Table of Contents Lesson 1 How to use this book...1 Introduction...2 Quiz 1 Pretest...4 Looking at Igneous Rocks...5 Lesson 2 Where Igneous Rocks Form...10 Quiz 2...13 Picturing Your Rocks...14 Lesson 3 Crystal Size...17 Quiz 3...19 Building Crystals...20 Lesson 4 Physical Properties...23 Quiz 4...26 Rock Trees...27 Lesson 5 Color: Key to Igneous Rocks...30 Quiz 5...32 Charting My Rocks...33 Lesson 6 Rock Forming Minerals...35 Quiz 6...39 Mineral Concentration...40 Lesson 7 Tephra...43 Quiz 7...46 T-Notes on Igneous Rocks...47 Lesson 8 Lava Rocks...49 Quiz 8...52 Weighty Rocks...53
Lesson 9 Intrusive Rocks...55 Quiz 9...58 Granite Cookies...59 Lesson 10 Lava Tubes...61 Quiz 10...64 Cave Cards...65 Lesson 11 Fun Facts...68 Quiz 11...70 Each Rock Is Unique...71 Lesson 12 Igneous Rock Review...74 Quiz 12 Posttest...78 Mapping Igneous Rocks...79 Answer Key...82 Glossary...83 Bibliography...90 Books by Myrna Martin...91 About the Author...92
How to Use This Book Igneous Rocks Level 1 is designed for students in the elementary grades. The book contains 12 lessons, quizzes and hands-on activities. The lessons will take approximately one hour to complete. Families with students in several grades can use this book for their entire family. Contact Myrna Martin by email for more information. Students will be learning about many different igneous (IG-nee-us) rocks in this book. In prior editions, a set of rocks was required to complete the textbook. This book has been revised so that students can learn about igneous rocks without purchasing a set of rocks. Twelve important igneous rocks students will learn about in this textbook Diorite Ash tuff Granodiorite Obsidian Welded tuff Andesite Scoria Dacite Rhyolite Granite Gabbro Students should take the Pretest in Lesson 1 before starting the unit on Igneous Rocks. Students are not expected to know all the answers to the questions in the pretest. The quiz is designed for teachers to understand how much information students know before starting the unit. The Answer Key is located at the back of the book. After taking the Pretest students should complete the rest of Lesson 1. The rest of the lessons in the book should be completed in the order they are written. Students should be able to finish each Level 1 textbook in one month if they complete three lessons per week. Students interested in a semester of Earth Science should complete four Level 1 textbooks 18 weeks. 1
Introduction Lesson 1 I gneous rocks (IG-nee-us) that form during violent volcanic eruptions are some of the most beautiful and deadliest natural events on Earth. All igneous rocks were once molten rock that formed during volcanic eruptions or cooled underground. The amount of quartz in the rock determines the type of igneous rock that forms. There are four broad categories of igneous rocks based on their quartz content. Basalt 45% to 54% quartz. Andesite 54% to 62% quartz. Dacite 62% to 69% quartz. Rhyolite 69% to 80% quartz. Photo by J.D.Griggs USGS Scientist monitoring eruption of PuuOo on Kilauea, Hawaii Magma, which is molten rock underground, becomes lava when it reaches the surface of the Earth. Gases in magma expand as it reaches the Earth s surface forcing the molten rock out of the volcano during volcanic eruptions. Pyroclastic rock is a general term given to all rock that forms during volcanic eruptions. Individual names of pyroclastic rocks are based on their size. Ash is as fine as flour or as large as a grain of rice. It is gritty to the touch. Scoria (cinders) are larger than a grain of rice up to the size of a golf ball. 2
