COLLEGE LEVEL geology
College Level
GEOLOGY
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TABLE OF CONTENTS Preface........................................................................................................ 1 Chapter 1: Introducing Geologic Terms ....................................................... 1 Basic Geology Terminology ............................................................................................. 1 A through D: ................................................................................................................. 1 E through H: ................................................................................................................. 4 I through M: ................................................................................................................. 6 N through R: ................................................................................................................. 8 S through Z: ................................................................................................................ 10 Rock Types and What they Mean .................................................................................. 12 Key Points in this Chapter ............................................................................................. 16 Chapter 1: Questions and Answers .................................................................................17 Chapter 2: Earth Then and Now ................................................................ 19 First Conditions on Earth .............................................................................................. 19 The Oxygen Catastrophe ................................................................................................ 23 The Earth's Spheres ....................................................................................................... 24 The Internal Earth ......................................................................................................... 26 The Crust ........................................................................................................................ 28 The Mantle ..................................................................................................................... 29 The Outer Core ............................................................................................................... 29 The Inner Core ............................................................................................................... 30 The Rock Cycle ............................................................................................................... 31
Major Features of the Ocean Floor and Continents ...................................................... 32 The Continents ............................................................................................................... 34 Key Points in this Chapter ............................................................................................. 39 Chapter 2: Questions and Answers................................................................................ 40 Chapter 3: Geologic Time .......................................................................... 42 Known Geologic Time Periods ....................................................................................... 42 Proterozoic Era .............................................................................................................. 43 The Paleozoic Era ........................................................................................................... 45 The Mesozoic Era ........................................................................................................... 48 The Cenozoic Era ........................................................................................................... 49 Dating Rocks .................................................................................................................. 50 Fossils and Fossil Types ................................................................................................. 55 Key Points in this Chapter ............................................................................................. 58 Chapter 3: Questions and Answers................................................................................ 59 Chapter 4: Plate Tectonics ......................................................................... 61 Theories of Plate Tectonics from the Beginning ........................................................... 61 Plate Tectonic Basics ...................................................................................................... 63 How do the Plates Move? ............................................................................................... 65 Plate Boundaries......................................................................................................... 65 Examples of these Phenomena in Geology ................................................................ 67 Measuring Plate Motion ............................................................................................. 68 Key Points in this Chapter ............................................................................................. 70 Chapter 4: Questions and Answers.................................................................................71
Chapter 5: Minerals in Detail .................................................................... 73 What is a Mineral in Geology? ....................................................................................... 73 How Minerals Form ....................................................................................................... 78 Classifying Minerals ....................................................................................................... 81 The Mohs Hardness Scale .............................................................................................. 83 More on Silicate Minerals .............................................................................................. 85 Nonsilicate Minerals ...................................................................................................... 86 Key Points in this Chapter ............................................................................................. 89 Chapter 5: Questions and Answers ................................................................................ 90 Chapter 6: Igneous Rocks in Detail ........................................................... 92 What is Magma? ............................................................................................................ 92 How Magma turns to Rock ............................................................................................ 93 Silicates in Igneous Rock ............................................................................................... 96 Igneous Textures ............................................................................................................ 97 How to Name Igneous Rocks ......................................................................................... 98 Intrusive Igneous Rock ................................................................................................ 100 Diamonds and their Origin ...........................................................................................101 Key Points in this Chapter ........................................................................................... 103 Chapter 6: Questions and Answers.............................................................................. 104 Chapter 7: Volcanoes .............................................................................. 106 Early Volcanic Activity ................................................................................................. 106 Volcano Anatomy ......................................................................................................... 107 Types of Volcanoes ....................................................................................................... 109 Different Volcano Characteristics ................................................................................. 111
