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Structural effects of OH ⇒ F substitution in trioctahedral micas of the system

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  • Mohammed V University in Rabat

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Original languageEnglish
Pages (from-to)55-67
Number of pages13
JournalSchweizerische Mineralogische und Petrographische Mitteilungen
Volume81
Issue number1
Publication statusPublished - Jan 2001

Abstract

The OH ⇒ F substitution in trioctahedral ferrous micas has been investigated at 720 °C, 1 kbar P H2O, under fO 2 conditions set by the MW (Fe 2O 3-Fe 1-xO) buffer. The starting compositions belong to the annite-siderophyllite join: K(Fe 3-x)Al x)(Si 3-xAl 1+x)O 10(OH) 2 with x = 0 (annite), 0.5 (Fe-eastonite), and 0.75 (Es). In F-bearing system, the compositions investigated belong to (OH,F)-annite, (OH,F)-Fe-eastonite and (OH,F)-Es joins. A single mica phase was observed for (OH,F)-annite in 0 ≤ X F ≤ 0.5 compositional range, and in 0 ≤ X F ≤ 0.2 range for (OH,F)-Fe-eastonite and (OH,F)-Es. Beyond these values, toward to F-rich compositions, topaz, quartz, magnetite and glass coexist with mica. The correlation of the reticular distance d 060 as a function of X F shows that (OH,F)-annite and (OH,F)-Es behave differently as X F increases. Mössbauer measurements along the annite and Es (OH,F) joins demonstrate that the Fe 3+ content decreases from X Fe 3+ (Fe 3+/Fe ^t otal = 9.1% for X F-^a nn = 0 to 3.1% for X F-^a nn = 0.5 and it increases slightly from X Fe 3+ = 2.4% at X F-Es = 0 to 3% at X F-Es = 0.2. FTIR spectroscopy in the far-infrared region (200-50 cm -1) also shows an opposite trend wavenumber-shift between (OH,F)-annite and (OH,F)-Es with increasing X F. In the single phase range, the band observed at 67 cm -1 in the (OH)-annite, corresponding to torsional vibration motion of the tetrahedral layer (mode III), shifts to higher wavenumbers with X F. In contrast, this band (mode III) decreases from 91 cm -1 in the (OH)-Es end-member down to 88 cm -1 at X F = 0.2. These shifts are related to changes in the K-site configuration, particularly to the variations of the tetrahedral rotation angle (α). The angle a increases from ≈ 2° for X F-ann = 0 to 5.5° for X F+ann = 0.5 and it decreases from 8.5° at X F-Es = 0 to 5.3° at X F+Es = 0.2. The OH ⇒ substitution induces local cationic changes and consequently a dimensional adaptation of sheets (limited in such micas to α = 5.5°), which in turn controls the fluorine solubility in these studied micas. The results also show that the Fe 3+/Fe total ratio in F-bearing micas is not only controlled by fO 2 but also by structural constraints. The fluorine content of natural biotites has to be taken into account to estimate oxygen fugacities prevailing in the rocks.

Keywords

    FIR, Fluorine, Mössbauer, Tetrahedral rotation (α), Trioctahedral ferrous micas

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Structural effects of OH ⇒ F substitution in trioctahedral micas of the system. / Boukili, B.; Robert, J. L.; Beny, J. M. et al.
In: Schweizerische Mineralogische und Petrographische Mitteilungen, Vol. 81, No. 1, 01.2001, p. 55-67.

