Oct 22, · Igneous rock is formed when magma, which is liquid molten rock, cools or sets, solidifying into rock and rock formations. Extrusive rocks are rocks that have formed on the surface of the earth. This occurs when magma bursts forth from the mantle or crust on to the surface. Intrusive rock is rock that forms within small pockets beneath the earth’s ebrovary.comted Reading Time: 6 mins. Igneous rocks (from the Latin word for fire) form when hot, molten rock crystallizes and solidifies. The melt originates deep within the Earth near active plate boundaries or hot spots, then rises toward the surface. Igneous rocks are divided into two groups, intrusive or extrusive, depending upon where the molten rock solidifies.
The terminology Igneous means fire or heat. They are simply the rocks formed through heating then followed by cooling. As per Wikipedia. Igneous rock is formed through the cooling and solidification of magma or lava.
Igneous rock may form with or without crystallization, either below the surface as intrusive plutonic rocks or on the surface as extrusive volcanic rocks. Learn more about Sedimentary Rocks and Metamorphic Rocks. Because of the high temperatures and pressure changes, the molten materials sometimes shoot up to the surface in the form of volcanic eruption and they cool down to form volcanic or extrusive igneous rocks.
It is because of the extreme iy levels and changes in pressure that igneous rocks do not contain organic matter or fossils. The molten minerals interlock and crystallize as the melt cools and forms solid materials. The rocks may be made up entirely roock one mineral or various minerals, and their sizes are determined by the cooling process. Rapid cooling results in smaller crystals while slow cooling results in large crystals.
Gabbro and granite are examples of intrusive igneous rocks. Intrusive rocks are very hard in nature and are often coarse-grained. Extrusive igneous ajd are formed when molten magma spill over to the surface as a result of a volcanic eruption. The magma on the surface lava cools faster jgneous the surface to form igneous rocks that are fine-grained. Ofrmed of such kind of rocks include pumice, basalt, or obsidian.
On this basis, we are going to look at the commonly identified types of igneous rocks, both intrusive igneou extrusive.
They include:. Granites are the light-colored and coarse-grained igneous rocks. They are intrusive rocks and they contain three major minerals including feldspar, mica and quartz. They appear pinkish, gray or tan depending on the grain sizes and concentrations and grain sizes of the three flrmed. Granites are often used in construction activities iw of its strength and presence in great quantities.
Gabbros are the dark-colored and coarse-grained igneous rocks. They are intrusive rocks and they are made up of mineral elements including pyroxene, feldspar, and sometimes olivine. They appear grey in color with minute dark spots all over them.
Basalts are the dense dark-grey colored and fine-grained igneous rocks. They are extrusive aan are chiefly composed of plagioclase and pyroxene. They are the commonest type of how to purge bho wax lava. Basalts are also frequently used in building and construction. Diorites are the coarse-grained igneous rocks just like the Gabbros and Granite. They are intrusive and contain a mixture of minerals including hornblende, pyroxene, feldspar and sometimes quartz.
They appear light-colored with some dark spots. Andesites are light grey-colored and fine-grained igneous rocks. They are extrusive rocks which are mainly made up of plagioclase minerals mixed up with biotite, pyroxene, and hornblende. Obsidians are the dense dark-colored and smooth igneous rocks.
They are the granitic or volcanic glass formed by the rapid cooling us lava without crystallization. Obsidians usually appear dark, but transparent jow thin pieces. Pegmatite is a form of igneous rock consisting of extremely coarse granite resulting from the crystallization of forrmed rich in rare elements.
Pegmatite is light-colored and often contains rare minerals that are not rockk in other parts of the magma chamber. Pumice is a light-colored vesicular and porous like an igneous rock that forms as a result of very fast solidification of molten rock material. The vesicular and porous like texture is due to the gas trapped within the melt during the rapid solidification. Pumice stones are commonly used as abrasive materials. Peridotite is a dark coarse-grained igneous rock consisting principally of olivine.
It is an intrusive rock and may also contain some small amount of minerals such as feldspar, quartz, amphibole, pyroxene, or quartz. Rhyolites are light-colored and fine-grained igneous rocks. They fprmed extrusive igneous rocks and they are typically composed feldspar and quartz minerals.
They often have a smooth surface. Welded Tuffs are extrusive igneous rocks made up of the materials discharged during a volcanic event. Welded Tuffs are mostly composed of volcanic ash and at times include large size pieces such as clinkers. Fire opals are the igneous rocks that are flaming orange or yellow and red in color.
At times they are found in rhyolite and are categorized as one of the most spectacular igneous geological rocks. Scoria is a dark-colored vesicular ibneous porous like an igneous rock. It is an extrusive rock and the vesicles or porous like composition is due rodk the gas wbat within the melt during cooling and solidification.
Scoria usually forms as a bubbling crust on top of the lava as it flows down from the volcanic vent and eventually what does the 5 stars on the china flag mean with some air trapped inside.