Volcanic Eruptions ........................................................................................................ 111 Lava Flows and Pyroclastic Flows ................................................................................ 112 Volcano Seismology ...................................................................................................... 116 Key Points in this Chapter ............................................................................................ 118 Chapter 7: Questions and Answers ............................................................................... 119 Chapter 8: Weathering and its Effects on Geology .................................... 121 Mechanical Weathering Types...................................................................................... 121 Types of Chemical Weathering .................................................................................... 123 Weathering Rates ......................................................................................................... 125 Wind and Desert Features ........................................................................................... 126 Soil .................................................................................................................................127 Soil Formation and Classification ............................................................................... 129 Soil Orders.................................................................................................................... 130 Basic Soil Types ............................................................................................................ 132 Ore Deposits and Weathering ...................................................................................... 133 Key Points in this Chapter ........................................................................................... 134 Chapter 8: Questions and Answers ............................................................................. 135 Chapter 9: Sediments and Sedimentary Rocks ......................................... 137 How Sediment Forms ...................................................................................................137 Sedimentary Rock Basics ............................................................................................. 138 Naming Sedimentary Rocks ........................................................................................ 139 Detrital Sedimentary Rocks ......................................................................................... 142 Non-clastic Rocks......................................................................................................... 143 How Sedimentary Rocks are Structured ..................................................................... 144
Sedimentary Rocks and Past Life Forms ..................................................................... 145 Resources we get from Sedimentary Rocks ................................................................. 145 Key Points in this Chapter ........................................................................................... 147 Chapter 9: Questions and Answers.............................................................................. 148 Chapter 10: Metamorphic Rocks in Detail ............................................... 150 How Metamorphism Works ........................................................................................ 150 Metamorphic Textures................................................................................................. 153 Foliated Metamorphic Rocks ................................................................................... 153 Slate ....................................................................................................................... 153 Gneiss .................................................................................................................... 154 Phyllite................................................................................................................... 156 Hornfels+ .............................................................................................................. 156 Schist ......................................................................................................................157 Non-foliated Metamorphic Rocks ............................................................................ 159 Quartzite ................................................................................................................ 159 Marble ................................................................................................................... 160 Conditions of Metamorphism ....................................................................................... 161 Metamorphic Environments........................................................................................ 162 Key Points in this Chapter ........................................................................................... 165 Chapter 10: Questions and Answers ............................................................................ 166 Chapter 11: Earthquakes and Seismology ................................................ 168 Earthquake Definition ................................................................................................. 168 Earthquake Features .....................................................................................................172 Earthquake Measurements ...........................................................................................173 Measuring Magnitude of an Earthquake ..................................................................... 174 Earthquakes Underwater ............................................................................................. 176
Determining Earthquake Locations ............................................................................ 176 Earthquake Predictions ................................................................................................ 177 Key Points in this Chapter ........................................................................................... 178 Chapter 11: Questions and Answers ............................................................................ 179 Chapter 12: Crustal Deformation and Mountains .................................... 182 How Rocks Deform ...................................................................................................... 182 Ductile versus Fragile Rock ......................................................................................... 183 Strike and Dip Explained ............................................................................................. 185 Faults and Joints .......................................................................................................... 186 Rock Folding ................................................................................................................ 189 Folding and Mountain Building .................................................................................. 192 Key Points in this Chapter ........................................................................................... 194 Chapter 12: Questions and Answers ............................................................................ 195 Chapter 13: Effects of Gravity .................................................................. 198 Landslides .................................................................................................................... 198 Components of a Landslide ......................................................................................... 199 Types of Landslides ..................................................................................................... 200 Can Landslides be Predicted? ......................................................................................202 Earth Flows ............................................................................................................... 203 Avalanches ................................................................................................................204 Key Points in this Chapter ...........................................................................................206 Chapter 13: Questions and Answers ............................................................................ 207 Chapter 14: Water and Geology ............................................................... 210 Water in the Study of Geology ..................................................................................... 210
