Mars may be named for the god of war, but these weird things aren’t cannonballs. They&

Mars may be named for the god of war, but these weird things aren’t cannonballs. They’re pebbles. 

The round 0.2 inch (5 mm) concretion I found (top) contains calcium sulfate, sodium and magnesium, making it different from the hematite-rich “blueberries” (bottom) the Opportunity rover found. Cool!