A strong hexagonal blue core can be seen in this ruby from Mong Hsu, Burma (Myanmar). These blue zones are a common feature of Mong Hsu ruby, and are often removed with heat treatment.
Natural Ruby • Myanmar (Burma); Mong Hsu • Enhancements: None Detected (None) • Lighting Conditions: Dark Field
Photographer: E. Billie Hughes •
Image Number: A-003-5279-1 • Field of View = 3 mm • Date Posted: 18 November 2019
Smith, C.P. and Surdez, N. (1994) The Mong Hsu ruby: A new type of Burmese ruby. JewelSiam, Vol. 4, No. 6, Dec–Jan, pp. 82–98; RWHL.
Hughes, R.W., Manorotkul, W. et al. (2017) Ruby & Sapphire: A Gemologist's Guide. Bangkok, Lotus Publishing, 816 pp.; RWHL*.