Basalt is a fine-grained mafic igneous rock. E. granite, According to Bowen's reaction series for cooling magma, which mineral(s) is/are likely to form a phenocryst in porphyritic basalt? 4. andesite A magma chamber is a large underground reservoir of molten rock. The audio, illustrations, photos, and videos are credited beneath the media asset, except for promotional images, which generally link to another page that contains the media credit. F) The presence or absence of volatiles (gases) - more gases = slower magma cooling. 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. What is magma? Basalt is one of the most common rocks in Earths crust as well as the volcanic islands created by hot spots. When lava is extruded onto the surface, or intruded into shallow fissures near the surface and cools, the resulting igneous rock is called extrusive or volcanic. Lava is molten rock flowing out of fissures or vents at volcanic centres (when cooled, they form rocks such as basalt, rhyolite, or obsidian). A. biotite Rhyolite refers to the volcanic and felsic igneous rocks and granite refer to intrusive and felsic igneous rocks. D. and c. only B. mineral grains are roughly equal size and coarse enough to be seen without the aid of a microscope or magnifying lens This non-crystalline material is not classified as minerals but as volcanic glass. The path of rising magma is called a diapir. They are typically more than 100 km2 in area, associated with subduction zones, and mostly felsic in composition. Because of this, dikes are often vertical or at an angle relative to the pre-existing rock layers that they intersect. Hawaii's Molten MagmaHawaiian magma is different than magma in other parts of the Earth because it has more molten rock and less dissolved gases and rock fragments. Magma that has cooled into a solid is called igneous rock. Why are thin sections of rocks used to study igneous rocks? The composition of the original magma is critical to magma crystallization because it determines how far the reaction process can continue before all of the silica is used up. D) the lava in the crystallizing magma chamber before eruption. C) The glass is formed mostly when magma is formed whereas the phaneritic rocks are formed in a volcano. The rock then cools into new crust. The presence of quartz is a good indicator of granite. Arndt, N. T. Chapter 1 Archean Komatiites. D) The rock contains broken fragments and is volcanic in origin. Igneous rocks are classified based on texture and composition. d. C) basalt; extrusive rock that formed from cooling of relatively high silica lava These groups refer to differing amounts of silica, iron, and magnesium found in the minerals that make up the rocks. This magma solidifies in the air to form volcanic rock called tephra. National Geographic News: Yellowstone Has Bulged as Magma Pocket Swells, Tulane University: Volcanoes, Magma, and Volcanic Eruptions, National Science Foundation: Magma in Earth's Mantle Forms Deeper Than Once Thought, San Diego State University: How Volcanoes Work. 3. rhyolite E. pyroxene Magma can intrude into a low-density area of another geologic formation, such as a sedimentary rock structure. If the fragments accumulate while still hot, the heat may deform the crystals and weld the mass together, forming a welded tuff. B) the rock's likely parent magma composition This creates magma in places where it originally maintained a solid structure. As with dikes, sills are younger than the surrounding layers and may be radioactively dated to study the age of sedimentary strata. B) amount of space available for crystals to fill B. komatiite Composition refers to a rocks chemical and mineral make-up. 1. Magma is hot, molten rock that exists beneath the Earth's surface. Because felsic lavas are less mobile, it is less common than granite. F. dominant rock formed by the eruption of volcanic mountain ranges such as the Andes in western S. America Areas of lower pressure always have a lower melting point than areas of high pressure. Types of MagmaAll magma contains gases and a mixture of simple elements. B) granodioritic 3. decompression melting B) gabbro C. often occur with basalt and other mafic igneous rocks The composition of magma depends on the rock it was formed from (by melting), and the conditions of that melting. C. Al and Si are the least abundant elements in the magma. Steady and relatively calm lava fountains continue to change and expand the Big Island of Hawaii. When volcanoes erupt explosively, vast amounts of lava, rock, ash, and gases are thrown into the atmosphere. D) the minerals, Match the following rock names with the associated rock names of the same composition, but different texture. D. plate tectonics, Match the appropriate term associated with the production of magma to its best description. 