Research output: Contribution to journalArticleResearchpeer review

Boukili, B, Robert, JL, Beny, JM & Holtz, F 2001, 'Structural effects of OH ⇒ F substitution in trioctahedral micas of the system', Schweizerische Mineralogische und Petrographische Mitteilungen, vol. 81, no. 1, pp. 55-67.
Boukili, B., Robert, J. L., Beny, J. M., & Holtz, F. (2001). Structural effects of OH ⇒ F substitution in trioctahedral micas of the system. Schweizerische Mineralogische und Petrographische Mitteilungen, 81(1), 55-67.
Boukili B, Robert JL, Beny JM, Holtz F. Structural effects of OH ⇒ F substitution in trioctahedral micas of the system. Schweizerische Mineralogische und Petrographische Mitteilungen. 2001 Jan;81(1):55-67.
Boukili, B. ; Robert, J. L. ; Beny, J. M. et al. / Structural effects of OH ⇒ F substitution in trioctahedral micas of the system. In: Schweizerische Mineralogische und Petrographische Mitteilungen. 2001 ; Vol. 81, No. 1. pp. 55-67.
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abstract = "The OH ⇒ F substitution in trioctahedral ferrous micas has been investigated at 720 °C, 1 kbar P H2O, under fO 2 conditions set by the MW (Fe 2O 3-Fe 1-xO) buffer. The starting compositions belong to the annite-siderophyllite join: K(Fe 3-x)Al x)(Si 3-xAl 1+x)O 10(OH) 2 with x = 0 (annite), 0.5 (Fe-eastonite), and 0.75 (Es). In F-bearing system, the compositions investigated belong to (OH,F)-annite, (OH,F)-Fe-eastonite and (OH,F)-Es joins. A single mica phase was observed for (OH,F)-annite in 0 ≤ X F ≤ 0.5 compositional range, and in 0 ≤ X F ≤ 0.2 range for (OH,F)-Fe-eastonite and (OH,F)-Es. Beyond these values, toward to F-rich compositions, topaz, quartz, magnetite and glass coexist with mica. The correlation of the reticular distance d 060 as a function of X F shows that (OH,F)-annite and (OH,F)-Es behave differently as X F increases. M{\"o}ssbauer measurements along the annite and Es (OH,F) joins demonstrate that the Fe 3+ content decreases from X Fe 3+ (Fe 3+/Fe ^t otal = 9.1% for X F-^a nn = 0 to 3.1% for X F-^a nn = 0.5 and it increases slightly from X Fe 3+ = 2.4% at X F-Es = 0 to 3% at X F-Es = 0.2. FTIR spectroscopy in the far-infrared region (200-50 cm -1) also shows an opposite trend wavenumber-shift between (OH,F)-annite and (OH,F)-Es with increasing X F. In the single phase range, the band observed at 67 cm -1 in the (OH)-annite, corresponding to torsional vibration motion of the tetrahedral layer (mode III), shifts to higher wavenumbers with X F. In contrast, this band (mode III) decreases from 91 cm -1 in the (OH)-Es end-member down to 88 cm -1 at X F = 0.2. These shifts are related to changes in the K-site configuration, particularly to the variations of the tetrahedral rotation angle (α). The angle a increases from ≈ 2° for X F-ann = 0 to 5.5° for X F+ann = 0.5 and it decreases from 8.5° at X F-Es = 0 to 5.3° at X F+Es = 0.2. The OH ⇒ substitution induces local cationic changes and consequently a dimensional adaptation of sheets (limited in such micas to α = 5.5°), which in turn controls the fluorine solubility in these studied micas. The results also show that the Fe 3+/Fe total ratio in F-bearing micas is not only controlled by fO 2 but also by structural constraints. The fluorine content of natural biotites has to be taken into account to estimate oxygen fugacities prevailing in the rocks.",
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author = "B. Boukili and Robert, {J. L.} and Beny, {J. M.} and Francois Holtz",
note = "Copyright: Copyright 2012 Elsevier B.V., All rights reserved.",
year = "2001",
month = jan,
language = "English",
volume = "81",
pages = "55--67",
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TY - JOUR

T1 - Structural effects of OH ⇒ F substitution in trioctahedral micas of the system

AU - Boukili, B.

AU - Robert, J. L.

AU - Beny, J. M.

AU - Holtz, Francois

N1 - Copyright: Copyright 2012 Elsevier B.V., All rights reserved.

