This view from the Mars Hand Lens Imager (MAHLI) on the arm of NASA's Curiosity Mars rover is a close-up of a two-tone mineral vein at a site called "Garden City" on lower Mount Sharp.
The area shown is roughly one inch (2.5 centimeters) wide. The image was taken at night, using illumination from MAHLI's light-emitting diodes, during the 935th Martian day, or sol, of Curiosity's work on Mars (March 25, 2015).
The vein includes both light-toned and dark-toned materials. The whiter material appears to have ripped up and incorporated portions of both the darker vein material (black arrows in Figure 1) and a third material (white arrow in Figure 1). The Curiosity mission's examination of material in these veins may provide clues about multiple episodes of fluids moving through fractured rock at this site. The fluid movement through fractures occurred later than wet environmental conditions in which the host rock formed, before it hardened and cracked.