Answer questions 32 through 67, referring to text and Figures 1-7 for guidance. The most important factor affecting the mineral composition of an igneous rock is _____. As magma cools, it begins to crystallise and form solid rock. Most intrusive rocks have large, well-formed crystals. The size of crystals in an igneous rock is an important indicator of the conditions where the rock formed. Thus, mineral composition and rock type will differ based on rate of cooling. Examples include granite, gabbro, and diorite. The texture of those rocks would be coarse to very coarse, and they would be non-vesicular. The video below is a clip of crystals forming in solution. For example, rocks that feature larger crystals were more likely formed at lower levels below Earth's surface. spreading center continent/continent collision zone subduction zone. 1. d. glassy . Most bodies of magma rising to the surface get emplaced (stuck) inside the earth’s crust. In rocks with coarse-grained groundmasses, the phase of slow cooling was followed by a phase of faster underground cooling. Topaz on albite: A crystal of imperial topaz on an albite matrix from a pocket in the Katlang Pegmatite of Pakistan. What is the textural term that best describes each sample? 19. Obsidian exhibits this texture. 1) Andesite (A) Diorite (B) 1 cm 1. Molten (liquid) rock is called magma. ... DIORITE PORPHYRY Volcanic rocks of this type are sometimes known as porphyries, with the phenocrysts used as a modifier (e.g. Pegmatite• Aphanitic-crystals not visible e.g. Glassy. a. by magma that cooled slowly. Emplaced bodies of intrusive rock are called "plutons". In the simplest terms, Granite and Basalt are end members. Compositions range from rocks rich in the framework silicates quartz and potasium feldspar, to those rich in minerals containing magnesium and iron (olivines and pyroxines). (Table 2) 4. Granite and granodiorite are also found west of the San Andreas fault near Monterey, Pacifica, and Point Reyes, where granite from the south end of the Sierra range has been transported northward by San Andreas … 0.01 m/d from 1984 to 1986. 18. Bowen's Fractionation Principle The fractionation principle is that if equilibrium is not maintained, if the melt cools too quickly for all the reactions to take place, or crystals are removed before they have time to react, then the melt can be divided into two fractions of different compositions. c. porphyritic-aphanitic. rock which originates from processes during the cooling of a molten rock body called magma; B. Major minerals include feldspar and hornblende. Igneous rocks are formed from molten rock that has cooled and solidified. Cooling Rate and Crystal Size. Diorite produced coarse grain sizes from slow cooling. Cooling Rate: slow, intrusive; Extrusive Equivalent: basalt; Other Characteristics: reflective cleavage surfaces on the visible minerals distinguish gabbro from basalt. Granite & Gabbro• Pegmatite-exceptionally large crystals e.g. Intrusive rocks form plutons and so are also called plutonic. The rock to the right may have formed in which of the following tectonic settings? Igneous rocks are formed from the cooling of the magma that is found beneath the crust. Diorite is an intrusive plutonic rock with a composition that is intermediate between gabbro and granite. It is recognized by its glassy texture. The magma, which is brought to the surface through fissures or volcanic eruptions, rapidly solidifies.Hence such rocks are fine-grained or even glassy.Basalt is the most common extrusive igneous rock and forms lava flows, lava sheets and lava plateaus. Rocks: There are three basic types of rocks: igneous, sedimentary, and metamorphic. have similar texture. 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