Unusual Aquamarine–White Beryl
Recently, the author analyzed an interesting 41.51 ct faceted bicolor beryl (figure 1) composed of aquamarine and opaque white beryl. This gem belongs to Brazilian gem dealer Veber Leite and is part of his collection containing several similar specimens. According to Leite, the bicolor beryls were mined in Brumado, a city located in the state of Bahia, Brazil, but their geographic origin could not be confirmed.
Standard gemological testing of both sections revealed a specific gravity of 2.70 and a refractive index of 1.581–1.592. Ultraviolet/visible/near-infrared (UV-Vis-NIR) spectra revealed an absorption band centered at about 810 nm, also present in both sections. In beryl, this band is associated with Fe2+ (D.L. Wood and K. Nassau, “The characterization of beryl and emerald by visible and infrared absorption spectroscopy,” American Mineralogist, Vol. 53, No. 5, 1968, pp. 777–800; Y. Hu and R. Lu, “Color characteristics of blue to yellow beryl from multiple origins,” Spring 2020 G&G, pp. 54–65) and possibly enhanced by neighboring Fe3+ (S. Saeseaw et al., “Geographic origin determination of emerald,” Winter 2019 G&G, pp. 614–646). The blue section exhibited an anisotropic band around 600 nm when viewing an e-ray oriented absorption spectrum, typical of aquamarine (Hu and Lu, 2020). The white color was caused by an isotropic absorption band ranging from 400 to 700 nm with a nearly identical absorption coefficient through all wavelengths.
Although seemingly opaque, when exposed to the polariscope’s intense light source, the white portion allowed the passage of light and showed no extinction under crossed polarizers, suggesting a polycrystalline composition.
Raman spectra were collected at room temperature using a Horiba Scientific LabRAM HR Evolution spectrometer coupled with an Olympus Scientific Solutions BX-41 microscope with a 50× magnification lens. The acquisition time was 120 seconds, grating: 500 nm. For this analysis, a 532 nm excitation laser was selected. Both sections exhibited major peaks around 321, 395, 520, 683, 1011, and 1066 cm–1 (figure 2). Minor peaks were observed at 448, 622, and 1141 cm–1. The spectra were compatible with beryl and, although clarity treatment was not observed, displayed relatively strong absorptions at approximately 1504 and 1567 cm–1 (again, see figure 2) that may suggest the presence of a filling agent (M.L. Johnson et al., “On the identification of various emerald filling substances,” Summer 1999 G&G, pp. 82–107). Additional Raman analysis with a spectral range of 100–3500 cm–1 is required to determine whether the peaks are indeed related to a filling substance.
Microscopic analysis revealed a well-defined aquamarine–white beryl boundary (figure 3, left). Channels parallel to the c-axis were also observed (figure 3, right).
The author is aware of similar aquamarine−white bicolor beryl from the state of Minas Gerais, but this was the author’s first encounter with such beryl reportedly from Brumado, Bahia.
