It can be found in the Andes Mountains and in some island arcs (see. A. a decrease in the confining pressure (decompression) There are three different types of . F. olivine 1. As a mafic magma starts to cool, some of the silica combines with iron and magnesium to make olivine. A) Mafic is a magma/rock that is rich in feldspar and silica (quartz), whereas felsic refers to that which is rich in Fe and Mg. 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. Andesitic rocks are often found at continental volcanic arcs, such as the Andes Mountains in South America, after which they are named. Pyroclastic texture is usually recognized by the chaotic mix of crystals, angular glass shards, and rock fragments. A. Bowen's reaction process 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) . Andesite is a rock typically found in volcanoes above convergent plate boundaries between continental and oceanic plates. TRUE. At about the point where pyroxene begins to crystallize, plagioclase feldspar also begins to crystallize. Most magma chambers sit far beneath the surface of the Earth. D) considered "volcanic" rocks because they form from lava extruded at the surface; considered "plutonic" rocks because they form from magma beneath the surface. Lava is molten rock flowing out of fissures or vents at volcanic centres (when cooled, they form rocks such as basalt, rhyolite, or obsidian). Note that these 8 elements make up about 99 percent of the Earth's crust. The results were studied under the microscope and by chemical analysis. 1. Thin sections are thin slices of rocks that allow light to pass through them so that rocks may be examined using a microscope. 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Magma is a molten and semi- molten rock mixture found under the surface of the Earth. Texture describes the physical characteristics of the minerals, such as grain size. C. aphanitic or glassy texture Because felsic lavas are less mobile, it is less common than granite. C. biotite and olivine National Geographic Society is a 501 (c)(3) organization. Texture describes the physical characteristics of the minerals, such as grain size. D. lower silica, high iron and magnesium, phaneritic texture They are typically more than 100 km2 in area, associated with subduction zones, and mostly felsic in composition. If magma cools slowly, deep within the crust, the resulting rock is called intrusive or plutonic. All rights reserved. 4. porphyritic basalt Most of the mantle and crust are solid, so the presence of magma is crucial to understanding the geology and morphology of the mantle. 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. A) highly viscous, cools slowly The __________ of an igneous rock involves the sizes, shapes and arrangements of mineral grains. E. pyroxene 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. Much like hot fudge being poured over cold ice cream, this transfer of heat is able to melt the surrounding rock (the ice cream) into magma. 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). B. magma mixing Diorite is identifiable by its Dalmatian-like appearance of black hornblende and biotite and white plagioclase feldspar. The gas bubbles become trapped in the solidifying lava to create a vesicular texture, with the holes specifically called vesicles. If that magma is then involved in a volcanic eruption, the rest of the liquid will cool quickly to form a porphyritic texture. Texture describes the physical characteristics of the minerals, such as grain size. Intrusive rocks, forming underground with larger, stronger crystals, are more likely to last. As it falls to Earth, tephra includes rocks such as pumice. An intrusion can form features such as dikes and xenoliths. Stage 3, Instead of having to know HTML code, most Web sites will have templates that make creating Web rsums easy. A) rhyolitic 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. A sill is a concordant intrusion that runs parallel to the sedimentary layers in the country rock. B. mineral grains are roughly equal size and coarse enough to be seen without the aid of a microscope or magnifying lens A. peridotite C. assimilation of "foreign" rocks by the magma Some igneous rocks have a mix of coarse-grained minerals surrounded by a matrix of fine-grained material in a texture called porphyritic. Basalt is one of the most common rocks in Earths crust as well as the volcanic islands created by hot spots. For information on user permissions, please read our Terms of Service. A. crystal settling A) Intrusive magma is cooler because it is well insulated by the surrounding rock. The other is how fast the magma cools. 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. Mafic magmas have 45% to 55% SiO2, about 25% total of FeO and MgO plus CaO, and about 5% Na2O + K2O. C) Mafic is hard rock, felsic is soft rock. False, Applications and Investigations In Earth Science, Dennis G. Tasa, Edward J. Tarbuck, Frederick K. Lutgens, Charles C. Plummer, Diane Carlson, Lisa Hammersley. Obsidian is a rock consisting of volcanic glass. A single magma may generate several mineralogically different igneous rocks. Name one advantage and one disadvantage of drug combination therapy. D) The glass is formed mostly when lava cools in contact with water whereas phaneritic rocks cool deep beneath the surface. Extrusive igneous rocks are _________, whereas intrusive igneous rocks are _________. The large crystals are called phenocrysts and the fine-grained matrix is called the groundmass or matrix. 4. andesite A) mafic - very fluid magma makes for passive (fluid) eruptions B) The magma was rich in volatiles (like water) which aided in fast crystallization of large, but few numbers of crystals. 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. Classification of Igneous Rock Series. These differences in chemical composition are directly related to differences in gas content, temperature, and viscosity. Granite: Granite is the intrusive equivalent of rhyolite but has a coarser texture. 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. If you have questions about licensing content on this page, please contact ngimagecollection@natgeo.com for more information and to obtain a license. 