Cat’s-Eye Kornerupine
A dark, translucent, yellowish green oval cabochon (figure 1) was recently submitted to the New York lab for identification. The 1.44 ct stone displayed an intense chatoyancy. With a spot refractive index reading of 1.67 and a hydrostatic specific gravity of 3.32, the stone was identified as kornerupine, a rare borosilicate mineral found in boron-rich volcanic and sedimentary rocks that have undergone metamorphism (http://rruff.info). Raman spectroscopy confirmed the identification.
Cat’s-eye kornerupine is an extremely rare gemstone. Its chatoyancy is caused by rutile and graphite inclusions (H.N. Lazzarelli, Gemstones Identification: Blue Chart, 2010, www.gembluechart.com). However, we were unable to identify the needles in this stone using Raman spectroscopy. Fiber-optic illuminated magnification exposed dense clusters of these needles, some displaying iridescence (figure 2). This was GIA’s first encounter with this material in more than a decade.
