Natural iron-containing blue and colorless euclase studied by electron paramagnetic resonance |
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| Authors: | K J Guedes K Krambrock M V B Pinheiro L A D Menezes Filho |
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| Institution: | (1) Departamento de Física, ICEx, Universidade Federal de Minas Gerais, CP 702, 30.123-970 Belo Horizonte, MG, Brazil;(2) Luiz Menezes Minerais, Rua Esmeralda 534, Prado, 30.410-080 Belo Horizonte, MG, Brazil |
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| Abstract: | Natural blue and colorless rare-gem mineral specimens of euclase from Brazil are investigated by electron paramagnetic resonance (EPR). Angular dependences of Fe3+ EPR spectra in three mutually perpendicular crystal planes are analyzed revealing g and D tensors with significant low-symmetry effects, as for example, the high asymmetry parameter E/D = 0.28. Fourth-order degree Stevens parameters are also included in analysis. The anisotropy of both g and D tensors is consistent with Fe3+ substituting for Al3+ ions in strongly distorted AlO5(OH) octahedra in which the oxygen distances range from 1.85 to 1.98 Å. Fe3+ is not responsible for the blue color because colorless and blue euclase show nearly the same Fe3+ concentration as measured by EPR. However, total iron content in blue sample is much higher than in the colorless one suggesting that the existing model that Fe2+–Fe3+ intervalence charge transfer transition may explain the blue color of euclase. |
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| Keywords: | EPR Fe3+ Euclase Low symmetry |
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