Deeply Tenebrescent Sodalite (Hackmanite) from Greenland
Greenland produces some of the most tenebrescent sodalite found anywhere. These pieces darken when exposed to SW UV in seconds, and fade just as rapidly upon exposure to a bright white light. This process can be repeated over and over. They are also perhaps the most fluorescent of the sodalites found around the world - a bright yel/orange under LW and SW, but under SW as the tenebrescence sets it, the color darkens to a rusty orange. Photos show SW and LW, as well as the tenebrescence. The animation shows this color change before/after UVC.