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. B. Olivine - pyroxene - amphibole - biotite C) Each vesicle was filled by magma trapped in the solidified lava, and later escaped. FALSE. As the magma rises to the surface, the drop in pressure causes the dissolved volatiles to come bubbling out of solution, like the fizz in an opened bottle of soda. molten rock below Earths surface 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]. The fine-grained texture indicates the quickly cooling lava did not have time to grow large crystals. A) the lava after it erupted from a crystallizing magma chamber Obsidian as a glassy rock shows an excellent example of conchoidal fracture similar to the mineral quartz (see Chapter 3). Sills are another type of intrusive structure. An igneous rock is any crystalline or glassy rock that forms from cooling of a magma. Figure 3.3.1, 3.3.4, 3.3.5, 3.3.6, 3.3.7, 3.3.8: Steven Earle. The Journal of Geology 39, 5467 (1931). 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). For the rock to be called porphyritic there has to be a significant difference in crystal size, where the larger crystals are at least 10 times larger than the average size of the smaller crystals. if((replacementValue > 0) && (replacementValue < limit)). C. the lower crust St. Helens. If solid, obsidian. This type of magma has a low gas content and low viscosity, or resistance to flow. C. potassium feldspar As a mafic magma starts to cool, some of the silica combines with iron and magnesium to make olivine. Figure 3.3.2 shows a zoned plagioclase under a microscope. What does it mean if a rock has a coarse texture? Igneous rocks are classified based on texture and composition. C) basalt; extrusive rock that formed from cooling of relatively high silica lava When magma is ejected by a volcano or other vent, the material is called lava. C. granite C) the rock's color A) Basalt B) granodioritic cooled rock with large crystals C) highly fluid, cools quickly 1. In the discontinuous branch, olivine is typically the first mineral to form (at just below 1300C). Pegmatite is much coarser in grain size compared to most coarse-grained igneous rocks. Peacock, M. A. Melted rock originates within Earth as magma . B) granite; intrusive rock that formed from cooling of relatively high silica magma Extrusive or volcanic rocks crystallize from lava at the earth's surface. 1. heat As the magma rises to the surface, the drop in pressure causes the dissolved volatiles to come bubbling out of solution, like the fizz in an opened bottle of soda. Magma is a mixture of molten and semi-molten rock found beneath the surface of the Earth. Gabbro is a major component of the lower oceanic crust. D. glassy and frothy texture The rock that results from this is an igneous rock from the Latin word ignis, meaning "fire." D. and c. only A) mafic - very fluid magma makes for passive (fluid) eruptions Geothermal drilling projects discovered two magma sites on the Big Island of Hawaii, and one on Iceland. B. may be composed of grains of olivine and pyroxene phenocrysts 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. 2 minutes, Web rsums are posted to the Internet in HTML format. A. K.C. The layers of magma may be documented by the type of eruption material the volcano emits. Transfer of HeatMagma can also be created when hot, liquid rock intrudes into Earths cold crust. Pyro, meaning fire, refers to the igneous source of the tephra and clastic refers to the rock fragments. There are 3 main agents that cause metamorphism. light colored, less dense and more viscous (sticky) C) Mafic is hard rock, felsic is soft rock. C. Crystal settling may produce different melting conditions for a rock in different plate tectonic scenarios. National Geographic News: New Magma Layer Found Deep in Earth's Mantle? Andesite is a rock typically found in volcanoes above convergent plate boundaries between continental and oceanic plates. A. convergent plate boundaries D. Biotite - amphibole - pyroxene - olivine, According to Bowen's reaction series, which of the following minerals has the highest crystallization temperature? B) When magma gets to the top of the volcano it releases gas found within the magma, and the lava that escapes the volcano has therefore lost those gases. C) basaltic, rhyolitic A) pyroclastic 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). 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 most familiar way for magma to escape, or extrude, to Earths surface is through lava. 5. pumice Felsic MagmaFelsic magma has the highest silica content of all magma types, between 65-70%. An eruption reduces the pressure inside the magma chamber. The Rights Holder for media is the person or group credited. Granite is a good approximation for the continental crust, both in density and composition. C. a non-crystalline rock, likely formed due to extreme rapid cooling of lava A) highly viscous, cools slowly 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. D. extrusion 4. mafic obsidian. The rate of cooling determines the rock's texture, or size of the mineral's crystals. In a porphyritic texture, what is represented by the rock's "groundmass"? The other is how fast the magma cools. The most abundant elements are oxygen and silicon, followed by aluminum, iron, calcium, sodium, magnesium, and potassium. LAVA - magma that reaches the Earth's surface before cooling (most gasses have escaped). G. high silica, low iron and magnesium, aphanitic texture 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. 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? = 15 * 3/20 Pyroclastic texture is usually recognized by the chaotic mix of crystals, angular glass shards, and rock fragments. 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? Arndt, N. T. Chapter 1 Archean Komatiites. But most magma remains molten or partly molten beneath Earths surface. C. Mt. D) gabbroic, What composition magma is beneath the Mt. A significant exception to this is active volcanoes, which are discussed in a later section on volcanism. Typical intermediate rocks are diorite and andesite. d. National Geographic Society is a 501 (c)(3) organization. (The values are similar to those shown in Figure 3.3.4.). A. As a result of its higher viscosity and gas content, intermediate magma builds up pressure below the Earths surface before it can be released as lava. . E. pyroxene 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. B. volume is very large, comparable in size with granitic batholiths The large crystals are called phenocrysts and the fine-grained matrix is called the groundmass or matrix. All rights reserved. Some igneous rocks have a mix of coarse-grained minerals surrounded by a matrix of fine-grained material in a texture called porphyritic. Diorite is identifiable by its Dalmatian-like appearance of black hornblende and biotite and white plagioclase feldspar. This answer has been confirmed as correct and helpful. These eruptions eject lava violently into the air, which cools into dacite and rhyolite rock. The presence of quartz is a good indicator of granite. A. both quartz and muscovite 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). Match the igneous rock texture and its appropriate description. As a magma cools below 1300C, minerals start to crystallize within it. B) the rock's composition MAGMA - molten material and dissolved gas (in the subsurface). solid and pinstriped A magma consists mostly of liquid rock matter, but may contain crystals of various minerals, and may contain a gas phase that may be dissolved in the liquid or may be present as a separate gas phase. 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. A) the magma heats up and ions in crystals break their bonds due to expansion and Si and O ion vibration E. phaneritic texture, relatively high silica content A) granite; gabbro. In some cases, extrusive lava cools so rapidly it does not develop crystals at all. Magma is a molten and semi- molten rock mixture found under the surface of the Earth. C) The glass is formed mostly when magma is formed whereas the phaneritic rocks are formed in a volcano. C. assimilation of "foreign" rocks by the magma 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. 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). As with dikes, sills are younger than the surrounding layers and may be radioactively dated to study the age of sedimentary strata. C. high silica, low iron and magnesium, phaneritic texture

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