[Phil V.]

I'm struck by the black patina on the reddish rocks. It reminds me of the black patina seen in the canyonlands on some of the red sand stones of the American South West. In those cases the black is actually of organic origins. . . . long shot here, though. The blackish patina on the mars rocks is probably just weathered ferrous material.

[bonesmccoy]

What makes the dark color?

Is that unoxidized iron content in the soil?