Via NASA:
This extreme close-up, a mosaic from the Mars Hand Lens Imager (MAHLI) on the Curiosity rover, spans a breathtaking 5 centimeters. It captures what appear to be elongated crystal shapes formed by the precipitation of minerals dissolved in water, a likely result of the evaporation of ancient lake or river from the Martian surface. Brushed by a dust removal tool and illuminated by white LEDs, the target rock named Mojave was found on the Pink Cliffs outcrop of the Pahrump Hills at the base of Mount Sharp.