High Pressure Raman and Nd3+ Luminescence Spectroscopy of Bastnaesite-(Ce)
Abstract
Bastnäesite-(Ce) is a relatively dense rare earth element (REE) bearing carbonate, (Ce,La,Y,Nd,Pr)CO3F, which crystallizes in the hexagonal crystal system (space group P-62c). Bastnäesite is one of the most common REE-bearing minerals, and has importance from both economic and geologic perspectives due to its large REE concentration. REEs (incompatible elements) are expected to occur in carbon rich regions of the mantle; hence, bastnaesites high pressure behavior has implications for rare-earth and halogen-storage in oxided regions of the deep Earth. We report Raman vibrational and Nd3+ luminescence (the 4F3/2->4I9/2. 4F3/2->4I11/2 and 4F5/2+2H9/2->4I9/2 transitions) spectra of natural bastnäesite-(Ce) to 50 GPa at 300 K. Bastnäesite-I remains the stable phase up to 25 GPa, where it undergoes a subtle phase transition to bastnaesite-II: this is likely produced by a change in symmetry of the carbonate ion. Bastnaesite-II further transforms to bastnaesite-III at 38 GPa, as demonstrated by changes in the luminescence, and specifically within the 4F3/2->4I9/2 transitions. There are additional modest changes to the Raman spectra and the other luminescent transitions at this pressure. The implications of the high-pressure transitions of bastnaesite include the marked stability of this rare earth carbonate under compaction, and the relative invariance of the nine-fold coordinate rare earth element site under compression. Additionally, the monotonic character of the Nd3+ luminescence indicates that it could be used as a near IR pressure standard up to 38 GPa.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFMMR23B0093V
- Keywords:
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- 1038 Mantle processes;
- GEOCHEMISTRYDE: 3924 High-pressure behavior;
- MINERAL PHYSICSDE: 3630 Experimental mineralogy and petrology;
- MINERALOGY AND PETROLOGYDE: 5199 General or miscellaneous;
- PHYSICAL PROPERTIES OF ROCKS