Mogok is not the only active ruby mining area in Burma. Stones from the  Mong Hsu  deposit, is located in  Myanmar's Shan State,  northeast   of   Taunggyi,   first began appearing in Bangkok in mid 1992. Since that time they have  completely dominatedthe world's ruby trade in sizes of less than 3 cts. Indeed, 99% of all the rubies traded today in Chanthaburi (Thailand) are from Mong Hsu.In terms of quality, Mong Hsu rubies cannot compete with Mogok stones.Before heat treatment,the Mong Hsu ruby is certainly an "ugly stone".

There are two major problems with those stones:
The first is dense silk clouds and a strong purplish color, making most stones look
like low-grade.   Ordinary heat-treatment removes the blue, as well as removing silk, making the final product a rich, clear red.
Most Mong Hsu stones are heavily fractured.Some specialists have masked the cracking by healing the cracks with a flux of barax...
See the excellent article of   R.W. Hugues on  internet. 

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