The following table illustrated one way (admittedly quite over-simplified) that a geologist could choose to classify igneous rocks. Rhyolite is rarely found as lava. The rate of cooling of the magma is rapid, and crystal growth is inhibited. The high silica content and lower temperatures of rhyolite magma result in high viscosities and violent eruptive styles. The large crystals, called phenocrysts, are usually feldspar crystals. — One is extrusive and one is intrusive. Pegmatites form from waters that separate from a magma in the late stages of crystallization; this activity often occurs in small pockets along the margins of a batholith. Slow cooling facilitates the growth of large mineral crystals in the rock. flow banding (formed by shearing of the lava as it flows), and vesicles (open cavities that … The dashed lines are drawn to reflect three mineral assemblages : high temperature - olivine, pyroxene and Ca-rich plagioclase; intermediate temperature - amphibole, biotite and Na-rich plagiolase; and. What interpretations can you make about the cooling rate of the magma from which each rock formed? Slow cooling of diorite results into coarse grain size due to large crystals formation with more ion transport. They grew as the magma cooled very slowly deep in the magma chamber. Feldspar is one of the first minerals to form large crystals as magma solidifies. Sample 1-1 Has What Texture? Refer to Figures 8.6 through 8.9 for guidance. slowly Lavas that cool extremely rapidly may have a glassy texture. 1) Andesite (A) Diorite (B) 1 cm 1. — One forms from cooling magma, and one forms from cooling lava. 8.7: Lab Exercise (Part B and C) - … Intrusive rocks. It is generally well known that the slower the rate of cooling the coarser the rocks will be. Those that form slowly within the earth's crust (intrusive igneous rocks) are coarse-grained (granite & gabbro). rhyolite porphyry GABBRO BASALT DIORITE ANDESITE (PORPHYRY) GRANITE RHYOLITE PUMICE OBS ID AN Cooling History/Texture Slow Cooling and Coarse Grained Fast Cooling and Fine Grained Very Fast Cooling and Glassy/Cellular Mafic and Dark Color Felsic When the magma forms pockets underground it cools much more slowly. Note that the feldspars represent a wide range of temperatures -- Calcium-rich Plagioclase, Sodium-rich Plagioclase and Alkali Feldspar. Diorite is usually grey to dark grey in colour, but it can also be black or bluish-grey, and frequently has a greenish cast. 32. Granite is 73%. Fig. That is, if the rate of cooling is very slow a granite will form. Diorite produced coarse grain sizes from slow cooling. With the singular exception of quartz, the other phases present represent solid solution series; that is, their composition varies between fixed limits. Answer Questions 32 Through 67, Referring To Text And Figures 1-7 For Guidance. a. by magma that cooled slowly b. by fast cooling lava c. by a very fast cooling of a lava d. by a very fast cooling magma during a volcanic eruption e by magma that was cooling slowly, then as a lava that cooled quickly 24. There are two fundamental properties of igneous rocks that are used to assign a name. Those that cool quickly at the earth's surface (extrusive igneous rocks) are glassy (obsidian & pumice) or fine-grained (basalt & rhyolite). gabbro Geoscientists at the University of British Columbia has prepared a nice figure which summarizes information about the Classification of Igneous Rocks. Note that a granite is the coarse grained equivalent of a rhyolite. ... records the rocks cooling history. Which Doesn't Fit? What is the textural term that best describes each sample? It is recognized by its glassy texture. — They formed differently 10. Cooling rate and gas content create other textures (see Figure below for examples of different textures). The chemical composition of diorite is intermediate, between that of mafic gabbro and felsic granite. diorite, andesite porphyry Bowen's Reaction Series points out that there are commonly occurring mineral assemblages (based on similar temperatures of formation/crystallization). The same magma on Andesite and Diorite rapidly crystallizes on the Earth's surface and forms Andesite. igneous rock is formed. Rhyolite. The rate at which the magma cools determines the kind of … ... very rapid cooling slow cooling slow followed by rapid cooling none of the above. The viscosity (resistance to flow) of a melt (magma/lava) increases with decreasing temperature; the viscosity of a melt is lowered if water is present in the melt. Diorite is an intrusive igneous rock composed principally of the silicate minerals plagioclase feldspar (typically andesine), biotite, hornblende, and/or pyroxene. However, the outcome of whether extrusive or intrusive cooling is evident in the final texture of the igneous rock. low temperature - muscovite, alkali feldspar and quartz. With the singular exception of quartz, the other phases present represent solid solution series; that is, their composition varies between fixed limits. In general, igneous rocks have very low porosities. As magma cools, it begins to crystallise and form solid rock. with a two-stage cooling history Note that a granite is the coarse grained equivalent of a rhyolite. Molten rock material can solidify below the surface of the earth (plutonic igneous rocks) or at the surface of the Earth (volcanic igneous rocks). (See Bowen's chart. Quartz occurs in both granites and rhyolites. Basalt. What is the cooling/crystallization history of the igneous rock Obsidian? Continental hotspot 2. For example, quartz and olivine (at least the magnesium-rich variety) are not expected to occur together as an equilibrium assemblage. 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