Low-iron volcanic plains filling the Caloris impact basin make a large pale-orange patch (C) in this false-color image of Mercury from MESSENGER. White arrows mark locations of young smooth plains whose composition appears related to the Caloris plains. Around the edge of Caloris and elsewhere lie small volcanic centers thought to form by explosive eruptions (black arrows). The widespread dark blue areas are older rocks that may be rich in the mineral ilmenite. Credit: NASA/JHUAP/Arizona State University