Ruby From The Vatomandry Area Of Eastern Madagascar

(via Gemmology Queensland, Vol.5, No.3, March 2004)

For about a year, Thai gem merchants have been selling considerable amounts of ruby from a recently discovered alluvial source in central eastern Madagascar. The principal source of this ruby is an area about 15km south-west of the central coastal town of Vatomandry. Ruby from this deposit has several interesting features:
- A considerable proportion of the rough does not require heat treatment.
- Some of the ruby closely resembles premium Burmese ruby in color.

In the recently published July 2001 issue of The Journal of Gemmology (pp 409-416), Schwartz & Schemetzer have described the identifying features of this ruby. The authors research has revealed that although ruby from this deposit displays the conventional properties of ruby, their fluorescence was weak to medium for LWUV and inert to very weak for SWUV (due to their 0.1-0.7 wt% content of Fe³+).

Characteristic inclusions observed in specimens that had not been treated included:
- Twin lamellae oriented in two directions.
- Intersecting twin lamellae decorated by tube to needle-like masses of white boehmite particles.
- Short needles and twinned or elongated plate-like crystals of rutile that are oriented in three directions.
- No visible growth zoning.
- Clusters of small, colorless to whitish birefringent zircon crystals.
- A few large apatite crystals.
- Healed fractures of variable shapes.

Trace element analysis of Vatomandry ruby revealed that this ruby has a higher (0.1-0.7 wt%) iron content than Burmese ruby (0.005 wt%), and it contains more vanadium (0.005-0.07 wt %) that Thai-Cambodian ruby (0.01 wt%).

Further, the authors suggest that heat treatment of this ruby at low temperature (<1450°C) to remove any purplish overtone could be difficult to detect—particularly if the rubies only had rutile and clusters of zircon as their only inclusions.

The authors conclude that this ruby’s unique trace element chemistry, combined with its lack of growth zoning, short rutile needles, and clusters of small zircon, will allow its discrimination from ruby of similar color but differing provenance such as Burma and Thailand-Cambodia.