Rubies with Unusual Characteristics

Since November 2007, the Gem Testing Laboratory of Gem and Jewelry Institute of Thailand (GIT-GTL) has received a number of ruby samples said to be originated from Madagascar. Microscopic examination reveals some unusual internal features, such as wispy veil-like fingerprints filled with quite dense fluid, numerous tiny clusters of colourless inclusions and isolated colourless crystal inclusions which could not yet be identified by Raman spectroscopic technique (Figs.1-2).

All of those stones show strong red luminescence in LWUV. The chemical analyses by EDXRF indicate rather high chromium contents (0.43-1.54 wt% Cr2O3), moderate-to-high iron contents (0.04-0.49 wt% Fe2O3), very low-to-low titanium (0.007-0.014 wt% TiO2) and vanadium (0.000-0.016 wt% V2O5) contents, and moderate-to-high gallium contents (0.006-0.046 wt% Ga2O3) in those samples.

The absorption spectra in IR range show no OH-related peaks in those samples. In contrast the UV-Vis-NIR absorption spectra show not only the strong Cr absorption bands and lines as normally expected for a ruby sample but also an unusual broad absorption band centered at around 900 nm, which normally appear in basaltic-related sapphires. This extra absorption band may possibly related to Fe2+ /Fe3+ charge transfer in which its intensity seems to be directly related to the amount of Fe in the sample (Figs. 3-5).

This unusual absorption band has not been so far observed in natural rubies, not even in rubies containing equally high Fe contents from basaltic-type origin (e.g., about 0.442 wt% from Africa; see Fig. 6).

With such the suspicious internal features including undeterminable inclusions and the presence of absorption band at around 900 nm, these, to us, are quite ambiguous evidences and are uncommon characteristics being found in a natural ruby Because of the aforementioned reasons, the GIT-GTL needs to make further in depth investigations on those samples. We, therefore, regret to temporarily suspend issuing of the report on the authenticity of this type of ruby samples for the time being. We remain in touch with our clients soonest on the progress of our investigations.

We would also request stone dealers and/or individuals who may come across or have experiences with such ruby samples or rough of the same material to contact us or one of members of LMHC. So far the GIT-GTL still has not yet received any information related to our requests. We thank for your kind cooperation and responsibility.