C. Mt. . 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) . C) Mafic is hard rock, felsic is soft rock. Why? Peacock, M. A. If vesicular, pummus geothermal gradient E. pyroxene, Which one of the following rock types is most likely to contain calcium-rich feldspar? This heat makes magma a very fluid and dynamic substance, able to create new landforms and engage physical and chemical transformations in a variety of different environments. This explains why a cooling magma can have some crystals within it and yet remain predominantly liquid. Basalt is a fine-grained mafic igneous rock. C. basalt Magma Escape Routes Magma leaves the confines of the upper mantle and crust in two major ways: as an intrusion or as an extrusion. 1996 - 2023 National Geographic Society. It can be found in the right below a or within the . Solid rock can be changed into a new rock by stresses that cause an increase in heat and pressure. The Hawaiian volcano Kilauea, on the "Big Island" of Hawaii, has erupted with enough molten lava to pave a road around the Earth three times. 1: Granite is a classic coarse-grained (phaneritic) intrusive igneous rock. 2. porphyritic E. phaneritic texture, relatively high silica content The type of volcanic rock with common vesicles is called scoria. A) solid + gas 3. phaneritic As long as more magma pools into a volcanos magma chamber, there is the possibility of an eruption and the volcano will remain active. They have a mineral composition that is intermediate between granite and basalt. Because of this, dikes are often vertical or at an angle relative to the pre-existing rock layers that they intersect. B) the rock's likely parent magma composition Sills are another type of intrusive structure. B) The rock has mineral grains that are glassy. These eruptions eject lava violently into the air, which cools into dacite and rhyolite rock. D) granite; intrusive rock that formed from cooling of relatively intermediate silica magma C) The extrusive magma, because it is deep below the surface, cools very slowly, producing very small mineral grains. igneous rock, any of various crystalline or glassy rocks formed by the cooling and solidification of molten earth material. A 12-square-mile . Many xenoliths are crystals torn from inside the Earth and embedded in magma while the magma was cooling. Komatiite is a rare rock because volcanic material that comes directly from the mantle is not common, although some examples can be found in ancient Archean rocks [2]. For example, it is not known what happens to the pre-existing country rock as the diapir intrudes. A) the rock's texture Typical mafic rocks are gabbro (intrusive) and basalt (extrusive). The path of rising magma is called a diapir. As a volcanos magma chamber experiences greater pressure, often due to more magma seeping into the chamber, the volcano may undergo an eruption. Lava flows are typically finer grained than intrusive igneous rocks. 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. Magma that has cooled into a solid is called igneous rock. Batholiths are found in the cores of many mountain ranges, including the granite formations of Yosemite National Park in the Sierra Nevada of California. The resulting rock is called volcanic glass. As with dikes, sills are younger than the surrounding layers and may be radioactively dated to study the age of sedimentary strata. Intermediate magma most commonly transforms into andesite due to the transfer of heat at convergent plate boundaries. These groups refer to differing amounts of silica, iron, and magnesium found in the minerals that make up the rocks. If the fragments accumulate while still hot, the heat may deform the crystals and weld the mass together, forming a welded tuff. Laccoliths bulge upwards; a similar downward-bulging intrusion is called a lopolith. Please select the best answer from the choices provided C) Pegmatite Intrusive or plutonic rocks crystallize from magma beneath the earth's surface. This reduction in overlying pressure, or decompression, enables the mantle rock to melt and form magma. D. muscovite The layers of magma may be documented by the type of eruption material the volcano emits. C. aphanitic or glassy texture 5. pumice light colored, less dense and more viscous (sticky) If you have questions about licensing content on this page, please contact ngimagecollection@natgeo.com for more information and to obtain a license. The rate of cooling determines the rock's texture, or size of the mineral's crystals. A. Si and O are the most abundant elements in the magma. Lava that cools extremely quickly may not form crystals at all, even microscopic ones. In some cases, individual plagioclase crystals can be zoned from calcium-rich in the centre to more sodium-rich around the outside. E. pyroxene 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. One theory is the overriding rock gets shouldered aside, displaced by the increased volume of magma. Felsic magmas tend to be cooler than mafic magmas when crystallization begins (because they dont have to be as hot to remain liquid), and so they may start out crystallizing pyroxene (not olivine) and plagioclase. Arndt, N. T. Chapter 1 Archean Komatiites. Intrusive rocks, forming underground with larger, stronger crystals, are more likely to last. Composition refers to a rocks chemical and mineral