4. volatiles, A heated crystalline solid most likely melts when ________. Extrusive or volcanic rocks crystallize from lava at the earth's surface. 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. B. diorite A. the rock has two or more distinctly different-size populations of mineral grains 2. porphyritic For a volcano to erupt, it must have a source of magma. If magma cools slowly, deep within the crust, the resulting rock is called intrusive or plutonic. 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. True Magmas derived from crustal material are dominated by oxygen, silicon, aluminum, sodium, and potassium. Laccoliths are blister-like, concordant intrusions of magma that form between sedimentary layers. These compounds cause the rock to melt at lower temperatures. Intermediate MagmaIntermediate magma has higher silica content (roughly 60%) than mafic magma. C) light colored, less dense and more viscous (sticky); User: She worked really hard on the project. 3. phaneritic Because mafic lava is more mobile, it is less common than basalt. E) Both a. and c. Flux MeltingFlux melting occurs when water or carbon dioxide are added to rock. As the denser tectonic plate subducts, or sinks below, or the less-dense tectonic plate, hot rock from below can intrude into the cooler plate above. Extrusive rocks, because of their small crystals and glass, are less durable. A) Intrusive magma is cooler because it is well insulated by the surrounding rock. Who was Bowen, and what is a reaction series? A. If vesicular, pummus geothermal gradient CC BY. G. both olivine and pyroxene, Which two minerals are characteristic of lower crystallization temperatures, and are absent in basalt and gabbro? This non-crystalline material is not classified as minerals but as volcanic glass. C. the lower crust Are plutons assembled over. Dikes are therefore discordant intrusions, not following any layering that was present. One theory is the overriding rock gets shouldered aside, displaced by the increased volume of magma. B. basalt Igneous rocks constitute one of the three principal classes of rocks, the others being metamorphic and sedimentary. C. biotite Peacock, M. A. 2. why is it helpful to measure the specific gravity of a mineral? To give an example of how large these crystals can get, transparent cleavage sheets of pegmatitic muscovite mica were used as windows during the Middle Ages. 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. 4. mafic obsidian. FALSE. Match the rock name with the best description. Plutons can include dikes and xenoliths. 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. Condie) 11, 1144 (Elsevier, 1994). Please select the best answer from the choices provided B. variable silica, iron and magnesium content, glassy texture C) rate of cooling Magma that has cooled into a solid is called igneous rock. A) striped and dotted; It is found in its namesake, the Andes Mountains as well as the Henry and Abajo mountains of Utah. It is commonly vesicular and aphanitic. B) Andesite If the magma has a low viscosity (i.e., its runny)which is likely if it is maficthe crystals that form early, such as olivine (Figure 3.3.6a), may slowly settle toward the bottom of the magma chamber (Figure 3.3.6b). It is found in its namesake, the Andes Mountains as well as the Henry and Abajo mountains of Utah. She or he will best know the preferred format. This occurs when calcium-rich early-forming plagioclase crystals become coated with progressively more sodium-rich plagioclase as the magma cools. As a magma cools below 1300C, minerals start to crystallize within it. 2 minutes, Web rsums are posted to the Internet in HTML format. St. Helens. Laccoliths bulge upwards; a similar downward-bulging intrusion is called a lopolith. A) the rock's texture 2. granite and granodiorite They are formed when magma exploits a weakness between these layers, shouldering them apart and squeezing between them. Rhyolite is commonly pink and will often have glassy quartz phenocrysts. The cracks, called fissures or vents, are tell-tale signs of a volcano. Magma is extremely hotbetween 700 and 1,300 Celsius (1,292 and 2,372 Fahrenheit). C) basalt; extrusive rock that formed from cooling of relatively high silica lava Peacock, M. A. C) andesite Diorite is identifiable by its Dalmatian-like appearance of black hornblende and biotite and white plagioclase feldspar. Magma compositions vary, but will have eight main elements in different proportions. This non-crystalline material is not classified as minerals but as volcanic glass. = 2 5/20 User: Alcohol in excess of ___ proof Weegy: Buck is losing his civilized characteristics. C) andesitic A. consist of very large grains of quartz, olivine and pyroxene in relatively large bodies of former sedimentary rock D. and c. only 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. A magmatic dike is simply a large slab of magmatic material that has intruded into another rock body. B. olivine and pyroxene Areas of lower pressure always have a lower melting point than areas of high pressure. D) chemical composition of the magma or lava. Magma is molten rock inside the earth. It has also been proposed that diapirs are not a real phenomenon, but just a series of dikes that blend into each other. The Rights Holder for media is the person or group credited. For igneous rock, the composition is divided into four groups: felsic, intermediate, mafic, and ultramafic. Why? In violent eruptions, the volume of magma shrinks so much that the entire magma chamber collapses and forms a caldera. Magma originates in the lower part of the Earths crust and in the upper portion of the mantle. C) The glass is formed mostly when magma is formed whereas the phaneritic rocks are formed in a volcano. molten rock below Earths surface 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. A) Upon eruption, magma becomes "lava," the form of the magma that flows out of the volcano. C ) andesite Diorite is identifiable by its Dalmatian-like appearance of black hornblende and biotite and olivine National Geographic is... 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