PY - 2001/1

Y1 - 2001/1

N2 - The OH ⇒ F substitution in trioctahedral ferrous micas has been investigated at 720 °C, 1 kbar P H2O, under fO 2 conditions set by the MW (Fe 2O 3-Fe 1-xO) buffer. The starting compositions belong to the annite-siderophyllite join: K(Fe 3-x)Al x)(Si 3-xAl 1+x)O 10(OH) 2 with x = 0 (annite), 0.5 (Fe-eastonite), and 0.75 (Es). In F-bearing system, the compositions investigated belong to (OH,F)-annite, (OH,F)-Fe-eastonite and (OH,F)-Es joins. A single mica phase was observed for (OH,F)-annite in 0 ≤ X F ≤ 0.5 compositional range, and in 0 ≤ X F ≤ 0.2 range for (OH,F)-Fe-eastonite and (OH,F)-Es. Beyond these values, toward to F-rich compositions, topaz, quartz, magnetite and glass coexist with mica. The correlation of the reticular distance d 060 as a function of X F shows that (OH,F)-annite and (OH,F)-Es behave differently as X F increases. Mössbauer measurements along the annite and Es (OH,F) joins demonstrate that the Fe 3+ content decreases from X Fe 3+ (Fe 3+/Fe ^t otal = 9.1% for X F-^a nn = 0 to 3.1% for X F-^a nn = 0.5 and it increases slightly from X Fe 3+ = 2.4% at X F-Es = 0 to 3% at X F-Es = 0.2. FTIR spectroscopy in the far-infrared region (200-50 cm -1) also shows an opposite trend wavenumber-shift between (OH,F)-annite and (OH,F)-Es with increasing X F. In the single phase range, the band observed at 67 cm -1 in the (OH)-annite, corresponding to torsional vibration motion of the tetrahedral layer (mode III), shifts to higher wavenumbers with X F. In contrast, this band (mode III) decreases from 91 cm -1 in the (OH)-Es end-member down to 88 cm -1 at X F = 0.2. These shifts are related to changes in the K-site configuration, particularly to the variations of the tetrahedral rotation angle (α). The angle a increases from ≈ 2° for X F-ann = 0 to 5.5° for X F+ann = 0.5 and it decreases from 8.5° at X F-Es = 0 to 5.3° at X F+Es = 0.2. The OH ⇒ substitution induces local cationic changes and consequently a dimensional adaptation of sheets (limited in such micas to α = 5.5°), which in turn controls the fluorine solubility in these studied micas. The results also show that the Fe 3+/Fe total ratio in F-bearing micas is not only controlled by fO 2 but also by structural constraints. The fluorine content of natural biotites has to be taken into account to estimate oxygen fugacities prevailing in the rocks.

AB - The OH ⇒ F substitution in trioctahedral ferrous micas has been investigated at 720 °C, 1 kbar P H2O, under fO 2 conditions set by the MW (Fe 2O 3-Fe 1-xO) buffer. The starting compositions belong to the annite-siderophyllite join: K(Fe 3-x)Al x)(Si 3-xAl 1+x)O 10(OH) 2 with x = 0 (annite), 0.5 (Fe-eastonite), and 0.75 (Es). In F-bearing system, the compositions investigated belong to (OH,F)-annite, (OH,F)-Fe-eastonite and (OH,F)-Es joins. A single mica phase was observed for (OH,F)-annite in 0 ≤ X F ≤ 0.5 compositional range, and in 0 ≤ X F ≤ 0.2 range for (OH,F)-Fe-eastonite and (OH,F)-Es. Beyond these values, toward to F-rich compositions, topaz, quartz, magnetite and glass coexist with mica. The correlation of the reticular distance d 060 as a function of X F shows that (OH,F)-annite and (OH,F)-Es behave differently as X F increases. Mössbauer measurements along the annite and Es (OH,F) joins demonstrate that the Fe 3+ content decreases from X Fe 3+ (Fe 3+/Fe ^t otal = 9.1% for X F-^a nn = 0 to 3.1% for X F-^a nn = 0.5 and it increases slightly from X Fe 3+ = 2.4% at X F-Es = 0 to 3% at X F-Es = 0.2. FTIR spectroscopy in the far-infrared region (200-50 cm -1) also shows an opposite trend wavenumber-shift between (OH,F)-annite and (OH,F)-Es with increasing X F. In the single phase range, the band observed at 67 cm -1 in the (OH)-annite, corresponding to torsional vibration motion of the tetrahedral layer (mode III), shifts to higher wavenumbers with X F. In contrast, this band (mode III) decreases from 91 cm -1 in the (OH)-Es end-member down to 88 cm -1 at X F = 0.2. These shifts are related to changes in the K-site configuration, particularly to the variations of the tetrahedral rotation angle (α). The angle a increases from ≈ 2° for X F-ann = 0 to 5.5° for X F+ann = 0.5 and it decreases from 8.5° at X F-Es = 0 to 5.3° at X F+Es = 0.2. The OH ⇒ substitution induces local cationic changes and consequently a dimensional adaptation of sheets (limited in such micas to α = 5.5°), which in turn controls the fluorine solubility in these studied micas. The results also show that the Fe 3+/Fe total ratio in F-bearing micas is not only controlled by fO 2 but also by structural constraints. The fluorine content of natural biotites has to be taken into account to estimate oxygen fugacities prevailing in the rocks.

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