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How do igneous rocks form and how are they classified?
Igneous rocks are formed by the cooling of lava (above Earth's surface) or magma (below). Rocks in general are classified by their mineral composition, texture, and origin. Igneous rocks all have the origin of molten material, there are two categories within this: intrusive and extrusive. Intrusive rocks formed below earth's surface and extrusive rocks above. Their mineral composition varies greatly and depends on each individual rock. The classification of igneous rocks in texture is linked to their origin. The texture of a rock is defined by its grain: can you see and feel the little rocks that make it up? If you can, that rock has a coarse grain, if you can't see the bits, it is fine grained. Intrusive igneous rocks are usually fine grained; extrusive, coarse grained.
Can an intrusive rock form underground and then become extrusive?
No. But an igneous rock can exhibit a texture which has characteristics of both intrusive and extrusive rock. It's called a porphyry, and results from some slow crystal growth of certain minerals in a magma before being erupted. The product will be a rock with visible mineral crystals which are dispersed in a fine grained background matrix. In some cases, igneous intrusive rock fragments may become trapped in magma of a differing composition and then be erupted onto the surface. These fragments are known as xenoliths and they may undergo some form of alteration due to contact metamorphism. In this case, the rock fragment has been extruded (in the physical sense) with the other molten material, however in geology, the term "extrusive" is generally applied to molten lava which is erupted onto the Earth's surface before cooling. Xenoliths do not exactly fit this definition so it would perhaps be inappropriate to describe them as such. However they can be very important sources of information on the composition of the upper mantle and so are worthy of discussion here. Please see the related links.
How can you compare igneous and sedimentary rocks?
Extrusive rocks are... extruded... onto the surface as the lava that we all think of. It cools fairly quickly, into rocks with fairly small crystals (might need a magnifying lens to see them). The exact chemistry of the parent magma will determine the type of rock. Oceanic volcanoes are generally basaltic (mafic or ultramafic), continental are generally granitic (felsic or intermediate). They're put down in "relatively thin" layers Intrusive rocks cool for thousands of years beneath the surface in huge plutons or batholyths. This allows them to grow very large crystals (easily seen by the unaided eye). These intrusive rocks are almost always granitic-type rock. My sources are: from my science teacher who worked at the science museum yahooanswer.com ask.com wikipedia the free encyclopedia I hope this information helped. Good luck!
Why are metamorphic rocks created deep in earth's crust not on the surface?
Metamorphic rocks rarely form on Earth's surface because it needs an intense amount of heat & pressure to form. Earth's surface doesn't have as much heat as the mantle and the core. It also doesn't have much pressure but gravity.
What type of rocks are dolerite rocks?
Dolerite rocks are a type of igneous rocks (formed as a result of cooling of magma or lava). They are mafic (45-52% SiO2), and subvolcanic (formed within the earth's crust). Within this characterisation there is considerable variation. Please see the link.
How are intrusive rocks formed?
They are formed from the solidification of magma below the ground.
How do igneous rocks form and how are they classified?
Igneous rocks are formed by the cooling of lava (above Earth's surface) or magma (below). Rocks in general are classified by their mineral composition, texture, and origin. Igneous rocks all have the origin of molten material, there are two categories within this: intrusive and extrusive. Intrusive rocks formed below earth's surface and extrusive rocks above. Their mineral composition varies greatly and depends on each individual rock. The classification of igneous rocks in texture is linked to their origin. The texture of a rock is defined by its grain: can you see and feel the little rocks that make it up? If you can, that rock has a coarse grain, if you can't see the bits, it is fine grained. Intrusive igneous rocks are usually fine grained; extrusive, coarse grained.
Do you think extrusive or intrusive igneous rocks are likely to have larger crystals?
If a rock has large crystals, it is an intrusive rock. Intrusive rocks form underneath the Earth's surface. Magma cools slowly so it has time to form large crystals. An example is granite, where you can see the crystals with your naked eye. Rocks that have small crystals are extrusive rocks. Extrusive rocks are ones that form from lava (blasted out of a volcano) so they cool very quickly, not allowing large crystals to form. An example is obsidian, where you cannot visibly see the small crystals; it just looks like one black, glassy rock.