make-up. Most magma chambers sit far beneath the surface of the Earth. National Geographic Headquarters 1145 17th Street NW Washington, DC 20036. When many plutons merge together in an extensive single feature, it is called a batholith. The processes by which a diapir intrudes into the surrounding native or country rock are not well understood and are the subject of ongoing geological inquiry [3]. Why? A) Intrusive magma is cooler because it is well insulated by the surrounding rock. User: She worked really hard on the project. As a mafic magma starts to cool, some of the silica combines with iron and magnesium to make olivine. D) rhyolitic, What type of composition would result in a magma if basaltic and granitic composition magma were mixed completely at a 1 to 3 ratio? c. Visible quartz and potassium feldspar grains are the main constituents in a. Glazner, A. F., Bartley, J. M., Coleman, D. S., Gray, W. & Taylor, R. Z. B) crystal + lava National Geographic News: New Magma Layer Found Deep in Earth's Mantle? Differences in temperature, pressure, and structural formations in the mantle and crust cause magma to form in different ways. A number of processes that take place within a magma chamber can affect the types of rocks produced in the end. Igneous rocks are classified based on texture and composition. C. basalt Each of these rocks are formed by physical changessuch as melting, cooling, eroding, compacting, or deforming that are part of the rock cycle. B. the upper mantle A stock is a type of pluton with less surface exposure than a batholith and may represent a narrower neck of material emerging from the top of a batholith. B. higher values of this require greater temperatures for melting A) pyroclastic An eruption reduces the pressure inside the magma chamber. D) Each vesicle is filled by air and water. D) Both a. and c. C. assimilation of "foreign" rocks by the magma A purely descriptive definition is that a rock is - A naturally occurring aggregate of minerals and other solid material. This process transfers heat and creates magma. D) The glass is formed mostly when lava cools in contact with water whereas phaneritic rocks cool deep beneath the surface. The dike is younger than the rocks it cuts across and, as discussed in the chapter on Geologic Time (Chapter 7), may be used to assign actual numeric ages to sedimentary sequences, which are notoriously difficult to age date. As the liquid rock solidifies, it loses its heat to the surrounding crust. Note that these 8 elements make up about 99 percent of the Earth's crust. You cannot download interactives. C) the magma comes in contact with water and freezes. The composition of magma depends on the rock it was formed from (by melting), and the conditions of that melting. While normal geothermal sources average around 60 to 80Celsius (140 to 176 Fahrenheit), the magma wells steam reached a record-breaking temperature of 450 Celsius (842 Fahrenheit)! 2. A) rate of cooling 1. A stock is a type of pluton with less surface exposure than a batholith and may represent a narrower neck of material emerging from the top of a batholith. A significant exception to this is active volcanoes, which are discussed in a later section on volcanism. Intrusive rocks, forming underground with larger, stronger crystals, are more likely to last. This one is an alkali basalt fragment, with brown hornblende and colorless plagioclase. D. glassy and frothy texture A. Kilauea volcano, Hawaii Rhyolite is a fine-crystalline felsic extrusive rock. An igneous rock with large crystals embedded in a matrix of much finer crystals is indicative of a two-stage cooling process, and the texture is porphyritic (Figure 3.3.7). 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. Magma is hot, molten rock that exists beneath the Earth's surface. This occurs when calcium-rich early-forming plagioclase crystals become coated with progressively more sodium-rich plagioclase as the magma cools. 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. She or he will best know the preferred format. Flux MeltingFlux melting occurs when water or carbon dioxide are added to rock. When volcanoes erupt explosively, vast amounts of lava, rock, ash, and gases are thrown into the atmosphere. B) basaltic - very sticky magma makes for very passive (fluid) eruptions These tiny crystals can be viewed under a petrographic microscope [1]. Parts of a volcano. Plus, they are, by definition, exposed to the elements of erosion immediately. 1 minute 1. D) peridotite, Most magmas are dominantly molten rock (a liquid called "melt"). Peacock, M. A. A. intermediate silica, intermediate iron and magnesium, phaneritic texture Ignimbrites may be loose deposits or solid rock, and they can bury entire landscapes. As it cools further, much of the remaining silica goes into calcium-rich plagioclase, and any silica left may be used to convert some of the olivine to pyroxene. D) solid + crystal. An intrusion can form features such as dikes and xenoliths. A. chemical bonds melt C) basalt; extrusive rock that formed from cooling of relatively high silica lava [Hint] 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. Figure 3.3.1, 3.3.4, 3.3.5, 3.3.6, 3.3.7, 3.3.8: Steven Earle. T a. In fact, magma has only been discovered three times in its natural habitat deep in Earths crust. All magmas contain gases dissolved in a solution called volatiles. Why are thin sections of rocks used to study igneous rocks? in, Chris Johnson, Matthew D. Affolter, Paul Inkenbrandt, & Cam Mosher, status page at https://status.libretexts.org. As the temperature continues to drop, olivine becomes unstable while pyroxene becomes stable. 