The first detailed examination of clay mineralogy in its original setting on Mars is offering new insights on the planet's past habitability, research led by Planetary Science Institute Senior Scientist David T. Vaniman has found.

The sedimentary rock samples tested were collected by NASA's Mars Science Laboratory rover Curiosity at Yellowknife Bay in Gale Crater on Mars. The rover's Chemistry and Mineralogy X-Ray Diffraction and Fluorescence (CheMin XRD/XRF) instrument analyzed the samples.

"The in situ X-ray diffraction results reveal the presence of smectite, a type of clay mineral typical of soils and sediments that have not been deeply buried, heated, or otherwise altered," Vaniman said.

"The X-Ray diffraction data are also important for what they do not detect - clay minerals such as chlorite or illite that would have formed in strongly alkaline or hydrothermal fluids."

Vaniman is lead author of a paper in Science titled "Mineralogy of a Mudstone at Yellowknife Bay, Gale Crater, Mars" that was discussed at a press conference today at the American Geophysical Union's Fall Meeting in San Francisco.

The paper discusses that this is the first analysis of a complete mineral assemblage in a Martian sediment, accounting for all of the associated debris that settled into a lake as well as minerals formed in the lake and after it dried out.

"Here too, this complete mineral analysis is important not only for what is seen but also for what is not present. Unlike the sediments that the Mars Exploration Rover Opportunity has found at Meridiani Planum, the Gale Crater mudstone lacks iron sulfates that indicate an acidic environment," Vaniman said.

"The only sulfates found in the mudstone are calcium sulfates, associated with veins that formed after the lake was gone and not indicative of an acidic system. The mudstone mineralogy is consistent with a geochemically benign and potentially habitable environment."

Vaniman's research was funded by a cooperative agreement from NASA's Mars Science Laboratory mission under a subcontract to NASA Ames Research Center.