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Article Dans Une Revue The American Mineralogist Année : 2005

The origin of the green color of variscite.

Résumé

The color of variscite from three different localities (Pannecé, France; Sarrabus, Sardinia; Ervedosa, Portugal) and metavariscite from Utah was investigated by diffuse reß ectance and EPR spectroscopy. These samples contain low levels of transition elements such as V, Cr, and Fe, the relative concentra- tion of which varies with origin, although they remain in the wt% range. The presence of peculiar antiresonance features indicates that octahedral Cr3+ ions are responsible for the absorption bands that cause the green coloration of variscite and metavariscite. Trivalent iron ions, which give only a weak absorption band in some samples, and V3+ ions do not contribute to the green coloration of the samples from these locations. The crystal-Þ eld splitting and B Racah parameter of Cr3+ in variscite and metavariscite are 1590 and 657 cm–1 and 1610 and 575 cm–1, respectively. These values indicate a weak crystal Þ eld and an important Cr-O covalence. Electron paramagnetic resonance spectra show the presence of minor amounts (300–500 ppm) of vanadyl groups substituted for Al. The absence of V3+ indicates that variscite and metavariscite formed in an oxidizing environment.
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Dates et versions

hal-00021928 , version 1 (29-03-2006)

Identifiants

  • HAL Id : hal-00021928 , version 1

Citer

Georges Calas, Laurence Galoisy, Amonmat Kiratisin. The origin of the green color of variscite.. The American Mineralogist, 2005, 90, pp.984-990. ⟨hal-00021928⟩
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