Trap rock, also known as either trapp or trap, is any dark-colored, fine-grained, non-granitic intrusive or extrusive

igneous rock Igneous rock ( ), or magmatic rock, is one of the three main rock types, the others being sedimentary and metamorphic. Igneous rocks are formed through the cooling and solidification of magma or lava. The magma can be derived from partial ...

. Types of trap rock include

basalt Basalt (; ) is an aphanite, 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 planetary surface, surface of a terrestrial ...

peridotite Peridotite ( ) is a dense, coarse-grained igneous rock consisting mostly of the silicate minerals olivine and pyroxene. Peridotite is ultramafic, as the rock contains less than 45% silica. It is high in magnesium (Mg2+), reflecting the high pr ...

, diabase, and

gabbro Gabbro ( ) is a phaneritic (coarse-grained and magnesium- and iron-rich), mafic intrusive igneous rock formed from the slow cooling magma into a holocrystalline mass deep beneath the Earth's surface. Slow-cooling, coarse-grained gabbro is ch ...

.Neuendorf, K.K.E., J.P. Mehl, Jr., and J.A. Jackson, J.A., eds. (2005) ''Glossary of Geology'' (5th ed.) American Geological Institute, Alexandria, Virginia. 779 pp. Trap is also used to refer to flood (plateau) basalts, such as the Deccan Traps and Siberian Traps.Le Maitre, R. W., ed. (2002) ''Igneous Rocks: A Classification and Glossary of Terminology''. Cambridge University Press, New York. 236 pp. The erosion of trap rock created by the stacking of successive

lava Lava is molten or partially molten rock (magma) that has been expelled from the interior of a terrestrial planet (such as Earth) or a Natural satellite, moon onto its surface. Lava may be erupted at a volcano or through a Fissure vent, fractu ...

flows often creates a distinct stairstep landscape from which the term ''trap'' was derived from the Swedish word , which means "stairs". The slow cooling of

magma Magma () is the molten or semi-molten natural material from which all igneous rocks are formed. Magma (sometimes colloquially but incorrectly referred to as ''lava'') is found beneath the surface of the Earth, and evidence of magmatism has also ...

either as a sill or as a thick

flow sometimes creates systematic vertical fractures within the resulting layer of trap rock. These fractures often form rock columns that are typically hexagonal, but also four- to eight-sided.Muller, G. (1998) "Experimental simulation of basalt columns". ''Journal of Volcanology and Geothermal Research''. vol. 86, no. 1–4, pp. 93–96Spry, A. (1962). "The origin of columnar jointing, particularly in basalt flows". ''Journal of the Geological Society of Australia''. Vol. 5, pp. 191–216.

Uses

Trap rock, i.e. basalt or diabase, has a variety of uses. A major use for basalt is crushed rock for road and housing construction in

concrete Concrete is a composite material composed of aggregate bound together with a fluid cement that cures to a solid over time. It is the second-most-used substance (after water), the most–widely used building material, and the most-manufactur ...

, macadam, and paving stones. Because of its insensitivity to chemical influences, resistance to mechanical stress, high dry relative density, frost resistance, and seawater resistance, trap rock is used as ballast for railroad track bed and hydraulic engineering rock ( riprap) in coast and bank protection for paving embankments. It is also used for the production of cast rock that is used in corrosion and abrasion protection, as for sewage pipes and acid-resistant rocks. Other uses include gardening and landscaping, for the production of millstones, for the production of mineral wool, as a flux in ceramic masses and glazes, for the production of glass ceramics, crushed as a filter aggregate (air filtration of poison gas) in ABC bunkers, as filter bed material at water treatment facilities, and ground as a soil improvement product.Lorenz, W., and W. Gwosdz (2003). ''Manual on the Geological-technical Assessment of Mineral Construction Materials''. Geological Yearbook Special Issue series H, issue SH15. Federal Institute for Geosciences and Natural Resources and the State geological surveys in the Federal Republic of Germany, Commission E. Hense (Naegele and Obermiller), Hanover, Germany. 497 pp. . Trap rock has been used to construct buildings and churches: Trinity Church on the Green with trap rock quarried from Eli Whitney's quarry is a particularly colorful example of a red-orange-brown-colored, natural-faced trap rock.

