Hackmanite from Greenland offers the most striking color change (tenebrescence) I have seen from any place in the world. Most sodalite from the Ilimaussaq Complex is colored - either blue, green, gray, yellow, or some shade in between.
Upon exposure to SW UV the sodalite on this piece changes color from pale green/yel to purple - in seconds! It exhibits one of the deepest color changes of all the spectacular hackmanites found in Greenland. Expose it to a bright white light (UV free halogen held directly on the rock) and it reverts back to its natural color almost immediately. Even under LW the color shifts to a pinkish hue. When we first discovered these pieces we did not recognize anything special until we cracked them and set them out under sunlight. They turned a nice red. Then we lamped them and discovered how truly amazing they were.
The sodalite fluoresces a bright orange under LW. Initially under SW the fluorescence is a bright orange. and turns a deeper orange as the tenebrescence sets in (the rusty color is caused by the deepening tenebrescence - you can actually watch the color shift as the piece darkens). Areas of green fluorescence are likely uranyl activated.
The first pic below shows this tenebrescent color change. It starts out with the natural color, darkens slightly after exposure to longwave UV (UVA) and deepens to a grape purple after exposure to shortwave UV (UVC). Further below are the fluorescent pics - SW, LW, Tene - click any image for a slideshow.
