Raman spectroscopic study of pyroxene structures from the Munni Munni layered intrusion, Western Australia

Abstract

Raman spectra were obtained for a series of clinopyroxenes, orthopyroxenes and inverted pigeonites from the Munni Munni layered maÐc-ultramaÐc intrusion in Western Australia. Their composition varies from to mg 48 where mg = mg number = atomic 100 Mg/(Mg + Fe) and Fe = total Fe. The characteristic Raman bands mg 87 , of pyroxene are mainly due to vibrations of the tetrahedra and occur in the 300-400, 650-700 and 980-1020 SiO 4 wavenumber regions of the spectra. Clinopyroxene shows only one intense Raman band in the 650-700 cm-1 region and is readily distinguished from orthorhombic pyroxene which has two intense bands in this region. This di †erence is probably due to the single symmetrically distinct tetrahedral site in the C2/c structure, whereas orthopyroxene has two symmetrically distinct tetrahedral chains. The pyroxenes showed systematic shifts in the wavenumber of the Raman bands with increasing mg number with the orthopyroxene spectra being the most sensitive to variations in mg number. The variations in wavenumber are believed to be related to the straightening of the tetrahedral chains and the corresponding changes in the SiÈO bond lengths and OÈSiÈO angles caused by substitution of Fe for Mg. These changes are greater in the orthorhombic Pbca structure, because the edge-sharing polyhedra enclosing the Fe2' and Mg2' cations form wide bands which are separated by voids or rifts parallel to the c-axis. In the monoclinic C2/c structure, however, these polyhedra are linked in a continuous layer which restricts structural adjustments of the polyhedra and the adjacent tetrahedral chains. Therefore, since Raman SiO 4 spectroscopy is sensitive to changes in crystal structure, it may be used to obtain a semi-quantitative chemical analysis of pyroxene when calibrated with a suitable solid solution series. The number of Raman bands observed and their width also gives an indication of cation order/disorder within the crystal. 1997Crown Copyright ( reserved.

Thermodynamic mixing properties of olivine derived from lattice vibrations

“…Figure 1 illustrates that these frequencies depend nearly linear on the composition for a number of solid solution phases. According to Huang et al (2000) and Mernagh and Hoatson (1997) a similar trend is present in pyroxenes and according to Hofmeister and Mao (2001) in silicates with the spinel structure. Guyot et al (1986) have shown that a quantitative theoretical interpretation of the substitutional effect of magnesium by iron is not straightforward.…”

“…Figure 1a indicates that for three internal vibrational modes in olivine these frequencies show a near-linear behavior with composition. According to Huang et al (2000) and Mernagh and Hoatson (1997) such a trend is also present in at least 17 internal-and lattice vibrational modes of pyroxenes and Fig. 1b exemplifies that this is the case for a number of these modes.…”

Micro‐Raman characterizations of Pompei'smortars

“…The spectrum (g) is assigned to clinopyroxene with is Raman bands at about 323, 353, 390, 508, 530, 557, 663, 821, 862, 926, 1007, and 1038 cm 1 . 25 Clinopyroxene is still observed in the spectrum (h), showing a slightly different pattern. The spectrum (i) shows two broad bands at 484 and 676 cm 1 .…”

“…25,26 The spectrum (b) is due to a superposition of materials: the Raman bands at about 289, 405, 493, 512, and 599 cm 1 can be assigned to the hematite, while the band at about 660 cm 1 is assigned to the presence of magnetite. 27 -32 These two iron minerals are generally associated with the investigated samples but in some cases the spectrum of isolated magnetite is obtained, as in spectrum (c).…”

Brownish inclusions and dark streaks in Libyan Desert Glass: Evidence for high-temperature melting of the target rock

“…5b). According to systematic Raman studies of pyroxenes, these bands, especially the splitting of the doublet in the 650-680 cm )1 region, are typical for orthopyroxene (Mernagh and Hoatson 1997).…”