Explained: Why asteroid Bennu's surface is rocky?
Near-Earth asteroid Bennu was long thought by scientists to have surface like a sandy beach, abundant in fine sand and pebbles, and to also have large swaths of fine-grained material smaller than a few centimetres called fine regolith.
United States Saverio Cambioni Planetary Laboratory University Of Arizona Asteroid Bennu Bennus Surface
Source: ummid.com