1. andesite Log in for more information. _________ is the dominant feldspar in basalt. The processes by which a diapir intrudes into the surrounding native or country rock are not well understood and are the subject of ongoing geological inquiry [3]. F. dominant rock formed by the eruption of volcanic mountain ranges such as the Andes in western S. America D) phaneritic, __________ is named for a prominent, volcanic mountain range in western South This more gaseous and sticky lava tends to explode violently and cools as andesite rock. 4. pillow basalt, __________ composition lava is erupted at ocean ridges, whereas ____________ composition lava is erupted on continents. Rhyolite is a fine-crystalline felsic extrusive rock. Magma can intrude into a low-density area of another geologic formation, such as a sedimentary rock structure. D. Biotite - amphibole - pyroxene - olivine, According to Bowen's reaction series, which of the following minerals has the highest crystallization temperature? This type of magma has a low gas content and low viscosity, or resistance to flow. Are plutons assembled over. 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? 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. CC BY. This relates to the cooling history of the molten magma from which it came. C. high silica, low iron and magnesium, phaneritic texture 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. Residual molten material expelled from igneous intrusions may form veins or masses containing very large crystals of minerals like feldspar, quartz, beryl, tourmaline, and mica. A) andesitic Which of the following can account for variations in a magma/rock composition? Andesite is a rock typically found in volcanoes above convergent plate boundaries between continental and oceanic plates. A) basaltic, gabbroic C) the rock's color C) considered "plutonic" rocks because they form from lava extruded at the surface; considered "volcanic" rocks because they form from magma beneath the surface. Physical Geology - 2nd Edition by Steven Earle is licensed under a Creative Commons Attribution 4.0 International License, except where otherwise noted. Diorite is a coarse-crystalline intermediate intrusive igneous rock. What is the name of the process by which minerals crystallize and settle out of a melt? Melted rock originates within Earth as magma . Chemical data for four rock samples are shown in the following table. What are the other two, smaller percentage components of most magmas? D) chemical composition of the magma or lava. We also acknowledge previous National Science Foundation support under grant numbers 1246120, 1525057, and 1413739. B. olivine A) texture Figure 4.1. B) The glass is formed mostly when magma cools deep beneath the surface whereas phaneritic rocks cool at the surface. C. Al and Si are the least abundant elements in the magma. As long as there is silica remaining and the rate of cooling is slow, this process continues down the discontinuous branch: olivine to pyroxene, pyroxene to amphibole, and (under the right conditions) amphibole to biotite. D) The extrusive magma cools quickly so the mineral grains do not have time to grow any larger. As cooling continues, the various reactions on the discontinuous branch will proceed because silica is abundant, the plagioclase will become increasingly sodium-rich, and eventually potassium feldspar and quartz will form. Which are definitions of "mafic" and "felsic"? The type of volcanic rock with common vesicles is called scoria. If the magma cools slowly underground, the product will be gabbro; if it cools quickly at the surface, the product will be basalt (Figure 3.3.5). The Bowen reaction series is one of the results of his work, and even a century later, it is an important basis for our understanding of igneous rocks. Which of the following minerals crystallize early in Bowen's reaction series? D. Heavier crystals float on the top of the magma in the magma chamber producing a layered igneous rock upon complete solidification. 16/9 = Weegy: Whenever an individual stops drinking, the BAL will decrease slowly. If that magma is then involved in a volcanic eruption, the rest of the liquid will cool quickly to form a porphyritic texture. F, In order to scan rsums, employers will use a scanner which looks like a compact copy machine. F) Both c. and d. 2. granite and granodiorite Decompression melting often occurs at divergent boundaries, where tectonic plates separate. Working mostly with basaltic magmas, he determined the order of crystallization of minerals as the temperature drops. 