A rock is a rock. Unless it is Martian. The first Martian rock NASA’s Curiosity rover has reached out to touch presents a more varied composition than expected from previous missions. The rock also resembles some unusual rocks from Earth’s interior. The rover team used two instruments on Curiosity to study the chemical makeup of the football-size rock called “Jake Matijevic”. The results support some surprising recent measurements and provide an example of why identifying rocks’ composition is such a major emphasis of the mission. Rock compositions tell stories about unseen environments and planetary processes. “This rock is a close match in chemical composition to an unusual but well-known type of igneous rock found in many volcanic provinces on Earth,” said Edward Stolper of the California Institute of Technology in Pasadena, who is a Curiosity co-investigator. “With only one Martian rock of this type, it is difficult to know whether the same processes were involved, but it is a reasonable place to start thinking about its origin.”