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]. Much like heat transfer, flux melting also occurs around subduction zones. Large eruptions can nearly empty the magma chamber. The compositions of typical mafic, intermediate, and felsic magmas are shown in Figure 3.3.4. Intrusive rocks, forming underground with larger, stronger crystals, are more likely to last. Peacock, M. A. A) Pressure of the environment - lower P = slower magma cooling. Lava that cools extremely quickly may not form crystals at all, even microscopic ones. What are the other two, smaller percentage components of most magmas? A. high levels are necessary for melting of rocks The path of rising magma is called a diapir. in, Chris Johnson, Matthew D. Affolter, Paul Inkenbrandt, & Cam Mosher, status page at https://status.libretexts.org. Typical intermediate rocks are diorite and andesite. C. often occur with basalt and other mafic igneous rocks The other is how fast the magma cools. The minerals present will be olivine, pyroxene, and calcium-rich plagioclase. 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. b. 20/3 Batholiths are found in the cores of many mountain ranges, including the granite formations of Yosemite National Park in the Sierra Nevada of California. Because mafic lava is more mobile, it is less common than basalt. Which are definitions of "mafic" and "felsic"? This relates to the cooling history of the molten magma from which it came. How Magma Forms Earth is divided into three general layers. Lava is molten rock flowing out of fissures or vents at volcanic centres (when cooled, they form rocks such as basalt, rhyolite, or obsidian). Magma Chamber In areas where temperature, pressure, and structural formation allow, magma can collect in magma chambers. C) andesitic A sill is a concordant intrusion that runs parallel to the sedimentary layers in the country rock. 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. light colored, more dense and less viscous (not sticky), What type of composition would result in a magma if equal amounts of basaltic and granitic magma were mixed? Andesitic rocks are often found at continental volcanic arcs, such as the Andes Mountains in South America, after which they are named. A. a decrease in the confining pressure (decompression) 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. c. For igneous rock, the composition is divided into four groups: felsic, intermediate, mafic, and ultramafic. 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. 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. Inflammation of the lymph vessels is known as________. Why are thin sections of rocks used to study igneous rocks? Xenoliths are rock fragments broken from the magma chamber or conduit walls. Which of the following best describes an aphanitic texture? It is found in its namesake, the Andes Mountains as well as the Henry and Abajo mountains of Utah. 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. In violent eruptions, the volume of magma shrinks so much that the entire magma chamber collapses and forms a caldera. An active volcano always has a magma chamber beneath the cone. Extrusive igneous rocks have a fine-grained or aphanitic texture, in which the grains are too small to see with the unaided eye. 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. What is a likely reason for this phaneritic texture? C) Both of these. light colored, less dense and more viscous (sticky) A. B) Intrusive magma flows onto the Earth's surface and cools very slowly, allowing many small mineral grains to grow. The Rights Holder for media is the person or group credited. B. the upper mantle Peacock, M. A. 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. These eruptions eject lava violently into the air, which cools into dacite and rhyolite rock. A. Si and O are the most abundant elements in the magma. B. higher values of this require greater temperatures for melting B. diorite C. Al and Si are the least abundant elements in the magma. The presence of quartz is a good indicator of granite. b. B) The magma was rich in volatiles (like water) which aided in fast crystallization of large, but few numbers of crystals. B. quartz Lava cools to form volcanic rock as well as volcanic glass. B) highly fluid, cools slowly These tiny crystals can be viewed under a petrographic microscope [1]. 1: Granite is a classic coarse-grained (phaneritic) intrusive igneous rock. Typical felsic rocks are granite and rhyolite (Figure 3.3.5). A. rhyolite B) Andesite 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]. In a porphyritic volcanic rock, which mineral grains are the last to crystallize? The presence of quartz is a good indicator of granite. Earth Science, Geology, Geography, Physical Geography. 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. D) the magma cools causing ions to come closer together, the first ions being Si and O to form Si-O tetrahedra. D) komatiite Match the rock name with the best description. It can be found in the Andes Mountains and in some island arcs (see. America. Accessibility StatementFor more information contact us atinfo@libretexts.orgor check out our status page at https://status.libretexts.org. These rocks usually have a coarse texture (individual minerals are visible without magnification), because the magma cools slowly underground, allowing crystal growth. Who was Bowen, and what is a reaction series? D. gabbro A. convergent plate boundaries They have a mineral composition that is intermediate between granite and basalt. C) Pressure of the environment - higher P = slower magma cooling. Volcanic glass and coarse-grained igneous rocks differ by which of the following? C. aphanitic or glassy texture Obsidian is a rock consisting of volcanic glass. 