Micro-World Gems & Gemology, Winter 2022, Vol. 58, No. 4

Volcano-Shaped Internal Feature in Trapiche-Like Sapphire

Xiaojing Lai and Suqin Xia

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Figure 1. Each of these trapiche-like sapphires from Changle, Shandong Province, has a brown-black hexagonal core in the center and six white radiating arms. Three of the four sample slices weigh ~3.1 ct with a thickness of ~2.1 mm; the sample slice on the bottom right weighs ~0.7 ct with a thickness of ~1 mm. Photos by Suqin Xia.
 
Figure 1. Each of these trapiche-like sapphires from Changle, Shandong Province, has a brown-black hexagonal core in the center and six white radiating arms. Three of the four sample slices weigh ~3.1 ct with a thickness of ~2.1 mm; the sample slice on the bottom right weighs ~0.7 ct with a thickness of ~1 mm. Photos by Suqin Xia.

Trapiche-like sapphires with hexagonal color zoning have been found in the Changle area of Shandong Province, China. Samples examined by the authors possessed a brown-black hexagonal core and a distinct six-rayed pattern (figure 1). The six rays or fibrous arms were oriented perpendicular to the sides of the core and the hexagonal growth structure. Graphite was randomly distributed in the dark core region in this sapphire, identified by Raman spectroscopy.

Figure 2. Inclusions along the white arms of trapiche-like sapphire. A: Thin-film inclusions display colorful interference colors under reflected light. B: Triangle-shaped fissures, which are perpendicular to the crystallographic <i>c</i>-axis, resemble overlapping hills, including a volcano just right of center. These fissures show spectral interference colors under reflected light. C: In transmitted light, the pattern of inclusions resembles a Chinese landscape painting with a volcano in it. Photomicrographs by Xiaojing Lai; fields of view 0.30 mm (A) and 0.15 mm (B and C).
 
Figure 2. Inclusions along the white arms of trapiche-like sapphire. A: Thin-film inclusions display colorful interference colors under reflected light. B: Triangle-shaped fissures, which are perpendicular to the crystallographic c-axis, resemble overlapping hills, including a volcano just right of center. These fissures show spectral interference colors under reflected light. C: In transmitted light, the pattern of inclusions resembles a Chinese landscape painting with a volcano in it. Photomicrographs by Xiaojing Lai; fields of view 0.30 mm (A) and 0.15 mm (B and C).

Through further microscopic observation, we found that these fibrous arms were composed of thin-film fluid inclusions and fine fissures generally parallel to their elongation direction (figure 2). Many of these inclusions were two-phase, containing both gas and liquid, and a few were gas-liquid-solid three-phase. Interestingly, the fissures were triangular, scalloped, striped, or irregular in shape and about 10 to 40 μm in size, with spectral interference colors (figure 2A). With overhead lighting, the internal features presented a dramatic scene reminiscent of a post-eruption volcano surrounded by overlapping hills and rivers (figure 2B). In transmitted light, however, the same features resembled a Chinese landscape painting, and the previous “rivers” looked more like clouds surrounding the volcano and hills (figure 2C). The internal features found in this sapphire are interesting to gemologists both scientifically and artistically.

Xiaojing Lai and Suqin Xia are affiliated with the Gemmological Institute at the China University of Geosciences in Wuhan, China.