Water Basins ................................................................................................................ 212 Surface Water Explained ............................................................................................. 213 Fluvial Processes .......................................................................................................... 215 Sediment in Streams .................................................................................................... 216 Channel Types in Streams ............................................................................................217 Deltas............................................................................................................................ 218 Water under the Ground.............................................................................................. 218 Hydrology-based Earth Features .................................................................................220 Coastlines ..................................................................................................................... 221 Geothermal Features ................................................................................................... 224 Key Points in this Chapter ........................................................................................... 226 Chapter 14: Questions and Answers ............................................................................ 227 Chapter 15: Glaciers and Glaciation ........................................................ 230 Glaciers and their Formation....................................................................................... 230 How Glaciers Move ...................................................................................................... 231 Glacial Budget .............................................................................................................. 231 Landforms caused by Glaciers ..................................................................................... 232 Glacial Lakes ................................................................................................................ 234 Key Points in this Chapter ........................................................................................... 236 Chapter 15: Questions and Answers ............................................................................ 237 Summary ................................................................................................ 240 Course Questions .................................................................................... 244 Answers to Questions.............................................................................. 285 Answers to Chapter 1 ................................................................................................... 285
Answers to Chapter 2 ................................................................................................... 286 Answers to Chapter 3 ................................................................................................... 287 Answers to Chapter 4 ...................................................................................................288 Answers to Chapter 5 ................................................................................................... 289 Answers to Chapter 6 ...................................................................................................290 Answers to Chapter 7 ................................................................................................... 291 Answers to Chapter 8 ................................................................................................... 292 Answers to Chapter 9 ................................................................................................... 293 Answers to Chapter 10 ................................................................................................. 294 Answers to Chapter 11 .................................................................................................. 295 Answers to Chapter 12 ................................................................................................. 296 Answers to Chapter 13 ................................................................................................. 297 Answers to Chapter 14 ................................................................................................. 298 Answers to Chapter 15 ................................................................................................. 299 Answers to Course Questions ..................................................................................... 300
Is geology a real science, or is it only something of interest to wacky rockhounds? In this college-level course, you will see just how important geology is to the study of the earth when it was first created 4.5 billion years ago and in today's time. You'll see how this planet was first formed and follow it through to more modern times when things like weathering, wave action, and global warming are still impacting the landscape around you. Not only will you be able to name many types of rocks and minerals, you will understand the mystery of why each rock on the ground is so unique. You will also learn why geology is so much more than rocks – it’s really the science of our entire planet all packed into one fascinating audio-course!
PREFACE If you are taking this course because you like rocks and want to learn more about them, you have come to the right place. By the end of this course, you'll understand more about rocks than you thought there was to know about them. If you decided to take this course because you want to learn about geology as a college subject, you have come to the right place. This is because geology is much more than just rocks; this course covers it all. You will learn about early earth as it existed billions of years ago and how rocks are created in the first place. This will take you further onto lessons about volcanoes and how they create igneous rocks, glaciation, how rivers and lakes help form sediment to make sedimentary rocks, how to date rocks, and how wind and weather form rock formations on the earth's surface. Yes, geology is much greater as a subject than can be found in a simple rock. By the end of the course, you will have a new appreciation for every rock you see – even the ugly ones that probably reveal tiny sea creatures embedded within them. You will know why boulders sit in the middle of a field and why certain rocks have lines or speckles in them. All of this you will know from a much deeper perspective as you study geology from the most basic terms to the understanding of complex concepts regarding rock formation. Geology is a complicated topic and one that has a lot of terminologies to study before you can get into more complex topics. In chapter one, you will begin to learn some of the terms you need to know to make sense of everything in geology. You also need to know the basic types of rocks and how they become the size, shape, and color you see when you pick them up off the ground. This chapter gets your feet wet in the study of geology. Chapter two begins a discussion of planet earth and its rocky surface by looking directly at its origins. The earth is about 4.54 billion years old and began as a giant cloud of swirling space dust. Fortunately, it has changed a lot since then. We'll look at how all
