In a Context Camera (CTX) image, there is a large angular fragment that appears to have light and dark-toned bands. HiRISE images of similar fragments nearby also show this banding, and the resolution of our camera may help determine what these layers are.
Nili Fossae was once considered a potential landing spot for the Mars Science Laboratory, and has one of the largest, most diverse exposures of clay minerals. Clay minerals contain water in their mineral structure and may preserve organic materials.
Written by: HiRISE Science Team (audio: Tre Gibbs) (26 March 2014)
More info and image formats at http://hirise.lpl.arizona.edu/ESP_035062_1995
Image: NASA/JPL/University of Arizona