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.