Minerals which are capable of this reversible color change by exposure to UV (or other energy sources), without any change in their essential composition, are said to be tenebrescent
Recently I posted a question about Afghan sodalite (hackmanite) after reviewing the MinRec article about Sar-E-Sang. Someone reminded me that there was a large discussion on this topic last year. I dug out that discussion and copied it here to the blog. This is one reason we created Nature's Rainbows - to capture these excellent discussions.
Tenebrescence of Greenland sodalite is amazing. This is a piece of a deeply tenebrescent sodalite.
Tenebrescence is when minerals change color when exposed to sunlight, also known as reversible photochromism.