classify igneous rocks on the basis of occurrence
Answers
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Igneous rocks are classified according to mode of occurrence, texture, mineralogy, chemical composition, and the geometry of the igneous body. ... Igneous rocks that have crystals large enough to be seen by the naked eye are called phaneritic; those with crystals too small to be seen are called aphanitic.
Answer:
Explanation:
Magmas erupted from volcanoes are either poured out as coherent fluidal lava flows or
blown out as fragments of various sizes. A body of magma may also be emplaced and
cool beneath the surface of the Earth. Igneous rocks result from the final solidification
of magma at the surface or at variable depths within the Earth, as well as from the
eventual consolidation of fragmented debris.
Igneous rocks thus occur in two ways, either as “extrusive” (on the surface) rocks or as
“intrusive” (below the surface) bodies. Intrusive rocks are also called “plutonic” (Pluto,
the Greek god of infernal regions, therefore deep-seated) and extrusive rocks
“volcanic.” The terms intrusive and extrusive only refer to the place where the rock
solidified. Extrusive rocks cool rapidly because they have erupted at the Earth’s surface,
but intrusive rocks cool more slowly within an insulating blanket of surrounding rocks
into which they have been emplaced. The rapid cooling of magma gives a fine-grained
rock, which may even be glassy, whereas slower cooling gives coarse-grained rock with large crystals .