Module 6 Assignment Igneous Rock Identification Isaias Espiritusanto

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University of Texas, Permian Basin *

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1301

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Geology

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Apr 3, 2024

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docx

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1 Module Assignment – 6: Igneous Rocks and Volcanism (50 pts) Part One: Identification of Igneous Rocks (36 pts) Classification of igneous rocks is based on their texture (i.e. grain size) and mineralogical make up. The size of the mineral grains, or phenocrysts, in igneous rocks are directly related to their cooling history. Fine-grained igneous rocks cooled quickly, whereas large grained igneous rocks cooled slowly. The fine-grained textures are what we call aphanitic and are often associated with quick cooling of lava on the surface of the Earth. The large grained igneous textures are called phaneritic and are associated with slow cooling of magma within the Earth. Color can also be useful as it is related to the mineralogical composition of the rock. In this laboratory exercise you will collect data from the selected igneous rocks to fill in the table below. Then using some of the specimens you will evaluate the magma composition, cooling history, elemental makeup, and plate tectonic setting for the formation of various igneous rocks. All of these attributes will help us to illustrate the life of an igneous rock . You will need the following to complete this assignment:  The laboratory resources in the Kendall Hunt Platform o Igneous Rock Texture Flow Chart o Igneous Rock Texture Photo Guide  The following from your Physical Geology Rock and Mineral Kit o 9 rocks (#16-#24) o Copper nail, iron nail, glass plate to test hardness, white streak plate to collect streak color and a hand lens (10X) Instructions and Observations Step 1: Retrieve the igneous rock samples (16 to 24) from your kit. Remember the best practice is to set them on a white sheet of paper. Read through the Igneous Rock Texture Flow Chart and Photo Guide then use what you learned to identify each of the igneous rocks. Step 2: Describe, in your own words, the texture and color of each rock in the kit. Can you identify any individual mineral grains? After describing the phenocrysts, identify the igneous rock texture based on phenocryst size (i.e. is the rock aphanitic, phaneritic, porphyritic, or pegmatitic), then write in the composition term (mafic, intermediate, or felsic) based on the rocks color. Step 3: Name each sample using the distinguishing characteristics and write the name in the following table.

3 Igneous Rock Identification Table (1 pt for each blank space) # Texture and Color Texture Composition Rock Name 16 Grey and white. Mixed crystal sizes mostly small to medium Mixed- phaneritic Sodium-rich plagioclase feldspar and hompiper diorite 17 White/Black and tan specks Mixed- phaneritic Orthoclase Feldspar and quartz Granite 18 Grey Felsic aphanitic texture Feldspar & quartz Rhyolite 19 Black Glassy texture Volcanic glass Obsidian 20 Light orange Volcanic tuff Volcanic ash Tuff 21 Grey/silver Intermediate Aphanitic Texture ‘Plagioclase and mafic minerals Andesite 22 Red/coral Mafic versicolor texture Basalt Scoria 23 Grey Intermediate Aphanitic Texture Plagioclase and mafic minerals (basalt/granite) Andesite 24 Light Grey/ Black Specks Por phyntic texture porphyrite rhyolite

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