The smooth light-toned deposits on the floor of Noctis Labyrinthus, a series of depressions at the westernmost end of Valles Marineris, may contain a form of hydrated silica, perhaps opal, which is a gemstone.
The opal could have formed by chemical weathering of basaltic lava flows or volcanic ash in the presence of water. Also visible in the left side of the enhanced-color subimage are sand dunes with two colors, perhaps due to dark sand covered in places by bright reddish dust, and an impact crater with dark ejecta. (The subimage width is 1.2 kilometers.)
Written by: Alfred McEwen (31 August 2011)
This is a stereo pair with ESP_023003_1710 .
More info and image formats at http://hirise.lpl.arizona.edu/ESP_023359_1710
Image: NASA/JPL/University of Arizona