Rock (geology)
As a rock is called a fixed, naturally occurring, usually microscopic heterogeneous combination of minerals, rock fragments, glasses or residues of organisms. The mixing ratio of these components to each other is largely constant, so that a uniform rock acts, despite its detailed composition at freiäugiger consideration.
The investigation of the Lithogenesis ( gr λίθος lithos = stone, rock, rock), petrogenesis ( πετρος petros meaning stone ) or rock formation is a central area of Petrology and Geology, but also in geophysics and geochemistry.
Most rocks of the Earth's crust (and also the terrestrial planets ) are silicate rocks (main components feldspars and quartz), only a small percentage are carbonates.
- 7.1 Notes and references
- 7.2 Literature
- 7.3 External links
- 7.4 See also
Definition
The geologic term is broader than the colloquial and is also naturally occurring metal alloys, volcanic glass, ice, loose sand or coal one. The doctrine of the rocks, petrology, is a branch of earth sciences. Examples of different types of rock are found in the list of rocks.
The Earth and the inner planets of the solar system are made up of very large, spatially contiguous masses of rocks. However, they are visible and accessible only at the surface of the earth's crust, especially in the mountains, caused by tectonic processes of orogenesis.
The doctrine of the treatment and processing of rocks and earth, whose character is non-metallic, called Mineral Engineering.
Composition, microstructure and structure
Rocks consist mainly of minerals, of which only about thirty have a significant proportion of the rock formation, which are therefore called rock-forming minerals '. Above all, these are silicates, such as feldspars, quartz, mica, amphibole or olivine, but also carbonates such as calcite or dolomite are important components of rocks. In addition to these Hauptgemengteilen ( the mineral components that make up more than 10% of the total mass ) contain most of the rocks are so-called Nebengemengteile ( components that make up 10-1 %) and accessory minerals ( components that are included only to < 1%). Often the last accessories for a rock are eponymous. Furthermore, it is consistently a certain amount of water present as water of crystallization or pore water.
As the structure of a rock is known especially its texture - the spatial location and distribution of the minerals in a rock resulting from the properties and the ratio of the rock-forming minerals to each other - and the structure is related to the geometric properties of the individual rock components. These include relative and absolute size, the shape of the crystals or mineral grains, and the type of grain Association.
Lithoclasses and development
Natural stone can be classified according to their origin ( genesis ) divided into three rock classes. Instead of, rock class ' is often the term rock ' is used.
In geotechnical engineering and numerous related sciences such as soil science rocks are generally differentiated into two groups, the hard rocks and unconsolidated rocks. In the technical sense ( in processing ) a distinction is made in hard rock and soft rock.
Igneous rocks ( igneous rocks )
Igneous rocks ( rocks solidification ) caused by the cooling and crystallization of molten material from the Earth's interior, the so-called magma. The nomenclature of igneous rocks by their mineral constituents found in the Streckeisen diagram.
Finds the cooling underground ( deeper than 5 km) instead, it is called plutonic or intrusive ( plutonic rock ). Due to the relatively good thermal insulation of the overlying rocks, the magma melt cools slowly so that large mineral crystals can occur. Examples of plutonic rocks are granite, granodiorite, syenite, diorite, gabbro or. The magma can form huge masses of rock, the so-called plutons, which often contain several thousand cubic kilometers of rock.
However, magma may come to light in the liquid state. On the surface in contact with air, it cools quickly and then forms the so-called volcanic or Extrusivgesteine ( igneous rocks ). The rapid cooling occurs only in the formation of very small crystals such as the basalt or andesite. Other examples are rhyolite and trachyte. Often even exists at all, no crystalline order, and there is volcanic glass such as obsidian.
Dyke rocks form the intermediate members of plutonic and volcanic rocks. They penetrate gaps between magma chamber and surface of the earth, and there grow cold as transitions. Typical of these rocks is porphyritic structure so-called. The relatively rapid cooling state leads to the formation of a uniform matrix (matrix). However, crystals have been on the way there, in the magma chamber, exactly as in the plutonic rocks, emerged. These crystals are then such as the granite porphyry, as larger phenocrysts in the groundmass visible. Other examples of dike rocks are, for example, Pegmatites, aplites and lamprophyres.
Metamorphic rocks ( metamorphic )
Metamorphic rocks ( rocks conversion ) arise from older rocks of any type through metamorphosis, ie by conversion under high pressure or high temperature. In the conversion changes the mineral composition of the rock, because new minerals and mineral aggregates are formed; the Gesteinschemismus remains largely the same. In addition, the stone structure is transformed. Example is the formation of quartz sands by recrystallization and the formation of a fine cement between the crystal grains, the metamorphic rock quartzite, limestone is formed from marble.
Expansive metamorphism of rocks usually takes place at a great depth, local transformations can also occur near the earth's surface, usually in connection with volcanism or shallow granite intrusions. Also meteorite impacts cause rock metamorphoses.
- Regional metamorphism is related to the formation of mountains and is often pressure stresses. The associated folding of rocks by compression leads to recrystallization and Einregelung of minerals and the formation of a foliation. An example is the conversion of argillaceous sediments in slate, or of igneous rocks in gneiss.
- Contact metamorphism refers to the conversion of the rock out due to heat from the surrounding rock, either on a local scale by heating the rock to smaller magmatic transitions around to large transformation zones, so-called halos that form around large, deep-seated plutonic granite intrusions around.