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that dust collected into the wide range of rocks, minerals, and amazing geological structures on land and sea we now research in geology. At the end of the chapter, you will learn about the continental features and seafloor landscape and why they exist as they do now. Chapter three examines the concept of geologic time. This time dates back to the first days when the earth's crust was being developed. Older rocks look different from younger rocks; you need to know the difference between them. You will learn how to date rocks and how you can use rocks to indicate the age of fossils. The chapter also looks at the different types of fascinating fossils you can find in your own back yard or nearby rock quarry. Chapter four will involve a discussion of what we know about plate tectonics. It is still called "plate tectonic theory" even though there aren't any legitimate counter-theories on why the continents exist at all and where they are located. What plate tectonics means for geologists is that the earth is still changing and phenomena like earthquakes and mountain-building can be easily explained by understanding how the lithosphere moves on this planet. Chapter five in the course begins to talk about what many people think geology is all about – cool rocks and minerals. A mineral is a hardened substance from the earth that is made from single element or just a few elements in a chemical compound. The two main mineral classifications are the silicates and non-silicates. You will learn how to classify and identify the most common minerals you'll find around the world and even in your own backyard. In chapter six of the we get into detail on the subject of igneous rocks and their formation. Igneous rocks are literally born out of fire – the first rocks to be spit out of our molten interior. After reading this chapter, you will understand what's in magma and how it turn into the rocks you see all the time. Magma is more than just underground lava. You will see the amazing things that happen when it cools and the ways the minerals precipitate out of it when that occurs. Chapter seven delves into volcanism and the volcanoes we have on earth. Volcanoes help dispel the heat from inside our planet and contribute to new land formation in some
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parts of the world. Magma is extruded from deep within the earth through volcanic activity. You will see the difference between lava and magma in this chapter and you will learn that there are several types of volcanoes and volcanic eruptions all over the world. We will also discuss how volcanic eruptions might be predicted. Chapter eight covers weathering and its effects on geology. Weathering is inevitable and can change rock faces in different ways. You will learn how these work with regard to sedimentary rocks and how weathering creates soil. Soil is different all over the world for many reasons. You will see how soil forms and what makes each soil type unique. Weathering can create metal ore deposits, as you will soon learn. Chapter nine allows you to learn about sedimentary rocks. If igneous rocks are basically the primary rocks, then sedimentary rocks are secondary. These are the rocks that start out as smaller pieces called sediments, becoming lithified to form their own kind of stone. You'll learn how to name sedimentary rocks and what we gain economically from products these types of rocks provide us on earth. Chapter ten rounds out the discussion of rock types by revealing how we get metamorphic rock. Pressure and heat cause metamorphic change in rocks, leading to many different rock types. You will soon understand from this chapter the complexities of metamorphism and how they lead to several types of new rock from old rock. Chapter eleven in the course is about earthquakes. Studying earthquakes reminds us that geology isn't just about rocks. Earthquakes are perhaps the best proof that plate tectonics is not theoretical. They happen mainly when two or more plates are moving in directions that are not congruent with one another. You will learn how earthquakes are measured and see why they cause so much damage. Chapter twelve teaches you how and why rocks are deformed. Rocks seem so solid and yet the awesome powers of earth movement can create giant mountains and crush sedimentary rock into much harder metamorphic rock. You will learn the patterns of rock deformation and the types of stress the earth's crust is under on a daily basis. It will help you understand why the earth has the interesting topography it has now, and see that it will probably continue to have changing topography in the future.
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Chapter thirteen in the course helps you understand better the geological phenomena seen due to the effects of gravity. Gravity pulls everything toward the center of the earth so heavy things that don't have the necessary friction or infrastructure to hold up properly will fall down. Rock, dirt, sediment, snow, and ice all participate in this process to create things like landslides, mudslides, flows, and even avalanches. You'll see that there are more forces at play in these gravity-based situations besides the law of gravity. Chapter fourteen is about water; it is important to study water in any course on geology mainly because water shapes geologic structures to a huge degree. Water is contained in the hydrosphere but it interacts with the geosphere all over the world. You'll learn about streams, rivers, deltas, and basins and why they are critical parts of the geology of the earth. Chapter fifteen in the course covers glaciers and how they shape the geomorphology of the earth. Glaciers represent the cryosphere of the earth. You'll learn how important glaciers have been in shaping the land and water features in all continents of the planet. Let's dig right in and study the fascinating science of our rocky earth!
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CHAPTER 1: INTRODUCING GEOLOGIC TERMS It is hard to study any complex topic without knowing the lingo. In this chapter, we will start by discussing some of the most important terminology you need to know to get started in the study of geology. All terms will be explained in detail later in the course; this is just a chance to get your feet wet. We will also talk about the three basic types of rock and how they become the color and shape they are when you see them on the ground.
BASIC GEOLOGY TERMINOLOGY There are so many terms in geology that you may not understand. For this reason, we will begin this course by looking at the basic terms you need to know to get started. Almost all of the terms will be very familiar to you by the end of this course. Here are some terms you don't have to memorize but should familiarize yourself with:
A THROUGH D: •
Abrasion – when rocks are worn down by other rocks or minerals, especially during transport.
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Andesite – an igneous rock that is gray and fine-grained; made from thick, viscous lava.
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Anticline – a fold of rock that bulges up in the middle.
