Researchers used NASA's Mars Exploration Rover Opportunity to find a water-related mineral [Montmorillonite] on the ground that had been detected from orbit, and found it in the dark veneer of rocks on the rim of Endeavour Crater.
This false-color view from the panoramic camera (Pancam) on Opportunity shows a dark veneer, exposed after brushing with the rover's rock abrasion tool. These finely layered rocks with dark veneers are in the "Whitewater Lake" outcrop on "Matijevic Hill" on the western rim of Endeavour. The deposits are part of the ancient Matijevic formation, which predates the Endeavour impact event. The brushed area is about 1.5 inches (3.8 centimeters) wide. This image was taken on the 3,098th Martian day, or sol, of Opportunity's mission (October 11, 2012).
Photo credit: NASA/JPL-Caltech/Cornell University/Arizona State University
Note: For more information, see PIA17756: 'Esperance6' and 'Lihir' Rover Targets and PIA17757: Mineral Plot from 'Esperance' Target.