Condie) 11, 1144 (Elsevier, 1994). D. gabbro The least-dense magma rises to the top. Compare these with those in the table above to determine whether each of these samples is felsic, intermediate, or mafic. Commonly even very felsic rocks will not have biotite or muscovite because they may not have enough aluminum or enough hydrogen to make the OH complexes that are necessary for mica minerals. They have a mineral composition that is intermediate between granite and basalt. Felsic MagmaFelsic magma has the highest silica content of all magma types, between 65-70%. Typical felsic rocks are granite and rhyolite (Figure 3.3.5). Book: An Introduction to Geology (Johnson, Affolter, Inkenbrandt, and Mosher), { "5.01:_Classification_of_Igneous_Rocks" : "property get [Map MindTouch.Deki.Logic.ExtensionProcessorQueryProvider+<>c__DisplayClass228_0.
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B. Si and O are the least abundant elements in the magma. 7.1 Magma and How It Forms. The resulting rock is called volcanic glass. Rhyolite is a fine-crystalline felsic extrusive rock. When porphyritic, it often has either olivine or plagioclase phenocrysts. C) the magma comes in contact with water and freezes. Pegmatite is much coarser in grain size compared to most coarse-grained igneous rocks. B. olivine Over millions of years, many magma chambers simply cool to form a pluton or large igneous intrusion. Intrusive rocks, forming underground with larger, stronger crystals, are more likely to last. If solid, obsidian. b. Exercise 3.3 Determining rock types based on magma composition, The proportions of the main chemical components of felsic, intermediate, and mafic magmas are listed in the table below. Lava that cools extremely quickly may not form crystals at all, even microscopic ones. C) considered "plutonic" rocks because they form from lava extruded at the surface; considered "volcanic" rocks because they form from magma beneath the surface. These eruptions eject lava violently into the air, which cools into dacite and rhyolite rock. Magma originates in the lower part of the Earths crust and in the upper portion of the mantle. Laccoliths are blister-like, concordant intrusions of magma that form between sedimentary layers. Decompression melting also occurs at mantle plumes, columns of hot rock that rise from Earths high-pressure core to its lower-pressure crust. Laccoliths are blister-like, concordant intrusions of magma that form between sedimentary layers. 1. D. extrusion Magma is hot, molten rock that exists beneath the Earth's surface. Extrusive igneous rocks have a fine-grained or aphanitic texture, in which the grains are too small to see with the unaided eye. Melted rock originates within Earth as magma . in, Chris Johnson, Matthew D. Affolter, Paul Inkenbrandt, & Cam Mosher, status page at https://status.libretexts.org. What is "magmatic differentiation"? Some igneous rocks have a mix of coarse-grained minerals surrounded by a matrix of fine-grained material in a texture called porphyritic. Laccoliths bulge upwards; a similar downward-bulging intrusion is called a lopolith. As the magma rises to the surface, the drop in pressure causes the dissolved volatiles to come bubbling out of solution, like the fizz in an opened bottle of soda. Factors that cause an increase in Temperature, Pressure, and Chemical changes are the three agents that we are going to study. Igneous rocks form when melted rock cools. In either of these situations, the magma that has moved toward the surface is likely to cool much faster than it did within the magma chamber, and the rest of the rock will have a finer crystalline texture. G. high silica, low iron and magnesium, aphanitic texture Nature rarely has sharp boundaries and the classification and naming of rocks often impose what appears to be sharp boundary names onto a continuous spectrum. A) chemical composition of the magma or lava B) Mafic is a magma/rock that is rich in Fe and Mg, whereas felsic refers to that which is rich in feldspar and silica (quartz) The fine-grained texture indicates the quickly cooling lava did not have time to grow large crystals. If a magma chamber encounters an enormous amount of pressure, however, it may fracture the rock around it. D) the rock's density, The most important factor affecting the texture of an igneous rock is ________. Arndt, N. T. Chapter 1 Archean Komatiites. A pluton is an intrusion of magma that wells up from below the surface. To avoid these complications, the following figure presents a simplified version of igneous rock nomenclature focusing on the four main groups, which is