Lab Notes Gems & Gemology, Winter 2013, Vol. 49, No. 4

Stellate Zircon Inclusions in Vivid Purple-Pink Morganite

IMG - WN13 LN 157448 636x358
Figure 1. Stellate clusters of zircon needles were observed in this purple-pink morganite. Vertical field of view 0.58 mm. Photomicrograph by Nathan Renfro.
The Carlsbad laboratory recently examined a 4.95 ct vivid purple-pink morganite (figure 1). In addition to its saturated color, the stone was particularly noteworthy because of the inclusions it contained. Microscopic examination revealed numerous stellate inclusions, each with many delicate tapered legs.

Gemological properties revealed an RI of 1.577–1.583 and a hydrostatic SG of 2.73. It did not show fluorescence under either long- or short-wave UV. All of these properties were consistent with beryl, which was further confirmed by FTIR and Raman spectroscopy.

Inclusions in the stone showed an interesting starburst pattern, with thin needles radiating from a central point of nucleation. Viewed with polarized light, the needles exhibited birefringence. A sub-adamantine luster was observed where some of the needles broke the surface (figure 2). Raman spectroscopy identified the inclusions as zircon, consistent with our initial observations. Zircon inclusions are occasionally found in pegmatitic beryl, but they usually occur as prismatic or rounded crystals that cause damage to their host due to zircon’s relative instability (E.J. Gübelin and J.I. Koivula, Photoatlas of Inclusions in Gemstones, ABC Edition, Zurich, 1986, p. 197).

IMG - WN13 LN 157447 636x358
Figure 2. The needle-like zircons showed a sub-adamantine luster when examined using reflected light. The largest surface-breaking needle measures approximately 10 microns in the longest cross-sectional direction. Photomicrograph by Nathan Renfro.
In addition to the zircon clusters, the stone also contained fluid inclusions, transparent crystals, particulate clouds, and singular needles. The distinctive morphology of the zircon inclusions, coupled with the vivid purple-pink color, create a rather unique gemstone.

Tara Allen is a staff gemologist, and Nathan Renfro is analytical manager of gem identification, at GIA's laboratory in Carlsbad, California.