1. heat 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? Figure 3.3.1, 3.3.4, 3.3.5, 3.3.6, 3.3.7, 3.3.8: Steven Earle. As it falls to Earth, tephra includes rocks such as pumice. D. obsidian Condie) 11, 1144 (Elsevier, 1994). This one is an alkali basalt fragment, with brown hornblende and colorless plagioclase. C. basalt Classification of Igneous Rock Series. Plus, they are, by definition, exposed to the elements of erosion immediately. The most familiar way for magma to escape, or extrude, to Earths surface is through lava. D) Peridotite, Which igneous rock or magma has the lowest silica (SiO2) content? Figure 3.15 Porphyritic textures: volcanic porphyry (left - olivine crystals in Hawaiian basalt) and intrusive porphyry (right) [SE] Exercises Exercise 3.4 Porphyritic Minerals solid and pinstriped A. rhyolite The rock that results from this is an igneous rock from the Latin word ignis, meaning "fire." Soon after that, all of the magma is used up and no further changes takes place. FALSE. C. assimilation of "foreign" rocks by the magma This was done over and over, each time allowing the magma to cool to a lower temperature before quenching. Learn how BCcampus supports open education and how you can access Pressbooks. As with dikes, sills are younger than the surrounding layers and may be radioactively dated to study the age of sedimentary strata. 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) 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. The sequence in which minerals crystallize from a magma is known as the Bowen reaction series (Figure 3.3.1 and Figure 3.3.3). As a magma cools below 1300C, minerals start to crystallize within it. Which of the following best describes an aphanitic texture? B) highly fluid, cools slowly C) number of ions The core is the superheated center, the mantle is the thick, middle layer, and the crust is the top layer on which we live. Gabbro is a major component of the lower oceanic crust. All magmas contain gases dissolved in a solution called volatiles. Text on this page is printable and can be used according to our Terms of Service. B) The rock has mineral grains that are glassy. 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. 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. 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. Sills are another type of intrusive structure. Over millions of years, many magma chambers simply cool to form a pluton or large igneous intrusion. 4. glassy. A. convergent plate boundaries 4. porphyritic basalt An eruption reduces the pressure inside the magma chamber. What would happen if you replaced the ">=" operator in the test with ">" so that it reads A) considered "volcanic" rocks because they form from magma beneath the surface; considered "plutonic" because they form from lava erupted from a volcano. D) If the magma has no crystals or gases within it, it is called "lava." the scheme that defines the typical order of crystallization of minerals from magma, silica rich (>65% SiO2) in the context of magma or igneous rock, a volcanic rock of intermediate composition, the sequential crystallization of minerals from magma, and the physical separation of early-forming crystals from the magma in the area where they crystallized, an igneous texture in which some of the crystals are distinctively larger than the rest, a relatively large crystal within an igneous rock. The cracks, called fissures or vents, are tell-tale signs of a volcano. Tapping into Magmas PotentialIn 2009, the Icelandic Deep Drilling Project created a well that uses magma to generate geothermal energy. Therefore, most landforms and rock groups that owe their origin to igneous rocks are intrusive bodies. C) basaltic, rhyolitic 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. _________ is the dominant feldspar in basalt. D) pressure. B. basalt 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. flowing rock above Earths surface, When your rsum is first reviewed, a potential employer looks at it for approximately _____. When porphyritic, it often has either olivine or plagioclase phenocrysts. 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. 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). Felsic MagmaFelsic magma has the highest silica content of all magma types, between 65-70%. 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. Decompression MeltingDecompression melting involves the upward movement of Earth's mostly-solid mantle. D. Heavier crystals float on the top of the magma in the magma chamber producing a layered igneous rock upon complete solidification. C. cause rocks to melt at lower temperatures, magnified by an increase in pressure, important at convergent plate boundaries Are plutons assembled over. C) andesitic C) The extrusive magma, because it is deep below the surface, cools very slowly, producing very small mineral grains. 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). The crystals that settle might either form an olivine-rich layer near the bottom of the magma chamber, or they might remelt because the lower part is likely to be hotter than the upper part (remember, from Chapter 1, that temperatures increase steadily with depth in Earth because of the geothermal gradient). Intrusive rocks, forming underground with larger, stronger crystals, are more likely to last. = 2 1/4. 