How does wind abrade stones?
A ventifact is a stone whose surface has been worn by wind-driven sand or other grains. It may develop polished faces, sharp edges or facets facing different directions.
Sand as an abrasive
Airborne grains strike exposed rock and remove tiny fragments. Grain size, wind speed, rock hardness and exposure time affect the result. Abrasion can be strongest near the ground where more sand travels. Such features occur in cold open terrain as well as hot deserts.
Can facets reveal a single wind direction?
Several facets may suggest different wind episodes, but the stone may have moved or rotated. Its shape alone cannot provide a precise chronology. Surrounding sediment and abrasion marks help distinguish wind work from water-worn rocks. Removing ventifacts from their setting loses evidence about past environments.