6. IGNEOUS ROCKS AND VOLCANIC HAZARDS

Transcription

1 LAST NAME (ALL IN CAPS): FIRST NAME: 6. IGNEOUS ROCKS AND VOLCANIC HAZARDS Instructions: Refer to Laboratory 5 in your lab book on pages to answer the questions in this work sheet. Your work will be graded on the basis of its accuracy, completion, clarity, neatness, legibility, and correct spelling of scientific terms. Some rocks that you would be working with may have sharp edges and corners, therefore, be careful when working with them! When you are done with your lab work, please clean the desk and leave all materials you worked with in the same way you found them! INTRODUCTION MAFIC COLOR INDEX (MCI): Is an estimate of the % of mafic (dark) minerals by volume. Mafic minerals are dark colored minerals such as olivine, pyroxene, amphibole, and biotite; minerals are light colored minerals such as quartz, plagioclase feldspar, k-feldspar, and muscovite. Ultramafic rocks: CI > 85% (made up of more than 85% mafic minerals) Mafic rocks: CI 46-85% Intermediate rocks: CI 16-45% rocks: CI 0-15% ORIGIN OF ROCK (INTRUSIVE/EXTRUSIVE) Intrusive (plutonic): formed from magma; made up of large minerals (coarse-grained) Extrusive (volcanic): formed from lava; made up of microscopic crystals (fine-grained) TEXTURES OF IGNEOUS ROCKS Phaneritic: Coarse grain size; visible grains (1-10 mm); result of slow cooling Pegmatitic: Minerals are exceptionally large: > 1 cm long Porphyritic: Composed of crystals of 2 different sizes indicative of multistage cooling history (intrusive/extrusive) long period of slow partial cooling from a magma forms the large crystals sudden extrusion of the remaining magma and the already formed crystals Aphanitic: Fine grain size (< 1 mm); result of quick cooling Glassy: Lack crystals; superfast cooling Vesicular: Contains tiny holes called vesicles which formed due to gas bubbles in the lava. Very porous; may resemble a sponge. Commonly low density, pumice floats on water. Pyroclastic: Consist of mineral grains, volcanic glass, and rock fragments hurled into air by explosive volcanic eruptions. Grains that were hurled into the air will eventually settle to the ground or sea floor & form pyroclastic rocks. Page 1 of 5

2 QUESTIONS Q1. Using the Mineral Database (Figure 3.21, pages 93-97), look up each mineral name listed below and identify its picture on page 144. Match each numbered picture with the mineral names listed on page 144 and determine whether each mineral is mafic or felsic. All samples are shown at their actual size (X1). Plagioclase, Augite, Olivine, Quartz, Hornblende, Biotite, Muscovite, K-feldspar NUMBER MINERAL NAME MAFIC OR FELSIC Q2. The rock on the side figure has a porphyritic texture, which means that it contains two sizes of crystals. The large white plagioclase crystals are called phenocrysts and sit in a green-gray groundmass of more abundant, smaller (aphanitic) crystals. Explain how this texture may have formed. Q3. What is the Bowen s Reaction Series? Using one or two sentences, describe how it helps us understand igneous rock forming processes. Q4. Based on figure 5.7 (page 139, Lab Manual) list in which tectonic and geologic settings the various igneous rocks form. Use the next format to answer the question. TECTONIC/GEOLOGIC SETTING NAME OF IGNEOUS ROCK FORMED Hot Spot Divergent Plate Boundary Transform Plate Boundary Convergent Plate Boundary Earth s Mantle Page 2 of 5

3 Q5. Use figure 5.5, Igneous Rock Classification Chart (page 137) to fill out the blank boxes. MAFIC COLOR INDEX (MCI) MINERALS PRESENT ORIGIN TEXTURE/S ROCK NAME Musc., Qtz, K-Spar, Plag., Biot, Hbd Pegmatitic Qtz, K-Spar, Plag., Biot, Hbd Extrusive Andesite Mafic Phaneritic Glassy Mafic Intrusive & Extrusive Volcanic tuff Qtz, K-Spar, Plag., Biot, Hbd Phenocrysts in phaneritic groundmass Intrusive Syenite Mineral abbreviations used: Musc = Muscovite; Qtz = Quartz; K-Spar = K-feldspar; Plag = Plagioclase; Biot = Biotite; Hbd = Hornblende Page 3 of 5

4 Q6. Analyze and classify each igneous rock below, then infer the origin of each rock based on its texture. Refer to Figures 5.4 and 5.5 as needed. All rocks shown are actual size (X1). To better estimate the Mafic Color Index (MCI), please see the color images in your Lab Manual on pages 143 & 148. Please use the following % ranges for the MCI: 0-15%; 1-45%; or 46-85%. minerals present): mafic, intermediate, or felsic? Texture(s) present: Texture(s) present: Texture(s) present: Texture(s) present: The name of this rock is: The name of this rock is: The name of this rock is: The name of this rock is: rock form? Page 4 of 5

5 Q7. Obtain 6 igneous rocks from your instructor and for each rock fill in the information required on the Igneous Rocks Worksheet below. SAMPLE # TEXTURES PRESENT (Fig 5.4 or 5.5) (Pegmatitic, Phaneritic, Porphyritic, etc.) IGNEOUS ROCKS WORKSHEET ORIGIN: (INTRUSIVE OR EXTRUSIVE) MAFIC COLOR INDEX (Fig 5.5) (FELSIC, INTERMEDIATE, OR MAFIC) ROCK NAME (Fig 5.4 or 5.5) I-4 I-6 I-7 I-8 (Example) I-13 I-14 Page 5 of 5