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This view from the Mast Camera (Mastcam) in NASA's Curiosity Mars rover shows the "Marias Pass" area where a lower and older geological unit of mudstone -- the pale zone in the center of the image -- lies in contact with an overlying geological unit of sandstone.
Just before Curiosity reached Marias Pass, the rover's laser-firing Chemistry and Camera (ChemCam) instrument examined a rock found to be rich in silica, a mineral-forming chemical.
This scene combines several images taken on May 22, 2015, during the 992nd Martian day, or sol, of Curiosity's work on Mars. The scene is presented with a color adjustment that approximates white balancing, to resemble how the rocks and sand would appear under daytime lighting conditions on Earth.
Figure 1 includes a scale bar of 2 meters (79 inches).
Malin Space Science Systems, San Diego, built and operates the rover's Mastcam. NASA's Jet Propulsion Laboratory, a division of the California Institute of Technology, Pasadena, manages the Mars Science Laboratory Project for NASA's Science Mission Directorate, Washington. JPL designed and built the project's Curiosity rover.