The gem mining area at Bernardmyo village and surrounding vicinity was in operation before the commencement of the British occupation. These mines are located at high elevations, where the topography and geology are distinctly different from those of the Mogok valley area.
Around 1910, a large deposit of blue sapphires was discovered in this area, where considerable quantities of these stones were already being mined by the Burma Ruby Mines Co. Ltd. Few of these blue sapphires were of fine quality, magnificent in color and impressively large. But the majority of these sapphires were far of a less attractive dark blue color with a prominent greenish tinge that gave them an undesirable overall appearance. These dark blue sapphires were marketed in Mogok and elsewhere in 1913, creating a generally negative reputation for Mogok blue sapphires which continued well into the 1930s.
Since the early 1990s many of these dark blue sapphires have been heat-treated to lighten their dark blue/green color and improve their appearance, but the results from the treatment have not been very satisfactory.
Just east of Bernardmyo village, the famous peridot mines at Myasein Taung near Pyaung-gaung and Zalat-taung continue to produce peridot. Many other gems and minerals are found in the general area at Bernardmyo.
The principle rocks found at the general area at Bernardmyo are peridotite-dunite, occasionally intruded by biotite microgranite (Kabaing granite); other rocks found are leucogranite, syenite, marble, calc-silicate rocks and gneiss. - Ted Themelis (2008) Gems & mines of Mogok

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