A) andesitic Obsidian as a glassy rock shows an excellent example of conchoidal fracture similar to the mineral quartz (see Chapter 3). Magma can intrude into a low-density area of another geologic formation, such as a sedimentary rock structure. In some cases, extrusive lava cools so rapidly it does not develop crystals at all. A rock that chiefly consists of pegmatitic texture is known as a pegmatite. 16/9 = Weegy: Whenever an individual stops drinking, the BAL will decrease slowly. Cooling history is also related to changes that can occur to the composition of igneous rocks. Andesite is the name of a family of fine-grained, extrusive igneous rocks that are usually light to dark gray in color. There are three different types of . This creates magma in places where it originally maintained a solid structure. There are 3 main agents that cause metamorphism. An extreme version of scoria occurs when volatile-rich lava is very quickly quenched and becomes a meringue-like froth of glass called pumice. Its mean temperature ranges from 800o to 1000o Celsius (1472o to 1832o Fahrenheit). Intrusive rocks, forming underground with larger, stronger crystals, are more likely to last. The presence of quartz is a good indicator of granite. D) Temperature of the environment - higher T = slower magma cooling. Added 2/10/2022 11:11:08 PM This answer has been confirmed as correct and helpful. 2. granite and granodiorite Regardless, when a diapir cools, it forms a mass of intrusive rock called a pluton. Earth Science, Geology, Geography, Physical Geography. G. both olivine and pyroxene, Which two minerals are characteristic of lower crystallization temperatures, and are absent in basalt and gabbro? Lava that cools extremely quickly may not form crystals at all, even microscopic ones. B. komatiite Some igneous rocks have a mix of coarse-grained minerals surrounded by a matrix of fine-grained material in a texture called porphyritic. why is it helpful to measure the specific gravity of a mineral? This is a common component of volcanic ash and rocks like obsidian. Differences in temperature, pressure, and structural formations in the mantle and crust cause magma to form in different ways. Magma is like seltzer: It contains "Volatile gases" - H2O, CO2, SO2, N2, CH4and other dissolved gases. Peacock, M. A. All rights reserved. What is magma? MAGMA - molten material and dissolved gas (in the subsurface). 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. D. Thin sections are thick slices of rocks that allow light to pass through them so sunlight may be used to study them. D. a magnifying glass or microscope is needed to see individual mineral grains Granite is a course-crystalline felsic intrusive rock. A) highly viscous, cools slowly This occurs when calcium-rich early-forming plagioclase crystals become coated with progressively more sodium-rich plagioclase as the magma cools. Granite is a good approximation for the continental crust, both in density and composition. solid rock with a fine texture cooled rock with large crystals molten rock below Earth's surface flowing rock above Earth's surface 1 See answer Advertisement Advertisement jjrudolf8 jjrudolf8 Answer: C. molten rock below Earth's surface. A) rhyolitic Which are definitions of "mafic" and "felsic"? It is commonly vesicular and aphanitic. A) mafic - very fluid magma makes for passive (fluid) eruptions C) andesitic An intrusion can form features such as dikes and xenoliths. Plutons can have irregular shapes, but can often be somewhat round. Over millions of years, the magma in this subduction zone can create a series of active volcanoes known as a volcanic arc. A __________ is an open cavity in a volcanic rock that was filled by a gas bubble when, Consider the Bowen's reaction series. The method, in brief, was to melt the rock to a magma in a specially-made kiln, allow it to cool slowly to a specific temperature (allowing some minerals to form), and then quench it (cool it quickly) so that no new minerals form (only glass). Gabbro is a coarse-grained mafic igneous rock, made with mainly mafic minerals like pyroxene and only minor plagioclase. Because mafic lava is more mobile, it is less common than basalt. A. Which of the following is the likely cause of a vesicular texture (open cavities in a rock)? 1. A. intermediate silica, intermediate iron and magnesium, phaneritic texture If crystal settling does not take place, because the magma is too viscous, then the process of cooling will continue as predicted by the Bowen reaction series. 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%). F. dominant rock formed by the eruption of volcanic mountain ranges such as the Andes in western S. America Many volcanoes sit over magma chambers. Extrusive or volcanic rocks crystallize from lava at the earth's surface. Text on this page is printable and can be used according to our Terms of Service. Figure 4.1. If a media asset is downloadable, a download button appears in the corner of the media viewer. Intrusive rocks, forming underground with larger, stronger crystals, are more likely to last. Sills are another type of intrusive structure. D) the lava in the crystallizing magma chamber before eruption. Mafic rocks/magmas are ________, whereas felsic rocks/magmas are ________. At that temperature, the plagioclase is calcium-rich (anorthite) (see Figure 2.6.1). Porphyritic texture indicates the magma body underwent a multi-stage cooling history, cooling slowly while deep under the surface and later rising to a shallower depth or the surface where it cooled more quickly. B) amount of space available for crystals to fill If magma cools slowly, deep within the crust, the resulting rock is called intrusive or plutonic. This texture, which indicates a very slow crystallization, is called pegmatitic. C) the magma comes in contact with water and freezes. When it cools to solid rock, this intrusion is often called a pluton. In some cases, extrusive lava cools so rapidly it does not develop crystals at all. When located beneath the ocean, these plumes, also known as hot spots, push magma onto the seafloor. C) granite These eight elements . When many plutons merge together in an extensive single feature, it is called a batholith. B. higher values of this require greater temperatures for melting Glazner, A. F., Bartley, J. M., Coleman, D. S., Gray, W. & Taylor, R. Z. Pyro, meaning fire, refers to the igneous source of the tephra and clastic refers to the rock fragments. B) Temperature of the environment - lower T = slower magma cooling. = 15 ? If no button appears, you cannot download or save the media. 