by combining the integrated intensities of the OH-stretching
peaks assigned to various M1M2M2 local configurations with the wavenumber of
the MO<span class="inline-formula"><sub>6</sub></span> vibrational mode near 190 cm<span class="inline-formula"><sup>−1</sup></span>; (b) the <span class="inline-formula"><sup>M</sup></span>Ti content
can be estimated from the peak position and FWHM (full width at half maximum) of the second strongest
TO<span class="inline-formula"><sub>4</sub></span>-ring mode at <span class="inline-formula">∼</span> 680 cm<span class="inline-formula"><sup>−1</sup></span>, with a precision of
22 %; (c) the content of <span class="inline-formula"><sup>T</sup></span>Si can be estimated from the position of
the second peak related to TO<span class="inline-formula"><sub>4</sub></span>-ring vibrations near 650 cm<span class="inline-formula"><sup>−1</sup></span>; (d) for phlogopite the <span class="inline-formula"><sup>T</sup></span>Al content can indirectly be calculated by knowing
the amount of <span class="inline-formula"><sup>T</sup></span>Si, whereas for annite it is hindered by the plausible
presence of <span class="inline-formula"><sup>T</sup></span>Fe<span class="inline-formula"><sup>3+</sup></span>; (e) the <span class="inline-formula"><sup>A</sup></span>K content can be quantified by
the position of the peak generated by T-O<span class="inline-formula"><sub>b</sub></span>-T bond-stretching-and-bending vibration at <span class="inline-formula">∼</span> 730 cm<span class="inline-formula"><sup>−1</sup></span>; and (f) interlayer-deficient biotites and F-rich phlogopite can be identified via
their unique OH-stretching Raman peaks around 3570 cm<span class="inline-formula"><sup>−1</sup></span> and 3695 cm<span class="inline-formula"><sup>−1</sup></span>, respectively. Our results show a potential tool for
non-destructive quantitative estimations of the major (Mg, Fe, Si, Al, K)
and minor (Ti) elements of the crystal chemistry of the biotite mineral
group by using a non-destructive technique such as Raman spectroscopy,
although its sensitivity is generally lower than that of electron microprobe
analysis and therefore cannot detect trace elements. This is fundamental
within the framework of cultural heritage where samples cannot be powdered
or disassembled.</p> |
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| ISSN: | 0935-1221 1617-4011 |