Raman spectroscopy has recently become a common laboratory analytical technique due to the introduction of technology such as lasers, charge-coupled devices, and holographic filters. The information given by Raman spectroscopy is complimentary to infrared absorption spectroscopy, but sample preparation is often much easier, if any is needed at all. Because of this, the field of Raman spectroscopy has expanded in many areas, including mineralogy. The ongoing development of a database of Raman spectra of minerals enables facile identification of many minerals. Pyroxenes are a class of minerals that make up approximately 25% of the Earth's upper mantle, to a depth of 400 km. A recently discovered phase change in pyroxenes, accompanied by a volume change, is now accepted as the origin of some deep-focus earthquakes, which are clustered at a depth of approximately 225 km. However, the bonding change that accompanies this phase change is not completely understood. Raman spectroscopy was utilized to follow the phase change of spodumene. Polarized spectra of an oriented single crystal of spodumene were utilized to assign Raman modes that were previously ambiguously assigned in the pyroxenes. The pressure-induced phase transition was also followed in LiFeSi2O6 utilizing both Raman spectroscopy and single crystal x-ray diffraction. Similarities were noted between the Raman spectra of spodumene and LiFeSi2O6, enabling the assignment of Raman bands in the second material studied. Finally, a third pyroxene, LiCrSi2O6, was studied with Raman spectroscopy while the sample was subjected to pressure. This material changed color with application of pressure and the color change was quantified with visible absorption spectroscopy. Though no phase change occurred in this material, changes in the spectra did occur at high pressures. These high-pressure changes in the Raman spectra were observed in all three crystals studied and could provide a better understanding of the pyroxenes at high pressures. Additionally, none of the three pyroxenes in P21/c phase displayed a doublet of peaks in the spectroscopic region that had been previously utilized as a benchmark for the identification of the P21/c phase of the pyroxenes until higher pressures. Spodumene did not display a doublet at any pressure studied.
| Identifer | oai:union.ndltd.org:arizona.edu/oai:arizona.openrepository.com:10150/280444 |
| Date | January 2003 |
| Creators | Pommier, Carolyn Jane Snider |
| Contributors | Denton, M. Bonner |
| Publisher | The University of Arizona. |
| Source Sets | University of Arizona |
| Language | en_US |
| Detected Language | English |
| Type | text, Dissertation-Reproduction (electronic) |
| Rights | Copyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author. |
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