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. 1 minute C) highly fluid, cools quickly F) basalt; extrusive rock that formed from cooling of relatively low silica lava, Match the volcano with the appropriate rock formed by its eruption. Batholiths and stocks are discordant intrusions that cut across and through surrounding country rock. Haydn's opus 33 string quartets were first performed for A. a decrease in the confining pressure (decompression) 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. Intrusive or plutonic rocks crystallize from magma beneath the earth's surface. In some cases, however, partially cooled but still liquid magma, with crystals in it, will either move farther up into a cooler part of the crust, or all the way to the surface during a volcanic eruption. A) Basalt 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. C. Crystal settling may produce different melting conditions for a rock in different plate tectonic scenarios. The compositions of typical mafic, intermediate, and felsic magmas are shown in Figure 3.3.4. B. Andes mountains volcanoes A) Upon eruption, magma becomes "lava," the form of the magma that flows out of the volcano. Common rock types within the intrusive category are granite and diorite. They have textures or mineralogy different than the surrounding material, and so are generally easy to spot. Laccoliths bulge upwards; a similar downward-bulging intrusion is called a lopolith. This non-crystalline material is not classified as minerals but as volcanic glass. 2. pressure A __________ texture would be most UNLIKELY to occur in an extrusive igneous rock. 3. diorite If the fragments accumulate while still hot, the heat may deform the crystals and weld the mass together, forming a welded tuff. As the temperature drops, and assuming that some silica remains in the magma, the olivine crystals will react (combine) with some of the silica in the magma to form pyroxene. A) mafic - very fluid magma makes for passive (fluid) eruptions B) Each vesicle was filled by a crystal when the lava was mostly solid, and the crystals fell out later. In the atmosphere, tephra is more often called volcanic ash. D. Al and Si are the most abundant elements in the magma. This explains why a cooling magma can have some crystals within it and yet remain predominantly liquid. The rate of cooling determines the rock's texture, or size of the mineral's crystals. B) glassy 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). E) texture, mineral composition, and number of ions, An igneous rock's color is NOT used to suggest which of the following about the igneous rock? D. gabbro The minerals present will be olivine, pyroxene, and calcium-rich plagioclase. Rocks labeled as granite in laymen applications can be several other rocks, including syenite, tonalite, and monzonite. St. Helens volcano, Washington state We also acknowledge previous National Science Foundation support under grant numbers 1246120, 1525057, and 1413739. Obsidian as a glassy rock shows an excellent example of conchoidal fracture similar to the mineral quartz (see Chapter 3). A sill is a concordant intrusion that runs parallel to the sedimentary layers in the country rock. Regardless, when a diapir cools, it forms a mass of intrusive rock called a pluton. When located beneath the ocean, these plumes, also known as hot spots, push magma onto the seafloor. Andesite is a fine crystalline intermediate extrusive rock. These compounds cause the rock to melt at lower temperatures. True Laccoliths are blister-like, concordant intrusions of magma that form between sedimentary layers. This hot material rises to an area of lower pressure through the process of convection. Therefore, most landforms and rock groups that owe their origin to igneous rocks are intrusive bodies. Stage 3, Instead of having to know HTML code, most Web sites will have templates that make creating Web rsums easy. A. granite Geothermal drilling projects discovered two magma sites on the Big Island of Hawaii, and one on Iceland. One theory is the overriding rock gets shouldered aside, displaced by the increased volume of magma. C) pressure Which of the following can account for variations in a magma/rock composition? 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]. Thick, viscous felsic magma can trap gas bubbles in a volcanos magma chamber. E. intermediate silica, intermediate iron and magnesium, aphanitic texture The individual crystals in phaneritic texture are readily visible to the unaided eye. Obsidian as a glassy rock shows an excellent example of conchoidal fracture similar to the mineral quartz (see Chapter 3). C. potassium feldspar Basalt is the main rock which is formed at mid-ocean ridges, and is therefore the most common rock on the Earths surface, making up the entirety of the ocean floor (except where covered by sediment). a. A. both quartz and muscovite Rock formed from large deposits of tephra fragments is called tuff. Which of the following is the likely cause of a vesicular texture (open cavities in a rock)? 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