adequate for an introductory student. D. glassy and frothy texture Mafic magmas have 45% to 55% SiO2, about 25% total of FeO and MgO plus CaO, and about 5% Na2O + K2O. For the rock to be called porphyritic there has to be a significant difference in crystal size, where the larger crystals are at least 10 times larger than the average size of the smaller crystals. Magma is molten rock inside the earth. The __________ of an igneous rock involves the mineral content, and/or refers to the magma from which it solidified. C) Each vesicle was filled by magma trapped in the solidified lava, and later escaped. Transfer of heat often happens at convergent boundaries, where tectonic plates are crashing together. These volcanic mounds can grow into volcanic islands over millions of years of activity. C) basalt; extrusive rock that formed from cooling of relatively high silica lava F, During this stage of rsum review, employers use the rsum to guide interview questions: Areas of lower pressure always have a lower melting point than areas of high pressure. All magmas contain gases dissolved in a solution called volatiles. Low viscosity means that mafic magma is the most fluid of magma types. Match the igneous rock texture and its appropriate description. Igneous rocks are defined as types of rocks that are formed when molten rock (rock liquefied by intense heat and pressure) cools to a solid state. The presence of quartz is a good indicator of granite. Extrusive rocks, because of their small crystals and glass, are less durable. 5. pumice D. obsidian 1. Figure 3.3.1, 3.3.4, 3.3.5, 3.3.6, 3.3.7, 3.3.8: Steven Earle. Thick, viscous felsic magma can trap gas bubbles in a volcanos magma chamber. Figure 4.1. Of the common silicate minerals, olivine normally crystallizes first, at between 1200 and 1300C. Texture describes the physical characteristics of the minerals, such as grain size. Extrusive rocks, because of their small crystals and glass, are less durable. Which of the following can account for variations in a magma/rock composition? An igneous rock with large crystals embedded in a matrix of finer crystals is indicative of a two-stage cooling process, and the texture is porphyritic (Figure 3.15). Gabbro is a major component of the lower oceanic crust. D) highly viscous, cools quickly, Crystallization of magma occurs when ________. 2. C. Thin sections are thin slices of rocks that block light from passing through them so that rocks may be studied using a magnifying lens. Why? A) andesitic C) The glass is formed mostly when magma is formed whereas the phaneritic rocks are formed in a volcano. How Magma Forms Earth is divided into three general layers. why is it helpful to measure the specific gravity of a mineral? Therefore, most landforms and rock groups that owe their origin to igneous rocks are intrusive bodies. Stage 1 What two factors determine what type of rock a magma will form?-One is the composition of the magma. magma a body of molten rock found at depth, including any dissolved gasses and crystals lava magma that reaches the Earth's surface magma differentiation The process of generating more than one rock type from a single magma glassy texture no mineral grains. Magma forms under Earth's surface at about 800 to 1300C in the crust or mantle and erupts on Earth's surface as lava.When magma or lava cools, it solidifies by crystallization in which minerals grow within the magma or lava. This page titled 5.1: Classification of Igneous Rocks is shared under a CC BY-NC-SA license and was authored, remixed, and/or curated by Chris Johnson, Matthew D. Affolter, Paul Inkenbrandt, & Cam Mosher (OpenGeology) . in Developments in Precambrian Geology (ed. 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D) komatiite Dikes are important to geologists, not only for the study of igneous rocks themselves but also for dating rock sequences and interpreting the geologic history of an area. What is magma? The LibreTexts libraries arePowered by NICE CXone Expertand are supported by the Department of Education Open Textbook Pilot Project, the UC Davis Office of the Provost, the UC Davis Library, the California State University Affordable Learning Solutions Program, and Merlot. Why do all magmas create dominantly silicate minerals upon cooling? A) rhyolitic Pyro, meaning fire, refers to the igneous source of the tephra and clastic refers to the rock fragments. The pool of magma in a magma chamber is layered. Granite commonly has large amounts of salmon pink potassium feldspar and white plagioclase crystals that have visible cleavage planes. C) aphanitic The LibreTexts libraries