Tenebrescence of Greenland sodalite is amazing. This is a piece of a deeply tenebrescent sodalite. Note how when the SW light is first turned on the sodalite fluoresces a bright orange but almost immediately shifts to a burnt orange as the tenebrescence sets in This darkening continues until somewhere near the end where the rock is fully tenebresced. (around the middle of the movie you will see the UV light brighten; this is due to a custom ballast I designed which doubles the UV power after the bulb has been on for 20 secs). At the end the rock is in its full tenebrescent glory. Then a bright white light is applied to fade it back to its original state. The whole process takes around 75 seconds. Afghan material is much slower to react, and near impossible to fade.