Imitations d’aigues-marines présentant une altération « poilue »

A batch of 5 samples, sold in 2010 as a set of aquamarines in Madagascar, caught the eye of our team. Although these stones were kept in a safe away from light and humidity/temperature variations for around ten years, a thin fibrous white layer appeared on all of the so-called aquamarines. To date, this type of transformation has not yet been described in the gemological literature. The use of gemological characterization techniques coupled with laboratory characterization techniques (XRD, SEM/EDX, UV-Vis absorption) made it possible to elucidate the mystery of the nature of these stones and the associated deposit. These samples are in reality glasses of soda-silicate composition whose bluish-green color, to imitate aquamarine, is associated with the presence of iron (mainly Fe2+). As for the fibers, these were identified as sodium hydroxycarbonate [Na3H(CO3)2(H2O)2]. The observation of numerous cracks in the sample as well as the chemical composition of the film suggests that the samples are not stable over time, and their surface is modified. The presence of water and CO2 coupled with the sodium of this porous sample is fertile ground for the appearance of these films and hairs on the surface.