What are the rock types



As rock a solid, naturally occurring, usually microscopically heterogeneous combination of minerals, rock fragments, glasses or residues of organisms with a largely constant mixing ratio of these components to one another.

The term geological rock is broader than the colloquial one and also includes naturally occurring metal alloys, volcanic glass, ice, loose sand or coal. The study of rocks, petrology, is a branch of the geosciences. Examples of different types of rock can be found in the list of rocks.

The earth and the inner planets of the solar system are made up of very large, spatially connected masses of rocks. However, these are only visible and accessible on the surface of the earth's crust, especially in mountains that are created by tectonic processes of mountain formation.

Composition and structure

Rocks consist primarily of minerals, of which only about thirty have a significant share in rock formation. Above all, these are silicates such as feldspars, quartz, mica, amphiboles or olivine, but also carbonates such as calcite or dolomite are important components of rocks. Besides these Main mix parts most rocks still contain so-called Side effects or Accessories.

The structure of a rock is its texture, the distribution of minerals in a rock, which results from the properties and the ratio of the rock-forming minerals to one another. In particular, the size and shape of the crystals contained, as well as their spatial position and distribution in the rock, make up the structure.

Rock classes and formation

Natural stones can be divided into three stone classes according to their origin (genesis). The most commonly used term Rock type is misleading, because animal and plant species are only created through evolution. The nomenclature of rocks according to their mineral composition can be found in the route iron diagram.

In geotechnics and numerous related sciences such as soil science, rocks are basically divided into two groups, solid rock and loose rock. In the technical sense (during processing) a distinction is made between hard stone and soft stone.

Igneous rocks (igneous rocks)

Igneous rocks (solidification rocks) arise from the cooling and crystallization of hot molten material from the interior of the earth, the so-called magma.

If the cooling takes place underground (deeper than 5 km), one speaks of plutonites or intrusive rocks (deep rock). Due to the relatively good thermal insulation of the rocks lying on top, the magma melt cools only slowly, so that large mineral crystals can arise. Examples of plutonic rocks are granite, granodiorite, syenite, diorite or gabbro. The magma can form huge masses of rock, known as plutons, which often comprise several thousand cubic kilometers of rock.

However, magma can also emerge in a liquid state. On the surface of the earth in contact with the air, it cools down quickly and then forms so-called volcanic rocks or extrusive rocks (effluent rocks). The rapid cooling only results in the formation of very small crystals such as basalt or andesite. Other examples are rhyolite and trachyte. Often there is even no crystalline order at all, and volcanic glass such as obsidian is formed.

Dike rocks form the links between plutonites and volcanites. They penetrate the gaps between the magma chamber and the surface of the earth, where they cool down as corridors. The so-called porphyry structure is typical of these rocks. The relatively rapid cooling in the corridor leads to the formation of a uniform base mass (matrix). However, just like with the plutonites, crystals have already formed on the way there, in the magma chamber. These crystals are then, like e.g. the granite porphyry, visible as larger sprinkles in the base mass. Further examples of dike rocks are e.g. pegmatites, aplites and lamprophyres.

Metamorphic rocks (metamorphic rocks)

Metamorphic rocks (transformation rocks) arise from older rocks of any type through metamorphosis, i.e. through transformation under high pressure or high temperature. During the transformation, the mineral composition of the rock changes because new minerals and mineral aggregates are formed; the rock chemistry remains largely the same. In addition, the structure of the rock is also transformed. For example, the metamorphic rock quartzite is formed from quartz sands through recrystallization and the formation of a fine cement between the crystal grains, while limestone forms marble.

Large-scale metamorphosis of rocks usually takes place at great depths, but local transformations can also occur near the earth's surface, mostly in connection with volcanism or shallow granite intrusions. Meteorite impacts also lead to rock metamorphosis.

  • Regional metamorphosis is related to mountain formations and is often pressure-stressed. The associated folding of rocks through compression leads to recrystallization and regulation of minerals and the formation of foliation. One example is the transformation of clayey sediments into shale, or igneous rocks into gneiss.
  • Contact metamorphosis describes the rock transformation through the action of heat from the surrounding rock, either on a local scale by heating the rock around smaller igneous passages up to large transformation zones, so-called aureoles, which form around large, deep-seated plutonic granite intrusions.

Sedimentary rocks (sedimentites)

Sedimentary rocks (deposit rocks) are formed by weathering and erosion of rocks by wind (for example loess), water (for example clay and sand) or ice (for example tillite), the solution, the transport and the subsequent deposition of their components, as well as by biochemically induced precipitation (e.g. lime and chalk) or by evaporation (Evaporit). Depending on the type of genesis, a distinction is made between clastic, chemical or organogenic sedimentary rocks.