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Attrition – the wearing down of rock grains or pebbles during transport.
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Basalt – igneous rock that is black and fine-grained; usually made from thin lava.
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Batholith – a large intrusion of some type of igneous rock (often granite) that is formed so far beneath the surface that it cooled extremely slowly.
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Bedding or bedding planes – this involves the layering of sedimentary rocks so you can see the layer boundaries (called bedding planes).
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Bed load – this is the sand and gravel that gets carried own a river from changes in salt content and by traction.
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Boulder clay – a mixture of clay, pebbles, and boulders deposited by ice sheets (like glaciers).
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Calcite – a common "fizzy" mineral that fizzes when exposed to dilute acid. This is actually calcium carbonate and is what makes up most limestone.
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Cementation – when sediment grains are stuck together by minerals that were once in a liquid solution and then precipitated out to make sedimentary rock.
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Chalk – this is limestone made from microscopic pieces of calcium created by planktonic algae (the tiny pieces of calcium are called coccoliths).
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Coal – compressed sedimentary rock made from plant material that was carbonized over millions of years underground.
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Coarse-grained rock – what you call a rock with grains that are at least the size of peas.
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Columnar joints – these are cracks made from long pillars or columns of rock that are made when lava flows begin to cool.
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Conglomerate – what a rock is called if pebbles or boulders have been cemented for various reasons.
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Continental shelf – this is where the ocean is less than 200 meters deep near the edge of a continent.
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Contraction – what happens to rock when it shrinks during cooling.
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Contact metamorphism – this is metamorphism that happens when there is a lot of heat near hot magma.
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Creep – this is when small pebbles slide across desert lands from high winds across the desert.
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Cross-bedding – this happens when layers are formed on some angle because sediment has become deposited under the influence of wind or flowing water.
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Crystal – the regular ordering of a mineral due to its ionic structure. A crystal will generally split along a plane of some kind.
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Crystalline stone – this is any rock or stone made from crystals that are interlocking. Most igneous and metamorphic rocks are considered crystalline.
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Crystallization – this is when a solid substance that is often a crystal was once in solution but precipitates out of solution. It happens when seawater evaporates or when crystals form during the cooling of hot lava.
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Deformation – this is when there are forces that act on rocks to change something about their shape.
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Delta -this is the end of a river near the sea where it breaks into many channels, depositing sediment it disgorges out its mouth.
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Dyke – any intrusion of igneous rock that was formed through the action of magma flowing through other rocks or faults in rocks, so that it cuts through the different rock layers.
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E THROUGH H: •
Effusive eruption – this is when a volcano erupts, giving rise to hot and liquid lava rather than gas and ash.
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Erratic – this is a large rock or boulder carried a long distance from its origin after having been deposited by a retreating glacier.
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Estuary – the part of a river's mouth that experiences tides.
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Erosion – this is different from weathering and happens when moving ice, wind, or flowing water breaks down rock.
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Exfoliation – this is when surface rock is peeled away over time from weathering, layer by layer.
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Explosive eruption – this is when a volcano erupts to give rise to gas, bombs of pumice, ash, and other thick materials.
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Extrusive rocks – these are rocks that are made from eruptions of something at the surface of the earth.
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Faults – these are deep lines in the earth where movement of large chunks of earth can happen. Expect to see different rock types on either side of any Faultline.
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Feldspar – this is a common type of mineral you might see in igneous and sometimes in metamorphic rocks.
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Fine-grained rocks – these are those where the grains in the rock are too small to be seen with the naked eye. These are less than 0.1 mm in diameter.
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Floodplain – this is the flat land around a river or floor of a valley that can easily flood after a heavy rainfall.
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Folds – these are places where rock layers are bent through the compression by other rocks. This is how mountains get built at the time tectonic plates collide with one another.
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Foliated or foliation – this is when metamorphic rocks like schist line up in the same direction or are compressed into a flattened texture.
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Fragmental or clastic – this is when grains of sediment are made from erosion occurring after more ancient rocks or seashells have acted on them.
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Gabbro – dark and coarse-grained igneous rock made by slow cooling of lava. It is the same as basalt but has larger intrusions.
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Gneiss – this is metamorphic rock that is coarse-grained and often banded as darker and lighter elements are layered out.
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Grains – these are mineral crystals or particles of sediment you see in all types of rocks.
