The microscopic imager mounted on the Mars Exploration Rover testbed, FIDO. The Microscopic Imager is a combination of a microscope and a camera. It produces extreme close-up views of rocks and soils examined by other instruments on the instrument arm, providing contextual information for the interpretation of mineral and element composition data. This instrument's detailed pictures makes other types of observations more useful since we are able to associate them with a visual scene. Microscopic imaging aids in the characterization of sedimentary rocks that formed in water, and thus helps scientists understand past watery environments on Mars. This instrument also yields information on the small-scale features of rocks formed by volcanic and impact activity as well as tiny veins of minerals like the carbonates that may contain microfossils in the famous Mars meteorite, ALH84001.
Source: NASA, Cornell University