Sedimentary rocks ( sedimentary rocks )
Sedimentary rocks ( sedimentary rocks, sedimentary rocks ) occur
- By weathering and erosion of rocks and redeposition of weathering products, which can be transported by wind (for example, loess ), water ( for example, clay and sand) or ice (eg Tillit )
- By the separation of substances dissolved in water, due to evaporation of water ( evaporite )
- By precipitation of substances as a result of the metabolism of living organisms ( for example lime, chalk and radiolarite )
Thus, sedimentary rocks can be distinguished, depending on the nature of their genesis in clastic, chemical and organogenic ( biogenic ) sedimentary rocks.
If the deposits covered by sedimentation further material, they are condensed by pressure, binder supply and increased temperature with increasing water loss more and more until by Neukristallisation and compaction of the soft sediment a hard, brittle sedimentary rock is formed. It identifies the individual minerals and rock fragments through a fine-grained matrix, the matrix together. These changes after primary sedimentation is called diagenesis.
Examples of sedimentary rocks are sandstone, calcareous sandstone, limestone, conglomerates and breccias.
Sediments are deposited mostly in a cumulative sequence of horizontal layers from; by the order of deposition are of exceptional cases apart higher -lying layers younger than deeper, a knowledge that goes back as superposition principle or storage Act on the Danish physician and geologist Nicolaus Steno. After their formation sedimentary rocks may be subject to strong forces, as a result of which the formerly flat layers are folded and tilted, so that the position of the rock in the room can be changed so much that the original layer sequence is locally reversed.
Sediments can be roughly divided into terrestrial land and marine marine sediments. The former one is also deposits in fresh water lakes or rivers that have arisen out of sand or mud, and the organic remains of plants from which coal has emerged. Even desert sediments and deposits of glaciers are assigned to this group. A borderline case between volcanics and sediments are volcanic ashes and tuffs.
Marine sediments can be caused by deposition of eroded materials of other rocks on the seabed, by caused by biochemical processes precipitation as carbonates and by depositing inorganic skeletons of microorganisms such as foraminifera, coccolithophores ( Haptophyta ), radiolarians ( Radiolaria ) or diatoms ( Bacillariophyta ).
Meteorites
A special case among the rocks form the meteorite body of rock from space. Meteorites are remnants of the original matter of the solar system and contain many minerals that can not be found in other rocks of terrestrial origin. They can be according to their mineral content divided in stone meteorites composed primarily of silicates such as olivine or pyroxene, iron meteorites, which are often composed of iron -nickel minerals kamacite and taenite and stone -iron meteorites, which are a mixed type. The size of meteorites is between that of micrometeorites and huge, barrel- heavy rock bodies. From Sweden several hundred million year old fossil meteorites are known.
Earthly origin, but formed by meteorite impacts are the tektites, centimeter-sized glass objects, the earthly by weft conditional melting rock and subsequent rapid cooling in air arise, and the impactites, the most by the severe mechanical and thermal effects in a meteorite impact of the of impact existing rocks such as suevite occur.
The rock cycle
Igneous, metamorphic and sedimentary rocks are transformed by geodynamic processes such as erosion, sedimentation, metamorphism or another.
Thus, subject to erosion of the overburden exposed metamorphic and igneous intrusives as well as those formed on the surface sediment and igneous Extrusivgesteine of weathering and erosion. Primarily by wind- or water-borne transport, the weathering components are deposited as sediments and sedimentary rocks formed by compaction eventually. These are changing as well as magmatic intrusive rocks at great depths under high pressure and high temperature in metamorphic rocks around. The cycle is complete when either return to the surface or be melted by further lowering into the earth and thus form the raw material for the formation of igneous rocks.
The oldest rocks
The oldest yet a verified date rock comes from the Acasta - gneiss formation of the Slave craton in northwestern Canada with 4,031 ± 0,003 billion years (dated 1999). Researchers at McGill University in Canada in 2008 claimed to have found in Nuvvuagittuq greenstone belt on Hudson Bay in northern Canada an even older rock 4.28 billion years ago. This dating is still controversial, the age of these rocks is still under investigation.
Due to the cycle of rocks and sedimentary rocks, which consist of ingredients ( minerals ), which were released by erosion of older rocks and are therefore older exist. An example of this are the metasediments in the so-called Jack Hills (Western Australia) were deposited 3 billion years ago, however, contain up to 4.4 billion years old zircons.
Importance
Rocks were used in human history as the first material for the production of tools, the stone tools, and thus also the namesake for the oldest cultural-historical Earth Poche, the Stone Age. Archaeological finds from this period are mostly stone artifacts. Stones are the oldest solid building material of human culture and the oldest known surviving inscription support human written culture.
The art of working stones called Lithurgik.
In previous eras entire buildings were built from rocks. Today, they are an essential element in interior design ( flooring, staircase, window sill, vanity and kitchen countertop ) and exterior ( façade cladding or paving stone). Furthermore, they are the foundation of pictorial representations in art, particularly in lithography and as a starting material of the sculpture. Jewelery, precious stones and semi-precious stones are popular as jewelry. Cairns and dry stone walls were once used as a marker of fields and are today valuable biotopes. A landmark is used to delimit areas. Fossils in the form of fossils are evidence of past living organisms eons, eras and periods and play an important role for the study of past life forms, the evolutionary history as well as for the dating of rock layers.