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The origin of the green color of variscite

¹ Laboratoire de Minéralogie-Cristallographie, UMR CNRS 7590, Universités de Paris 6 et 7 et Institut de Physique du Globe de Paris, Case 115, 75252 Paris Cedex 05, France

Correspondence: ^* E-mail: calas{at}lmcp.jussieu.fr

The color of variscite from three different localities (Pannecé, France; Sarrabus, Sardinia; Ervedosa, Portugal) and metavariscite from Utah was investigated by diffuse reflectance and EPR spectroscopy. These samples contain low levels of transition elements such as V, Cr, and Fe, the relative concentration 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-field 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 field 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.

This article has been cited by other articles:

				K. Druppel, A. Hosch, and G. Franz The system Al2O3-P2O5-H2O at temperatures below 200 {degrees}C: Experimental data on the stability of variscite and metavariscite AlPO4{middle dot}2H2O American Mineralogist, October 1, 2007; 92(10): 1695 - 1703. [Abstract] [Full Text] [PDF]