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Granite – this is light-gray or pink, coarse-grained igneous rock made by slow cooling so large intrusions are found. This is the same as pumice but is a lot harder.
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Hydrolysis – this is a weathering process involving acid rain that slowly wears away minerals to make clay plus salts that dissolve from the acidity of the rain.
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I THROUGH M: •
Igneous rock – these are formed with magma from a volcano and cooled, compressing with intrusions of other things.
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Interlocking rock – this is a rock where grains of minerals or crystals form a mosaic due to their interlocking nature.
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Intrusions – these are areas of igneous rocks that have cooled and later crystallized when magma is cooling deep under the earth.
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Invertebrates – these are animals without any backbone, such as insects, shellfish, and worms.
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Joints – these are cracks you see in rocks due to the release of pressure from erosion above the rock that decrease the weight on them, or shrinkage of rocks. Most joints are vertical.
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Lahar – a mudflow formed from the combination of water and volcanic ash. This can damage large areas of land and homes.
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Landslide – any mass movement of rocks and earth down some type of slope. Mudflows, rock falls, and landslips are all types of landslides. A Landslip is similar but often involves clay that slips on an already-defined surface.
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Lava – this is molten basalt rock that has escaped from a volcano. Magma is not the same thing as lava.
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Limestone – this is sedimentary rock made mostly of calcium carbonate and formed when marine animals with shells die.
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Lithosphere – this is the main outer layer of the earth containing the top part of the mantle and the earth's crust.
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Longshore drift – this is movement of any type of sediment due to wave action near a shoreline.
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Magma – this is the molten rock containing mostly dissolved gases from a volcano that resides beneath the surface of the earth.
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Marble – this is a type of metamorphic rock that is made out of limestone.
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Medium-grained – this is a rock where the grains in it are of any type and are between microscopic and pea-sized in nature.
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Metamorphic rock – a rock type where the rock was once one type but was reshaped later due to any combination of heat and pressure.
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Metamorphic areole – any area around an intrusion where hot magma managed to heat and then alter the surrounding rocks.
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Metamorphism – the process altering a rock from one form to another through heat, pressure, or both.
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Mineral – any natural compound that crystallizes with a regular structure.
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Mica – a type of mineral that is flaky and shiny. You will see it in schist, gneiss, and granite mainly.
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Moraine – this is rocky material that is carried in a glacier and gets dumped in a spot wherever the glacier has retreated and melted.
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Mudstone – soft rock actually made of fine clay that is compressed later. This is also known as shale.
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N THROUGH R: •
Oolith – this is a small, round piece of calcium carbonate made through the rolling wave action of water in shallow seas.
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Oolitic limestone – this is limestone you see with small grains in it called ooliths. It is made when calcium carbonate precipitates in warm seawater near the shallow coastline.
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Oxidation – a chemical process occurring between certain metal elements and oxygen. It is what happens to make rust-colored oxides and "rust" out of surface iron deposits.
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Pahoehoe – this is the Hawaiian name for the ropy surface lava formed in a skin that folds into twisty shapes while hotter lava flows beneath it.
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Pebbles – a rock piece that is usually round and less than 10 cm in total size (but usually larger than 1 cm).
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Pele's hair -this is a form of lava that forms a fine stringy pattern as it cools rapidly so it looks like hair.
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Physical weathering – this is the type of weathering that happens from mechanical breakdown of surface rocks.
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Pillow lava – this is lava that looks like pillows formed when it comes into contact with cold seawater. It comes up from the seafloor.
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Plate tectonics – this describes the very slow motion of the major ridge plates on the earth's lithosphere.
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Playa – this is a lake you might see in a desert that is only temporary. Usually these are seen dried out unless there has been recent rainfall.
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Plucking – this is a glacial term where rock at the base of a glacier gets eroded from a combination of icing and movement.
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Porous – this is a phenomenon where sedimentary rock (mostly) has spaces that have filled in with groundwater.
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Pumice – extremely lightweight igneous rock made from gas-rich magma that has erupted under explosive conditions.
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Pyroclastic and pyroclastic flow – this is when hot gases and ash with rock are erupted from a volcano, rushing down the hillside at more than 100 miles per hour. The term "pyroclastic" refers to this rock and ash.
