Rocks facts

In the United States. Dry Falls is a 3.5 mile long scalloped precipice in central Washington. According to the current geological model, catastrophic flooding channeled water over this 400-foot (120 m) rock face at the end of the last ice age. At this time, it is estimated that the flow of the falls was ten times the current flow of all the rivers in the world combined.

Metamorphosed limestone. Marble is a metamorphic rock. It is formed deep under the Earth surface, under high pressure and temperature between 500 and 700°C. Under such conditions calcite recrystallises and limestone is transformed into marble.

A kind of chemical decomposition. Karst is a topography formed from the dissolution of soluble rocks such as limestone, dolomite, and gypsum. It is characterized by underground drainage systems with sinkholes and caves. It has also been documented for more weathering-resistant rocks, such as quartzite, given the right conditions.

The Mountain of Tariq. The name "Gibraltar" is the Spanish derivation of the Arabic name Jabal Ṭariq, meaning "Mountain of Ṭariq". Following a raid in 710, a predominately Berber army under the command of Tariq ibn Ziyad crossed from North Africa in April 711 and landed somewhere in the vicinity of Gibraltar (though most likely not in the bay or at the Rock itself). Tariq's expedition led to the Islamic conquest of most of the Iberian peninsula.

Granite is a type of felsic intrusive igneous rock. It is granular and phaneritic in texture. The rock mainly consists of quartz, feldspar, mica, and amphibole minerals.

New South Wales. The Three Sisters are an unusual rock formation in the Blue Mountains of New South Wales, Australia, on the north escarpment of the Jamison Valley. They are close to the town of Katoomba and are one of the Blue Mountains' best known sites.

Studying rocks. Petrology is the branch of geology that studies rocks and the conditions under which they form.

Gneiss. The Acasta Gneiss in the Canadian Shield in the Northwest Territories, Canada is composed of the Archaean igneous and gneissic cores of ancient mountain chains that have been exposed in a glacial peneplain. Analyses of zircons from a felsic orthogneiss with presumed granitic protolith returned an age of 4.031 ±0.003 Ga.