Sapphires of ‘teal’ colour from Pein-Pyit, East Mogok

By Dr. M.S. Krzemnicki, first published in Facette 29 (May 2024)

Figure 1: Paddy fields near the mining sites at Pein-Pyit in 2014, and three typical sapphires of slight to distinct greenish blue colour from that area about 10 km northeast of Mogok. Photo: M.S. Krzemnicki, SSEF.

The Mogok area in northern Myanmar has been known as a major source of rubies and other gems since historic times. Often referred to as the ‘MogokStoneTract’, this gem-rich area is located within the central part of the Mogok Metamorphic Belt which forms part of a larger metamorphic belt structure, extending for more than 2000 km from the Himalayan mountain range in the North to the Andaman Sea in the South. The Mogok area stretches about 25 km from East to West and about 10 km from North to South with the main townships Kyatpyin and Mogok located in the centre of the area. Gems are found at numerous localities and mining sites within this larger area mainly composed of upper amphibolite to granulite facies marbles, schists and gneisses which were intruded by various felsic to mafic igneous rocks (Phyo et al. 2023, see also article in this Facette on page 34).

Figure 2: Map of the Mogok Stone Tract indicating the location of the gem deposit at Pein-Pyit. Map slightly adapted from Phyo et al. 2019.
At Pein-Pyit, a village about 10km northeast of Mogok (Figures 1 & 2), mining of alluvial gem deposits on small stream banks and in paddy fields has been ongoing for many years, producing rubies, spinel, but mainly also sapphires of yellowish-green to greenish blue and greyish blue colour. The greenish blue colour of these sapphires is the result of a rather high iron concentration, predominantly present as ferric iron (Fe3+) and thus resulting in strong Fe3+ peaks in the absorption spectrum (Figure 3). Especially the high and broad Fe3+ peak at 450 nm has a major effect on the colour of sapphire, as it shifts the transmission window towards the green (local absorption minimum at about 480 nm). In some cases, the broad absorption band at about 560 nm (related to the Fe2+-Ti4+ intervalence charge transfer IVCT) is further reduced or nearly missing, resulting in green to yellowish green fancy sapphires from this same mining area near the village Pein-Pyit.
Figure 3: Absorption spectrum of a sapphire of slightly greenish blue colour from Pein-Pyit, Mogok area. Figure: M.S. Krzemnicki, SSEF.
Interestingly, these ‘teal’ coloured sapphires are occasionally quite large (50 ct and more) and of excellent clarity. They usually contain only few inclusions (Figure 4) such as tiny rutile needles, but geometric (fluid) platelets, step-like healing fissures, and diaspore exsolutions (‘ice flowers’) in fissures, features which are in many aspects similar to inclusions known from ‘classic’ Burmese sapphires (Gübelin & Koivula 2008; Kan-Nyunt et al. 2017; Soonthorntantikul et al. 2021).
Figure 4: Inclusions in these sapphires from Pein-Pyit. Magnification 50x. Microphotos: M.S. Krzemnicki, SSEF.

For quite some time, sapphires from Pein-Pyit were not much sought after, as they obviously fall outside the ‘royal blue’ colour range for which classic Burmese sapphires have been cherished in the past. However, this has changed in recent years, as new collectors with broader colour preferences have entered the market. Consequently, the sapphires from the Pein-Pyit area have gained much interest in the trade in recent years (Figure 5), mostly due to their Burmese origin combined with an attractive ‘teal’ colour, exceptional quality, and size.

Figure 5: Flat polished sapphire of 36 ct from Pein-Pyit before and after cutting into a beautiful hexagonal gem sapphire of 19 ct. The journey of this sapphire from pre-shaped to cut was documented by request of the client with a SSEF GemTrackTM report. Photo: J. Xaysongkham, SSEF.