(Before It's News)
See the above figure in its largest size:
NASA’s Mars Rover Curiosity acquired the above microscopic image on Jan 19, 2016 (Sol 1228) at Namib Dune in Bagnold dune field, Gale Crater, Mars. Twelve red arrows point to well-preserved ooids. Twelve green arrows point to eroded ooids that expose their nucleus.
These ooids are smaller than 1 mm in diameter, as the imaged area is actually ~ 3.3 cm wide. The rover dumped the scooped and sieved particles onto the ground after analyzing similar particles for their chemistry and mineralogy in its laboratory instruments. Image Credit: NASA/ JPL-Caltech/MSSS;