desert surface related
Ventifacts and desert varnish are features of a stable desert surface. Ventifacts are rocks that have been faceted by wind-blown sand. The classical example looks like a three-sided hat and is called a dreikanter. Textbook examples of these are not easily found. We have them occasionally.
Desert varnish is a manganese and iron oxide coating on the upper side of rocks that maintain a stable position for thousands of years, and on vertical surfaces and cliff faces. We occasionally have hand specimens with a desert varnish surface in stock.