Hanamataw-lay (Royal Small Sister), On-dan, Mogok Township, Pyin-Oo-Lwin District, Mandalay Region, Myanmar
Blue sapphires are found in syenite pegmatite (plumasite-like) throughout the Hanamataw-lay range, often with non-gem quality tourmaline and mica. In the primary deposit ruby, spinel and chondrodite are found in different types of marble.Most sapphire crystals show deep horizontal striations and rhombohedral parting. They are highly fractured, with pronounced colour zoning and their colour range from light tp dark blue. Purple, purple-blue and black sapphires are also found. An important feature is the "white silk" displayed in most specimens. The silk is thick, dense and distributed throughout the host substance, often exhibiting a 6-ray star. In some cases the "white silk" may be removed by heating, thus the clarity is improved.
Ref: Ted Themelis (2008) Gems and Mines of Mogok, p. 272