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Raman spectra of Py40Gr60 garnets synthesized at different temperatures from 1000 to 1400 °C, showing same overall appearance
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A study of the effect of substitution of Mg and Ca in garnet solid solution (Grtss) was carried out using Raman spectroscopy to probe changes to the crystal lattice. The garnet solid solutions with composition changing along pyrope (Py; Mg3Al2Si3O12) and grossular (Gr; Ca3Al2Si3O12) binary were synthesized from glass at 6 GPa and 1400 °C and a seco...
Citations
... The range of Raman spectra of garnets can be grouped in five regions: the highest frequency modes (1100~850 cm [16,18]. ...
... As shown in Figure 3 the patterns and frequencies of modes below 300 cm −1 [T(SiO 4 ) 4− and T(A 2+ ) modes] have much difference among the five garnet species, which could be used to discriminate between the garnet species' minerals. However, because it is still difficult to describe the external vibrations as originating from certain atoms or polyhedral units [18], low-frequency modes are not suitable to establish correlations among chemical composition, structure, and Raman spectra. So, they are not described in detail and discussed herein Crystals 2022, 12, 104 9 of 16 A total of 25 modes are Raman active, which are A1g−, Eg−, and F2g− modes, and 17 F1u modes are active in the infrared [16]. ...
... On the other hand, some gem properties of garnet, such as the values of SG and RI, also change because of chemical composition. Many studies had discussed the correlation between the IR or Raman spectra and cation substitutions in binary garnet samples [17][18][19][20]. However, the correlations among gemological properties, chemical composition, and infrared spectroscopy of the pyralspite and ugrandite series are only discussed by Adamo et al. (2007) [1]. ...
Garnet has many species because of its common isomorphism. In this study, a suite of 25 natural gem-quality garnets, including pyrope, almandine, spessartine, grossular, and andradite, were examined by standard gemological testing, LA-ICP-MS, FTIR, and Raman analysis. Internal stretching and bending vibrations of the SiO4-tetrahedra of garnet exhibit correlate with the type of cations in garnet’s dodecahedral position (A site) and octahedral position (B site). FTIR and Raman spectra showed that with the increase of the radius of Mg2+, Fe2+, Mn2+, and Ca2+ in A site, or the unit cell volumes of pyrope, almandine, spessartine, and grossular, the spectral peaks of Si–Ostr and Si–Obend modes shift to low wavenumber. Because of the largest cations both in A site (Ca2+) and in B site (Fe3+), andradite exhibited the lowest wavenumber of Si–Ostr and Si–Obend modes of the five garnet species. Therefore, garnet has correlations between chemical composition and vibration spectroscopy, and Raman or IR spectroscopy can be used to precisely identify garnet species.
... All data are provided in supplementary materials. Du et al. (2017). The IR data of pyrope are from Hofmeister et al. (1996), and the grossular data are from McAloon and Hofmeister (1995). ...
To better understand the behaviors of calcium (Ca) isotopes during igneous and metamorphic processes that differentiate the Earth and other rocky planets, we investigated the effects of pressure and Ca/Fe concentration on the average CaO bond length and the reduced partition function ratio of ⁴⁴Ca/⁴⁰Ca (10³ln44/40Caβ) in garnet using first-principles calculations. Our calculations show that (1) the average CaO bond length increases with increasing Ca concentrations, significantly decreasing 10³ln44/40Caβ (approximately 0.41‰ at 1000 K from a Ca/(Fe + Ca + Mg) of 1/24 to 12/12). In contrast to orthopyroxene and forsterite, whose CaO bond lengths and 10³ln44/40Caβ are sensitive to Ca concentrations only in a narrow range, the garnet CaO bond length and 10³ln44/40Caβ vary with Ca concentrations in a large range. (2) The average CaO bond length increases and 10³ln44/40Caβ decreases with increasing Fe concentrations (by 0.12‰ at 1000 K, FeO content of 12.4 wt%). (3) The average CaO bond length decreases by ~0.014 Å, and 10³ln44/40Caβ increases by 0.1‰–0.2‰ at 1000 K when the pressure increases from 0 to 3 GPa. (4) However, the pressure effect on 10³ln44/40Caαgarnet–clinopyroxene is insignificant.
Using our new results of the effects of pressure and Ca/Fe concentration on 10³ln44/40Caαgarnet–clinopyroxene, we evaluated the observed difference in Ca isotope compositions between garnet and clinopyroxene in natural samples. Most have reached equilibrium, whereas some samples exceed our prediction, which might reflect the majorite effect or kinetic fractionation.
... The structure, elastic properties, and electrical conductivity of garnet end-members have been extensively studied, but detailed studies on structure by X-ray single-crystal diffraction and Raman spectroscopy of garnet solid solutions are limited. In particular, Raman spectroscopy studies have only focused on grossular-andradite join, pyrope-grossular join, and almandine-pyrope (Alm-Pyr) join [7][8][9][10]. To date, even in the most studied Alm-Pyr join, the structural properties of Alm-Pyr solid solution by the X-ray single-crystal diffraction are very limited, only several garnet compositions along the Alm-Pyr solid solution have been investigated by the X-ray single-crystal diffraction in details [11]. ...
... However, our results should show nearideal mixing properties because of the small difference in ionic radii of Mg 2+ (0.89 Å) and Fe 2+ (0.92 Å) in eightfold coordination [21]. There are lots of possible factors that could have caused excess volume such as dampness, synthesizing some unidentified phase and the distortion of the SiO4 tetrahedra, etc. [9,25]. In this study, we think the cause might be the rotational orientation of the SiO4 tetrahedra. ...
