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Electron Spin Resonance Studies of Mn2+ in Freshwater Snail Shells: Pomacea Canaliculata Lamarck and Fossilized Snail Shell |
| N. Udomkan1,2;S. Meejoo3;P. Limsuwan1;P. Winotai3;Y. Chaimanee4 |
| 1Department of Physics, Faculty of Science, King Mongkut’s University of Technology Thonburi, Prachautid Road, Bangkok 10140, Thailand
2846/227 Bangmod Prachautid 44, Thungkru, Bangkok 10140, Thailand
3Department of Chemistry, Faculty of Science, Mahidol University, Rama VI Road, Bangkok 10400, Thailand
4Paleontology Section, Geological Survey Division, Department of Mineral Resources,Rama VI Road, Bangkok 10400, Thailand |
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| Cite this article: |
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N. Udomkan, S. Meejoo, P. Limsuwan et al 2005 Chin. Phys. Lett. 22 1780-1783 |
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Abstract We study paramagnetic Mn2+ ions present in the nowadays shells of univalve freshwater snails of Pomacea canaliculata lamarck (PCL) and the fossilized freshwater snail (FFS), Viviparus. All these shells are abundant in Thailand. The PCL shells were ground into fine powder. A set of seven samples were then separately annealed for 2h in air atmosphere at different annealing temperatures while the FFS powder was characterized as-received. The PCL shells mainly consist of aragonite and a fraction of calcite. The heat treatments of the PCL powder samples at temperature higher than 450°C resulted in an irreversible phase transformation from aragonite to calcite. However, it is found that the FFS shell is mainly made of calcite, with a minor fraction of aragonite. The crystal structure of the high-temperature-annealed PCL samples are quite similar to that of FFS, which indicates that the metamorphosis (aragonite → calcite) in the FFS shell had occurred but was not yet completed, although it had remained under the pressure and temperature of the Earth’s crusts over millions of years. Our detailed ESR spectral analyses of PCL and FFS show that Mn2+ ions enter the Ca2+ sites during a biomineralization process. Simulated ESR parameters of PCL-500 of Mn2+ at a uniaxial site of calcite are reported. It is surprising to find that the ratio of Mn2+ concentration present in FFS to those in PCL shells evaluated from ESR spectra is as much as 10:1.
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| Keywords:
76.30.Fc
78.30.Hv
87.64.Hd
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Published: 01 July 2005
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