Re: If Mars is so full of iron, why are the rocks gray?

According to the Mars Rovers' website (1), the gray rocks are hematite, 
which is a mineral made up of iron and oxygen. The chemical interactions of 
these 2 elements give the rocks a gray color.  In powdered form, it is 
rust-colored and gives Mars the red color (2) we're so familiar with.


(1) http://marsrovers.jpl.nasa.gov/
(2) http://marsrovers.jpl.nasa.gov/spotlight/hematite01.html