Aquamarine with Zigzag Growth Line Inclusions
A 55 ct cushion-cut aquamarine (figure 1, left) was recently submitted to Guild Gem Laboratories in Shenzhen for testing. This stone exhibited a very intense blue color accompanied by a subtle greenish secondary hue. A refractive index of 1.580–1.586 was obtained, together with a specific gravity of approximately of 2.71. Fourier-transform infrared (FTIR) and Raman spectroscopy confirmed its identity as beryl. The transmission FTIR spectrum exhibited distinct peaks at 2731, 2686, and 2641 cm–1 and a carbon dioxide–related signal at 2359 cm–1. Peaks at 3235, 3162, 3111, and 3021 cm–1 were assigned to the presence of water (figure 2, left). This collection of FTIR peaks has been reported in natural aquamarine, but no synthetic counterpart has been reported to show this pattern (I. Adamo et al., “Aquamarine, Maxixe-type beryl, and hydrothermal synthetic blue beryl: Analysis and identification,” Fall 2008 G&G, pp. 214–226). No organic-related peaks were found around the 2800–3200 cm–1 range, suggesting no clarity enhancement had been applied (L. Jianjun et al., “Polymer-filled aquamarine,” Fall 2009 G&G, pp. 197–199). Strong deep blue and light bluish green pleochroism (figure 1) was observed using a dichroscope. Similar beryl materials with a deep blue color have been reported in previous studies (Fall 2014 GNI, pp. 244–245; Fall 2019 GNI, pp. 437–439). The ultraviolet/visible/near-infrared spectrum (figure 2, right) showed a broad Fe2+-related band centered at around 835 nm and narrow absorption bands at 370 and 426 nm related to Fe3+ (D.S. Goldman et al., “Channel constituents in beryl,” Physics and Chemistry of Minerals, Vol. 3, No. 3, 1978, pp. 225–235; K. Schmetzer, “Hydrothermally grown synthetic aquamarine manufactured in Novosibirsk, USSR,” Fall 1990 G&G, pp. 206–211; Adamo et al., 2008). Using a polariscope equipped with a conoscope, the optic axis was observed parallel to the table along the long axis of the cushion shape. Further chemical analysis by energy-dispersive X-ray fluorescence showed a high iron content (around 13000 ppmw), which likely contributed to the saturated blue color (Y. Shang et al., “Spectroscopy and chromaticity characterization of yellow to light-blue iron-containing beryl,” Scientific Reports, Vol. 12, No. 1, 2022, article no. 10765).
Microscopic observation under darkfield illumination revealed fluid inclusions and minute voids. Under the table, a circular thin film with a strong light reflection was visible (figure 3). The image in figure 3 (left) was captured at an angle to the table of the aquamarine, since the thin film was easier to see under an oblique light source. Because beryl has imperfect cleavage along its basal plane {0001}, the space between the basal planes caused by initial cleavage was sufficient to form the thin film.
An interesting inclusion was observed only with oblique light: a distinct series of fluids resembling dots and broken lines. Higher magnification (figure 4) revealed that these zigzag lines consisted of discrete and minute fluid inclusions. Further observation along the optic axis confirmed that the planes were parallel to the c-axis of the aquamarine.
A previous study described similar inclusions in emeralds from Colombia as resembling a DNA double helix (Summer 2019 G&G Micro-World, p. 262). The authors have also encountered this type of inclusion before. Based on our observations, these helical inclusions spiral along the optic axis of the emerald. To our knowledge, this is the first time such helical inclusions have been reported in an aquamarine. This finding will help advance our understanding of the beryl family.