What is an intrusive rock is?
Sedimentary rocks are not intrusive. Igneous rocks are though. See the link below.
What does the term intrusive igneous rock mean?
Intrusive igneous rocks are formed from magma that cools and solidifies beneath the Earth's surface, resulting in a coarse-grained texture. Examples of intrusive igneous rocks include granite and diorite. They are characterized by their larger crystal size, which are a result of the slow cooling process.
What is the difference between the formation of intrusive and extrusive igneous rocks?
It is a matter of time. Crystallization processes can occur more easily when the rock is kept at a certain temperature during a long time. Because of that, well-formed and well crystallized minerals will appear in intrusive igneous rocks (such as granitoids). On the opposite, when a rock spreads rapidly over the Earth's surface, the temperature decreases rapidly, keeping the minerals from forming. A homogeneous paste will form, without any (or few) minerals in it. It is the case for volcanics rock.
How are intrusive and extrusive rock different?
Intrusive Rocks are found underneath Earths crust, while Extrusive rocks are found above Earths crust.
How do intrusive and extrusive igneous rocks form?
Igneous rocks are formed when magma crystallizes and cools into a solid form. There are two types of igneous rocks--intrusive igneous rocks and extrusive igneous rocks.Intrusive:Intrusive igneous rocks are formed when the melted rock (magma) slowly rises toward, but does not reach the surface. As these pockets of magma cool slowly underground, minerals crystallize and the magma solidifies, becoming intrusive igneous rock, like granite and gabbro.Extrusive:Igneous rocks are also formed when volcanoes erupt, causing the magma to rise above the Earth's surface. When magma appears above the surface, it is called lava. Extrusive igneous rocks are formed as the lava cools above ground. Examples of extrusive igneous rock are basalt, rhyolite, pumice, and scoria.igneous rocks are formed by lavaWell When melted rock cools quickly, it hardens before any mineral crystals can grow large. as a result, igneous rocks that form above ground have small or no crystals :)Igneous Rocks are made of magma and lava because it comes out of a volcanoFrom volcanoes.from lava cooling.Molten rock cools and turns solid.
How do rocks that astronauts gathered on the moon compare with rocks and minerals on the earth?
They appear to be igneous in nature with earth common minerals. Because the earth is geologically active and has flowing water, we see all rock types on the surface.
What type of rock is there most of?
Most of the Earth's crust is made up of igneousrocks but much of igneous rock is under the surface and not seen. Most of the rocks you see, those exposed on the surface, are sedimentary rocks.
How are the textures of extrusive and intrusive igneous rocks different?
Extrusive igneous rocks have come to the surface when cooling down. Intrusive igneous rocks stay within the earth. This difference is important. When a magma comes to the surface, it's called a lava. On the surface, the lava will be subject to cooling by wind and water. This will happen fast. When a magma stays inside the earth, it will cool down considerably slower, because it has to radiate it's heat to the rest of the earth. This doesn't go fast because while water and air can flow, rock can't. The texture of an igneous rock has everything to do with the cooling speed. As a magma or a lava cools, it forms crystals. When the cooling happens relatively fast, these crystals do not have a lot of time to grow together, so you will get a lot of small crystals. When the cooling is very slow, the crystals will have more time to grow, and the crystal size will be a lot bigger. Take for instance granite. If you've ever seen it, you know you can see the crystals with the naked eye, because they are very large. Basalt, on the other hand has a very fine structure, you can't see the crystals without magnifying equipment like a microscope. So there you have it: an extrusive igneous rock will have a very fine texture, with small crystal sizes, an intrusive igneous rock will have a very coarse texture, with large crystal sizes.
Would a rock with no mineral crystals be called a intrusive?
No, but it's easier to see if you reverse the logic of the question. Intrusive rocks are igneous by definition, and these are all blends of crystalline minerals.