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Quartz – this is white or gray glassy material sometimes seen within granite. It is made from silicon dioxide.
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Quartzite – this is extremely hard, nearly white sandstone that is actually quartz grains that have become completely cemented together.
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Re-crystallization – this is when a mineral changes form from something like clay to a form such as mica. This occurs because of a chemical change in the rock and not because of melting or dissolving.
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Regional metamorphism – large-scale metamorphic changes in rocks because of widespread heat and pressure changes (the kind that builds mountains are an example).
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Rhyolite – a type of igneous rock with fine grains made from extremely thick lava.
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Rock salt – this is sodium chloride that came from the sea at one time but evaporated and got incorporated into certain rocks.
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S THROUGH Z: •
Salt – this is any ionic compound that dissolves in water. Calcium salts and sodium salts are commonly discussed in geology.
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Saltation – this is when sand grains bounce along because of the activities of flowing water or windy conditions.
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Sand – these are tiny particles up to 2 mm in diameter that are made from quartz and resistant to most chemical breakdown techniques.
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Sandstone – this is sedimentary rock that has medium grains within its structure and that consists of cemented sand grains.
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Schist – this is metamorphic rock that has shiny mica in it that is arranged in a foliated way.
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Sea-stack – this is a tall pillar of rock you can see coming up out of the sea and worn into a pillar by the action of waves eroding the rock.
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Sediment – this is any type of material that layers out due to the action of standing water and gravity. This can be anything – sand, organic material, shells, mud, or pebbles. Sediment may or may not become rock.
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Sedimentary rock – are formed on or near the Earth's surface from the compression of ocean sediments or other processes.
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Shale – this is a rock that was compressed to make dark-colored, grayish sedimentary rock. Expect to see fine, microscopic grains.
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Sill – this is an intrusion or influx of igneous rock that has seeped in along the planes of other rock layers.
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Slate – this is metamorphic rock made through compression of mudstone.
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Soil creep – this is mass movement that happens gradually due to gravity on steeper mountains or hillsides.
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Strata – these are any layers you see within rock itself, usually made by sediment of some kind. 10
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Strike-slip fault – this is a fault that involves a section of rock that moves past another in a horizontal fashion.
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Suspension load – this is a load of clay or other fine particles that get carried through the action of water and wind; they settle out eventually when the conditions are less fierce.
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Syncline – this is when a rock has bulged in a downward fashion or appears sunken in the middle.
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Tectonic forces – these are those forces that either crush or stretch the surface of the earth. This leads to faults, mountain building, and folding or shearing of the earth.
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Tectonic plates – these are stiff or rigid sections of the earth's crust that move independently from other plates.
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Texture – rock texture is described completely according to the size of the grains in the rock itself and the rock's shape due to the presence or absence of weathering and other factors.
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Thrust fault – this is often called a reverse fault because large sections of rock have slid up and over another section of rock.
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Unconformity – this involves the boundary layer between two separate rock sections that have cut across one another, leading to an apparent gap in geological time.
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Uplift – this is when a section of the earth's crust is squashed by tectonic plate activity or perhaps by ice sheets that have melted in varying ways.
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Vent – this is often seen in volcanic craters and is where gases and magma erupt to allow contents beneath it to escape.
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Vesicles – these are bubbles of rock that are made when gases beneath the earth are emitted from volcanoes. The lava cools and freezes the lava into vesicles.
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Volcanic ash and gases – these are the "stuff" emitted from a volcano. Gases are often made from carbon dioxide, water vapor, and sulfur gases. 11
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Wave-cut platform – this is a flattened area of rock that has become eroded by tide and waves, usually existing between high and low tidal areas.
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Weathering – this is rock breakdown for any reason, such as mechanical, biological, and chemical forces.
Wow, that's a bunch of terms! Don't worry if you haven't gotten them all because you will gradually have a deeper appreciation for what they mean.
ROCK TYPES AND WHAT THEY MEAN While every rock is unique and different, this doesn't mean that you can't categorize them in some way. There are actually only three major types of rocks. These are igneous, sedimentary, and metamorphic rocks. The term igneous refers to "fire" or molten lava. Rocks of this type of form only when hot lava cools into rock. Particles can settle as this happens or minerals can precipitate to create something more interesting than a black rock. Look for different mineral grain sizes and textures. The texture depends on how slowly or quickly the lava cools. Larger crystals come from slower-cooling lava and vice versa. Some interesting options among these: •
Granite pegmatite – this is igneous rock formed near the top of a magma chamber. It has many possible colors, including quartz gray, white, pink, and dark-colored mica.
