Nanodiamonds and silicate minerals in ordinary chondrites as determined by micro‐Raman spectroscopy

Abstract

We present here the Raman spectroscopic study of silicate and carbonaceous minerals in three ordinary chondrites with the aim to improve our understanding the impact process including the peak metamorphic pressures present in carbon-bearing ordinary chondites. The characteristic Raman vibrational peaks of olivines, pyroxenes, and plagioclase have been determined on three ordinary chondrites from India, Dergaon (H5), Mahadevpur (H4/5), and Kamargaon (L6). The Raman spectra of these meteorite samples show the presence of nanodiamonds at 1334-1345 cm À1 and 1591-1619 cm À1 . The fullwidth at half maximum (FWHM) of Raman peaks for Mahadevpur and Dergaon reflect the nature of shock metamorphism in these meteorites. The frequency shift in Raman spectra might be because of shock effects during the formation of the diamond/graphite grains.

Raman and Infrared Spectroscopic Tentative Identification of Organic Traces in Sadiya (LL5) Ordinary Chondrite

“…Figure 1 displays different carbon phases observed in Raman spectra in between 1100-2000 cm -1 . In general, the Raman spectra of nanodiamonds reveal two broad bands centred at 1326 cm -1 and 1590 cm -1 [26]. The first-order Raman band (F 2g ) of diamond occurring at ~1332 cm -1 corresponds to carbon sp3 bonding (the main C-C bond vibration in diamond) and the band (E 2g ) at ~1590 cm -1 is assigned to carbon sp2 bonding graphitic structures [28].…”

“…coming from its interior. The Raman spectra were collected on bulk powdered meteorite samples using an Ar ion laser laser with a power of ~5 mW, which used an excitation source having wavelength 488 nm coupled with a Jobin-Yvon Horiba LabRam-HR Micro-Raman spectrometer equipped with an Olympus microscope with 10X, 50X and 100X objectives, using the method described elsewhere [26,27]. The powdered sample was homogenized in spectrophotometric grade KBr (1:20) in an agate mortar and was pressed 3mm pellets with a hand press.…”

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“…The slits used consisted of 1° fixed divergence and anti-scatter slits and a 0.2mm receiving slit. 14…”

Spectroscopy and Mineralogy of a New Meteorite Kamargaon (L6) Chondrite

“…The peaks of the 813-852 cm -1 doublet is assigned to a mixed contribution of the symmetric (ν1) and asymmetric (ν3) stretching modes of Si-O nb bonds (Non-Bridge Oxygen, NBO) in SiO 4 tetrahedra (Lam et al, 1990). Raman spectra indicates the characteristic doublet at 822.06 cm -1 and 851.79 cm -1 from the coupling between the symmetric (ν1) and anti symmetric (ν3) stretching modes of Si-O nb bonds in SiO 4 tetrahedra of olivine (Saikia et al, 2016(Saikia et al, , 2017b. This peak position may shift upwards as the values of F o increase (Chopelas, 1991).…”