Raman spectroscopy of natural silica in Chicxulub impactite,MexicoSpectroscopie Raman de silices naturelles dans l'impactite de Chicxulub,Mexique |
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| Authors: | Mikhail Ostroumov Eric Faulques Elena Lounejeva |
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| Institution: | 1. Mineralogical Departement, Metallurgical Institute, University of Michoacan, C.P. 58000, Morelia, Michoacan, Mexico;2. Institut des matériaux Jean-Rouxel, université de Nantes, 2, rue de la Houssinière, BP 32229, 44322, Nantes, France;3. Geological Institute, University of Mexico, CP 04510, Mexico, D.F., Mexico |
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| Abstract: | A series of natural silica impactite samples from Chicxulub (Mexico) was investigated by Raman microprobe (RMP) analysis. The data yield evidence for high-pressure shock metamorphism in the rock. The impactite contains three polymorphs of silica: the original α-quartz, and two high-pressure varieties – coesite and disordered quartz representing various degrees of crystallinity. We found systematic changes in frequencies and half-widths of the Raman bands, caused by increasing irregularities of bond-lengths and bond-angles and a general breaking-up of the structure as a result of impact events. Therefore, RMP is an adequate tool for measuring the crystallinity of disordered quartz. The half-width Γ and the frequency ω of the symmetric SiOSi stretching vibrational band (A1 mode) of the SiO4 tetrahedra are the most amenable parameters for estimating the degree of crystallinity. In well-crystallized quartz, Γ=5 cm?1 and ω=464 cm?1, while in highly disordered quartz this line shifts up to ω=455 cm?1 and broadens up to Γ=30 cm?1. The Raman lineshapes appear to depend strongly on the degree of lattice disorder subsequent to impact events. To cite this article: M. Ostroumov et al., C. R. Geoscience 334 (2002) 21–26 |
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| Keywords: | Raman spectroscopy impactite Chicxulub disordered quartz Mexico spectroscopie Raman impactite de Chicxulub quartz désordonné Mexique Géomatériaux Minéralogie Geomaterials Mineralogy |
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