Felsic rocks are found in the Nili Patera caldera, an irregularly shaped volcanic caldera in Syrtis Major that is about 65 kilometers (40 miles) in diameter. Felsic materials (red) are exposed as bedrock at the lowest elevations within the caldera. Small remnant mounds scattered across this felsic bedrock suggest it was previously buried beneath at least several meters of material that has since been eroded away. The central portion of each felsic exposure appears texturally smooth and exhibits the strongest feldspar absorptions, whereas peripheral felsic rocks are more chaotically fractured and display spectral evidence of minor amounts of water, consistent with physical and chemical weathering.
The Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) is one of six science instruments on NASA's Mars Reconnaissance Orbiter. Led by The Johns Hopkins University Applied Physics Laboratory, the CRISM team includes expertise from universities, government agencies and small businesses in the United States and abroad.
CRISM's mission: Find the spectral fingerprints of aqueous and hydrothermal deposits and map the geology, composition and stratigraphy of surface features. The instrument also tracks seasonal variations in dust and ice aerosols in the Martian atmosphere, and water content in surface materials — leading to new understanding of the climate.