Dravite

Single Dravite crystal exhibiting the \"Usambara effect\" color change (named after nearby mountains). This is a different type of color change than the Alexandrite effect, where the color changes in different types of lighting. In this case, the Dravite crystal appears green in normal lighting, however when a single light source is transmitted through the crystal, at a certain thickness, a sudden color shift from green to red is observed, while less thick areas remain green.