On-dan-pyant, On-dan, Mogok Township, Pyin-Oo-Lwin District, Mandalay Region, Myanmar
The sapphires are found in nepheline syenite rocks, exposed as segregation, and in the alluvium. Mining methods areMost of the sapphires are opaque, very dark blue to black, highly fractured, non-gem quality without gemmological interest. Some of these sapphires show six-sided outline but most of them lack crystal form. Nearly all sapphires are characterized by dense black silk, which cannot be removed by heat-treatment. At the same localion opaque, low quality pink-red spinels are found.
Ref: Ted Themelis (2008) Gems and Mines of Mogok, p. 271