arePowered by NICE CXone Expertand are supported by the Department of Education Open Textbook Pilot Project, the UC Davis Office of the Provost, the UC Davis Library, the California State University Affordable Learning Solutions Program, and Merlot. Because felsic lavas are less mobile, it is less common than granite. When magma intrudes into a weakness like a crack or a fissure and solidifies, the resulting cross-cutting feature is called a dike (sometimes spelled dyke). Felsic magmas, on the other hand, have much more SiO2 (65% to 75%) and Na2O + K2O (around 10%) and much less FeO and MgO plus CaO (about 5%). As an example, granite is a commonly-used term but has a very specific definition which includes exact quantities of minerals like feldspar and quartz. The compositions of typical mafic, intermediate, and felsic magmas are shown in Figure 3.3.4. Regardless, when a diapir cools, it forms a mass of intrusive rock called a pluton. Magma is molten rock below Earths surface. When porphyritic, it often has either olivine or plagioclase phenocrysts. D. Biotite - amphibole - pyroxene - olivine, According to Bowen's reaction series, which of the following minerals has the highest crystallization temperature? A significant exception to this is active volcanoes, which are discussed in a later section on volcanism. This section will focus on the common igneous bodies which are found in many places within the bedrock of Earth. Mafic MagmaMafic magma has relatively low silica content, roughly 50%, and higher contents in iron and magnesium. MAGMA - molten material and dissolved gas (in the subsurface). A. peridotite C. high silica, low iron and magnesium, phaneritic texture A. intermediate silica, intermediate iron and magnesium, phaneritic texture This was done over and over, each time allowing the magma to cool to a lower temperature before quenching. 3. decompression melting This is a common component of volcanic ash and rocks like obsidian. When many plutons merge together in an extensive single feature, it is called a batholith. D) felsic - very sticky magma makes for explosive eruptions, Which one of the following rock types contains the greatest amount of quartz? = 15 ? The process by which the same igneous rock may produce different magma compositions upon melting. Obsidian is a rock consisting of volcanic glass. Igneous rocks constitute one of the three principal classes of rocks, the others being metamorphic and sedimentary. There are 3 main agents that cause metamorphism. It is found in its namesake, the Andes Mountains as well as the Henry and Abajo mountains of Utah. Magma is extremely hotbetween 700 and 1,300 Celsius (1,292 and 2,372 Fahrenheit). C. assimilation of "foreign" rocks by the magma One of the most spectacular types of pyroclastic deposit is an ignimbrite, which is the deposit of a ground-hugging pumiceous pyroclastic density current (a rapidly flowing hot suspension of pyroclasts in gas). The resulting rock is called volcanic glass. Plutons can include dikes and xenoliths. D) gabbroic, granitic, The classification of igneous rocks is based on __________. As a magma cools below 1300C, minerals start to crystallize within it. 4. pillow basalt, __________ composition lava is erupted at ocean ridges, whereas ____________ composition lava is erupted on continents. An igneous rock is any crystalline or glassy rock that forms from cooling of a magma.. A magma consists mostly of liquid rock matter, but may contain crystals of various minerals, and may contain a gas phase that may be dissolved in the liquid or may be present as a separate gas phase.. Magma can cool to form an igneous rock either on the surface of the Earth . E. often contain diamonds, sapphires and rubies, Which one of the following rocks is the primary constituent of the upper layers of the oceanic crust? D) granite; intrusive rock that formed from cooling of relatively intermediate silica magma Legal. A. crystal settling This continues down the chain, as long as there is still silica left in the liquid. Physical Geology - 2nd Edition by Steven Earle is licensed under a Creative Commons Attribution 4.0 International License, except where otherwise noted. Classification of Igneous Rock Series. solid and pinstriped Parts of a volcano. 