Gem News International Gems & Gemology, Summer 2014, Vol. 50, No. 2

Assemblage of Synthetic Ruby in Calcite Matrix

Nazar Ahmed and Sutas Singbamroong

Synthetic ruby in matrix
Figure 1. This synthetic ruby was fixed in a white and cream-colored matrix and represented as natural ruby. Photo by Sutas Singbamroong, Dubai Central Laboratory.
Recently, the Dubai Central Laboratory received a white and cream-colored rough sample for identification (figure 1). The 124.4 × 107.7 × 65.8 mm, 5917.35 ct specimen had two openings, the larger one about 25 mm long and 10 mm wide. A hexagonal red stone embedded in the matrix could be seen through these openings (figure 2). Only the prism side was visible, and the rough concealed both terminations.

Synthetic ruby in matrix under incandescent light
Figure 2. The synthetic ruby was embedded in a calcite matrix, seen here under incandescent light. Photo by Nazar Ahmed, Dubai Central Laboratory.
The red stone’s refractive index and specific gravity were impossible to determine, and only a very small portion was visible for obtaining other information. A spectroscope was the only option, and the stone clearly showed a ruby spectrum. It also displayed strong and medium red reactions to long- and short-wave UV radiation, respectively. Microscopic examination with fiber-optic light revealed a group of round gas bubbles and tiny fractures, but curved striae were not seen. These properties indicated a flame-fusion synthetic ruby cleverly embedded in matrix to imitate natural ruby.

Raman spectroscopy identified the matrix as calcite. Close examination indicated that the cream-colored side of the stone had been drilled to make a hole for inserting the synthetic ruby. After the drilled area was sealed with a mixture of glue and calcite powder, two openings were cut to reveal the synthetic ruby inside. Under long-wave UV radiation, the drilled area showed strong greenish blue fluorescence, while the rest of the stone was inert or exhibited a light greenish blue reaction (figure 3).

Synthetic ruby under long-wave UV radiation
Figure 3. Under long-wave UV radiation, the drilled area showed strong greenish blue fluorescence. Photo by Nazar Ahmed, Dubai Central Laboratory.
These types of artificial assemblages should alert traders to exercise caution when purchasing rough stones, especially in newer, less established markets. 

Nazar Ahmed (nanezar@dm.gov.ae) is a principal gemstone analyst, and Sutas Singbamroong is a senior gem specialist, in the Gemstone Unit, Dubai Central Laboratory, United Arab Emirates.