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

  • Water Table

    ByGeo Forward

    Water Table Water Table: In the hydrogeology branch of geology, the water table represents the surface of an unconfined groundwater aquifer, where the hydraulic pressure is equal to atmospheric pressure. Additionally, a water table is present in a perched groundwater zone. Although, there is no water table in a confined aquifer.

  • Effective Stress (σ’)

    ByGeo Forward

    Effective Stress (σ’) “Effective Stress” (σ’) is a geotechnical engineering term. Effective Stress is a function of “total stress,” and is due to the solid particles of soil. Effective stress represents an excess of stress above pore-water pressure (or neutral stress). Effective Stress Formula Effective Stress = Total Stress – Pore-Water Pressure.

  • Metamorphic Rock

    ByGeo Forward

    Metamorphic Rock Definition In the field of geology, the term “Metamorphic Rock” refers to a rock classification that is the result of the alteration of prior existing sedimentary rocks or igneous rocks. The alteration process is “metamorphosis, and can take place by various methods and environments. The metamorphosis process produces specific metamorphic rocks, on the…

  • Environmental Consultant

    ByGeo Forward

    Environmental Consultant Environmental Consultant: An environmental consultant is an expert of any profession or field, who focuses their skills and knowledge towards matters that improve the environment. Environmental consultants are typically scientists with expertise in geology, chemistry, physics, and engineering. Environmental Consultants Working Towards Environmental Sustainability Environmental consultants generally provide professional services that aim towards…

  • Thermosphere

    ByGeo Forward

    Thermosphere Thermosphere: The thermosphere of a terrestrial planet is the fourth and final member of the atmosphere. On Earth, the thermosphere starts atop the mesosphere at approximately 85 kilometers above mean sea level. The upper limit of the thermosphere is reasonably presumed to terminate approximately 95 kilometers above mean sea level. In fact, most of…