The texture of the "Brown/Orange Soil" of Gusev Crater - Sol 1177

Caption NASA:"On Sol 1177, Spirit used the Rock Abrasion Tool (RAT) to brush away dust covering the surface of a small, nodule-rich outcrop nicknamed "Slide" at the edge of the circular plateau known as "Home Plate". This image mosaic, acquired by the Microscopic Imager (MI), shows the nature of the weathered outcrop surface, just beneath the dust coating. The science team has a special interest in the rocks in this general area, some of which show the highest silica content yet measured on Mars".