The inclusion scene contained several elements that are commonly present in blue sapphire, such as rutile and clusters of zircon crystals (both identified using Raman spectroscopy; figure 2). A large transparent quartz crystal (again, see figure 2) was the only inclusion that would be uncharacteristic for blue sapphire. Growth tubes resembled those seen in corundum; however, these could be distinguished by the intersection angles. Corundum growth tubes intersect at 60°–120°; in kyanite, they intersect at 90°. Angular blue zoning confined above a colorless zone in the bottom half of the pavilion also resembled that seen in sapphire, but it did not show corundum's characteristic hexagonal growth features.

In the visible spectrum, the kyanite displayed red transmission and corresponding lines in the desk-model spectroscope due to chromium content, which can also appear in Cr-rich blue sapphires. The 450, 460, and 470 nm iron lines that are occasionally present in blue sapphire were absent, but weak 430 and 445 nm lines caused by Fe³⁺ substituting for Al³⁺ (see Spring 2002 G&G Lab Notes, pp. 96–97) could have been mistaken for corundum iron lines.

Advanced testing using UV-Vis spectrophotometry further highlighted the similarities between blue sapphire and kyanite spectra. This was particularly evident in the 380–385 nm and 430–450 nm regions, where Fe³⁺ substitutes for Al ³⁺, as well as the presence of a broad 610 nm band, which is responsible for the blue color and caused by the Fe²⁺–Fe³⁺ charge transfer for both kyanite and blue sapphire.

The many similarities had led the client to believe the stone was a blue sapphire. However, the RI, SG, and closer examination of the inclusions provided a correct identification as kyanite.

Alethea Inns
GIA Laboratory
Carlsbad, California