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Diabase – this is rock solidifying just below the earth's surface. It cools rapidly, giving rise to a salt and pepper appearance. Basalt and gabbro are identical but differ in the size of the crystals. Diabase is in-between the two. Gabbro has the largest inclusions. Figure 1 shows a boulder with some diabase and gabbro in it:
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Figure 1.
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Diorite – this is rock that crystalized in a mountainous area where black hornblende and white plagioclase come together. Like diabase, it is black and white.
Sedimentary rocks are layered in some way. They are made whenever rock particles or other minerals settle out from within the water or air. Minerals can also simply precipitate out of solution at varying times or concentrations, giving rise to a layered look. Lithification is when these layers become rock. Here are some interesting choices: •
Limestone – limestone is extremely common. It comes from organisms that have shells or other calcium carbonate-containing structures. These settle out as organisms die off to make layered limestone in shallow waters. Figure 2 is a good image of limestone:
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Figure 2.
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Shale – shale is made from fine silt and clay that gets deposited in slow moving waters, often outside of river deltas where water cannot keep particles within it. Shale settles out as a grayish material in these waters. The layers flake off each other easily.
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Sandstone – this is made from sand that builds up in waters that is quickly moving. It will also layer out in desert areas, eventually forming fine-grained sandstone.
Metamorphic rocks are either igneous or sedimentary or both at some point but get changed due to pressure, heat, or chemical reactions. Minerals and texture help define these rocks. These are rocks with different grain sizes and layering orientations compared to what they were. Foliation is seen in these rocks, which is a deformation of the shape of intrusions/grains due to pressure forces. Some interesting examples include these:
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Manhattan schist – this is rock that was once shale and now has fine grains of biotite along with gray quartz or white orthoclase. The layering comes from compression on the shale.
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Gneiss – this used to be granite but became deformed by applied pressure and heat to make layers that are even-grained but more layered than the original rocks. Figure 3 shows what gneiss might look like:
Figure 3.
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KEY POINTS IN THIS CHAPTER •
Review the terms and sort out which represent processes involved in geography, which are structures involved in geography, and which are just types of rock.
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The three main types of rock are igneous, metamorphic and sedimentary.
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Rocks get acted on by chemical, mechanical, and biological forces to change them.
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Sediment can get layered out in air or water.
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All magma eventually cools with grains that depend on the rate of cooling. High rate means small grains, while low rates of cooling lead to larger grains.
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Pay attention to colors in rock as many represent a type of mineral.
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CHAPTER 1: QUESTIONS AND ANSWERS 1.
What form of lava looks like thick ropes of smooth hardened lava? A. Aa B. Pahoehoe C. Basalt D. Pele's hair
2.
What is light-weight gas-filled cooled lava called? A. Basalt B. Diorite C. Pumice D. Intrusion
3.
Areas of igneous rock that crystallize and are seen in rocks after they cool are called what? A. Intrusions B. Anticlines C. Synclines D. Joints
4.
From where do you see most magma reaching the earth's surface? A. Tidal pools B. Tectonic plates C. Earthquakes D. Volcanoes
5.
What type of rock would you see foliation in the most? A. Diorite B. Granite C. Schist D. Sandstone
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6.
What is the dangerous emission from volcanoes that travels quickly at 100 miles per hour or more down the volcano's side, made of both gases and ash called? A. Magma B. Pyroclastic C. Playa D. Pele's hair
7.
What type of grayish rock is made in shallow waters outside of river deltas as the stuff suspended in the river merges into slower moving waters? A. Shale B. Limestone C. Sandstone D. Bedrock
8.
What activity or process most creates mountains around earth? A. Vulcanism B. Weathering C. Unconformity D. Plate tectonics
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What process specifically acts on rock due to acid rain? A. Oxidation B. Saltation C. Hydrolysis D. Plucking
10.
Which type of rock might you see foliation as part of its structure? A. Igneous rock B. Metamorphic rock C. Feldspar D. Porous rock
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