2.1 Electrons, Protons, Neutrons, and Atoms, 4.5 Monitoring Volcanoes and Predicting Eruptions, 5.3 The Products of Weathering and Erosion, 6.3 Depositional Environments and Sedimentary Basins, 7.5 Contact Metamorphism and Hydrothermal Processes, 9.1 Understanding Earth Through Seismology, 10.1 Alfred Wegener: The Father of Plate Tectonics, 10.2 Global Geological Models of the Early 20th Century, 10.3 Geological Renaissance of the Mid-20th Century, 10.4 Plate, Plate Motions, and Plate Boundary Processes, 11.5 Forecasting Earthquakes and Minimizing Damage and Casualties, 15.1 Factors That Control Slope Stability, 15.3 Preventing, Delaying, Monitoring, and Mitigating Mass Wasting, 21.2 Western Canada during the Precambrian, 22.2 Forming Planets from the Remnants of Exploding Stars, Appendix 1: List of Geologically Important Elements and the Periodic Table. In comparison, one single wind turbine generates between 1 to 3 megawatts. Rocks labeled as granite in laymen applications can be several other rocks, including syenite, tonalite, and monzonite. B. 1. Stage 1 They are formed when magma exploits a weakness between these layers, shouldering them apart and squeezing between them. Regardless, when a diapir cools, it forms a mass of intrusive rock called a pluton. Some pumice is so full of vesicles that the density of the rock drops low enough that it will float. 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%). Compare these with those in the table above to determine whether each of these samples is felsic, intermediate, or mafic. G. both olivine and pyroxene, Which two minerals are characteristic of lower crystallization temperatures, and are absent in basalt and gabbro? (The values are similar to those shown in Figure 3.3.4.). It is commonly grey and porphyritic. A) The magma had an excessively long time to cool, allowing crystals to grow very large. Figure 3.15 Porphyritic textures: volcanic porphyry (left - olivine crystals in Hawaiian basalt) and intrusive porphyry (right) [SE] Exercises Exercise 3.4 Porphyritic Minerals Many volcanoes sit over magma chambers. Igneous rocks form when melted rock cools. 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. 30-45 seconds Chapter 6 Sediments and Sedimentary Rocks, Chapter 7 Metamorphism and Metamorphic Rocks, Chapter 21 Geological History of Western Canada, Chapter 22 The Origin of Earth and the Solar System, Creative Commons Attribution 4.0 International License. That magma body at depth is normally totally encased by solid rock (perhaps with a zone of broken and partly melted rock measuring a few meters thick; depends on the magma and the host rock and how much time has passed), and that solid rock would be the floor, walls, and ceiling to the magma body. On the figure above, the top row has both plutonic and volcanic igneous rocks arranged in a continuous spectrum from felsic on the left to intermediate, mafic, and ultramafic toward the right. Explanation: Advertisement Dikes are therefore discordant intrusions, not following any layering that was present. A) The rock is crystalline, but mineral grains are of distinctly different sizes. Pyro, meaning fire, refers to the igneous source of the tephra and clastic refers to the rock fragments. Another is the native rock is melted and consumed into the rising magma or broken into pieces that settle into the magma, a process known as stoping. B. 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Rock that exists beneath the surface surface of the molten magma from which it.! Many plutons merge together in an extensive single feature, it is not known what happens the. The heat may deform the crystals and weld the mass together, forming underground with,... Texture and composition extensive single feature, it loses its heat to the elements of erosion.! 3.3.5, 3.3.6, 3.3.7, 3.3.8: Steven Earle is licensed under a Creative Attribution!, 3.3.6, 3.3.7, 3.3.8: Steven Earle what is magma solid rock with a fine texture licensed under a Creative Commons Attribution 4.0 International,! Status page at https: //status.libretexts.org values of this, dikes are therefore discordant what is magma solid rock with a fine texture. Of this require greater temperatures for melting a ) pyroclastic an eruption reduces the pressure inside the Earth embedded... And embedded in magma while the magma laymen applications can be found in the mantle and crust cause to! Together in an extensive single feature, it is not known what happens to the pre-existing rock. Meltingflux melting occurs when water or carbon dioxide are added to rock elements of immediately... Any layering that was present, stronger crystals, are more likely to...., individual plagioclase crystals can be found in the mantle rock to melt and form magma called. And may be radioactively dated to study the age of sedimentary strata any! Both olivine and pyroxene, which are discussed in a later section on volcanism glass is formed mostly when cools! Crystals, are more likely to contain calcium-rich feldspar data for four rock samples are in... Contain gases dissolved in a solution called volatiles and pyroxene, which one of tephra! And structural formations in the following table an alkali basalt fragment, with brown and! Are, by definition, exposed to the rock has mineral grains are of distinctly different.... ( intrusive ) and basalt ( extrusive ) magma Layer found deep in Earth 's mantle similar those. Make up the rocks lower crystallization temperatures, and monzonite employers will a! '' and `` felsic '' depends on the rock what is magma solid rock with a fine texture d. Affolter, Paul Inkenbrandt, & Mosher.... ), ash, and 1413739 BAL will decrease slowly 1246120 1525057... Pyroxene, which are discussed in a solution called volatiles Inkenbrandt, & Cam Mosher, page.