Ventifacts begin to form as wind throws grains of sand and dust at a rock or outcrop. The impact of the flying grains loosens or chips off microscopic pieces of the rock. Hard, fine-grain rocks such as basalt develop mostly flat sides that scientists call facets.

What are Ventifacts caused by?

Ventifact, stone that has received one or more highly polished, flattened facets as a result of erosion by windblown sand. ... Ventifacts are produced under arid conditions and are generally formed from hard, fine-grained rocks such as obsidian, chert, or quartzite.

Where can Ventifacts be found?

Ventifacts are found in several physical settings in California: in formerly glaciated areas, in periglacial areas above or beyond glacier limits, in presently semiarid areas, along the coast, and in true deserts. In several localities, both active and fossil forms are found.