TY - JOUR

T1 - Raman spectra of a graphite–nontronite association in marbles from Oltrek Island (Lake Baikal, Russia)

AU - Moroz, T. N.

AU - Edwards, H. G.M.

AU - Ponomarchuk, V. A.

AU - Pyryaev, A. N.

AU - Palchik, N. A.

AU - Goryainov, S. V.

N1 - Publisher Copyright: © 2019 John Wiley & Sons, Ltd. Copyright: Copyright 2020 Elsevier B.V., All rights reserved.

PY - 2020/9/1

Y1 - 2020/9/1

N2 - The graphite in marbles from Oltrek, an uninhabited island on Lake Baikal, has been investigated by micro-Raman spectroscopy using visible and near-ultraviolet wavelength excitation. All graphite samples exhibit a sharp first-order Raman band at about 1,580 cm−1 with a width from 10 to 19 cm−1, and sometimes a D1 band with very low intensity, which is occasionally absent. Using Raman spectra data it was estimated that the temperature of graphite formation in the Oltrek marbles is about 530–650°C and possibly even higher. This evaluation is in good agreement with the temperatures (about 700°C) determined by a graphite isotope geothermometer of the graphite–calcite pair. Scanning electron microscopy images have recorded a сonical graphite morphology on the surface of plate crystals of graphite. Raman spectra of samples with cones about 200–400 nm sizes showed that the graphite was associated with nontronite in the specimens studied. Natural nontronite, a clay mineral of the smectite group, has not been well characterized using Raman spectroscopy. Here, the Raman spectra of the Oltrek nontronite were compared with the spectrum of nontronite from the weathered crust of the Salair Ridge, Russia. The formation of hexagonal–pyramidal structures on the surface of graphite with the participation of clay and bio-organic matter in marble is discussed.

AB - The graphite in marbles from Oltrek, an uninhabited island on Lake Baikal, has been investigated by micro-Raman spectroscopy using visible and near-ultraviolet wavelength excitation. All graphite samples exhibit a sharp first-order Raman band at about 1,580 cm−1 with a width from 10 to 19 cm−1, and sometimes a D1 band with very low intensity, which is occasionally absent. Using Raman spectra data it was estimated that the temperature of graphite formation in the Oltrek marbles is about 530–650°C and possibly even higher. This evaluation is in good agreement with the temperatures (about 700°C) determined by a graphite isotope geothermometer of the graphite–calcite pair. Scanning electron microscopy images have recorded a сonical graphite morphology on the surface of plate crystals of graphite. Raman spectra of samples with cones about 200–400 nm sizes showed that the graphite was associated with nontronite in the specimens studied. Natural nontronite, a clay mineral of the smectite group, has not been well characterized using Raman spectroscopy. Here, the Raman spectra of the Oltrek nontronite were compared with the spectrum of nontronite from the weathered crust of the Salair Ridge, Russia. The formation of hexagonal–pyramidal structures on the surface of graphite with the participation of clay and bio-organic matter in marble is discussed.

KW - cone morphology

KW - graphite

KW - nontronite

KW - Raman spectroscopy

KW - BACTERIA

KW - CONES

KW - SMECTITE

KW - CARBONACEOUS-MATERIAL GEOTHERMOMETER

KW - METAMORPHIC ROCKS

KW - THERMOMETRY

KW - SPECTROSCOPY

KW - HIGHER COMPARABILITY

KW - NANOTUBES

KW - BOTTOM SEDIMENTS

UR - http://www.scopus.com/inward/record.url?scp=85075399641&partnerID=8YFLogxK

U2 - 10.1002/jrs.5763

DO - 10.1002/jrs.5763

M3 - Article

AN - SCOPUS:85075399641

VL - 51

SP - 1885

EP - 1893

JO - Journal of Raman Spectroscopy

JF - Journal of Raman Spectroscopy

SN - 0377-0486

IS - 9

ER -