Tourmaline that stays red
Rubellite is the trade name for red to deep pink tourmaline that keeps its colour in daylight and under warm light alike. Stones that shift to brown or orange in one or the other are pink tourmaline, not rubellite.
Brazil, Nigeria, Mozambique and Madagascar produce it. Rubellite is usually included, so clean stones carry a premium, and much pink tourmaline in trade has been heated or irradiated.
SOURCE
Brazil, Nigeria
Also Mozambique and Madagascar.
CLARITY
Usually included
Eye-clean rubellite is the exception and priced as such.
TREATMENT
Often irradiated
Untreated, eye-clean stones are uncommon.