Igneous rocks

The earth’s crust made up of different types of rocks. The rocks that make up the maximum volume of the earth’s crust are called igneous rocks. The word igneous derived from the Latin word  Ignace which means fire. These rocks are associated with volcanic eruptions. Igneous rock forms 15% of the earth’s land and most of the oceanic crust made up of igneous rocks. The igneous rocks first form and also known as primary rocks.

Extrusive igneous rocks

The liquid rock matter that coming out from volcanoes it is called magma.it is a hot liquid made up of melted minerals. when this magma reaches the surface it is known as lava.

The cooling and solidification of lava at the earth’s surface result in the formation of extrusive igneous rocks. Which also known as volcanic rocks due to rapid cooling crystals are fine-grained. Hot gas bubbles are often trapped in the quenched lava, forming a bubbly, vesicular texture. Pumice and obsidian are extrusive igneous rocks. Pumice is used to making lightweight concrete. Obsidian is used in ornaments. These rocks include andesite, basalt, dacite, obsidian, pumice, rhyolite, scoria, and tuff.

RocksTextureMineralsComposition
AndesiteFine-grainedNa-plagioclase, amphibole, pyroxene, biotiteIntermediate
BasaltFine-grainedCa-plagioclase, pyroxene, olivine, amphiboleMafic
DaciteFine-grainedNa-plagioclase, quartz, orthoclase, amphibole, biotiteIntermediate
RhyoliteFine-grainedNa-plagioclase, orthoclase, quartz, biotite, amphibole, muscoviteFelsic
Obsidian Glassy textureglass (no minerals)Felsic to Mafic
PumiceVesicularglass (may contain a few minerals typical of felsic rocks)Felsic
Rhyolite,Fine-grainedNa-plagioclase, orthoclase, quartz, biotite, amphibole, muscoviteFelsic
ScoriaVesicularglass (may contain a few mineral typical of mafic rocks)Mafic

Intrusive igneous rocks

Some of the magma can’t come out and settled inside the surface. Magma cools slowly beneath the surface as completely surrounded by pre-existing rocks(called country rocks). The cooling and solidification at the dept within the earth’s crust result in the formation of large crystals known as intrusive igneous rocks. The mineral grains in such rock generally can be identified with the naked eye. Intrusive formations are batholiths, stocks, laccoliths, sills, and dikes. When the magma solidifies within the earth’s crust, it cools slowly forming coarse textured rocks, such as granite, gabbro, or diorite. Both Granite and diorite igneous rocks used as building materials. Examples of intrusive igneous rocks are diabase, diorite, gabbro, granite, pegmatite, and peridotite.

RocksTextureMineralsComposition
DioriteCoarse-grainedNa-plagioclase, amphibole, pyroxene, biotiteIntermediate
GabbroCoarse-grainedCa-plagioclase, pyroxene, olivine, amphiboleMafic
GraniteCoarse-grainedNa-plagioclase, orthoclase, quartz, biotite, amphibole, muscoviteFelsic
PegmatiteCoarse-grainedNa-plagioclase, orthoclase, quartz, biotite, amphibole, muscoviteFelsic
PeridotiteCoarse-grainedolivine. It may contain small amounts of amphibole, feldspar, quartz, or pyroxeneUltramafic 

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