STS103-728-022 (19-27 December 1999)--- One of the astronauts aboard the Earth-orbiting Space Shuttle Discovery used a handheld 70mm camera to photograph the Tifernine dunes (note, the dunes are below the "beak" of sandstone rock). According to NASA scientists studying the STS-103 photo collection, the dunes were created when the dark sandstone rocks trapped sand. Winds, they continued, then piled the sand into dunes up to 457.2 m (1,500 ft). The color of the sandstone is due to a desert varnish, the scientists reported. The varnish is composed of manganese, iron oxides, hydroxides, and clay minerals, they said.