blue-toned rocks (IMAGE) The University of Hong Kong Caption The blue-toned rocks in the upper-left of the image are depleted in iron because it was removed during weathering on ancient Mars. This is geological evidence that iron was lost from the rocks in reduced conditions. Credit The University of Hong Kong Usage Restrictions None License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.