are found in nepheline syenite rocks, exposed as segregation, and in the alluvium. Mining methods are and lebin-dwin.
Most 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