Exercise 3 (Igneous Rocks and Volcanoes)-1.docx

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sedGeneral Earth Science Lab Exercise #3 Igneous Rocks and Volcanoes READINGS: Earth Science ; Chapter 3 and Chapter 9 OBJECTIVES: Upon completion of this exercise the student should be able to: 1. Understand the formation of igneous rocks within the context of the rock cycle 2. Identify common igneous rock samples, based on physical properties 3. Be able to associate lava composition with the physical property of viscosity. 4. Use data for two volcanoes to calculate slope and compare with the characteristics of the three different types of volcanoes. Introduction Rocks form a major part of this planet's crust. A rock is an aggregate of minerals and/or solid organic matter. Consequently, the study of the earth sciences would be incomplete without the knowledge of the three basic rock types: igneous, sedimentary , and metamorphic . The interrelationships between the basic rock types are expressed in Figure 3.2 of the text. Question 1: Using the rock cycle shown in Figure 3.2 of the textbook, answer the following questions: a) These rocks form via lithification, which involves the compaction and cementation of sediments: sedimentary rocks b) Melting and solidification are necessary to produce this type of rock: magma c) These rocks form when pre-existing rocks are altered due to intense heat and pressure: metamorphic Igneous Rocks Igneous rocks are those that form from the cooling and solidification of magma. Magma , molten rock material, either intrudes into preexisting crustal rocks, or extrudes onto the surface of Earth. This determines how quickly the magma will cool. The cooling history of an igneous rock determines the size of its crystals. As a general rule, the deeper the magma, the more slowly it cools, the larger the crystals. This is because slowly cooling allows more time for crystals to form before the magma solidifies. Rock texture is defined as the size, shape, and arrangement of crystals within the rock. Igneous rocks are classified on the basis of their texture and their mineral composition (Refer to Figure 3.9 in the textbook). Igneous rock textures include coarse-grained (individual crystals are visible to the unaided eye), fine-grained (individual crystals cannot be seen, so the rock looks dull and all one color), vesicular (full of small holes, called vesicles, from escaping gases), and glassy (no crystals formed at all, so the rock looks glassy, with conchoidal fracture common). Individual minerals can be identified where possible to 1
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determine the mineral composition, or more easily, the general color of the rock (light versus dark) is used to indicate the mineral composition. Although the mineral composition may be the same, different rates of cooling may result in the formation of distinctly different rock types.
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  • Spring '18
  • Biology, Igneous rocks, Volcano, Basalt, Felsic Lava

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