Blocks and bombs are the largest pyroclastic rocks. Blocks are chunks of rock blown out of a volcano during violent eruptions that can be as large as a house. Lava bombs are molten clots of lava blown out of a volcano that cool while in the air. They often take on a football shaped appearance. Shield volcanoes, stratovolcanoes, dome volcanoes and cinder cones are all types of mountains formed by volcanic eruptions. Shield volcanoes form when basalt flowing out of a volcano s vent forms thin layers of lava creating a volcano with gentle slopes that remind people of a warrior shield. The Hawaiian Islands are shield volcanoes. Pyroclastic rocks on the side of a cinder cone Stratovolcanoes are large steep sided mountains. The volcano grows as andesitic lava erupting out of the volcano alternates between thick lava flows and pyroclastic eruptions. Mount Rainer and Mount Shasta are two examples of this type of volcano. Dome volcanoes are small volcanoes that usual form in craters or on the sides of large stratovolcanoes. These small volcanoes are usually made of dacite lava. The thick pasty lava oozes out of the ground forming a dome over the volcano s vent. Cinder cones are small cone shaped volcanoes created entirely of pyroclastic rocks. The lava breaks apart as it erupts from a volcano forming cinders. Scientists often use the generic term cinder to describe all rocks produced during the formation of a cinder cone. Paricutin, a cinder cone in Mexico, was the first volcano that scientists were able to study from its birth in a farmer s cornfield until its eruptions ceased. Lesson summary All igneous rocks were once molten rock that formed during volcanic eruptions or cooled underground. Magma, which is molten rock underground, becomes lava when it reaches the surface of the Earth. Basalt, andesite, dacite and rhyolite are four broad categories of igneous rocks based on their quartz content. Shield volcanoes, stratovolcanoes dome volcanoes and cinder cones are all types of mountains formed by volcanic eruptions. 3
Name Date Quiz 1 Igneous Rocks Pretest Fill in the blanks using words from the Word Bank 1. Olivine is the most common mineral in the upper. 2. Porphyritic igneous rocks contain minerals that are different sizes. 3. are very large formations that occupy large areas on the Earth s surface. 4. Basalt and are dark-colored igneous rocks containing ferromagnesian minerals that are rich in iron and magnesium. 5. Rhyolite is associated with volcanoes like Yellowstone Volcano in Wyoming and Valdes Caldera in New Mexico. 6. Pumice forms when or dacite begins to froth as the magma nears the Earth s surface forming a light glassy rock that floats. 7. Paint pots have compounds in the water that stain the mud creating colorful pools of bubbling mud. 8. Scoria (cinders) is a rock that is too heavy to float. 9. shorten segments of lava tubes and open up areas for cave exploration. 10. (cinders) are igneous rocks that have rough outer surfaces. Word Bank batholiths skylights super iron gabbro rhyolite mantle scoria two glassy 4
Looking at Igneous Rocks Activity 1 Introduction Volcanoes erupting rivers of lava that flow down the slopes of a volcano and molten rock cooling deep underground are examples of igneous rocks. In this activity you will be studying twelve important igneous rocks and making notes about them. Materials Paper Pencil Notes on Lesson page Directions 1. Read the information about the twelve igneous rocks on the next three pages. 2. Make short notes about each rock on your Notes on the Lesson page that follows the activity pages. 3. Here are some ideas of things you might include in your notes. a. Is the rock a solid color or does it have spots? b. Is the rock rough or smooth when you run your fingers over the rock? c. When you pick up the rock, does it feel heavy or light compared to the other rocks in your kit? Photo by Sarah Masters Lava formation on Iceland d. Is the surface of the rock shiny or dull? e. Did it form in a lava flow or during an explosive eruption? f. List several facts that will help you remember the name of the rock. g. You can use the information you gathered in future lessons. * General information on recording information about the lessons and activities a. Write down the date and lesson title at the top of the Notes on the Lesson page. b. Summarize information you learned in the lesson. c. Write the title of the activity beneath the lesson summary. d. Summarize information about the activity. 5
