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CHAPTER 14 ROCKS: MINERAL MIXTURES • Rocks change through a process called the Rock Cycle and rocks are classified by how they form, by what they are made of, and by their texture.
Chapter 14 Objectives • • We will learn about the Rock Cycle We will learn about the three types of rocks We will learn how each type is formed We will learn how each type is classified
Section 1: The Rock Cycle • What we will learn in this section: – Describe two ways in which rocks are used by people. – Describe the four processes that shape Earth’s features. – Describe how rocks move through the rock cycle. – List two characteristics of rocks that help classify them.
The Rock Cycle • Rock- naturally occurring solid mixture of one or more minerals or organic matter. – Rocks are always changing. • Rock Cycle- the series of processes in which a rock forms, changes from one type to another, is destroyed, and forms again by geological processes.
The Rock Cycle
Value of rock • Rock has always been valuable. • Rocks were the first form of tools. • It has been used to make things in ancient and modern times.
Processes That Shape the Earth • Weathering, Erosion, and Deposition – Erosion- the process by which wind, water, ice, or gravity transports soil and sediment from one location to another. – Deposition- the process in which material is laid down.
Processes That Shape the Earth • Heat and Pressure – Rocks also form under high heat and pressure. – High pressure can create sedimentary rocks. – Add heat to those rocks and they can melt and turn into Metamorphic rocks.
Processes That Shape the Earth • Magma can reach the surface through volcanoes or can cool in the ground and create igneous rocks.
Processes That Shape the Earth • How the cycle continues…. . – Buried rock can come to the surface by uplift and erosion. – Picture the Earth as a float in a pool, the land is the float and we are “floating” on hot magma.
Round and Round It Goes • The rock cycle is always moving very slowly. • New rocks are created, then destroyed, just to be created again. • There is no set path to the Rock Cycle, rocks travel in all directions.
Rock Classification • Rocks are divided into three main classes, but now we go further. • Rocks are divided further on how they form. • Scientist study rocks closely to find out how to classify them. • The two main characteristics are composition and texture.
Rock Classification • Composition- the chemical makeup of a rock; describes either the minerals or other materials in the rock. – Composition means the percentage of minerals or other materials that make up each rock.
Rock Classification • Texture- the quality of a rock that is based on the sizes, shapes, and positions of the rocks grains. – Three types of texture: fine-grained, mediumgrained, and coarse-grained. – Texture tells us how and where the rocks were formed.
Section 2: Igneous Rocks • What are going to learn: – We will describe the ways that igneous rocks form. – We will explain how the cooling rate of magma affects the texture of igneous rocks. – We will be able to distinguish between igneous rock that cools within the Earth’s crust and igneous rock that cools at Earth’s surface.
Igneous Rocks • Igneous is Latin for “FIRE”! • Igneous rocks form when hot magma or lava cools and hardens. • Magma- molten rock INSIDE the Earth. • Lave- molten rock OUTSIDE the Earth.
Origins of Igneous Rock • Begins as magma. • Three ways magma is formed: – When rock is heated. – When pressure is released. – When rock changes composition.
Origins of Igneous Rock • When water freezes, it makes ice. When magma “freezes”, it makes igneous rock. • Each mineral has its own melting and freezing point. • Remember, rocks are made from many minerals put together. This means the igneous rock freezes at different temperatures. (Some parts freeze faster than others. )
Composition and Texture of Igneous Rocks • Composition- Rocks made from light colored minerals are called felsic rocks. Rocks made from dark colored minerals are called mafic rocks.
Composition and Texture of Igneous Rocks • Texture- Texture of igneous rocks depend on how fast they cool. • Faster cooling causes SMALLER crystals. • Slower cooling causes LARGER crystals.
Igneous Rock Formations • Igneous rocks form both inside the Earth and outside the Earth. • Intrusive Igneous Rock- rock formed from the cooling and solidification of magma beneath the Earth’s surface. • Plutons are large intrusive bodies of igneous rock. – Types of plutons include: Batholiths, Stocks, dikes, and sills.
