Ohn-bin-ywe-htwet (Coconut Tree mine), Mogok Valley, Mogok Township, Pyin-Oo-Lwin District, Mandalay Region, Myanmar
The locality covers the northeastern part of the Mogôk valley at the base of Oak-saung-taung. It is a secondary deposit, a large basin where numerous gems originated from the hills of Dattaw, Oak-saung-taung and Hta-yan-sho were accumulated on the basin floor.By the end of 2004, after most of the alluvium was mined out, the mining operations continued at the skarns and at the marbles lying at the bottom of the pit, where rubies and spinels are found in the primary rock comprising different types of marble; other gems are found in the skarns.
Mining is performed using myaw-dwin and large mechanized open-pit schemes.
Some translucent rubies are exceedingly silky, although not in sufficient amounts to produce a star. These silky rubies are suitable for heat treatment to reduce or remove their intense amounts of silk, thus improving their transparency and color suitable for faceting.
The impurity of rubies is quite high and there is a considerable variety in their chemical composition and in the types of guest crystals found in them, with corresponding variety in the results of heat treatment. Corundums of changing or shifting color can also be found, usually small, with their color changing from greenish under fluorescent light to red/pinkish in incandescent light.
Ref: Ted Themelis (2008) Gems and Mines of Mogok, p. 206