Sandstone is a soft, medium-grained, sedimentary rock that consists of compacted sand (mostly quartz and feldspar), usually held together by natural cements such as clay, silica, and iron oxide. The contents of both the sand and cement determine the sandstone’s color. Iron oxide (rusted iron) is red; manganese is black; sulfur is yellow; silica and calcite are lighter colors. Sandstone poor in natural cements is usually brittle and white.
Petra, Wadi Dana, and Wadi Rum (see Liesegang Banding).