Abstract
Chalcedony is a spatial arrangement of hydroxylated nanometre-sized α-quartz (SiO2) crystallites that are often found in association with the silica mineral moganite (SiO2). A supplementary Raman band at 501 cm−1 in the chalcedony spectrum, attributed to moganite, has been used for the evaluation of the quartz/moganite ratio in silica rocks. Its frequency lies at 503 cm−1 in sedimentary chalcedony, representing a 2 cm−1 difference with its position in pure moganite. We present a study of the 503 cm−1 band’s behaviour upon heat treatment, showing its gradual disappearance upon heating to temperatures above 300 °C. Infrared spectroscopic measurements of the silanole (SiOH) content in the samples as a function of annealing temperature show a good correlation between the disappearance of the 503 cm−1 Raman band and the decrease of structural hydroxyl. Thermogravimetric analyses reveal a significant weight loss that can be correlated with the decreasing of this Raman band. X-ray powder diffraction data suggest the moganite content in the samples to remain stable. We propose therefore the existence of a hitherto unknown Raman band at 503 cm−1 in chalcedony, assigned to ‘free’ Si–O vibrations of non-bridging Si–OH that oscillate with a higher natural frequency than bridging Si–O–Si (at 464 cm−1). A similar phenomenon was recently observed in the infrared spectra of chalcedony. The position of this Si–OH-related band is nearly the same as the Raman moganite band and the two bands may interfere. The actually observed Raman band in silica rocks might therefore be a convolution of a silanole and a moganite vibration. These findings have broad implications for future Raman spectroscopic studies of moganite, for the assessment of the quartz/moganite ratio, using this band, must take into account the contribution from silanole that are present in chalcedony and moganite.
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References
Bustillo MA, Pérez-Jiménez JL, Alonso-Zarza AM, Furio M (2010) Moganite in the chalcedony varieties of continental cherts (Miocene, Madrid Basin, Spain). In: Conference on micro-Raman spectroscopy and luminescence studies in the earth and planetary sciences (CORALS II), held 18–20 May 2011 in Madrid, Spain., Madrid (Spain). LPI Contribution, p 16
Cady SL, Wenk HR, Sintubin M (1998) Microfibrous quartz varieties: characterization by quantitative X-ray texture analysis and transmission electron microscopy. Contrib Miner Petrol 130(3):320–335
Cayeux L (1929) Les Roches sédimentaires de France. Roches siliceuses, vol 1. Impr. Nat., Paris
Flörke OW, Jones JB, Schmincke HU (1976) A new microcrystalline silica from Gran Canaria. Z Kristallogr 143:156–165
Flörke OW, Köhler-Herbertz B, Langer K, Tönges I (1982) Water in microcrystalline quartz of volcanic origin: Agates. Contrib Miner Petrol 80(4):324–333
Flörke OW, Flörke U, Giese U (1984) Moganite, a new microcrystalline silica-mineral. Neues Jahrbuch für Mineralogie Abhandlungen 149(3):325–336
Füchtbauer H (1988) Sedimente und Sedimentgesteine, 4th edn. Schweizerbart, Stuttgart
Fukuda J, Nakashima S (2008) Water at high temperatures in a microcrystalline silica (chalcedony) by in-situ infrared spectroscopy: physicochemical states and dehydration behavior. J Mineral Petrol Sci 103:112–115
Götze J, Nasdala L, Kleeberg R, Wenzel M (1998) Occurrence and distribution of “moganite” in agate/chalcedony: a combined micro-Raman, Rietveld, and cathodoluminescence study. Contrib Miner Petrol 133(1):96–105
Graetsch H, Flörke OW, Miehe G (1985) The nature of water in chalcedony and opal-C from Brazilian agate geodes. Phys Chem Miner 12(5):300–306
Graetsch H, Topalovic I, Gies H (1994) NMR spectra of moganite and chalcedony. Eur J Mineral 6(4):459–464
Heaney PJ, Post JE (1992) The widespread distribution of a novel silica polymorph in microcrystalline quartz varieties. Science 255(5043):441–443. doi:10.1126/science.255.5043.441
Heaney PJ, Post JE (2001) Evidence for an I2/a to Imab phase transition in the silica polymorph moganite at 570 K. Am Mineral 86(11–12):1358–1366
Heaney PJ, McKeown DA, Post JE (2007) Anomalous behavior at the I2/a to Imab phase transition in SiO2-moganite: an analysis using hard-mode Raman spectroscopy. Am Mineral 92(4):631–639
Kingma KJ, Hemley RJ (1994) Raman spectroscopic study of microcrystalline silica. Am Mineral 79:269–273
Miehe G, Graetsch H (1992) Crystal structure of moganite: a new structure type of silica. Eur J Mineral 4:693–706
Miehe G, Graetsch H, Flörke OW (1984) Crystal structure and growth fabric of length-fast chalcedony. Phys Chem Miner 10(5):197–199
Miehe G, Flörke OW, Graetsch H (1986) Moganit: Strukturvorschlag für ein neues mikrokristallines SiO2-mineral. Fortschritte der Mineralogie 64(Beiheft 1):117
Moxon T, Rios S (2004) Moganite and water content as a function of age in agate: an XRD and thermogravimetric study. Eur J Mineral 16(2):269–278. doi:10.1127/0935-1221/2004/0016-0269
Nash DJ, Hopkinson L (2004) A reconnaissance laser Raman and Fourier transform infrared survey of silcretes from the Kalahari Desert, Botswana. Earth Surf Proc Land 29(12):1541–1558
Rios S, Salje EKH, Redfern SAT (2001) Nanoquartz vs. macroquartz: a study of the a—ß phase transition. Eur Phys J B 20:75–83
Rodgers KA, Cressey G (2001) The occurrence, detection and significance of moganite (SiO2) among some silica sinters. Mineral Mag 65(2):157–167
Rodgers KA, Hampton WA (2003) Laser Raman identification of silica phases comprising microtextural components of sinters. Mineral Mag 67(1):1–13. doi:10.1180/0026461036710079
Schmidt P, Fröhlich F (2011) Temperature dependent crystallographic transformations in chalcedony, SiO2, assessed in mid infrared spectroscopy. Spectrochim Acta Part A Mol Biomol Spectrosc 78(5):1476–1481
Schmidt P, Badou A, Fröhlich F (2011) Detailed FT near-infrared study of the behaviour of water and hydroxyl in sedimentary length-fast chalcedony, SiO2, upon heat treatment. Spectrochim Acta Part A Mol Biomol Spectrosc 81(1):552–559
Scholze H (1960) Über die quantitative UR-spektroskopische Wasserbestimmung in Silikaten. Fortschr Mineral 38(2):122–123
Acknowledgements
We thank the Centre Européen de Recherches Préhistoriques de Tautavel (CERP) for the acquisition of the X-ray powder diffraction data used in this work. We are particularly indebted to Christian Perrenoud of the Muséum National D’Histoire Naturelle, Dpt. de Préhistoire UMR 7194 and Thibaud Saos from the CERP. We also thank the ANR program ProMiTraSil and in particular, Vanessa Léa and Philippe Sciau (Toulouse, FR) for financial support for fieldwork in Gran Canaria.
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Schmidt, P., Bellot-Gurlet, L., Slodczyk, A. et al. A hitherto unrecognised band in the Raman spectra of silica rocks: influence of hydroxylated Si–O bonds (silanole) on the Raman moganite band in chalcedony and flint (SiO2). Phys Chem Minerals 39, 455–464 (2012). https://doi.org/10.1007/s00269-012-0499-7
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DOI: https://doi.org/10.1007/s00269-012-0499-7