Rusting iron minerals in the rocks and soil blow into the air – occasionally in planetwide dust storms – giving the atmosphere a rusty tint.
The iron within the dust reacted with oxygen, producing a red rust colour, while the sky appears red as storms carried the dust into the atmosphere. This dusty surface, which is between a few millimeters and two metres deep, sits above hardened lava composed mostly of basalt. The concentration of iron in this basalt is much higher than that on Earth, contributing to the red appearance of Mars.
Picture Credit : Google