Pink Euclase
GIA’s Tokyo laboratory had the opportunity to examine an orangy pink faceted stone, weighing 4.08 ct and measuring 13.00 × 9.90 × 5.23 mm, with a hydrostatic specific gravity of 3.09 (figure 1). It had optically biaxial features based on trichroic colors of yellowish orange, pale orange, and orangy pink, and refractive index values of 1.652–1.671 with a birefringence around 0.019. The stone was inert to ultraviolet light sources.
Transparent platy crystals and straight graining were observed under the microscope (figure 2). There were no signs of treatment such as coating or clarity enhancement. Gemological properties matched euclase, which was confirmed by comparing the Raman spectrum with the RRUFF database (reference spectrum R050032).
Euclase is one of several collector’s minerals discovered in the eighteenth century in Brazil (D. Atencio, “The discovery of new mineral species and type minerals from Brazil,” Brazilian Journal of Geology, Vol. 45, No. 1, 2015, pp. 143–158) and classified as a beryllium aluminum hydroxide silicate, with an ideal chemical formula of BeAlSiO4(OH). Crystals are found worldwide and occur in a range of colors such as colorless or white, blue, green, and yellow (e.g., S.M. Stocklmayer, “A new occurrence of euclase in Western Australia,” Australian Journal of Mineralogy, Vol. 18, No. 2, 2017, pp. 39–44). Gem-quality pink euclase was first reported in 2018 (M.B. Leybov, “Denver 2018: ‘Minerals of Mexico,’” Mineralogical Almanac, Vol. 24, No. 1, pp. 58–63), and this color is considered rare.
The causes of color for euclase have been discussed in many studies (e.g., E. Gübelin, “Sapphire-blue euclase, a new collector’s gem,” Winter 1978-1979 G&G, pp. 104–110; M. Mattson and G.R. Rossman, “Identifying characteristics of charge transfer transitions in minerals,” Physics and Chemistry of Minerals, Vol. 14, No. 1, 1987, pp. 94–99; S. Stocklmayer, “Blue euclase from Zimbabwe – a review,” Journal of Gemmology, Vol. 26, No. 4, 1998, pp. 209–218). According to these three previous studies, blue to green color in euclase is believed to be caused by an Fe2+-Fe3+ charge transfer and Fe2+-Ti4+ transitions or the presence of trivalent iron. Moses et al. (Summer 1993 Gem Trade Lab Notes, pp. 125–126) reported a greenish blue euclase colored by chromium. Gilles-Guéry et al. (“Mn3+ and the pink color of gem-quality euclase from northeast Brazil,” American Mineralogist, 2021, in press) determined that pink coloration due to the absorption between green to blue with two broad peaks at 470 and 540 nm is caused by Mn3+, while the orange hue is related to the rising slope in the UV domain combined with an additional absorption peak at 381 nm originating from Fe3+. This stone showed a UV-Vis absorption spectrum (figure 3) similar to the pattern due to Mn3+ reported by Gilles-Guéry et al. (2021), and trace Mn concentrations around 60 ppm were detected by LA-ICP-MS. These characteristics suggest that the orangy pink color seen in this stone is possibly caused by manganese. This is the first such example examined at GIA.
