Basalt

Basalt ( /bəˈsɔːlt/, /ˈbæsɒlt/, /ˈbæsɔːlt/, or /ˈbeɪsɔːlt/) is a common extrusive igneous (volcanic) rock formed from the rapid cooling of basaltic lava exposed at or very near the surface of a planet or moon. By definition, basalt must be an aphanitic igneous rock with less than 20% quartz and less than 10% feldspathoid by volume, and where at least 65% of the feldspar is in the form of plagioclase. Basalt is usually grey to black in colour, but rapidly weathers to brown or rust-red due to oxidation of its mafic (iron-rich) minerals into rust. It almost always has a fine-grained mineral texture due to the molten rock cooling too quickly for large mineral crystals to grow, although it can sometimes be porphyritic, containing the larger crystals formed prior to the extrusion that brought the lava to the surface, embedded in a finer-grained matrix. Basalt with a vesicular or frothy texture is called scoria, and forms when dissolved gases are forced out of solution and form vesicles as the lava decompresses as it reaches the surface.

On Earth, most basalt magmas have formed by decompression melting of the mantle. Basalt commonly erupts on Io, and has also formed on Earth's Moon, Mars, Venus, and even on the asteroid Vesta. Source rocks for the partial melts probably include both peridotite and pyroxenite (e.g., Sobolev et al., 2007). The crustal portions of oceanic tectonic plates are composed predominantly of basalt, produced from upwelling mantle below ocean ridges.

The term basalt is at times applied to shallow intrusive rocks with a composition typical of basalt, but rocks of this composition with a phaneritic (coarse) groundmass are generally referred to as diabase (also called dolerite) or gabbro.

Read more about Basalt:  Etymology, Uses, Types, Petrology, Life On Basaltic Rocks, Distribution, Lunar and Martian Basalt

Other articles related to "basalt, basalts":

Mole Hill (Virginia) - Description
... The basalt itself, outcropping at the crest of the hill, is "dark greenish gray to grayish black, medium grained, and moderately porphyritic ... It is an olivine-spinel basalt with abundant large pale green pyroxene and minor yellow-brown olivine phenocrysts." ... The basalt intrudes through the Ordovician Beekmantown Group of carbonate rocks ...
Trimble Knob - Age
... The basalt at Trimble Knob (and other igneous dikes in the area) was originally thought to be of Paleozoic age by relative age dating using cross-cutting relationships ... In 1993, Southworth and others give a date of 35.0±0.5 Ma for basalt of Trimble Knob, placing it in the Eocene ... The basalt intrudes the Devonian Millboro Shale ...
Basalt, Idaho - Demographics
... There were 121 households out of which 47.9% had children under the age of 18 living with them, 72.7% were married couples living together, 8.3% had a female householder with no husband present, and 11.6% were non-families. 11.6% of all households were made up of individuals and 7.4% had someone living alone who was 65 years of age or older ...
Batoka Formation - Geology - Description
... consisting mainly of high-titanium, low-potassium tholeiitic basalt flows with small layers of aeolian sandstone and siltstone between some of the flows ... The lavas are dark, vesicular and porphyritic or massive basalts, with occasional pillows although rare dacites and rhyolites have been reported from ... The vesicular and massive basalts occur in alternating bands, with the vesicular bands usually being the top and base of each flow ...
Basalt Falls
... Basalt Falls is a waterfall on the Dean River in the Chilcotin District of the Central Interior of British Columbia, located north of the community of Anahim Lake ... (3.7 m) in height and is composed of columnar basalt of the Chilcotin Group ...