Rocks, or stones, are naturally occurring solid aggregates of minerals. They are being constantly formed, worn down, and then formed again in a process known. Like most Earth materials, rocks are created and destroyed in cycles. The rock cycle is a model that describes the formation, breakdown, and reformation of a. Igneous Rocks are formed by the cooling and crystallization of a silicate melt (dominated by oxygen and silicon, with a variety of other metals). The occurrence.


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In many cases no experiment is necessary. Based on their composition, sedimentary rocks are classified as organic, clastic, or non-clastic.

Formation of rocks

Organic sedimentary rocks are derived from organisms, and examples of formation of rocks are coal and limestone. Limestone is a rock that contains many fossils and is made of calcium carbonate and microscopic shells.

Clastic sedimentary rocks like conglomerates and shale are formed from any size particle of pre-existing rock. Conglomerate rock has rounded pebbles cemented together in a matrix.


The most common metamorphic minerals are: Aside of new minerals we can also observe the development of new textures in these rocks.

The most common of these textures is foliation layered texturemeaning that the minerals are aligned and grew under directed pressure see above. Foliation is caused by formation of new and the recrystallization grain growth, coarsening of preexisting mineral grains change in pressure and temperature.

Depending on the degree of foliation we distinguish formation of rocks major metamorphic rock types. Slates are the most fine grained variety of foliated rocks and are produced by low grade metamorphism of shales and mudstones.

The most characteristic feature is the so called slaty cleavage from newly formed micas. Slaty cleavage usually is oriented at a high angle to the original bedding of the shales. In the picture on the left the bedding of the original rock dips at about 40 degrees to the right sandy layers in brownand the slaty cleavage dips at about formation of rocks degrees to the right.

Slates tend to split apart at this cleavage, and fall apart in platy fragments used in former times as a writing surface, that could easily be wiped off, A clean Slate. The development formation of rocks slaty cleavage depends on the amount formation of rocks clay and detrital micas available in a rock starting material for metamorphic mica growth.

Formation of rocks - Wikipedia

Schists are medium to coarse grained foliated rocks, in which the parallel aligned micas and the foliation are readily visible to the eye.

They do not only form from shales, but also from other parent rocks such as basalt, granite, sandstones and tuffs. They are by volume the most abundant metamorphic rock type. The picture at formation of rocks left shows a handspecimen of greenschist. The greenish mineral in the foliation plane is chlorite.

Gneisses are very coarse grained metamorphic rocks that form during high grade metamorphism.

How Are Rocks Formed? - Universe Today

They are distinctly banded segregation of newly formed minerals into bandsand their main minerals formation of rocks quartz, potassium feldspar, and biotite or hornblende ferromagnesian formation of rocks. It is of similar composition than granite, and if a gneiss is heated just a little bit further, a granitic melt will rise from it.

The picture at the left shows a garnet-biotite gneiss garnet are the reddish spots, the black mineral is the biotite with quartz-feldspar groundmass white-gray.

Metamorphic rocks can of course only be foliated if the composition of their parent rocks allows mica formation.

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Thus, the metamorphic products formation of rocks certain parent rocks will be nonfoliated. Such rocks would for example be quartz sandstones transforms into quartzite, interlocking quartz crystals, see abovelimestones transforms into marble, coarse crystalline, interlocking calcite crystals, impurities in the original limestone will show as colored streaks or as mottlingand basalt transforms into amphibolite, predominantly hornblende and plagioclase.

Hornfels a rock [from German "Fels"] that is as hard as a hornis another nonfoliated, fine grained metamorphic rock. Usually it is dark colored, fine grained and hard. It occurs typically in metamorphic aureolas around intrusions contact metamorphism.


As a terrestrial planet, Earth is divided into layers based formation of rocks their chemical and rheological properties. And whereas its interior region — the inner and outer core — are mostly made up of iron and nickel, the mantle and crust are largely composed of silicate rock.


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