Peridotite in the context of "Igneous"

Earth's crust is its thick outer shell of rock, comprising less than one percent of the planet's radius and volume. It is the top component of the lithosphere, a solidified division of Earth's layers that includes the crust and the upper part of the mantle. The lithosphere is broken into tectonic plates whose motion allows heat to escape the interior of Earth into space.

The crust lies on top of the mantle, a configuration that is stable because the upper mantle is made of peridotite and is therefore significantly denser than the crust. The boundary between the crust and mantle is conventionally placed at the Mohorovičić discontinuity, a boundary defined by a contrast in seismic velocity.

Ultramafic rocks (also referred to as ultrabasic rocks, although the terms are not wholly equivalent) are igneous and meta-igneous rocks with a very low silica content (less than 45%), generally >18% MgO, high FeO, low potassium, and are usually composed of greater than 90% mafic minerals (dark colored, high magnesium and iron content). Earth's mantle is composed of ultramafic rocks. Ultrabasic is a more inclusive term that includes igneous rocks with low silica content that may not be extremely enriched in Fe and Mg, such as carbonatites and ultrapotassic igneous rocks.

Serpentinite is a metamorphic rock composed predominantly of serpentine group minerals formed by serpentinization of mafic or ultramafic rocks. The ancient origin of the name is uncertain; it may be from the similarity of its texture or color to snake skin. Greek pharmacologist Dioscorides (AD 50) recommended this rock to prevent snakebite.

Serpentinite has been called serpentine or serpentine rock, particularly in older geological texts and in wider cultural settings.

Kimberlite is an igneous rock and a rare variant of peridotite. It is most commonly known as the main host matrix for diamonds. It is named after the town of Kimberley in South Africa, where the discovery of an 83.5-carat (16.70 g) diamond called the Star of South Africa in 1869 spawned a diamond rush and led to the excavation of the open-pit mine called the Big Hole. Previously, the term kimberlite has been applied to olivine lamproites as Kimberlite II, however this has been in error.

Kimberlite occurs in the Earth's crust in vertical structures known as kimberlite pipes, as well as igneous dykes and can also occur as horizontal sills. Kimberlite pipes are the most important source of mined diamonds today. The consensus on kimberlites is that they are formed deep within Earth's mantle. Formation occurs at depths between 150 and 450 kilometres (93 and 280 mi), potentially from anomalously enriched exotic mantle compositions, and they are erupted rapidly and violently, often with considerable carbon dioxide and other volatile components. It is this depth of melting and generation that makes kimberlites prone to hosting diamond xenocrysts.

Trap rock, also known as either trapp or trap, is any dark-colored, fine-grained, non-granitic intrusive or extrusive igneous rock. Types of trap rock include basalt, peridotite, diabase, and gabbro. Trap is also used to refer to flood (plateau) basalts, such as the Deccan Traps and Siberian Traps. The erosion of trap rock created by the stacking of successive lava flows often creates a distinct stairstep landscape from which the term trap was derived from the Swedish word trappa, which means "stairs".

The slow cooling of magma either as a sill or as a thick lava flow sometimes creates systematic vertical fractures within the resulting layer of trap rock. These fractures often form rock columns that are typically hexagonal but could be four- to eight-sided.

The Lewis Hills are a section of the Long Range Mountains located on the west coast of Newfoundland, along the Gulf of Saint Lawrence.

An ophiolite and Peridotite complex, the Lewis Hills are the southernmost of four such complexes located within the Humber Arm Allochthon, a world-renowned geological area. They are located in an area stretching between the town of Stephenville in the south and the city of Corner Brook in the north.

Obduction is a geological process whereby denser oceanic crust (and even upper mantle) is scraped off a descending ocean plate at a convergent plate boundary and thrust on top of an adjacent plate. When oceanic and continental plates converge, normally the denser oceanic crust sinks under the continental crust in the process of subduction. Obduction, which is less common, normally occurs in plate collisions at orogenic belts (some of the material from the subducting oceanic plate is emplaced onto the continental plate) or back-arc basins (regions where the edge of a continent is pulled away from the rest of the continent due to the stress of plate collision).

Obduction of oceanic lithosphere produces a characteristic set of rock types called an ophiolite. This assemblage consists of deep-marine sedimentary rock (chert, limestone, clastic sediments), volcanic rocks (pillow lavas, volcanic glass, volcanic ash, sheeted dykes and gabbros) and peridotite (mantle rock). John McPhee describes ophiolite formation by obduction as "where ocean crust slides into a trench and goes under a continent, [and] a part of the crust—i.e., an ophiolite—is shaved off the top and ends up on the lip of the continent."