#1 Diorite (DIE-oh-rite) Diorite is an intermediate intrusive rock. Diorite has a combination of light and dark minerals that are large enough to be seen without the aid of a hand lens. Look for individual spots of black and white. These spots of color are individual minerals that grew large enough to be visible as the rock cooled. Diorite is usually medium to dark gray in color. #2 Ash tuff (ASH TOUGH) Tuff is created near volcanoes when ash blown out of a volcano compresses enough to form a soft rock. During the eruption of Mount Mazama thick layers of ash formed near the volcano. The hot layers of compacted ash creates the ash tuff you will be studying in this unit. #3 Granodiorite (GRAN-oh die-oh rite) Granodiorite is the intrusive form of dacite. The molten rock is thick and pasty and usually cools within the Earth. When dacite cools underground it forms granodiorite. Granodiorite is generally a lighter gray than andesite. #4 Obsidian (ob-sid-ee-an) Obsidian is a glassy rock created when rhyolite lava cools before it crystallizes. Rhyolite is a light colored lava and minute amounts of other minerals give obsidian its color. Black obsidian forms when small amounts of magnetite crystals color the rock. Obsidian is found in at least 29 different colors. 6
#5 Welded Tuff (WELL-did TOUGH) Welded tuff forms when pyroclastic flows of extremely hot gases and ash flow down the sides of a volcano. The material is hot enough to weld the ash together forming welded tuff. The glassy fragments of pumice in the pyroclastic flow deform readily and often form curved shapes during the welding process. The light pink in the rock is a piece of pumice. #6 Andesite (AN-dah-site) Andesite is an intermediate lava between basalt and dacite. Geologists first applied the name to rocks found in the Andes Mountains of South America. Andesite forms in subduction zones when an oceanic plate moves beneath a continental plate. Around the Pacific Ocean there is a string of andesitic volcanoes. The volcanoes have formed in subduction zones. Geologists refer to this string of volcanoes as the Andesite Line. #7 Scoria (SCO-ree-ah) Scoria is a rough glassy fragment of volcanic rock produced by basalt or andesite lavas. The rocks are generally a dark brownish black or red. Scoria forms when semiliquid lava sprays into the air during a volcanic eruption. It is composed of volcanic glass fragments, and has few mineral crystals. The rocks are similar to pumice but contain large amounts of iron rich minerals so they do not float. #8 Dacite (DAY-site) Dacite is an intermediate rock between andesite and rhyolite usually forming gray colored rocks. The dome forming inside the crater on Mt. St. Helens is made of dacite. Dacite often forms small dome volcanoes. The summit dome on Mt. Lassen is a dacite dome. Dacite contains more quartz than andesite but less than rhyolite. 7
#9 Basalt (bah-salt) Basalt is a fine-grained lava rock. Look for dark green, dark-gray, or black rocks. The molten magma forms in the upper mantle and flows out of vents on the ocean floor or hot spots. The lava has a low percentage of quartz. It is rich in iron and magnesium giving the rocks their dark color. The floors of all the oceans on Earth are made of basalt as well as the Hawaiian Islands. #10 Rhyolite (RHY-oh-lite) Rhyolite is associated with super volcanoes and great eruptions that produce calderas. The lava contains at least 69% quartz. This high percentage of quartz produces sticky lava that often erupts as pumice. Rhyolite lava is light-colored and usually produces rocks that are light gray, tan or beige. #11 Granite (GRAN-it) Granite is a common igneous rock. It forms when rhyolite cools and crystallizes within the Earth. Granite crystals are usually large and visible without a hand lens. All granite rocks contain quartz and feldspar minerals. Granites can be a variety of colors depending on the percentage of different minerals in the rock. The colors range from pink to dark gray. Black and white granites look speckled. Granite is widely used as a building block in construction and counter tops. #12 Gabbro (GAB-bro) Basalt that cools underground forms gabbro. Gabbro contains large amounts of black colored minerals that are rich in iron and magnesium. It is a popular building stone because of its beautiful dark colors. When contractors create buildings, counter tops and floors of black granite, they are probably using gabbro. 8