6. basalt For information on user permissions, please read our Terms of Service. 1. basaltic scoria The solid parts, called tephra, settle back to earth and cool into rocks with pyroclastic textures. This explains why a cooling magma can have some crystals within it and yet remain predominantly liquid. The dikes may be intruding over millions of years, but since they may be made of similar material, they would be appearing to be formed at the same time. As long as more magma pools into a volcanos magma chamber, there is the possibility of an eruption and the volcano will remain active. Decompression melting also occurs at mantle plumes, columns of hot rock that rise from Earths high-pressure core to its lower-pressure crust. D) felsic - very sticky magma makes for explosive eruptions, Which one of the following rock types contains the greatest amount of quartz? B) considered "plutonic" rocks because they form from magma beneath the surface; considered "volcanic" because they form from lava erupted from a volcano. The rock then cools into new crust. 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. Composition refers to the rocks specific mineralogy and chemical composition. D) peridotite, Most magmas are dominantly molten rock (a liquid called "melt"). C) Pegmatite The Journal of Geology 39, 5467 (1931). Finally, if the magma is quite silica-rich to begin with, there will still be some left at around 750 to 800C, and from this last magma, potassium feldspar, quartz, and maybe muscovite mica will form. The composition of magma depends on the rock it was formed from (by melting), and the conditions of that melting. 1996 - 2023 National Geographic Society. A. D. quartz Salt Lake Community College via OpenGeology. Typical intermediate rocks are diorite and andesite. C. biotite B) basalt Andesitic rocks are often found at continental volcanic arcs, such as the Andes Mountains in South America, after which they are named. CC BY. 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). Basalt and gabbro are the extrusive and intrusive names for mafic igneous rocks, and peridotite is ultramafic, with komatiite as the fine-grained extrusive equivalent. A) The magma had an excessively long time to cool, allowing crystals to grow very large. 1. 2. pressure The large crystals are called phenocrysts and the fine-grained matrix is called the groundmass or matrix. D) pressure. This process is known as fractional crystallization. What is "magmatic differentiation"? The means that the overall composition of the magma near the top of the magma chamber will become more felsic, as it is losing some iron- and magnesium-rich components. D) gabbroic, granitic, The classification of igneous rocks is based on __________. We also acknowledge previous National Science Foundation support under grant numbers 1246120, 1525057, and 1413739. National Geographic Society is a 501 (c)(3) organization. 2. gabbro The Hawaiian Islands are a direct result of mafic magma eruptions. The core is the superheated center, the mantle is the thick, middle layer, and the crust is the top layer on which we live. Arndt, N. T. Chapter 1 Archean Komatiites. 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. D. Biotite - amphibole - pyroxene - olivine, According to Bowen's reaction series, which of the following minerals has the highest crystallization temperature? D. Heavier crystals float on the top of the magma in the magma chamber producing a layered igneous rock upon complete solidification. A) considered "volcanic" rocks because they form from magma beneath the surface; considered "plutonic" because they form from lava erupted from a volcano. Typical mafic rocks are gabbro (intrusive) and basalt (extrusive). D. obsidian User: She worked really hard on the project. Plus, they are, by definition, exposed to the elements of erosion immediately. Want to create or adapt OER like this? B) the rock's composition 1. aphanitic Rocks labeled as granite in laymen applications can be several other rocks, including syenite, tonalite, and monzonite. 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. Why are thin sections of rocks used to study igneous rocks? 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. The cracks, called fissures or vents, are tell-tale signs of a volcano. The dikes may be intruding over millions of years, but since they may be made of similar material, they would be appearing to be formed at the same time. __________ is a volcanic rock that is extremely vesicular and glassy. What is magma? Basalt is a fine-grained mafic igneous rock. 1. andesite Transfer of heat often happens at convergent boundaries, where tectonic plates are crashing together. An active volcano always has a magma chamber beneath the cone. B. B) the first crystals to form when the magma was in the magma chamber Young, emerging subvolcanic intrusion cutting through older one, Xenolith (solid rock of high melting temperature which has been transported within the magma from deep below) or roof pendant (fragment of the roof of the magma chamber that has detached from the roof and sunk into the melt), Contact metamorphism in the country rock adjacent to the magma chamber (caused by the heat of the magma), Uplift at the surface due to laccolith emplacement in the near sub-ground, Active magma chamber (called pluton when cooled and entirely crystallized; a batholith is a large rock body composed of several plutonic intrusions), Old pegmatite (late-magmatic dyke formed by aggressive and highly mobile residual melts of a magma chamber). This magma solidifies in the air to form volcanic rock called tephra. Magmas derived from crustal material are dominated by oxygen, silicon, aluminum, sodium, and potassium. D. consist of very coarse grained crystals of potassium feldspar, muscovite and quartz solid rock with a fine texture cooled rock with large crystals molten rock below Earth's surface flowing rock above Earth's surface New answers Rating 3 capslock Magma is molten rock below Earth's surface. F. olivine Much like heat transfer, flux melting also occurs around subduction zones. D. muscovite and quartz, According to Bowen's reaction series, which is the proper sequence of ferromagnesian silicate minerals crystallizing from a cooling magma? Arndt, N. T. Chapter 1 Archean Komatiites. D. glassy and frothy texture They have a mineral composition that is intermediate between granite and basalt. 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. 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