Lab Notes Gems & Gemology, Summer 2019, Vol. 55, No. 2

Dyed Serpentine Imitating Sugilite

Two dyed serpentine beads.
Figure 1. These two beads, 6.96 ct (left) and 2.25 ct (right), were identified as dyed serpentine. Photo by Diego Sanchez.

The Carlsbad laboratory recently received a parcel of mottled purple beads (figure 1). A 2.25 ct translucent reddish purple broken bead from this parcel (shown on the right in figure 15) was examined for an identification report. At first glance, based on the color and structure, the sample resembled sugilite. Standard gemological testing revealed a refractive index of 1.56, a specific gravity of 2.71, weak orange fluorescence in both long-wave and short-wave UV, and a dye band with a handheld spectroscope. Sugilite has an RI of 1.607–1.610 and an SG of 2.74, and may show a concentrated band at 600 nm that can be confused with a dye band. The bead showed uneven color and a fibrous structure under the microscope (figure 2). There were no obvious dye concentrations, but the orange fluorescence and dye band in the spectroscope indicated the presence of dye. By performing a simple acetone test, we were able to prove that the material had been dyed. A light pink streak was examined after rubbing the test sample on a tissue soaked with acetone. The specimen’s infrared spectrum was not consistent with sugilite but ended up matching well with serpentine. Chemistry collected via laser ablation–inductively coupled plasma–mass spectrometry (LA-ICP-MS) was consistent with serpentine, ruling out the possibility of sugilite.

Fibrous internal structure of serpentine resembles that of sugilite.
Figure 2. The fibrous internal structure of the specimen resembling sugilite was actually consistent with serpentine. Photomicrograph by Jessa Rizzo; field of view 4.11 mm.

Without advanced testing, it would have been difficult to conclusively identify this material as serpentine. This is the first time reddish purple dyed serpentine imitating sugilite has been examined in the Carlsbad laboratory, and gemologists should be aware of this imitation when examining sugilite.

Jessa Rizzo is a staff gemologist at GIA in Carlsbad, California.