|Hikers pausing to view a rock formation known as The Wave in the Vermilion Cliffs National Monument in Arizona. AP Photo/Brian Witte|
The Vermilion Cliffs are the second "step" up in the five-step Grand Staircase of the Colorado Plateau, in northern Arizona and southern Utah. The Vermilion Cliffs are made up of deposited silt and desert dunes, cemented by infiltrated carbonates and intensely colored by red iron oxide and other minerals, particularly bluish manganese.
The rock unit called the Navajo Sandstone features prominently in much of this landscape, and contains some of the largest and most abundant iron concretions found anywhere in the world. The Navajo Sandstone was named for the “Navajo country” of Arizona, Utah, and New Mexico. The red rock country on the Colorado Plateau where the Navajo Sandstone and other related rock formations are prominently exposed is centered around the Four Corners region where the states of Utah, New Mexico, Colorado, and Arizona meet. This story of the red rocks started millions of years ago.
|Brett Pelletier Photography|
Blood of the Living RocksWhat colors the sandstone red? The red color is caused by a union of iron and oxygen (an iron oxide) known as hematite (Fe2O3), a mineral named from the Greek word for blood. Iron is a powerful pigment present in many sediments and rocks, thus it commonly imparts color to the rocks. Although red is the common pigment color, not all iron oxides are red; some are brown or yellow (minerals - limonite or goethite), and some are black (mineral - magnetite).
Some iron minerals are metallic yellow (mineral - pyrite consisting of iron sulfide) or green (minerals - chlorite or clay consisting of iron silicate). Although geologists have long understood that sandstone coloration is a function of varying amounts of iron, it is only recently that scientific studies detail how this happens.