The general topography at Lay-tha-anee-taw (Red Stone region) is characterized by unstable soil and eroded caverns, thus gem mining is difficult and dangerous. At the mining site in Lay-tha-anee-taw (1.485 meters above sea level) dark blue sapphires with dense silk are mined from syenite pegmatite deposit. Purplish-red rubies with dense silk are also mined from a secondary deposit using letkya-dwin
mining method. Many of these silky rubies and sapphires may be heat-treated to improve their transparency and luster. At the nearby area, spinels of all sizes and qualities are found. The majority of the rubies found are low quality, suitable only for cabochons.
Ref: Ted Themelis (2008) Gems & mines of Mogok, p. 173