Raman discrimination of garnet inclusions in Siberian diamonds

Abstract

The composition of garnet inclusions in natural garnets is exceptionally useful for identification of the chemical and physical properties of mantle lithologies in which they occur. The results of Raman study of garnet inclusions in Siberian diamonds are presented. Most of studied garnets belong to either peridotitic (P type, n = 101) or eclogitic (E type, n = 63), and some rare garnets are websteritic (n = 5). Detected spectroscopic features of garnets in diamonds reveal a wide wave number ranges for rotational R[SiO4], bending ν2, and stretching ν1 modes. The peak positions of the Raman bands correlate with content of major components of garnets. Raman shift of stretching ν1 and bending ν2 vibrations reflects Ca–Mg and Al–Cr isomorphism. The found correlations have been applied for rough estimation of the garnet compositions. This method allows to discriminate E‐type and P‐type garnets marking diamondiferous mantle rocks.

Raman Identification of Inclusions in Diamond

“…For diamond, Kalugina and Zedgenizov (2020) have evaluated suites of eclogitic and peridotitic garnet inclusions and found reasonable agreement between compositions measured by EPMA analysis and compositions estimated from Raman spectra using the approach of Bersani et al (2009). Kalugina and Zedgenizov (2020) used the rotation (R[SiO 4 ]) and stretching (Si-O) vibrations of SiO 4 -tetrahedra near 360 and 910 cm −1 , respectively, to estimate relative molar proportions of pyrope, almandine, and grossular. For their samples, R[SiO 4 ] was the most sensitive band position, with eclogitic garnet inclusions falling within 355.9-361.2 cm −1 and peridotitic garnet inclusions being within 361.2-365.2 cm −1 (Kalugina and Zedgenizov 2020).…”

“…It is possible to determine garnet compositions by considering their spectral features as linear combinations between end-members (Bersani et al 2009). For diamond, Kalugina and Zedgenizov (2020) have evaluated suites of eclogitic and peridotitic garnet inclusions and found reasonable agreement between compositions measured by EPMA analysis and compositions estimated from Raman spectra using the approach of Bersani et al (2009). Kalugina and Zedgenizov (2020) used the rotation (R[SiO 4 ]) and stretching (Si-O) vibrations of SiO 4 -tetrahedra near 360 and 910 cm −1 , respectively, to estimate relative molar proportions of pyrope, almandine, and grossular.…”

“…Kalugina and Zedgenizov (2020) used the rotation (R[SiO 4 ]) and stretching (Si-O) vibrations of SiO 4 -tetrahedra near 360 and 910 cm −1 , respectively, to estimate relative molar proportions of pyrope, almandine, and grossular. For their samples, R[SiO 4 ] was the most sensitive band position, with eclogitic garnet inclusions falling within 355.9-361.2 cm −1 and peridotitic garnet inclusions being within 361.2-365.2 cm −1 (Kalugina and Zedgenizov 2020). This difference in R[SiO 4 ] band position mainly reflects the difference in contribution from almandine and pyrope end-members at 342 cm −1 and 364 cm −1 , respectively (Kolesov and Geiger 1998).…”

GeoRaman

“…A combination of micro-Raman, cathodoluminescence and electron backscatter diffraction mapping techniques were used by Rezvukhina et al [2] in order to evidence microscopic characteristics (twinning, radial fibrous pattern and intergrowths) of kyanite porphyroblasts in metamorphic rocks from Kokchetav massif. Kalugina and Zedgenizov [3] use the main Raman features of garnets present as inclusions in diamonds in order to distinguish peridotitic from eclogitic garnets. This allows to discriminate between different diamondiferous mantle rocks.…”

Micro-Raman Spectroscopy Assessment of Chemical Compounds of Mantle Clinopyroxenes

“…The analysis of the chemical composition of inclusions traditionally involves the partial destruction of the samples, e.g., study of the chemical composition of inclusions in diamonds by EPMA (electron probe microanalysis) requires specific sample preparation, such as polishing or crushing of the host. Therefore, the methods of study of mineral inclusions using non-destructive methods are becoming more demanded [4][5][6][7][8][9]. Raman spectroscopy is an alternative high-resolution non-invasive non-destructive technique, which provides information about specific vibrations in solid materials reflecting the chemical and structural features of minerals, including those presented as inclusions in natural diamonds.…”