gems, glyptic, engraved gems, agate, cameo, intaglio, pyrite

A string of beads (Figure 31a) was recently submitted to the authors’ laboratory for verification of whether the stones were sapphire. The strand comprised 112 semi-transparent blue rondelles measuring 6.5–6.7 mm in diameter, with a total length of 40.5 cm and a weight of 168.88 ct (33.77 g). The rondelles exhibited a colour that could be described as ‘sapphire blue’, which led the client to believe they were sapphire. Furthermore, the overall colour distribution appeared uneven, and the material showed distinct colour zoning—features also observed in some natural sapphires. The material was identified as kyanite using Raman spectroscopy (Magilabs GemmoRaman-532SG with a 532 nm laser). Gem-quality blue kyanite is known from various sources (e.g. Nepal since 1995), and the potential for confusion with sapphire has been noted previously (e.g. Henn & Schollenbruch 2012). Beyond differing refractive index and specific gravity values, microscopic characteristics can help differentiate kyanite from blue sapphire—for example, the presence of cleavage cracks that often display prominent iridescent effects (cf. Henn & Schollenbruch 2012), as observed in some of the current bead samples.