Radium treatment of minerals such as beryl to produce a bluish-white fluorescence only on the basal planes. Under SWUV and LWUV light beryl fluoresces bluish-white.
See Alexandrite Tsarstone collectors guide, Definition of Radium fluorescence, http://w.alexandrite.com/viewpage.html?id=GG-103-00002 (Radium treatment of minerals such as beryl to produce a bluish-white fluorescence only on the basal planes. Under SWUV and LWUV light beryl fluoresces bluish-white.) (as of May. 31, 2026, 16:25 GMT).