Igneous Rock

Igneous Rock Definition

In the field of geology, the term “Igneous Rock” refers to one of the three major classifications of rock that comprises the earth. As opposed to sedimentary rocks or metamorphic rocks, igneous rock derives from the direct cooling and solidification of magmatic material. Igneous rock comprises a large amount of the planet earth’s crust. To illustrate, geologists today understand that about 90% of the earth’s oceanic crust, and about 60% of the earth’s continental crust, is igneous.

Classification of Igneous Rock

Igneous rock classifications are based on mineral composition and texture:

  • To illustrate, “texture” refers to the grain size and arrangement of the minerals in igneous rock. In fact, texture aids in the prediction of the rate of cooling. For instance, large crystals are indicative of a slower cooling process, whereas small crystals are indicative of a rapid cooling process. And textures are also influenced by water and gas content in magma.
  • On the other hand, “composition” refers to the individual mineral chemistry, as well as the chemical content of the igneous rock. In fact, the classification of igneous rocks breaks down compositions by feldspar, quartz, and mafic mineral content.

Extrusive Igneous Rock

Extrusive rocks are igneous rocks that have erupted on the surface of the earth. In some divisions of geology, eruptions near the earth’s surface may also classify as extrusive.

Intrusive Igneous Rock

Intrusive rocks are also igneous rocks that have formed within the earth by the replacement of magma within the deep subsurface. In fact, this may occur within another pre-crystallized igneous rock.

Similar Posts

  • Rigidity

    ByGeo Forward

    Rigidity Definition Rigidity – In geotechnical engineering and engineering geology, rigidity represents the ratio of the shear stress and the amount of angular rotation that it produces, within a rock sample.

  • Trench Dam

    ByGeo Forward

    Trench Dam Trench Dam: Per the Los Angeles Department of Building and Safety (LADBS) Methane Code, Ordinance Number 175790, a trench dam is part of a methane mitigation system. A trench dam is essentially a subsurface barrier that exists within a furrow or ditch, that is adjacent to the foundation of a building in a…

  • Phaneritic

    ByGeo Forward

    Phaneritic Definition In geology, the term Phaneritic applies to the texture of an igneous rock. A phaneritic plutonic rock has grains that are large enough to be seen with the naked eye. In fact, this indicates there was a slower rate of magmatic cooling.

  • Hydraulic Conductivity (K)

    ByGeo Forward

    Hydraulic Conductivity (K) “Hydraulic Conductivity” (K), in hydrogeology and hydrology, represents the capacity of a porous medium (such as soil) to transmit water, as per Darcy’s Law. To illustrate, the rate at which fluid can move through a permeable medium (such as soil), depends on the properties of that soil (such as intrinsic permeability) and…

  • Engineering Geology & Geological Engineering

    ByGeo Forward

    Engineering Geology or Geological Engineering Engineering Geology: Engineering geology is also referred to as “geological engineering,” and is a branch of geology that relates to the study of earth materials and processes, that are juxtaposed to proposed structures such as buildings, retaining walls, dams, roads, pipelines, and more. Whereby geologists assess any potential levels of…

  • Facies

    ByGeo Forward

    Facies Facies: In the field of geology, the term “facies” represents a mappable, areally restricted part of a rock body that has different fossils or lithology from other contiguous beds deposited at the same time.