What space igneous rocks?

Igneous rocks space the many basic type of rocks. They are formed when magma (molten rock, generally derived indigenous the earth"s mantle) solidifies. This can occur beneath or above the surface, bring about 2 subtypes:1) Intrusive rocks or Plutonic rocksWhen magma never reaches the surface and also cools to kind intrusions (dykes, sills etc) the resulting rocks are called plutonic. Depending upon their silica content, lock are called (in ascending order of silica content) gabbro, diorite, granite and also pegmatite. Through quantity, these space the by much most common rock types. Most magmas actually never ever reach the surface ar of the earth.

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2) Extrusive rocks or Volcanic rocksWhen magma does reach the surface throughout a volcanic eruption, the rocks that type there are dubbed lavas or volcanic rocks. The straightforward classification is the exact same as because that plutonic rocks: with raising silica content, lock include: basalt, andesites, dacites, rhyolite, pumice and also obsidian.

Main types of igneous rocks

The most widely used and also simplest group of igneous rocks is follow to the silica (SiO2) content in the bulk rock composition. The many common species are displayed in this table:
Weight % of SiO2Plutonic rock typeVolcanic rock equivalent

Gabbro is a silica-poor intrusive igneous (plutonic) rock chemically tantamount to basalt. The is normally coarse-grained, dark and also typically includes feldspar, augite and sometimes olivine.

Diorite is one intrusive igneous rock written principally the the silicate mineral plagioclase feldspar (typically andesine), biotite, hornblende, and/or pyroxene. The chemistry composition the diorite is intermediate in between gabbro and also granite. It synchronizes to the volcano rock form andesite
created when the same magma erupts to the surface and cools quickly.


Basalt from Ethiopia - the columnar jointing is a an outcome of slow cooling, enabling to distribute contraction fractures come arrange in a hexagonal columnar pattern, the geometry that needs the least energy to carry out the necessary space when the rock gradually contracts.

Rhyolite native Milos island, Greece, erupted approx. 84,000 years ago. Rhyolite is the extrusive equivalent to the plutonic rock type granite - both kind from the same magma. Rhyolite lava flows are very viscous. As result of their high viscosity, lock only relocate through laminar circulation along sheer planes that type where gas bubbles concentrate. These flow structures are usually visible in the cooled rock. They are additionally at the Greek beginning of the surname of the rock, stemming native rheo ("flowing") and also lithos ("rock").
Andesite is a volcano (=extrusive igneous) rock through an intermediary to high silica content. That is the eruptive tantamount of diorite,- the same magma that produces diorite as an intrusion will come to be andesite if erupted. Andesite is generally light come dark gray or pale-red in color and also typically consists of a fine-grained or glassy groundmass with embedded crystals (phenocrysts) of plagioclase, pyroxenes and/or amphiboles. It is just one of the most typical magmas erupted from subduction zone volcanoes and is usually connected with both effusive and explosive eruptions.
Granodiorite is an intrusive igneous absent in composition intermidiate in between diorite and granite. It frequently contains much more than 20% quartz by volume, a huge amount of salt (Na) and calcium (Ca) wealthy plagioclase, minor quantities of muscovite mica, and also biotite and also amphiboles as the darker minerals.The volcano rock tantamount of granodiorite is dacite.

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Granite, the tantamount of its extrusive (volcanic) rock kind rhyolite, is a very common type of intrusive igneous rock. That contains more than 68% weight % of silica in composition and is granular and also coarse-grained in texture. Its principal minerals room feldspars, quartz, and mica. Granites can be mostly white, pink, or gray in color, depending upon their mineralogy.