Intrusive Igneous Rock
Extrusive Igneous Rock • Extrusive Igneous Rock- rock that forms as a result of volcanic activity at or near the Earth’s surface. • Lava cools quickly so it has small or no crystals. • Lava cools to form fissures or plateaus. • Lava also forms in oceans to create new ocean floor.
Extrusive Igneous Rock
Section 3: Sedimentary Rock • What we are going to learn: – We will describe the origin of sedimentary rock. – We will describe three main categories of sedimentary rock. – We will describe three types of sedimentary structures.
Origins of Sedimentary Rock • Wind, water, ice, sunlight, and gravity cause rocks to break into pieces. • Through erosion the pieces, called sediment, are moved from one place to another.
Origins of Sedimentary Rock • Sediment is laid down in layers, over time these layers are compacted into rock. • The most noticeable feature of sedimentary rock is the strata. • Strata- layers of rock.
Composition of Sedimentary Rock • Sedimentary rock is classified by how it forms. • Three main categories of sedimentary rock: – Clastic Sedimentary Rock – Chemical Sedimentary Rock – Organic Sedimentary Rock
Clastic Sedimentary Rock • Made of rock fragments (chunks) that are cemented together. • Clastic Sedimentary Rocks have three types of textures: – Fine-grained – Medium-grained – Coarse-grained
Chemical Sedimentary Rock • Chemical Sedimentary Rock forms from solutions of dissolved minerals and water. • Rain dissolves minerals in rocks and carries them to oceans where they are deposited and harden to form rock.
Organic Sedimentary Rock • Organic Sedimentary Rock form from remains, or fossils, of animals that once lived in the ocean. • These fossils become cemented together to form fossiliferous limestone.
Sedimentary Rock Structures • Stratification- the process in which sedimentary rocks are arranged in layers. • Strata differ from one another depending on the kind, size, and color of their sediment.
Sedimentary Rock Structures • Sedimentary rocks can record the motion of wind and waves on lakes, oceans, rivers, and sand dunes. • Ripple marks and mud cracks are formed in the sediment and then hardened into rock. • Even rain drops and foot prints can be preserved in the mud.
Metamorphic Rock • What we will learn: – We will describe two ways a rock can undergo metamorphism. – We will explain how the mineral composition of rocks changes as the rocks undergo metamorphism. – We will describe the difference between foliated and nonfoliated metamorphic rock. – We will explain how metamorphic rock structures are related to deformation.
Metamorphic Rock • Rocks change through a process called metamorphism. • This comes from the Greek word meta, meaning “change”, and morphos, meaning “shape”. • Metamorphic rocks are rocks that have changed structure, texture, or composition.
Origins of Metamorphic Rocks • If the temperature or pressure surrounding a rock changes, a metamorphic rock is formed. • Most metamorphism takes place from 50°C and 1, 000°C, and at depths deeper than 2 km inside the Earth.
Contact Metamorphism • When hot magma flows through the Earth’s crust it heats up the rock it touches causing it to melt. • The rocks then re-harden into changed rocks.
Regional Metamorphism • When pressure builds up deep in the Earth it cause pieces of the crust to collide with each other. • This changes large areas underneath contiential crust.
Composition of Metamorphic Rocks • During metamorphism the minerals in a rock change form into more stable minerals. • Some of these minerals form at certain temperatures, these are called index minerals.
Composition of Metamorphic Rock • Scientist use these index minerals to tell at what temperature, depth, and pressure the new rocks were formed. • More heat and pressure can cause one metamorphic rock to morph into another kind.
Textures of Metamorphic Rock • All metamorphic rock have one of two textures, foliated and non-foliated. • Foliated- the texture of metamorphic rock in which the mineral grains are arranged in planes or bands.
Textures of Metamorphic Rock • If you see “bands” on the rock then it was formed with the highest temperature and pressure.
Textures of Metamorphic Rock • Non-foliated- the texture of metamorphic rock in which the mineral grains are not arranged in planes or bands. • Non-foliated rock are made from only a few minerals, these minerals melt and re-form in a process called recrystallization.
Metamorphic Rock Structures • Metamorphic rock structures are cause by force placed on the rock when it is formed. • Deformation is what the change in shape is called. • The rock becomes folded or bended, this can be really small or really large.