igneous_remote-2.docx - Igneous Rocks Do you have a granite...

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Igneous Rocks Do you have a granite countertop? Have you ever used a pumice stone? Do you ever wonder where these materials come from? In this lab you will learn about granite, pumice and other igneous rocks. Learning objectives: 1) Learn some basics of volcanoes 2) Learn how magmas crystallize 3) Learn to classify igneous textures and compositions 4) Learn to identify igneous rocks in hand sample. Introduction: Igneous rocks are the youngest rocks on earth, but they can also be some of the oldest rocks. Igneous rocks form when melted parts of the mantle and earth’s crust solidify into new rocks. Melting of earth’s crust can be caused by a variety of events ranging from sporadic asteroid impacts to constant plate tectonic processes. The place most commonly associated with melted crust, called magma or lava, is at volcanoes. Plate Tectonics, Volcanoes, and Plutonism Plate tectonics is the driving force behind all geological processes, one of the most exciting are the formation of molten rock. The most familiar type of molten rock is lava , which is extruded and cooled onto earth’s surface from volcanoes. Molten rock that cools below earth’s surface is called magma . Rocks that form from lava and rocks that form from magma look very different texturally (but more on this later). Depending on the type of plate tectonic environment that a magma or lava is from effects its composition. There are 4 types of compositions for igneous rocks: felsic , intermediate , mafic , and ultramafic . Felsic - high amount of quartz and feldspar, light colored igneous rock (usually pink or more white) Intermediate - “middle” composition between felsic and mafic (gray color) Mafic - high amount of pyroxene, amphibole, and Ca-rich feldspar (dark-near black color). Ultramafic - high amount of olivine and pyroxene (very dark, commonly green due to olivine) These compositions have a direct relationship to the violence of volcanic eruptions. Felsic and intermediate lavas are more explosive because they have a higher viscosity (does not flow easily, thick and sticky, “peanut butter”). Mafic and ultramafic are much less explosive due to lower lava viscosity (flows easily, thinner, “syrup”). Volatiles (such as water and CO2) can also have an effect on volcanic eruptions because they turn into gasses, which increase the explosiveness

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