rock

Igneous Rocks
Igneous rocks occur in a wide variety of forms and in different shapes and sizes. The major way they are classified is into the extrusive or volcanic rocks and the intrusive or plutonic rocks. Extrusive rocks occur as lava. It is debris that is ejected into the air during eruptions. Underwater lava flows form characteristic pods called pillows. Intrusive rocks also occur in a variety of forms. Vertical sheets of igneous rock are dikes. Dikes cut through the grain of the rock . Horizontal sheets, parallel to the grain, are sills. Fatter pods of crystal rock are called laccoliths. For more info link into the Plate Tectonics portion of our site.

Igneous rocks can also be classified into three factors. They are grain size and grain texture, intrusive and extrusive, and silica content . Each of those categories has been broken down in more detail below.

Vitreous is glassy and has no crystals.

Igneous rocks are one of the three major groups of rocks . Unlike sedimentary and metamorphic they have been formed by cooling and solidifying of magma. Depending on the conditions of when the magma cooled, the resulting rocks may differ in grain size. Plutonic rocks were formed from a magma in the earth's crust. The rocks cooled very slowly which allowed large crystals to form.
Volcanic rocks were formed when the molten magma rose from a depth and filled cracks close to the surface, or when the magma was extruded upon the surface of the earth through a volcano. When the magma hardens quickly it usually generates smaller grain size or glass like appearance This is the case with volcanic rocks. Igneous rocks are made up mostly of silica and make up most of the earth's crust.
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A metamorphic rock is a rock that has changed from its original form. In Greek “meta” means change and “morph” means form. There are three factors that make this change: heat, pressure and chemical activity.

Heat: When minerals are heated the bonds between atoms gets weaker. To get more info visit the Chemistry portion of our site. If it gets hot enough, the materials will melt. Not all bonds will break, only some. Then these atoms will flow and join up with other atoms to form another mineral. When this happens the rock changes its chemical composition and structure. This can happen when two plates collide and the rocks are pulled under. This is regional metamorphism. If the rock comes in contact with magma because of a volcano or something of that sort then this is contact metamorphism.

Pressure: Under great pressure atoms get stressed. Then some of the bonds will break, and the atoms will rejoin and be more compact. The effects of this happening is you get a more dense rock. This great pressure could be caused by two plates collide.

Chemical Activity: When ions dissolve, they make a soup of ions. When this soup of ions passes through cracks or fissures, they mix with the minerals in those rocks to create new ones.

Changes in Rocks: During metamorphism, the original rock changes. The minerals come together to make new ones. Now the old rock is gone and a new one is created.
The crystal shape, size and spacing can change during metamorphism. The density of a rock can also be changed do to the immense pressure. The rock pores will be closed, then you will have the same amount of weight in the same amount of space, which means the rock is more dense. Sometimes rock crystals will be arranged in layers or bands. Some can't be seen but some can be seen on a very large scale. If enough pressure is put on these bands they will be distorted.
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In geology, a sedimentary rock is composed of geologically altered materials, which is formed by the build up and condensation of mineral and particle matter deposited by the action of water. Less frequently, wind or glacial ice cause this change. Most sedimentary rocks are characterized by parallel or discordant bedding that shows differences in either the rate it was deposited or the nature of the material. You can tell these layers apart easily in nature on the basis of color or the resistance to erosion, both of which are attributed to the composition of the rocks. Sedimentary rocks can be divided into three fundamental types: clastic, chemical, and biochemical.

*Sedimentary rocks are formed in layers known as beds.
*Clastic sedimentary rocks are formed from fragments of rocks and minerals.
*Chemical sedimentary rocks are precipitated from solutions.
*Biochemical sedimentary rocks are formed by the actions of living things or from the remains of dead organisms.

The basic building blocks of clastic sedimentary rocks are sediments, rocks and mineral fragments formed when rocks disintegrate on the earth's surface. Clastic sedimentary rocks form in three steps that require the generation, transportation, and deposition of sediments.