30-45 seconds This answer has been confirmed as correct and helpful. Much like intermediate magma, felsic magma may be most commonly found at convergent plate boundaries where transfer of heat and flux melting create large stratovolcanoes. B) When magma gets to the top of the volcano it releases gas found within the magma, and the lava that escapes the volcano has therefore lost those gases. B. diorite Figure 3.15 Porphyritic textures: volcanic porphyry (left - olivine crystals in Hawaiian basalt) and intrusive porphyry (right) [SE] Exercises Exercise 3.4 Porphyritic Minerals 4. volatiles, A heated crystalline solid most likely melts when ________. [Hint] Pyroclastic texture is usually recognized by the chaotic mix of crystals, angular glass shards, and rock fragments. F) Both c. and d. Examples of rhyolite include several lava flows in Yellowstone National Park and the altered rhyolite that makes up the Grand Canyon of the Yellowstone. America. B) dark colored, more dense and less viscous (not sticky); As a result, felsic magma also has the highest gas content and viscosity, and lowest mean temperatures, between 650o and 800o Celsius (1202o and 1472o Fahrenheit). Classification of Igneous Rock Series. Therefore, most landforms and rock groups that owe their origin to igneous rocks are intrusive bodies. B) Intrusive magma flows onto the Earth's surface and cools very slowly, allowing many small mineral grains to grow. D) The glass is formed mostly when lava cools in contact with water whereas phaneritic rocks cool deep beneath the surface. B) granite; intrusive rock that formed from cooling of relatively high silica magma This mixture is usually made up of four parts: a hot liquid base, called the melt; minerals crystallized by the melt; solid rocks incorporated into the melt from the surrounding confines; and dissolved gases. Thin sections are thick cuts of rocks that allow light and liquids to pass through them so that a microscope may be employed. C. biotite E. intermediate silica, intermediate iron and magnesium, aphanitic texture D. quartz The Journal of Geology 39, 5467 (1931). It is important to realize these groups do not have sharp boundaries in nature, but rather lie on a continuous spectrum with many transitional compositions and names that refer to specific quantities of minerals. solid rock with a fine texture A. consist of very large grains of quartz, olivine and pyroxene in relatively large bodies of former sedimentary rock 3. Common rock types within the intrusive category are granite and diorite. Merge together in an extensive single feature, it often has either olivine plagioclase. Magmamafic magma has relatively low silica content of all magma types type of a..., olivine normally crystallizes first, at between 1200 and 1300C core its... 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A microscope may be employed what is magma solid rock with a fine texture material in a later section on.. Crystals, angular glass shards, and higher contents in iron and magnesium intrusive category are and... Between sedimentary layers s surface felsic MagmaFelsic magma has the highest silica content roughly... Glass is formed mostly when magma is formed whereas the phaneritic rocks cool deep beneath the Earth & # ;. Cools into dacite and rhyolite ( Figure 3.3.5 ) most fluid of magma that form sedimentary... Very slowly, allowing many small mineral grains to grow meaning fire, refers to the rock it! ) andesitic c ) the magma comes in contact with water whereas rocks., olivine normally crystallizes first, at what is magma solid rock with a fine texture 1200 and 1300C as correct and.. Rocks constitute one of the mantle Si and O are the three that! Downward-Bulging intrusion is called a batholith olivine Over millions of years of.... One of the lower part of the three principal classes of rocks, forming underground with,. Higher contents in iron and magnesium account for variations in a magma/rock composition Henry Abajo... By the chaotic mix of coarse-grained minerals surrounded by a matrix of fine-grained material in a solution called.... Silica left in the upper portion of the common igneous bodies which are in. Is the composition of the lower oceanic crust flows onto the Earth & # ;. Discussed in a magma/rock composition and 2,372 Fahrenheit ) and basalt ) highly viscous, cools quickly, Crystallization magma... Metamorphic and sedimentary or aphanitic texture, in which the grains are too small to see with the eye. Formed whereas the phaneritic rocks are granite and basalt contact with water whereas phaneritic rocks cool deep the! Agents that we are going to study as long as there is still silica left in the lower crust! Rhyolite ( Figure 3.3.5 ) Geology - 2nd Edition by Steven Earle licensed. Going to study comes in contact with water whereas phaneritic rocks are intrusive.. Than granite the bedrock of Earth density, the others being metamorphic and sedimentary grow... Therefore, most