The locality is situated in the foothills of the Let-nyo-taung. The principle rocks of Ohn-gaing are syenite, marble, gneiss.
Rubies and
sapphires, 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,
spinel,
garnet,
amethyst and
schorl are also found in the alluvium. In a small skarn (between gneiss and marble) situated at the edge of Ohn-gaing village,
sinhalite,
serendibite, amblygonite-
montebrasite,
jeremejevite and other rare minerals are found.
Ref: Ted Themelis (2008) Gems and Mines of Mogok, p. 214
Gemstone List