How are extrusive and intrusive rocks formed

How are rocks formed?



There are many rocks. Each stone is the result of a long period of creation and was created in different ways.



Definition of rock

A rock is a solid that consists of minerals, volcanic glass or other rocks (example: conglomerate).
The mineral mix of rocks can be monomineral (i.e. consisting of one type of mineral, e.g. dolomite, marble) or polymineral (i.e. consisting of different minerals, e.g. gneiss, rhyolite, granite).


Depending on the conditions under which rocks were formed, between igneous, metamorphic and sedimentary rocks differentiated.


Igneous rocks - igneous rocks

Definition: igneous rocks are rocks that emerge from magma and lava. While the hot, liquid rock slurry beneath the earth's surface is called magma, magma that comes to light is called lava.

Rocks that form from magma are also referred to as intrusive rocks, deep rocks or plutonites.
On the other hand, there are extrusive rocks - also known as effusion rocks or volcanic rocks - that are formed on the earth's surface.
An intermediate position is taken by the group of dike rocks or sub-volcanic rocks, which arise when magma rises like a dike in existing rock bodies, where it cools down and has properties such as plutonites and volcanic rocks.

Common to both volcanites and plutonites is the formation: Cool lava and magma below or above the surface of the earth, minerals crystallize and solidify into a coherent mixture - called rock. The temperature at which the first crystals (so-called early crystals) and thus the rocks develop is different and depends largely on the individual crystallization temperature of the minerals.

The SiO is important for an initial differentiation from igneous rocks2-Content that can be inferred from the rock color. Acid / Felsic Rocks (SiO2 < 63="" %)="" sind="" von="" heller="" farbe.="" basische/mafische="" gesteine="">2 45-52%) appear dark and rocks with intermediate chemistry are in the area in between.
The composition of magma and lava varies, as a result of which there are local differences in the distribution and occurrence of igneous rocks.

Well-known igneous rocks are granite, gabbro and norite as well as basalt, pumice and pitch stones.

Sedimentary stones

Another group of rocks represent the Sedimentary rocks represent.
Definition: Sedimentary rocks are also called deposit rocks and are Result of deposition and solidification various rock-forming materials, but can also do that Result of evaporation be.

The components of sedimentary rocks are weathered, crushed rocks (keyword sand) and minerals, biogenic products such as the shells of various mussels, snails and other organisms. At the time of its formation, new materials were continuously being deposited, the load was steadily increased - and since this process mainly took place in the water - water was pressed out of the sediments. The so-called mixed parts are held together by quartz solutions, limes or clays, which virtually concretize the former loose materials with one another. The process of sedimentation is comparatively “gentle”, so that a number of fossils can very often be found in sedimentary rocks.

The most common sedimentary rocks are limestone, chalk, travertine, sandstone and dolomite.

Rock salt is also one of the sedimentary rocks. But the formation differs from that of other sedimentary rocks. In short: Salt was in dissolved form in the water at the time it was formed. The water evaporated, for example in separate lagoons or shallow water areas, and left rock salt behind as an evaporated residue.

Metamorphic rocks - metamorphic rocks

The development of Metamorphic rocks, Transformation rocks.
Under the Influence of heat and / or high pressure conditions existing rocks are transformed in such a way that new rocks are created. It does not matter which rock is the parent rock.

The metamorphosis of rocks covers igneous rocks as well as metamorphic and sedimentary rocks. Depending on the pressure and / or temperature, the batch parts are either readjusted (e.g. slate), partially or completely melted. Under extreme conditions it can happen that the reactants turn into magma.

The characteristics of metamorphic rocks are very different and striking; range from foliation (plate-like segregation), band-like regulation of the minerals in the rock (gneiss) to the crystalline structure of marble or quartzite.

The prerequisites for metamorphosis are given, for example, when magma intrudes into existing rocks (so-called contact metamorphosis) or during tectonic events (mountain formation, earthquakes).

See also:
⇒ cycle of rocks
⇒ Main and secondary parts of rocks
⇒ What is the meaning of stacked stones?

Last updated: November 8, 2017

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