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Basalt (UK: / ˈ b æ s ɒ l t,-ɔː l t,-əl t /; [1] [2] US: / b ə ˈ s ɔː l t, ˈ b eɪ s ɔː l t /) [3] is an aphanitic (fine-grained) extrusive igneous rock formed from the rapid cooling of low-viscosity lava rich in magnesium and iron (mafic lava) exposed at or very near the surface of a rocky planet or moon.
Basalt is a very common volcanic rock with low silica content. Rhyolite is a volcanic rock with high silica content. Rhyolite has silica content similar to that of granite while basalt is compositionally equal to gabbro. Intermediate volcanic rocks include andesite, dacite, trachyte, and latite. [citation needed]
Basalt columns seen on Porto Santo Island, Portugal. Columnar jointing of volcanic rocks exists in many places on Earth. Perhaps the most famous basalt lava flow in the world is the Giant's Causeway in Northern Ireland, in which the vertical joints form polygonal columns and give the impression of having been artificially constructed.
Blocks of basalt made up the floor of the funerary temple east of Khufu's Great Pyramid [9] 11.5 km long, paved quarry road connecting Widan el-Faras and Qasr el-Sagha used basalt fragments from the quarry along with other materials such as limestone , sandstone , and petrified wood .
A flood basalt (or plateau basalt [1]) is the result of a giant volcanic eruption or series of eruptions that covers large stretches of land or the ocean floor with basalt lava. Many flood basalts have been attributed to the onset of a hotspot reaching the surface of the Earth via a mantle plume . [ 2 ]
Peridotite (US: / ˈ p ɛ r ɪ d oʊ ˌ t aɪ t, p ə ˈ r ɪ d ə-/ PERR-ih-doh-tyte, pə-RID-ə-) is a dense, coarse-grained igneous rock consisting mostly of the silicate minerals olivine and pyroxene.
Map of Minnesota bedrock by age. Shaded relief image: Superior Upland in the northeast, the flat Red River Valley in the northwest, Central Minnesota's irregular landscape, the Coteau des Prairies and Minnesota River in the southwest, and the southeast's dissected Driftless Area along the Mississippi River below its confluences with the Minnesota and St. Croix in East Central Minnesota
This hydraulic head combined with a flow depth of from 60 to 120 meters (200 – 400 ft) provided the energy to achieve flood flow velocities as high as 30 m/s (65 mph), which eroded the topsoil and underlying basalt, gouging the complex network of channels, basins, potholes and buttes that are found there even today.