The locality is situated in the foothills of the Let-nyo-taung. The principle rocks of Ohn-gaing are syenite, marble, gneiss. Rubies
, small to medium in size (usually not exceeding 3 carats) of faceting and cabochon grades are mined in lebin (lebin-dwin) and open-pit mining schemes. Good-quality star sapphire
, low-quality star ruby
are also found in the alluvium. In a small skarn (between gneiss and marble) situated at the edge of Ohn-gaing village, sinhalite
and other rare minerals are found.
Ref: Ted Themelis (2008) Gems and Mines of Mogok, p. 214