Micro-World Gems & Gemology, Winter 2017, Vol. 53, No. 4

Tourmaline Crystals on Burmese Ruby

Tourmaline and calcite on Burmese ruby.
Bluish green tourmaline crystals and white calcite on a Burmese ruby. Photo by Charuwan Khowpong; field of view 2.48 mm.

During a GIA field expedition to Mogok, Myanmar, a tiny but interesting sample was acquired. This 0.552 ct ruby was purchased from local Kanase miners who process the tailings of the larger mines in the Kyatpyin Valley, just west of the town of Mogok. The ruby is associated with pure white calcite and bluish green tourmaline (see above).

Many rubies form in marble, especially in the deposits related to the Himalayan orogeny (Afghanistan, Tajikistan, Myanmar, and Vietnam), so calcite as an inclusion or associated mineral with these gems is common. While tourmaline in combination with ruby is not unheard of, it is a relatively unusual combination. Laser ablation–inductively coupled plasma–mass spectrometry (LA-ICP-MS) chemical analysis showed that the tourmaline was a Na-Mg-rich dravite. Tourmalines are of great interest to geologists because their isotopic and trace element composition are potentially strong indicators of the formation environment of the tourmaline and the associated minerals, in this case ruby.

Wim Vertriest is supervisor of field gemology, and Charuwan Khowpong is a colored stones analyst, at GIA in Bangkok.