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Plutonic rocks are classified separately from extrusive igneous rocks, generally on the basis of their mineral content. The relative amounts of quartz, alkali feldspar, plagioclase, and feldspathoid are particularly important in classifying intrusive igneous rocks, and most plutonic rocks are classified by where they fall in the QAPF diagram.
Extrusive rock refers to the mode of igneous volcanic rock formation in which hot magma from inside the Earth flows out (extrudes) onto the surface as lava or explodes violently into the atmosphere to fall back as pyroclastics or tuff. [1] In contrast, intrusive rock refers to rocks formed by magma which cools below the surface. [2]
Bodies of intrusive rock are known as intrusions and are surrounded by pre-existing rock (called country rock). The country rock is an excellent thermal insulator, so the magma cools slowly, and intrusive rocks are coarse-grained . The mineral grains in such rocks can generally be identified with the naked eye.
Because the solid country rock into which magma intrudes is an excellent insulator, cooling of the magma is extremely slow, and intrusive igneous rock is coarse-grained . Intrusive igneous rocks are classified separately from extrusive igneous rocks, generally on the basis of their mineral content.
Monzonite – Igneous intrusive rock with low quartz and equal plagioclase and alkali feldspar – a plutonic rock with <5% normative quartz; Nepheline-bearing diorite – Form of intrusive igneous rock; Nepheline syenite – Holocrystalline plutonic rock – A silica-undersaturated plutonic rock of nepheline and alkali feldspar
In extrusive rocks, the phenocrysts are surrounded by a fine-grained (aphanitic) matrix or groundmass of volcanic glass or non-visible crystals, commonly seen in porphyritic basalt. Porphyritic intrusive rocks have a matrix with individual crystals easily distinguished with the eye, but one group of crystals appearing clearly much bigger than ...
A rock that cools within the Earth is called intrusive or plutonic and cools very slowly, producing a coarse-grained texture such as the rock granite. As a result of volcanic activity, magma (which is called lava when it reaches Earth's surface) may cool very rapidly on the Earth's surface exposed to the atmosphere and are called extrusive or ...
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. [1] Trap is also used to refer to flood (plateau) basalts, such as the Deccan Traps and Siberian Traps. [2]