Uluru

 
Uluru, also referred to as Ayers Rock, Northern Territory, Australia, is believed to be the world's largest free-standing rock. It is made of sandstone and measures 335m high, 3.6m long and 2 kilometer wide. The rock was formed more than 450 million years ago from horizontal layers of soft sands deposited on an ocean floor. Subsequent movements of the earth's crust upended the formation, turning the layers to a vertical position. The projecting remnant of a mountain that was once much larger was whittled to its present size and contours by long periods of wind and water erosion. The differences in the hardness of the upturned layers of sandstone have caused them to erode in different rates, resulting in the pattern of ridges and furrows across the surface of the rock.

The rock is composed of arkose, a course-grained sandstone rich in the mineral feldspar. Depending upon the atmospheric conditions and the time of the day, the rock can dramatically change color, anything from blue to violet to glowing red. During sunset the rock glows red and during rainy seasons the rock acquires a silvery-grey color, with streaks of black algae forming on the areas that serve as channels for water flow. Large caves are most numerous near the base of the rock. They have been used since time immemorial by the Aborigines, who decorated their walls with paintings and pictographs.