Star Beryl
Asterism is not a common phenomenon in beryl species, but it has previously been reported in emerald and aquamarine (K. Schmetzer et al., “Asterism in beryl, aquamarine and emerald – an update,” Journal of Gemmology, Vol. 29, No. 2, 2004, pp. 65–71; Fall 2015 Gem News International, pp. 334–335). Recently, the author observed several star black beryl bead bracelets purchased from a Chinese e-commerce platform. For this report, four beads with noticeable asterism were collected for testing. The material was called “Devil Blue” aquamarine. The beads ranged from 9.11 to 9.47 mm in diameter and displayed a star phenomenon.
Of the four beads, two had six-rayed stars with arms intersecting at 60° angles (figure 1, left) and two had twelve-rayed stars with two sets of six-rayed stars located in the same concentric point but with different orientations—the two stars were offset by approximately 10° (figure 1, right). Gemological testing of the beads provided the following characteristics: a hydrostatic specific gravity varying from 2.67 to 2.73, a spot refractive index of 1.57, an inert reaction under long-wave and short-wave UV, and no diagnostic absorption spectrum. These properties were consistent with beryl. Raman analysis confirmed the material was beryl.
Under the microscope, we observed numerous needle inclusions oriented perpendicular to the c -axis and parallel to the three a-axes, which caused the asterism (figure 2). Moreover, the needles were concentrated as layers, forming multiple parting planes (figure 3) parallel to the basal pinacoid plane in all beads. This parting, combined with the presence of twelve-rayed stars, suggested that the growth orientation of this beryl was changing during the growth process. Additionally, the samples also showed an intersecting structure (figure 2) with angles of 120°/60° that resembled part of the hexagonal growth structure previously observed on the pinacoid of an aquamarine (Spring 2022 G&G Micro-World, pp. 70–71). This structure highlights that the asterism is oriented perpendicular to the c -axis, allowing the easy determination of this direction in translucent to opaque beryl.
