Gem News International Gems & Gemology, Summer 2016, Vol. 52, No. 2

Tremolite and Diopside Bead with Unusual Texture and Color

Yanjun Song, Yungui Lui, Xiaoqiang Xia, and Juan Zhao

Barrel-shaped bead with unusual texture and color.
Figure 1. This 6.39 gram barrel-shaped bead was unusual for its texture and color. Photo by Yanjun Song.

In recent years, Buddhist prayer beads have become increasingly popular in Chinese jewelry. These beads are made into a variety of shapes from many kinds of gem materials.

At the 2015 China International Jewelry Fair in Beijing, a barrel-shaped bead with unusual green and white color (figure 1) attracted our interest. The bead weighed 6.39 g and measured approximately 30.5 × 10.8 × 10.5 mm. The hydrostatic specific gravity (SG) was 3.05, but it was difficult to obtain individual spot RIs from the white and green areas. The entire sample was inert to both long-wave and short-wave UV. The infrared reflectance spectrum (figure 2) of the whitish mineral indicated tremolite, with characteristic peaks at 1093, 988, 902, 743, 676, 529, and 470 cm–1, while the greenish mineral’s spectrum matched that of diopside, with peaks at 1060, 979, 921, 681, 511, and 410 cm–1.

IR spectra of bead.
Figure 2. IR spectroscopy identified the whitish mineral in the bead as tremolite (red trace, peaks at 1093, 988, 902, 743, 676, 529, and 470 cm–1) and the greenish one as diopside (blue trace, peaks at 1060, 979, 921, 681, 511, and 410 cm–1). The spectra are offset for clarity.

Raman spectra of the white and green areas (figure 3) were obtained using 785 and 532 nm laser excitation, respectively. Peaks at about 1058, 1028, 754, 673, 394, and 224 cm–1 indicated tremolite, while those at 1013, 667, 559, 393, and 326 cm–1 were consistent with diopside.

Raman spectra of bead
Figure 3. Raman spectra of the barrel-shaped bead. Left: Peaks at 224. 394, 673, 754, 1028, and 1058 cm–1 were indicative of tremolite. Right: Peaks at 326, 393, 559, 667, and 1013 cm–1 were consistent with diopside.

Tremolite and diopside are common gem materials in the jewelry trade. Both occur in nephrite, where tremolite is the main mineral and diopside is an accessory mineral. This was the first time we had encountered diopside rather than tremolite as the major mineral when both occurred within the same sample.

Yanjun Song is with the School of Earth Sciences and Resources at Chang’an University in Xi’an, China. Yungui Lui is with the College of Gemstone and Material Technology at Shijiazhuang University of Economics, China. Xiaoqiang Xia is with the Beijing Institute of Gemology. Juan Zhao is with the Xi’an Center of Geological Survey (CGS), China.