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What are Igneous Rocks? Intrusive Igneous Rocks 2. Granite 2. Gabbro 3. Basalt 4. Diorite 5. Andesite 6. Obsidian 7. Pegmatite 8. Pumice 9. Peridotite us Rhyolite Welded Tuff Fire Opal Related Posts
Oct 10, · Igneous rocks form when magma (molten rock) cools and crystallizes, either at volcanoes on the surface of the Earth or while the melted rock is still inside the crust. All magma develops underground, in the lower crust or upper mantle, because of the intense heat there. Igneous rocks can have many different compositions, depending on the magma they cool ebrovary.comted Reading Time: 3 mins. Igneous rocks form when hot, liquid magma from inside the Earth cools and becomes solid. When this happens below ground, the rocks are called intrusive. When magma comes to the surface as lava and cools above ground, the rocks are called extrusive. Find out more ›. Dec 16, · In essence, igneous rocks are formed through the cooling and solidification of magma (or lava). As hot, molten rock rises to the surface, it undergoes changes in temperature and pressure that cause Estimated Reading Time: 6 mins.
When it comes to the composition of the Earth, three main types of rock come into play. These are known as metamorphic rock, sedimentary rock, and igneous rock, respectively. They can also tell us much about the tectonic environment, given that they are closely linked to the convection of tectonic plates.
But just how are these rocks formed? In essence, igneous rocks are formed through the cooling and solidification of magma or lava. As hot, molten rock rises to the surface, it undergoes changes in temperature and pressure that cause it to cool, solidify, and crystallize. However, some are also formed on the surface as a result of volcanic activity. Those that fit into the former category are known as intrusive or plutonic rocks, while those that fit into the latter are known as extrusive or volcanic rock.
In addition to these, there is also hypabyssal or subvolcanic rock , a less common form of igneous rock that is formed within the Earth between plutonic and volcanic rocks. As this rock is surrounded by pre-existing rock, the magma cools slowly, which results in it being coarse grained — i. The most common types of plutonic igneous rock are granite, gabbro, or diorite. The central cores of major mountain ranges consist of large bodies of intrusive igneous rocks — also known as batholiths — since they are the result of magma cooling within preexisting solid rock on the surface.
In addition to batholiths, other types of igneous rock structures include stocks, laccoliths, lopoliths, phacolith, chonliths, sills, dikes, and volcanic pipes or necks. All of these are to be found in subterranean layers, but can sometimes breach the surface due to tectonic activity. Extrusive rocks are so named because they are the result of magma pouring onto the surface of the planet and cooling. When it reaches the surface, either on a continental shelf as a volcano or on the ocean floor as a submarine volcano, it becomes lava, by definition.
The viscosity of lava depends upon the temperature composition and crystal content of the molten rock itself.
Therefore, the lava can flow slowly, forming short steep flows; or it can flow rapidly, forming long, thin flows. It can also explode violently, dispersing magma into the air that falls back to the surface as ash and tuffs. Compared to intrusive rock, this type of igneous rock cools and crystallizes at a much faster rate due to it being exposed to air or water, which results in it being fine-grained. Sometimes, the cooling is so rapid as to prevent the formation of even small crystals after extrusion, resulting in rock that may be mostly glass such as obsidian.
If the cooling of the lava happened more slowly, the rocks would be fine-grained or porphyritic — where the crystals differ in size, with at least one group of crystals obviously larger than another group. Basalt is a common form of extrusive igneous rock and forms lava flows, lava sheets and lava plateaus.
Extrusive igneous rocks include andesite, basalt, obsidian, pumice, rhyolite, scoria, and tuff. Because the minerals are mostly fine-grained, it is much more difficult to distinguish between the different types of extrusive igneous rocks than between different types of intrusive igneous rocks.
Generally, the mineral constituents of fine-grained extrusive igneous rocks can only be determined by examination with a microscope, so only an approximate classification can usually be made in the field. Hypabyssal rock is a form of intrusive igneous rock that solidifies at medium to shallow depths within the crust, usually in fissures as dikes and intrusive sills. These rocks typically have an intermediate grain size and texture between that of intrusive and extrusive rock.
As might be expected, they show structures that intermediate between those of extrusive and plutonic rocks. Common examples of subvolcanic rocks are diabase, quartz-dolerite, micro-granite and diorite. Igneous rocks are classified according to their mode of occurrence, texture, mineralogy, chemical composition, and the geometry of the igneous body. Two important variables that are used for the classification of igneous rocks are particle size and the mineral composition of the rock.
Feldspar, quartz, olivines, micas, etc. Types of igneous rocks with other essential minerals are very rare. In simplified classification, igneous rocks are separated by the type of feldspar present, the presence or absence of quartz, and — in cases where feldspar or quartz are not present — by the type of iron or magnesium minerals present. Rocks containing quartz are silica-oversaturated, while rocks with feldspathoids are silica-undersaturated.
Igneous rocks which have crystals large enough to be seen with the unaided eye are classified as phaneritic, while those with crystals too small to be seen are aphanitic. Typically, rocks belonging to the phaneritic class are intrusive in origin, while aphanitic rocks are extrusive. An igneous rock with larger, clearly discernible crystals embedded in a finer-grained matrix is classified as porphyry. Porphyritic textures develop when lava cools unevenly, causing of some of the crystals to grow before the main mass of the molten rock.
So the next time you find yourself somewhere, just standing about, remember that the ground you walk on was formed under from a pretty hellish process.
It began deep in the Earth, where silicate rock, tormented by extreme heat and intense pressure, became a hot, oozing mess. Once it was churned up to the surface.
We have written many articles about igneous rocks for Universe Today. Geological Survey Website. Listen here, Episode Earth. What is unclear about that? Skip to content. Like this: Like Loading