Examples

Well-known examples of outcropping trap rock include both intrusive sills and extrusive lava flows. They include the Palisades Sill, a

Triassic The Triassic ( ; sometimes symbolized 🝈) is a geologic period and system which spans 50.5 million years from the end of the Permian Period 251.902 million years ago ( Mya), to the beginning of the Jurassic Period 201.4 Mya. The Triassic is t ...

, 200- Ma diabase intrusion that forms the Palisades along of the

Hudson River The Hudson River, historically the North River, is a river that flows from north to south largely through eastern New York (state), New York state. It originates in the Adirondack Mountains at Henderson Lake (New York), Henderson Lake in the ...

in New York and

New Jersey New Jersey is a U.S. state, state located in both the Mid-Atlantic States, Mid-Atlantic and Northeastern United States, Northeastern regions of the United States. Located at the geographic hub of the urban area, heavily urbanized Northeas ...

. Vast areas of trap rock in the form of thick lava flows and other volcanic rocks comprise the Deccan Traps of India and Siberian Traps of Russia. Other prominent basalt ridges, mountains, buttes, canyons, and other landscape features include: * In North America: ** The ridges and cliffs of the Columbia River Gorge in

Oregon Oregon ( , ) is a U.S. state, state in the Pacific Northwest region of the United States. It is a part of the Western U.S., with the Columbia River delineating much of Oregon's northern boundary with Washington (state), Washington, while t ...

and Washington. Behind Latourell Falls are columns of trap rock. ** Basalt Mountain near

Basalt, Colorado Basalt is a List of municipalities in Colorado#Home rule municipality, home rule town located in Eagle County, Colorado, Eagle and Pitkin County, Colorado, Pitkin List of counties in Colorado, counties, Colorado, United States. The town populat ...

. ** The Metacomet Ridge of

Connecticut Connecticut ( ) is a U.S. state, state in the New England region of the Northeastern United States. It borders Rhode Island to the east, Massachusetts to the north, New York (state), New York to the west, and Long Island Sound to the south. ...

and

Massachusetts Massachusetts ( ; ), officially the Commonwealth of Massachusetts, is a U.S. state, state in the New England region of the Northeastern United States. It borders the Atlantic Ocean and the Gulf of Maine to its east, Connecticut and Rhode ...

. ** The Watchung Mountains of New Jersey **

Devils Postpile National Monument A devil is the personification of evil as it is conceived in many and various cultures and religious traditions. Devil or Devils may also refer to: * Satan * Devil in Christianity * Demon * Folk devil Art, entertainment, and media Film and ...

and other parts of

California California () is a U.S. state, state in the Western United States that lies on the West Coast of the United States, Pacific Coast. It borders Oregon to the north, Nevada and Arizona to the east, and shares Mexico–United States border, an ...

's inner coastal range. ** Most of the

Hawaiian Islands The Hawaiian Islands () are an archipelago of eight major volcanic islands, several atolls, and numerous smaller islets in the Pacific Ocean, North Pacific Ocean, extending some from the Hawaii (island), island of Hawaii in the south to nort ...

and their mountains are composed of basalt or similar volcanic rock. ** The Green Gardens region of Gros Morne National Park in

Newfoundland Newfoundland and Labrador is the easternmost province of Canada, in the country's Atlantic region. The province comprises the island of Newfoundland and the continental region of Labrador, having a total size of . As of 2025 the population ...

* The Emeishan Traps in China *

Giant's Causeway The Giant's Causeway () is an area of approximately 40,000 interlocking basalt columns, the result of an ancient volcano, volcanic fissure eruption, part of the North Atlantic Igneous Province active in the region during the Paleogene period. ...

in Ireland * Organ Pipes National Park in Australia * The Paraná and Etendeka Traps of Brazil * The island of Surtsey in

Iceland Iceland is a Nordic countries, Nordic island country between the Atlantic Ocean, North Atlantic and Arctic Oceans, on the Mid-Atlantic Ridge between North America and Europe. It is culturally and politically linked with Europe and is the regi ...

, a new (1963) volcanic island. * The Vilyuy Traps of Russia

References

{{DEFAULTSORT:Trap Rock Igneous petrology Igneous intrusions Mafic intrusions

Uses

Examples

See also

References