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. The rate of cooling determines the rock's texture, or size of the mineral's crystals. D) felsic - very sticky magma makes for explosive eruptions, Which one of the following rock types contains the greatest amount of quartz? If any melting takes place, crystal settling will make the magma at the bottom of the chamber more mafic than it was to begin with (Figure 3.3.6c). B) dark colored, more dense and less viscous (not sticky); in Developments in Precambrian Geology (ed. Laccoliths bulge upwards; a similar downward-bulging intrusion is called a lopolith. Extrusive rocks, because of their small crystals and glass, are less durable. D. ocean ridge volcanoes Composition refers to a rocks chemical and mineral make-up. 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). 4. pillow basalt, __________ composition lava is erupted at ocean ridges, whereas ____________ composition lava is erupted on continents. C. Mt. Any interactives on this page can only be played while you are visiting our website. These tiny crystals can be viewed under a petrographic microscope [1]. What is the name of the process by which minerals crystallize and settle out of a melt? Andesite is the name of a family of fine-grained, extrusive igneous rocks that are usually light to dark gray in color. 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 molten rock below Earths surface D. ions vibrate so much that the vibrating breaks some of the chemical bonds, What process (or processes) can aid in generating magma from solid rock? 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). 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. A purely descriptive definition is that a rock is - A naturally occurring aggregate of minerals and other solid material. A. biotite Lava that cools extremely quickly may not form crystals at all, even microscopic ones. Because of this, dikes are often vertical or at an angle relative to the pre-existing rock layers that they intersect. Magma is molten rock inside the earth. In some cases, extrusive lava cools so rapidly it does not develop crystals at all. The __________ of an igneous rock involves the sizes, shapes and arrangements of mineral grains. This is a common component of volcanic ash and rocks like obsidian. Andesite and diorite likewise refer to extrusive and intrusive intermediate rocks (with dacite and granodiorite applying to those rocks with composition between felsic and intermediate). C. Crystal settling may produce different melting conditions for a rock in different plate tectonic scenarios. A. quartz and pyroxene B. magma mixing This relates to the cooling history of the molten magma from which it came. 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? This creates magma in places where it originally maintained a solid structure. D) gabbroic, granitic, The classification of igneous rocks is based on __________. A. the rock has two or more distinctly different-size populations of mineral grains The Journal of Geology 39, 5467 (1931). C. high silica, low iron and magnesium, phaneritic texture This huge increase in temperature allowed just one magma well to generate roughly 36 megawatts of electricity, powering 36,000 homes. Arndt, N. T. Chapter 1 Archean Komatiites. C) solid + melt For example, it is not known what happens to the pre-existing country rock as the diapir intrudes. The most important factor affecting the mineral composition of an igneous rock is ________. This type of magma has a low gas content and low viscosity, or resistance to flow. D) Each vesicle is filled by air and water. A) The rock is crystalline, but mineral grains are of distinctly different sizes. In some cases, extrusive lava cools so rapidly it does not develop crystals at all. A) pyroclastic 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. Pyroclastic texture is usually recognized by the chaotic mix of crystals, angular glass shards, and rock fragments. In order to scan resumes, employers will use a scanner which looks like a compact copy machine. 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. As a volcanos magma chamber experiences greater pressure, often due to more magma seeping into the chamber, the volcano may undergo an eruption. Batholiths are found in the cores of many mountain ranges, including the granite formations of Yosemite National Park in the Sierra Nevada of California. C. assimilation A) granite; gabbro. It is commonly grey and porphyritic. C) gabbroic Pyroclastic texture is usually recognized by the chaotic mix of crystals, angular glass shards, and rock fragments. 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. Some igneous rocks have a mix of coarse-grained minerals surrounded by a matrix of fine-grained material in a texture called porphyritic. Magma is a mixture of molten and semi-molten rock found beneath the surface of the Earth. As the temperature drops, and providing that there is sodium left in the magma, the plagioclase that forms is a more sodium-rich variety. dark colored, more dense and less viscous (not sticky) Magma Escape Routes Magma leaves the confines of the upper mantle and crust in two major ways: as an intrusion or as an extrusion. 1. basaltic scoria A 12-square-mile . When magma is ejected by a volcano or other vent, the material is called lava. Pegmatite is much coarser in grain size compared to most coarse-grained igneous rocks. St. Helens volcano, Washington state All magmas contain gases dissolved in a solution called volatiles. TRUE. This occurs when calcium-rich early-forming plagioclase crystals become coated with progressively more sodium-rich plagioclase as the magma cools. Composition refers to the rocks specific mineralogy and chemical composition. 30-45 seconds 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. D. Al and Si are the most abundant elements in the magma. Andesite is a rock typically found in volcanoes above convergent plate boundaries between continental and oceanic plates. And ultramafic d. Affolter, Paul Inkenbrandt, & Cam Mosher, status page at https: //status.libretexts.org Each. Contact us atinfo @ libretexts.orgor check out our status page at https: //status.libretexts.org granite and basalt employers use... 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