"Bathurst Inlet" Rock - Sol 54 (Natural Colors; credts: NASA/JPL-Caltech, Malin Space Science Systems)

NASA's Mars Rover Curiosity held its Mars Hand Lens Imager (MAHLI) camera about 10,5" (---> inches, such as about 27 centimeters) away from the top of a Rock called "Bathurst Inlet" for a set of 8 images combined into this merged-focus view of the Rock. This context image covers an area that is roughly 6,5 by 5" (such as 16 by 12 centimeters). Resolution is about 105 microns per pixel.
MAHLI took the component images for this merged-focus view, plus closer-up images of Bathurst Inlet, during Curiosity's 54th Martian Day, or Sol (such as September 30, 2012). The instrument's principal investigator had invited Curiosity's science team to "MAHLI it up!" in the selection of Sol 54 targets for inspection with MAHLI and with the other instrument at the end of Curiosity's Arm: the Alpha Particle X-Ray Spectrometer.
The "Bathurst Inlet" Rock is dark gray and appears to be so fine-grained that MAHLI cannot resolve Grains or Crystals in it. This means that the Grains or Crystals, if there are any at all, are smaller than about 80 microns in size. Some windblown sand-sized Grains or Dust Aggregates have accumulated on the Surface of the Rock, but this Surface is clean (if compared, for example, to the pebbly substrate below the rock - upper left and lower right in this context image).
MAHLI can do focus merging onboard the MER and, in fact, the full-frame versions of the 8 separate images that were combined into this view were not even returned to Earth -- just the thumbnail versions. In other words, merging the images onboard reduces the volume of data that is supposed to be downlinked to Earth.