Rocky Diversity on Mars
Scientists chose Gale crater as Curiosity's landing site because they knew it contained a wide variety of different rock types. What they didn't quite expect was to uncover a geologist's dream site so soon after landing. Whereas past Mars rovers have mostly encountered basaltic rocks, Curiosity has seen a large diversity in its year on Mars.
One of the first stones the rover encountered was a highly fractionated alkalic rock, a type never before seen on Mars. Such rocks are familiar on Earth at island chains and rift zones, suggesting that Gale crater has a dynamic geological past. Curiosity's laser and X-ray analyses have also detected other volcanic rocks and its surveys at Yellowknife Bay have found sedimentary rocks galore. And analysis from Curiosity's drillings have uncovered smectite minerals, which provide good evidence for an ancient benign, watery environment.
Image: X-ray diffraction analysis, showing the presence of olivine and feldspar. NASA/JPL-Caltech/Ames