... The Raman mode frequencies of the rotation of the SiO4-tetrahedron (R(SiO4)) decrease linearly with increasing Alm content, but the translational modes of the SiO4-tetrahedron (T(SiO4)) increase with increasing Alm content. The variation of the trends is attributed to a coupling between the vibrations of the translational modes of the SiO4-tetrahedron and those of the translational modes of the X-site cations [9,29]. ...
Crystal-chemical properties of synthetic Almandine-Pyrope (Alm-Pyr) solid solutions were investigated by X-ray single-crystal diffraction and Raman spectroscopy. Garnet solid solution with different compositions were synthesized from powder at 4.0 GPa and annealed at 1200 °C for 48 h by a multi-anvil pressure apparatus. Garnet crystals with different sizes (about 60-1000 μm) were obtained from synthesis. The results of X-ray single-crystal diffraction show that the unit cell constants decrease with increasing Pyr contents in the synthetic Alm-Pyr crystals due to the smaller ionic radius of Mg2+ in eightfold coordination than that of Fe2+. The data exhibit obviously positive deviations from ideal mixing volumes across the Alm-Pyr join which may be caused by the distortion of the SiO4 tetrahedron. Moreover, the significant decrease in the average M-O bond length and volume of the [MgO8]/[FeO8] dodecahedron with increasing Pyr contents are the most important factors to the decrease in the Alm-Pyr crystal unit cell constant and volume. On the other hand, selected bond distances (average , , and distances) have a linear correlation with the unit-cell parameter, but the distance has nonlinear correlation. With increasing the unit-cell parameter, the average distance increases significantly, followed by the average and distances. While the distance changes negligibly further confirming the conclusion that the significant decrease of the average M-O bond length of the [MgO8]/[FeO8] dodecahedron with increasing Pyr contents are the most important factors to the decrease in the Alm-Pyr crystal unit cell volume. In the Raman spectra collected for the Alm-Pyr solid solutions, Raman vibration mode assignments indicate that the Raman vibrational spectra change along the Alm-Pyr binary solution. The mode frequencies of Si-O stretching, Si-O bending, and the rotation of the SiO4-tetrahedron (R(SiO4)) decrease linearly, while the translational modes of the SiO4-tetrahedron (T(SiO4)) increase with increasing Alm contents.
A collection of Hellenistic–Roman glyptics, kept at the Regional Archaeological Museum “Paolo Orsi” (Syracuse, Italy), was investigated in situ with portable Raman spectroscopy with the aim of assessing the viability of this approach, not only for the immediate identification of the gemstones but also for a more in‐depth successive data treatment. At the same time, a corroboration of the autoptic identification of the materials, both archeological and belonging to historical collections, was looked for in order to verify and potentially correct what reported in the museum catalogue. Actually, most of the identifications could be confirmed, the glyptics being mainly made of chalcedony. Other materials found were garnet, glass, and amber. The larger group of chalcedony Raman spectra was subjected to principal components analysis treatment that, after appropriate pretreatment, resulted successful in separating spectra with higher or lower contribution of the band due to the presence of moganite and SiOH bonds. The garnet spectra were instead subjected to quantitative study to identify the main end member. Both the quick identifications and the more detailed studies on chalcedonies and garnets were achieved thanks to the nondestructive and noninvasive investigation, directly in situ , with no sample preparation and minimal interference with the museum's activities.
The lunar volcanic glasses and Mg-suite rocks represent the early enigmatic episodes of lunar magmatism. Due to the gravitational instability of the Fe–Ti enriched (± KREEP) layer, which is formed at the later stage of fractional crystallization, a post-magma-ocean cumulate overturn occurred contemporaneously or near-contemporaneously with the lunar magma ocean (LMO) solidification. The radioactive elements within the KREEP layer were transferred downward and provided continuous energy for the partial melting of the Moon’s interior. The melt from the Moon’s interior and those from decompression melting, in turn, provide source magma for the origin of lunar volcanic glasses and Mg-suite. However, experimental and theoretical studies on the formation process of lunar volcanic glasses and Mg-suite show that the origin of their parental magma is poorly constrained, which largely depends on the initial depth and composition of the LMO. This review examines the mineralogy, petrogenesis, and distribution of lunar volcanic glasses and Mg-suite. Combining with existing models, we constrain the degree, distribution, and timescale of lunar mantle overturn and explore their relationship with later stages of LMO differentiation. We propose an updated chemical composition of the lunar interior, which provides a useful reference for estimating the bulk composition and early differentiation of the Moon and the early Earth.
This chapter contains data on 2104 Raman spectra of more than 2000 mineral species taken from various periodicals. The data are accompanied by some experimental details and information on the reference samples used.
Cs2SnI6‐xBrx (x = 0–6) solid solutions have been synthesized by chemical solid solution reaction in conjunction with sintering under vacuum. The Rietveld refinements of powder X‐ray diffraction (XRD) patterns indicate that all the samples are cubic, with a symmetry of Fm3m. The lattice parameter a decreases linearly as a function of the Br content in Cs2SnI6‐xBrx. Raman spectra suggest that the new Raman peaks might derive from the short‐range ordering of I/Br anions. The UV/Vis reflection spectra reveal a nonlinear trend of energy band gap (Eg) from 1.25 eV to 3.01 eV with increasing Br content. Hence the wide range of Eg of Cs2SnI6‐xBrx solid solutions are capable to overlay almost the entire visual spectrum. Thermogravimetric analysis (TGA) results suggest that the thermal stability of Cs2SnI6‐xBrx increases gradually with increasing Br content. Cs2SnI6‐xBrx with the fine thermal stability and tunable Eg indicate high potential in the applications of solar cell devices.
