Images taken by NASA's Mars Reconnaissance Orbiter have revealed Martian rocks containing a hydrated mineral similar to opal (these are light-toned and appear cream-colored in this false-color image taken by the High Resolution Imaging Science Experiment camera). The opal minerals are located in distinct beds of rock outside of the large Valles Marineris canyon system and are also found in rocks within the canyon. Credit: NASA/JPL-Caltech/Univ. of Arizona