Win-hta-yan (Fence), Marble Ark, Mogok Township, Pyin-Oo-Lwin District, Mandalay Region, Myanmar
The mining area is situated just to the SW of the Pyaung-pyin village. The area is a large sinkhole where many gems had accumulated on the valley floor, derived from surrounding hillsides. The area is also characterized by numerous marble exposures and small scale karst topography.For many years these mines produced fine quality and large-size rubies and blue sappires, often asteriated. Fully transparent, colorless to near-colorless, violet/purple, yellowish, yellow sapphires and spinels of various colors are frequently recovered. Color-change and color-shift sapphires are also found here. Their color is described as reddish-bluish top purplish, shifting from lighter to darker blue when viewed under different lighting conditions.
Ref: Ted Themelis (2008) Gems and Mines of Mogok, p. 235