Weathered and UN-weathered Rocks and Soil: "Ginger"- Sol 18 (credits: NASA)

Caption NASA:"One of the more unusual rocks at the site is Ginger, located South-East of the Lander.
Parts of it have the reddest color of any material in view, whereas its rounded lobes are gray and relatively unweathered. These color differences are brought out in the inset, enhaced at the upper right. In the false color image at the lower right, the shape of the visible - wavelength spectrum (related to the abundance of weathered ferric iron minerals) is indicated by the hue of the rocks.

Blue indicates relatively unweathered rocks. Typical soils and drift, which are heavily weathered, are shown in green and flesh tones.
The very red color in the creases in the rock surface correspond to a crust of ferric minerals.
The origin of the rock is uncertain; the ferric crust may have grown underneath the rock, or it may cement pebbles together into a conglomerate. Ginger will be a target of future super- resolution studies to better constrain its origin".