If these are covered by sedimentation of further material, they condense more and more through pressure, the supply of binder and increased temperature, with increasing loss of water, until the hard, brittle sedimentary rock has emerged from the soft sediment through recrystallization and compaction. The individual minerals and rock fragments are held together by a fine-grained base mass, the matrix. These changes after the primary sedimentation are called diagenesis. Examples of sedimentary rocks are sandstone, sand-lime stone, limestone, conglomerates, and breccias.

Sediments are usually deposited cumulatively in a sequence of horizontal layers; Due to the order of the deposition, higher-lying layers are younger than lower-lying, apart from exceptional cases, a finding that as Superposition principle or Storage Act goes back to the Danish doctor and geologist Nicolaus Steno. After their formation, sedimentary rocks can 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 space can be changed so much that the original layer sequence is locally reversed.

Sediments can be roughly divided into the terrestrial Land and the marine Subdivide marine sediments. The former also include the deposits in freshwater lakes or rivers that have arisen from sand or mud, as well as the organic plant remains from which the coal has arisen. Desert sediments and deposits from glaciers are also assigned to this group. A borderline case between volcanic rocks and sediments are volcanic ashes and tuffs.

Marine sediments can arise from the deposition of erosion material from other rocks on the seabed, from the precipitation of carbonates, for example, caused by biochemical processes, and from the deposition of inorganic skeletons of microorganisms such as chamberlings (Foraminifa), coccolithophores (Haptophyta), radiolucent animals (Radiolaria) or diatoms (Bacillariophyta) .

Meteorites

Meteorites, rock bodies from space, are a special case of rocks. Meteorites are remnants of the original matter of the solar system and contain numerous minerals that cannot be found in other rocks of terrestrial origin. According to their mineral content, they can be divided into stone meteorites, which primarily consist of silicates such as olivine or pyroxene, iron meteorites, which are often composed of the 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 rock bodies weighing tons. Several hundred million year old fossil meteorites are known from Sweden.

Of earthly origin, but formed by meteorite impacts, are the tektites, centimeter-sized glass objects that are created by the melting of earthly rock caused by the impact and subsequent rapid cooling in the air, and the impactites, which are caused by the strong mechanical and thermal effects of a meteorite impact from the am Rocks from the site of impact arise, such as suevite.

Rock cycle

Main article: The cycle of rocks Igneous, metamorphic and sedimentary rocks are transformed into one another by geodynamic processes such as erosion, rock metamorphism or sedimentation.

Metamorphic and igneous intrusive rocks exposed by erosion of the cover rock, as well as the sedimentary and igneous extrusive rocks formed on the surface, are subject to weathering and erosion. Primarily through wind or water-related transport, the weathering components are deposited as sediments and finally form sedimentary rocks through compaction. Like igneous intrusive rocks, these transform into metamorphic rocks at great depths under high pressure and high temperature. The cycle closes when these either come back to the surface or are melted down further into the earth's interior and thus form the raw material for the formation of igneous rocks.

importance

In the history of mankind, stone served as the first material for the manufacture of tools, stone implements, and is therefore also the eponym for the oldest cultural and historical earth epoch, the Stone Age. Archaeological finds from that time are mostly stone artifacts. Stones are the oldest solid building material of human culture and the oldest known writing pad of human writing.

In earlier times, entire structures were built from stone. Today they are an essential part of interior construction (flooring, stairs, window sill, vanity and kitchen worktop) and exterior construction (facade cladding or paving stone). Furthermore, they are the basis of pictorial representations in art, especially in lithography and as the starting material for sculpture. Gemstones, precious stones and semi-precious stones are popular as jewelry. Stone piles and dry stone walls used to mark fields and are now valuable biotopes. A boundary stone is used to demarcate areas. Fossils in the form of fossils bear witness to living beings from earlier aeons, epochs and periods and play a major role in the study of past life forms, evolutionary history and the dating of rock layers.

literature

  • Maresch, W. and Medenbach O .: Steinbach's natural guide rocks. 287 pp., Munich, 1996. ISBN 3-576-10699-5
  • Peter Rothe: Rocks. Creation - destruction - transformation. Primus, Darmstadt, 2nd revised edition 2005, ISBN 3-89678-536-2
  • Roland Vinx: Rock determination in the field. 2005, 452 p., 7 b / w ill., 364 color ill., 14 b / w table. Spectrum Akademischer Verlag. ISBN 3-8274-1513-6

On the cultural history of the stone:

  • Matthias Bärmann (Ed.): The book from the stone - texts from 5 millennia. Jung & Jung, Salzburg and Vienna 2005. ISBN 3-902497-02-5

See also

Video

  • RealVideo: How do you know the age of rocks? (from the TV show Alpha Centauri)

Category: Rock