NASA's Opportunity rover has determined that the small mineral spherules, which scientists have been calling "blueberries", contain hematite. This furthers the theory that the region was once drenched with liquid water. On Earth, hematite crystals with the same size as the spherules usually form in a wet environment. Doing a chemical analysis on the spherules was difficult because they're too small for any of Opportunity's instruments. The rover had to find a spot which was covered with spherules to analyze.