An Unusual Two Toned Rock on Mars . ... Credit Copyright: Mars Exploration Rover Mission , Cornell , JPL , NASA Explanation: How did this unusual Martian rock form? The atypical two-toned rock, visible in the lower right of the above image , was photographed a few days ago by the robotic Spirit rover currently rolling across Mars . ... Finding unusual rocks is not unusual for Spirit or its twin rover Opportunity , however. ... NASA Web Site Statements, Warnings, and Disclaimers . ...