Unusual Solid Inclusions in Flame-Fusion Ruby
The author recently examined unusual dark red solid inclusions in a flame-fusion laboratory-grown ruby. Standard gemological testing yielded a refractive index of 1.760–1.768, a chromium emission line in red using a handheld spectroscope, medium red fluorescence under long-wave UV, and weak red fluorescence under short-wave UV. These properties were consistent with ruby. Microscopic examination using brightfield illumination revealed numerous dark red inclusions (figure 1) that resembled crystals commonly seen within natural corundum.
Furthermore, magnification showed characteristic internal features of flame-fusion ruby such as curved striae and gas bubbles. The strong curved growth lines and numerous gas bubbles (figure 2) suggested that this was an early type of flame-fusion ruby. Although flame-fusion corundum is widely available in the marketplace, it is unusual to encounter a specimen containing natural-looking dark red solid inclusions. These inclusions are possibly unmelted alumina powder, and the fact that Raman was unable to identify something other than alumina supports this (E.J. Gübelin and J.I. Koivula, Photoatlas of Inclusions in Gemstones, Volume 3, Opinio Publishers, Basel, Switzerland, 2008).
Identification of the natural or laboratory-grown origin of a stone with this type of natural-looking inclusion can be difficult. Careful observation is needed to correctly identify such a specimen’s origin.
