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Basalt: A fine-grained igneous rock the is generally black in color. The specimen displayed is about two inch (five centimeters) across.

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What is Basalt?

Basalt is a dark-colored, fine-grained, igneous absent composed mostly of plagioclase and also pyroxene minerals. It most frequently forms as an extrusive rock, such as a lava flow, however can also kind in tiny intrusive bodies, such together an igneous dike or a slim sill. It has actually a composition comparable to gabbro. The difference between basalt and gabbro is that basalt is a fine-grained rock while gabbro is a coarse-grained rock.


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Olympus Mons Volcano: This shield volcano is written of basalt and also has substantial calderas at the summit. Olympus Mons is the highest topographic attribute on Mars and is the largest recognized volcano in our solar system. The is around 375 mile (600 kilometers) in diameter and also 15 mile (25 kilometers) high. NASA Mars Orbiter Camera image.


Earth"s most Abundant Bedrock

Basalt underlies more of Earth"s surface than any type of other absent type. Most areas within Earth"s ocean containers are underlain by basalt. Back basalt is lot less usual on continents, lava flows and also flood basalts underlie several percent that Earth"s land surface. Basalt is a really important rock.

Basalt top top Moon and Mars

Basalt is also an numerous rock top top the Moon. Lot of the Moon"s surface ar is underlain by basaltic lava flows and also flood basalts. These locations of the Moon are recognized as "lunar maria." big areas the the Moon have been resurfaced by considerable basalt flows which may have been motivated by major impact events. The ages of lunar maria deserve to be approximated by observing the density of impact craters on your surface. Younger basalt operation will have fewer craters.


Olympus Mons is a shield volcano ~ above Mars. It, like most other volcanic attributes on Mars, was formed from basaltic lava flows. It is the greatest mountain top top Mars and also is the largest recognized volcano in our solar system.


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Igneous absent composition chart: This chart shows that basalt is typically composed the pyroxenes, plagioclase, micas, and also amphiboles.


Basalt-Forming Environments

Most that the basalt found on earth was created in just three rock-forming environments: 1) oceanic divergent boundaries, 2) oceanic hotspots, and 3) mantle plumes and hotspots beneath continents. The pictures on this page feature some of this basalt-forming environments.


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Sea floor pillow basalts ~ above the Juan de Fuca Ridge, a divergent plate boundary located about 150 miles (240 kilometers) west of the Washington-Oregon coast. This lava flow, created by a fissure eruption, was around five year old as soon as the photo was taken. NOAA Ocean explorer image.

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Hawaii Basalt Flows: Lava flows dump into the Pacific s on the coast of Hawaii. Multiple places where warm lava streams into the ocean have the right to be seen in this image along with a red-hot lava circulation traversing the lava field. This photograph shows the enormous extent of the flows. They extend from the coastline up come the horizon. A volcanic plume indigenous the Pu`u `O`o vent can be seen over the horizon close to the facility of the image. The lava in this flows originated from the Pu`u `O`o vent. USGS image.


Basalts in ~ Oceanic Divergent Boundaries

Most that Earth"s basalt is produced at divergent plate boundaries on the mid-ocean ridge system (see map). Right here convection currents supply hot rock from deep in the mantle. This warm rock melts as the divergent border pulls apart, and the molten rock erupts top top the sea floor. These submarine fissure eruptions often produce pillow basalts as presented in the picture on this page.


The energetic mid-ocean ridges hold repeated fissure eruptions. Most of this task is unnoticed because these limits are under an excellent depthsof water. At these deep locations, any type of steam, ash, or gas produced is absorbed by the water column and does not reach the surface. Earthquake task is the just signal to humans that numerous of these deep ocean ridge eruptions provide. However, Iceland is a place where a mid-ocean ridge has been lifted above sea level. There, world can straight observe this volcanic activity.


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Thermal image of a hot basalt flow on the flank that Hawaii"s Kilauea volcano. Warm lava in ~ the front of the flow is revealed in yellow, orange and also red colors. The channel the it flowed through on the vault day appears as a purple and also blue track. United claims Geological inspection image.


Oceanic Hotspots

Another ar where significant amounts of basalt are developed is above oceanic hotspots. This are locations (see map above) where a small plume of warm rock rises up with the mantle native a hotspot top top Earth"s core. The Hawaiian islands are an instance of wherein basaltic volcanoes have been built over an oceanic hotspot.

Basalt manufacturing at this locations starts with an eruption ~ above the s floor. If the hotspot is sustained, recurring eruptions can develop the volcano cone larger and also larger until it i do not care high sufficient to end up being an island. Every one of the archipelago in the Hawaiian Island chain were built up from basalt eruptions ~ above the sea floor.

The island the we know today together "Hawaii" is believed to be in between 300,000 and 600,000 year old. It began as one eruption on the floor that the Pacific Ocean. The volcanic cone flourished as recurrent eruptions built up layer after ~ layer of basalt flows. Around 100,000 years ago it is assumed to have grown tall enough to emerge from the s as one island.

Today it consists of five overlapping volcanoes. Kilauea is the most energetic of these volcanoes. It has been in amost continuous eruption because January, 1983. Basalt operation from Kilauea have actually extruded end one cubic mile of lava, which right now covers around 48 square mile of land. This flows have actually travelled over 7 miles to with the ocean, spanning highways, homes and entire subdivisions that were in your path.


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Columbia river Flood Basalts: The Columbia flow Flood Basalts are an extensive sequence of stacked lava flows that reach a accumulation thickness of up to 6000 feet. The outcrops in the foreground and in the street of this picture are all consisted of of layered basalt flows. Although basalt is generally a dark black color rock, it frequently weathers come a yellow-brown color similar to the rocks shown here. Public domain photo by Williamborg.

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Plumes & Hotspots below Continents

The 3rd basalt-forming setting is a continental atmosphere where a mantle plume or hotspot it is provided enormous quantities of basaltic lava with the continent crust and also up to Earth"s surface. This eruptions can be from either vents or fissures. Lock have developed the biggest basalt operation on the continents. The eruptions can occur repeatedly over millions of years, creating layer after ~ layer that basalt stacked in a vertical sequence (see outcrop photo).

The Columbia flow Flood Basalts in Washington, Oregon, and Idaho are an example of considerable flood basalts on land (see map below). Various other examples incorporate the Emeishan catch of China, the Deccan traps of India, the Keweenawan Lavas that the Lake exceptional region, the Etendeka Basalts of Namibia, the Karroo Basalts of south Africa, and also the Siberian traps of Russia. (The word "traps" is acquired from the swedish word because that "stairs," which describes the outcrop profile of this layered basalt deposits, as presented in the outcrop photo.)


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Uses of Basalt

Basalt is provided for a wide variety of purposes. The is most commonly crushed for use as an aggregate in building and construction projects. Crushed basalt is supplied for road base, concrete aggregate, asphalt pavement aggregate, rail ballast, filter stone in drain fields, and may other purposes. Basalt is additionally cut into measurement stone. Thin slabs of basalt room cut and sometimes sleek for use as floor tiles, structure veneer, monuments, and also other rock objects.


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