Igneous rock
Igneous or magnetite (after gr μάγμα Magma " kneaded mass " ) or igneous rock is rock formed by crystallization on cooling glutflüssiger molten rock ( magma ) has emerged. The igneous rocks are in addition to the sedimentary rocks ( Sedimentiten ) and the metamorphic rocks of one of the three main rock groups.
Grouping
After their formation and their structural characteristics magmatic rocks are petrographic divided into two groups: Plutonite ( plutonic rocks ) caused by solidification of magma inside the earth, volcanic rocks ( igneous rocks ) formed from magma that has emerged from the earth's interior to the surface ( lava) and there by cooling solidifies. Whether the cooling and solidification of molten rock above or below ground is carried out has a significant influence on the crystallization and texture of the resulting rock.
Plutonic rocks ( plutonic rocks )
Plutonite (after Pluto, the Greek god of the underworld ) or plutonic rocks are igneous rocks called that within the earth's crust - usually at a depth of one to several kilometers - solidify and crystallize. The plutonic rocks have a medium-to coarse-grained structure. Her most famous representatives are granite, syenite and diorite, and the.
The faster the melt cools, the more fine-grained is the rock. The longer the other hand, the process of solidification takes (eg, good insulation through the host rocks ), the more time the minerals to form larger crystals.
Volcanic rocks ( igneous rocks )
Volcanics (after Vulcan, the Roman god of fire) or igneous rocks are those igneous rocks which formed during the solidification of lava at the surface by volcanic magma escaped. As a result of rapid solidification, they are often very fine-grained or even glassy, as only little time for growth of larger crystals remains. Characteristic of many volcanic rocks is a porphyritic structure, with larger phenocrysts in a fine-grained groundmass. The igneous rocks are also called Extrusiv, eruption, effusive and Volcanic rocks. Among the best known representatives of this group of rocks are basalt and andesite and the trachyte.
Subvulkanite ( dykes )
Some of the dykes ( Subvulkanite, transitional or Mesomagmatite ) are managed as separate rock group, but partly associated with the two aforementioned groups. They are caused by intrusion of magmatic melts in or between existing rock body and have a connection to the earth's surface and volcanoes to plutons of the depth and corridors except can also form cupolas or sills; see also Lakkolith.
Group on the chemical composition
The igneous rocks can also be grouped according to their chemical composition. A distinction is made between
- Alkaline igneous rocks
- Subalkaline igneous rocks
The subalkalinen igneous rocks are described by the ratio K2O Na2O < Al2O3, while the alkaline igneous rocks show a higher content of K2O Na2O.
Classification
Igneous rocks can be classified according to various criteria. One of the most common methods is the division in the Streckeisen diagram on the basis of mineral deposits. Other current methods take into account the brightness ( color index ), the texture or the chemistry (such as the SiO 2 content or the content of alkalis, iron, magnesium or other elements ).