Concentration of hydroxyl defects in quartz from various rhyolitic ignimbrite horizons: results from unpolarized micro-FTIR analyses on unoriented phenocryst fragments
“…The limitation of the linear correlation to 300 µm is in good agreement with Biró et al (2016) for unpolarized measurements on unoriented quartz crystals, although the polarized measurements presented here show a significantly higher R 2 (0.96 versus 0.86). Spectra are normalized by thickness and vertically offset for graphical reasons.…”
Oriented sections of more than 500 quartz grains from sediments, igneous and metamorphic rocks from different localities in Sweden, Austria, Germany and South Africa were analyzed by FTIR spectroscopy, and their OH-defect content was determined with respect to the speciation and total defect water content. Systematic variations of defect speciation and statistical evaluation of total defect contents were used to evaluate the potential of FTIR spectroscopy on quartz as a thermometer in quartzite, as a tool for differentiation trends in granitic systems, and for provenance analysis of sedimentary rocks. In addition to the analyses of natural crystals, high-pressure annealing experiments at lower crustal conditions (1-3 kbar and 650-750°C) were performed in order to document the effect of high-grade metamorphism on the defect chemistry. Results indicate that (1) quartz grains from unmetamorphosed granite bodies reveal interesting differentiation trends, (2) sediments and sedimentary rocks are valuable archives to preserve the pre-sedimentary OH-defect chemistry, where individual signatures are preserved and can be traced back to potential source rocks, (3) OH-defects are retained up to 300°C over geological time scales, (4) long-term low-grade metamorphic overprint leads to a continuous annealing to lower defect water contents, where Al-specific OH-defects survive best, and (5) middle to high-grade annealing drives towards a homogeneous defect partitioning from grain to grain, where the degree of attainment of equilibrium depends on temperature and duration of the thermal event. In summary, OH-defects in quartz crystals monitor parts of their geological history, and the systematic investigation and statistical treatment of a large amount of grains can be applied as an analytical tool to study sedimentary, metamorphic and igneous processes.
“…The limitation of the linear correlation to 300 µm is in good agreement with Biró et al (2016) for unpolarized measurements on unoriented quartz crystals, although the polarized measurements presented here show a significantly higher R 2 (0.96 versus 0.86). Spectra are normalized by thickness and vertically offset for graphical reasons.…”
Oriented sections of more than 500 quartz grains from sediments, igneous and metamorphic rocks from different localities in Sweden, Austria, Germany and South Africa were analyzed by FTIR spectroscopy, and their OH-defect content was determined with respect to the speciation and total defect water content. Systematic variations of defect speciation and statistical evaluation of total defect contents were used to evaluate the potential of FTIR spectroscopy on quartz as a thermometer in quartzite, as a tool for differentiation trends in granitic systems, and for provenance analysis of sedimentary rocks. In addition to the analyses of natural crystals, high-pressure annealing experiments at lower crustal conditions (1-3 kbar and 650-750°C) were performed in order to document the effect of high-grade metamorphism on the defect chemistry. Results indicate that (1) quartz grains from unmetamorphosed granite bodies reveal interesting differentiation trends, (2) sediments and sedimentary rocks are valuable archives to preserve the pre-sedimentary OH-defect chemistry, where individual signatures are preserved and can be traced back to potential source rocks, (3) OH-defects are retained up to 300°C over geological time scales, (4) long-term low-grade metamorphic overprint leads to a continuous annealing to lower defect water contents, where Al-specific OH-defects survive best, and (5) middle to high-grade annealing drives towards a homogeneous defect partitioning from grain to grain, where the degree of attainment of equilibrium depends on temperature and duration of the thermal event. In summary, OH-defects in quartz crystals monitor parts of their geological history, and the systematic investigation and statistical treatment of a large amount of grains can be applied as an analytical tool to study sedimentary, metamorphic and igneous processes.
