Quarterly Crystal: Columbite(?) in Beryl
Those in the gem and mineral community can appreciate the near-perfection of a beautifully crystallized mineral specimen or a well-cut gemstone. But these surfaces are only the exterior, covering a complex, multilayered story within. These internal contents often remain unknown unless we choose to explore below the surface. Somewhat like trees and their rings, minerals and gems form as concentric, typically crystallized layers, recording the developmental details within each layer through changes in temperature, pressure, and chemistry. While some of these growth details are submicroscopic and remain hidden during microscopic observation, other features such as mineral inclusions and encapsulated fluids are waiting to be discovered. In a very real sense, inclusions and their developmental sequencing in their host gems and minerals are descriptions of mineralogical genetics.
Researchers focused specifically on inclusions usually cannot outbid serious gem and mineral collectors for crystals and fashioned gems with interesting internal targets. As a result, many such “gems” end up in private collections, and their inclusions are rarely, if ever, fully documented. This is a tremendous missed opportunity, because inclusions contain geological information that tells a story about themselves and their host.
For this issue’s Quarterly Crystal, we recently had the opportunity to document a well-formed gem-quality, transparent, very light greenish blue terminated hexagonal crystal of aquamarine, with a small amount of light brown matrix at the base and a clearly visible inclusion cluster at the near center (figure 1). The aquamarine was obtained from Muntazir Mehdi of Shad Fine Minerals International in Gilgit-Baltistan, Pakistan. The geographic source was reportedly the Kharguluk mine in Baltistan Province.
At 56.00 ct with corresponding measurements of 26.36 × 16.09 × 15.02 mm, this aquamarine played host to an easily eye-visible tight cluster of randomly arranged dark reddish brown to black bladed crystals (figure 2) that resembled the mineral columbite-(Mn), Mn2+Nb2O6, as shown by E.J. Gübelin and J.I. Koivula (Photoatlas of Inclusions in Gemstones, Volume 2, Opinio Verlag, Basel, Switzerland, 2005, pp. 263, 319).
Micro-Raman has significantly reduced the time required to instrumentally identify many inclusions. Some inclusion identifications that once took hours can now be made in a matter of minutes using this technique. The Raman instrument can also analyze some subsurface inclusions at depths of more than a millimeter in certain favorable instances, which means inclusions do not need to be exposed to the surface.
After several Raman attempts from different directions, we realized that destructive analysis would be needed to clearly identify the inclusion cluster deep within this stone. Due to the value of this inclusion specimen, we opted to forgo destructive analysis and keep the beryl crystal intact for future gemological exploration.