Generation:
Rocks physically disintegrate into smaller pieces and the constituent minerals may undergo weathering to form alternate minerals. Weathering is influenced by the original rock type and climate conditions. Weathered material form sediments that are classified by increasing grain size as mud, silt, sand, and gravel.

Transportation:
Sediment is transported from its origin by transporting agents such as running water (streams), winds, and/or glaciers. To get more info on water, go to Weather. A muddy river is an indication that the river is carrying a large amount of sediment. Clastic sediments are divided into coarse grain size particles (large particles, pebbles, rocks, and boulders), medium grain size (sand), fine grain size (silt), or very fine sediment (clay).

Deposition:
Clastic sediments are deposited when the velocity of the transporting stream, winds, or glacier drops. For example, rivers dump much of their sediment where they enter the relatively quiet waters of an ocean or lake; the land form that is created is a delta. Deposition concentrates sediments of the same size together (called sorting). As the pile of sediment grows, sediment at the base of the pile becomes compacted, squeezing out water and forcing the grains closer together. Fluids circulating through the pile cement the grains together, converting the sediment into a cohesive aggregate, i.e. a rock. The process of compacting and cementating sediment into sedimentary rock is called lithification.

Chemical sedimentary rocks are formed from a solution as a result of changing physical conditions. The most common solution is sea water. These minerals are dissolved from rocks on the continents and transported to the oceans by solution in streams. Rock salt forms as a result of changing physical conditions (increasing temperature). Minerals dissolved in sea water are precipitated when the water evaporates to form rocks like gypsum and halite. Evaporation typically occurs in restricted basins in arid climates. Thick salt deposits indicate that there must have been a constant supply of additional sea water to ensure the steady deposition of salts. These rock types are collectively termed evaporates.

Biochemical sedimentary rocks involve the actions of living organisms that cause minerals to be formed from a solution or are composed of the remains of dead organisms. Limestone forms when living marine organisms cause precipitation to build their skeletons. The actions of organisms in sea water change the composition of the water resulting in the formation of the mineral calcite (calcium carbonate), the main ingredient in limestone. Massive limestone coral reefs around the world were built up due to the actions of the coral organisms. The skeletons of some microorganisms collect on the sea floor to form chalk (a type of limestone). The shells of larger organisms may be broken down and sorted by wave action to form a Clastic form of limestone known as coquina. Additional disintegration may form sands or mud's to form medium to fine grained limestone. Some biochemical rocks are composed of the remains of dead organisms. The most common example is coal. These rocks are sometimes termed organic sedimentary rocks.
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The Rock Cycle
The rock cycle is a group of changes. Igneous rock can change into sedimentary or into metamorphic rocks.

Sedimentary rocks can change into metamorphic rock or into igneous rock. Metamorphic rock can also change into the other

Igneous rock forms when magma cools and makes crystals. Magma is a hot liquid made of melted minerals. The minerals can
form crystals when they cool. Igneous rock can form underground, where the magma cools slowly. Or igneous rock can form
above ground, where the magma cools quickly.

When it pours out on earth's surface, magma is called lava. Yes, the same liquid rock matter that you see coming out of
volcanoes.

On earth's surface wind and water can break rock into pieces. They can also carry the rock pieces to another place. Usually,
the rock pieces, called sediments, drop from the wind or water to make a layer. The layer can be buried under other layers
of sediments. After a long time the sediments can be cemented together to make sedimentary rock. In this way, igneous rock
can become sedimentary rock.

All rock can be heated and it comes from inside earth where there is heat and pressure.

The heat actually causes the rock to bake. Baked rock does not melt, but does change. It forms crystals. If it has crystals already, it forms larger crystals. Because this rock changes, it is called metamorphic. That change is called metamorphosis. Metamorphosis can occur in rock when they are heated to 300 to 700 degrees Celsius.

When earth's plates move around, they produce heat. When they collide, they build mountains and
metamorphic rocks.

The rock cycle continues. Mountains made of metamorphic rocks can be broken up and washed away by streams. New
sediments from these mountains can make new sedimentary rock.
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