“…The position of this band suggests that water is similar to that of ice in the range of 3000–3700 cm –1 or in inclusions. 16,34,35 However, the ice band is sharper than the band at 3300 cm –1 in the minerals, suggesting that ice is in a more structured environment. Figure 6.Attenuated total reflection spectra of single crystals are plotted in the IR range of 3000–3900 cm –1 .…”
This study focuses on particle size effect on monomineralic powders recorded using attenuated total reflection Fourier transform infrared (ATR FT-IR) spectroscopy. Six particle size fractions of quartz, feldspar, calcite, and dolomite were prepared (<2, 2-4, 4-8, 8-16, 16-32, and 32-63 µm). It is found that the width, intensity, and area of bands in the ATR FT-IR spectra of minerals have explicit dependence on the particle size. As particle size increases, the intensity and area of IR bands usually decrease while the width of bands increases. The band positions usually shifted to higher wavenumbers with decreasing particle size. Infrared spectra of minerals are the most intensive in the particle size fraction of 2-4 µm. However, if the particle size is very small (<2 µm), due to the wavelength and penetration depth of the IR light, intensity decreases. Therefore, the quantity of very fine-grained minerals may be underestimated compared to the coarser phases. A nonlinear regression analysis of the data indicated that the average coefficients and indices of the power trend line equation imply a very simplistic relationship between median particle diameter and absorbance at a given wavenumber. It is concluded that when powder samples with substantially different particle size are compared, as in regression analysis for modal predictions using ATR FT-IR, it is also important to report the grain size distribution or surface area of samples. The band area of water (3000-3620 cm) is similar in each mineral fraction, except for the particles below 2 µm. It indicates that the finest particles could have disproportionately more water adsorbed on their larger surface area. Thus, these higher wavenumbers of the ATR FT-IR spectra may be more sensitive to this spectral interference if the number of particles below 2 µm is considerable. It is also concluded that at least a proportion of the moisture could be very adhesive to the particles due to the band shift towards lower wavenumbers in the IR range of 3000-3620 cm.
“…The significant frequency difference between the experimental band at 3585 cm −1 and the theoretical component at 3416 cm −1 does not support the Griggs defect as a relevant model of the 3585 cm −1 band. Concerning the low-frequency component, it should be also noted that bands at ∼ 3200 and 3300 cm −1 are often present in quartz spectra, but these have been assigned to either Si-O overtones or combination vibrations of the quartz structure based on their insensitivity to annealing or H-D exchange (Kats, 1962), or to surficial OH (Biró et al, 2016). Furthermore, this Griggs_1 defect cannot be invoked to explain the broad H 2 O band at ∼ 3400 cm −1 -spectra including this band do not also include a second band at, or around, 3238 cm −1 .…”
Section: Methodsmentioning
confidence: 99%
“…These defects are known to modify some of the macroscopic physicalchemical properties of quartz, including its rheology and piezoelectric performance (e.g., Griggs and Blacic, 1965;Griggs et al, 1966;Mackwell and Paterson, 1985;Kronenberg et al, 1986;Cordier and Doukhan, 1991;Doukhan, 1995). The defects are also likely to provide pathways for diffusive hydrogen flux through quartz, by which quartz-hosted melt and fluid inclusions can be modified (Severs et al, 2007;Zajacz et al, 2009;Guo and Audétat, 2018;Myers et al, 2019) and OH contents of volcanic quartz can be modified before, during or post-eruption (Biró et al, 2016(Biró et al, , 2017Tollan et al 2019). The infrared spectra of these defects can also be used to identify the provenance of detrital quartz in sands, sandstones and other siliciclastic materials (e.g., Stalder and Neuser, 2013;Stalder et al, 2017Stalder et al, , 2019.…”
Abstract. The infrared spectra of natural quartz, and synthetic quartz produced in
conditions relevant to natural environments, generally contain some
association of OH-stretching absorption bands at 3596, 3585, 3483, 3431,
3379 and 3313 cm−1, and/or a broad band at ∼ 3400 cm−1. In this study, a series of OH-bearing defects has been
theoretically investigated from first principles within the density
functional theory framework. The optimized structure, infrared spectroscopic
properties and relative energy of defect configurations have been
determined. Comparison with experimental observations enables the
identification of atomic-scale configurations related to the
experimentally observed OH-stretching bands. Consistent with previous
interpretations, the results confirm the assignment of the bands at 3596 and
3483 cm−1 to OH defects associated with B3+ substituting for
Si4+ and to OH defects associated with Li+ cations located in the structural channels,
respectively. They also confirm the assignment of the bands at 3313 and 3379 cm−1 to OH associated with the Al3+-for-Si4+ substitution
and, by implication, the previously given interpretation of the 3431 cm−1 band in terms of Fermi resonance. The band at 3585 cm−1 does
not appear to be related to a hydrogarnet-type defect, as has been proposed
previously, but potentially corresponds to isolated OH− groups bridging
two Si atoms, where the charge compensation is ensured by a nonlocal
mechanism.
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