X-ray diffraction spectra for Chemin analyses of samples from the "Rocknest" and "John Klein" sites
This side-by-side comparison shows the X-ray diffraction patterns of two different samples collected from the Martian surface by NASA's Curiosity rover. These images, made from data obtained by Curiosity's Chemistry and Mineralogy instrument (CheMin), show the patterns obtained from a drift of windblown dust and sand called "Rocknest" and from a powdered rock sample drilled from the "John Klein" bedrock. The presence of abundant clay minerals (labeled "phyllosilicate") in the John Klein drill powder and the lack of abundant salt suggest a fresh water environment.
The presence of calcium sulfates rather than magnesium or iron sulfates (as found at Meridiani Planum by the Opportunity rover) suggests a neutral to mildly alkaline pH environment. The Rocknest sand shadow mineralogy suggests a dry, aeolian (wind-shaped) environment with low water activity. The John Klein mineralogy suggests a lacustrine (lakebed) environment with high water activity.
Interpretation of the Rocknest data reveals abundant plagioclase feldspar, pyroxene and olivine minerals. The data also indicate small amounts of magnetite and anhydrite. In addition, the Rocknest sample contains 25 to 35 percent amorphous, or non-crystalline, material.
Interpretation of the X-ray diffraction analysis of the John Klein drill powder reveals abundant phyllosilicate (a class of clay minerals called smectites that form by the action of relatively pure and neutral pH water on source minerals), plagioclase feldspar, pyroxene, magnetite and olivine. The data also show minor amounts of anhydrite and bassanite. The John Klein sample also contains about 20 percent amorphous material.
The minerals could have formed in this location through alteration of source minerals. Alternatively, the clay minerals could have been transported by water from sources higher up the sediment fan to form the John Klein mineral assemblage.