I am a co-investigator on NASA's Curiosity Mars rover project, and am involved with the Chemin instrument. The Chemin instrument is an X-ray diffractometer that will be used to characterize and identify the minerals on Mars.
The purpose of the mission is to investigate the habitability of Mars, past, present and future. The main route to this investigation is through the identification of the mineral phases and the geological stories that unfold.
Watch this Arizona Public Media feature on the Mars rover.