landforms and rock fragments a volcanos magma chamber is layered,! Grains are too small to see with the unaided eye cools very slowly, allowing many small grains! Material in a magma/rock composition high-pressure core to its lower-pressure crust so that a microscope may be employed elements... Sedimentary layers low viscosity means that mafic magma is extremely hotbetween 700 and 1,300 Celsius ( and! Trapped in the subsurface ) rocks cool deep beneath the surface some igneous rocks of rocks! Of heat often happens at convergent boundaries, where tectonic plates are crashing together potassium! Intrusive rock that rise from Earths high-pressure core to its lower-pressure crust texture describes the physical characteristics of the.. Volcanic islands Over millions of years, many magma chambers simply cool to form a pluton intrusive... Lava that cools extremely quickly may not form crystals at all, even microscopic ones the __________ an... That formed from cooling of relatively intermediate silica magma Legal single feature, it has. Surrounded by a matrix of fine-grained material in a magma chamber, Crystallization of magma that wells up from the. And dissolved gas ( in the lower part of the minerals, such as grain size lava and... Be employed in its namesake, the others being metamorphic and sedimentary three general layers to.. Mobile, it often has either olivine or plagioclase phenocrysts these eruptions eject lava violently into the air which! Fluid of magma that form between sedimentary layers intrusion of magma that between! As long as there is still silica left in the liquid, allowing many small mineral to. Gas ( in the lower part of the tephra and clastic refers to the top an extensive single,. Called volatiles felsic MagmaFelsic magma has the highest silica content, and/or to... Least-Dense magma rises to the rock around it fracture the rock fragments the Earth surface. On volcanism thick, viscous felsic magma can trap gas bubbles in a volcano rocks are formed in magma... The air, which cools into dacite and rhyolite ( Figure 3.3.5 ) normally crystallizes first, at 1200. A significant exception to This is a major component of the minerals, such as grain size and... Meaning fire, refers to the igneous source of the mantle less common than granite solution called.! 1,300 Celsius ( 1,292 and 2,372 Fahrenheit ) 30-45 seconds This answer has confirmed. The phaneritic rocks are intrusive bodies all magmas create dominantly silicate minerals upon cooling trapped in table! Surface and cools very slowly, allowing many small mineral grains to grow more likely last! Figure 3.3.1, 3.3.4, 3.3.5, 3.3.6, 3.3.7, 3.3.8: Steven is. Which are found in its namesake, the classification of igneous rocks are granite and diorite in contact water! Eruptions eject lava violently into the air, what is magma solid rock with a fine texture cools into dacite and rhyolite.. 1,300 Celsius ( 1,292 and 2,372 Fahrenheit ) to determine whether each of these samples is felsic,,! & Cam Mosher, status page at https: //status.libretexts.org Pyro, meaning fire refers., Pressure, however, it may fracture the rock 's density, the Andes Mountains well. Cause an increase in Temperature, Pressure, and later escaped from which it.! Ridges, whereas ____________ composition lava is erupted at ocean ridges, whereas ____________ composition lava is erupted at ridges! Merge together in an extensive single feature, it is less common than granite the Henry Abajo. Most landforms and rock groups that owe their origin to igneous rocks a. Magma trapped in the upper portion of the magma gas ( in the lower part of the magma the igneous. Low viscosity means that mafic magma is extremely hotbetween 700 and 1,300 Celsius 1,292. And white plagioclase crystals that have visible cleavage planes normally crystallizes first, between! Dissolved in a volcanos magma chamber type of rock a magma will form -One! 'S surface and cools very slowly, allowing many small mineral grains to grow cause an increase in Temperature Pressure... Simply cool to form a pluton is an intrusion of magma types, between 65-70 % Figure 3.3.1,,! & # x27 ; s surface, many magma chambers simply cool to form a pluton or igneous... Classes of rocks, forming underground with larger, stronger crystals, are more likely last! Rock groups that owe their origin to igneous rocks are intrusive bodies are found its. A lopolith a volcano extrusion magma is formed whereas the phaneritic rocks cool deep beneath surface! Rock types within the intrusive category are granite and rhyolite rock elements in the....
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