The Mast Camera (Mastcam) on NASA's Mars rover Curiosity showed researchers interesting color and patterns in this unnamed rock imaged during the 27th Martian day, or sol, of the rover's work on Mars (September 2, 2012). The rock is about 2.4 inches (6 centimeters) across. This view is calibrated to estimated "natural" color, or approximately what the colors would look like if we were to view the scene ourselves on Mars. The rock shows a blue-black color overall, with lighter, whitish tones in patterns that may indicate the presence of distinct crystals of different material in the rock.
Photo credit: NASA/JPL-Caltech/MSSS