A rind that appears bluish in this false-color view covers portions of the surface of a rock called "Whitewater Lake" in the top half of the view from NASA's Mars Exploration Rover Opportunity.  This rind is similar in appearance to weathering rinds previously seen by Opportunity on rocks elsewhere within the Meridiani Planum region where the rover has worked since landing in 2004.  Whitewater Lake is in the "Matijevic Hill" portion of the "Cape York" segment of the rim of Endeavour Crater.

The three exposures through different filters  that were composited into this image were taken by Opportunity's panoramic camera (Pancam) during the mission's 3,064th Martian day, or sol (Sept. 6, 2012).  The view is presented in false color that enhances color differences among various geological materials in the scene.

Whitewater Lake is the large flat rock in the top half of the image. From left to right it is about 30 inches (0.8 meter) across.  The dark blue nubby rock to the lower left is "Kirkwood," which bears non-hematite spherules shown in a close-up image at http://photojournal.jpl.nasa.gov/catalog/PIA16139 .  The rocks to the lower right look like breccias -- a type of rock containing jumbled fragments cemented together. They resemble other rocks in the area classed as the Shoemaker formation, which is hypothesized to hold deposits of material ejected when an impact excavated Endeavour Crater billions of years ago.

NASA's Mars Exploration Rover Opportunity inspected this mineral vein, called "Homestake," in November 2011 at the northern end of the "Cape York" section of Endeavour Crater's western rim.  The vein is about the width of a thumb and about 18 inches (45 centimeters) long, extending beyond the portion shown here.

This view, showing subtle linear texture on the bright vein, combines close-up detail recorded by Opportunity's microscopic imager (MI) and enhanced color information from Opportunity's panoramic camera (Pancam).  The area covered in this view spans about 2 inches (5 centimeters) across.  The MI exposures used in this view were taken while the vein was fully shadowed by the rover during the mission's 2,766th Martian day, or sol (Nov. 4, 2011). 

A Pancam view encompassing more of the Homestake vein is at http://photojournal.jpl.nasa.gov/catalog/PIA15033 . Researchers using the alpha particle X-ray spectrometer (APXS) on Opportunity determined that this vein is rich in calcium and sulfur, possibly the calcium-sulfate mineral gypsum.  

Image credit: NASA/JPL-Caltech/USGS/Cornell Univ./Arizona State Univ.