Curiosity brushed and then imaged a target called Wernecke with its MAHLI camera on sol 169, as the rover was preparing to drill for the first time. MAHLI was able to pose within only 1 centimeter of the surface of Wernecke, and so achieved its highest resolution of about 10 microns per pixel. MAHLI cannot resolve individual grains within the rock, so the grain size is smaller than fine sand. The rock does have small nodules, informally called "measles" by the team. Some team members think they were once gas bubbles within the wet sediment, some (but not all) of which later filled with minerals. You can also see that the brush has scratched the surface, indicating that the rock is soft.