Often chalky shortwave fluorescence is a sign of heat treatment in sapphire, but some stones from Madagascar, like this one, show a superficially chalky patch that is not associated with heat treatment.
Natural Sapphire • Madagascar • Enhancements: None Detected (None) • Lighting Conditions: Ultraviolet: Shortwave
Photographer: E. Billie Hughes •
Image Number: A-002-8709-1 • Date Posted: 03 April 2018
Hughes, R.W., Manorotkul, W. et al. (2017) Ruby & Sapphire: A Gemologist's Guide. Bangkok, Lotus Publishing, 816 pp.; RWHL*.
Hughes, R.W. and Emmett, J.L. (2005) Heat Seeker: UV fluorescence as a gemological tool. The Guide, Vol. 24, No. 5, Part 1, Sept.–Oct., pp. 1, 4–7; RWHL*.