The rock abrasion tool on NASA's Mars Exploration Rover Spirit ground two holes in a relatively soft rock called "Wooly Patch" near the base of the "Columbia Hills" inside Gusev Crater on Mars. This false-color image from the panoramic camera was taken on sol 200 (July 25, 2004) and generated using the camera's 750-, 530-, and 430-nanometer filters. It highlights the material ground up by the rock abrasion tool, grayish-blue in appearance in this image. The color of the material excavated suggests the interior of the rock contains iron minerals that are less oxidized than the dust or possibly weathered coating on the exterior of the rock. Scientists speculate that this relatively soft rock (compared to others analyzed by Spirit) may have been modified by water. Small cracks in the surface outside the drill holes may be the result of interactions with water-rich fluids.