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Rocks: Mineral Mixtures

Section 1 The Rock Cycle

Section 2 Igneous Rock

Section 3 Sedimentary Rock

Section 4 Metamorphic Rock

Chapter 4

Preview

Concept Mapping


Section 1 The Rock Cycle

BellringerMost of us try to recycle the items we use in our daily lives to minimize the pollution we cause. In a way, the Earth also recycles through the rock cycle.

How can a rock be recycled? How long would recycling a rock take? What would a rock look like before, during, and after the process of recycling?

Record your thoughts about these questions in your science journal.

Chapter 4


• Describe two ways rocks have been used by humans.

• Describe four processes that shape Earth’s features.

• Describe how each type of rock changes into another type as it moves through the rock cycle.

• List two characteristics of rock that are used to help classify it.

Objectives

Section 1 The Rock CycleChapter 4


The Rock Cycle• A rock is a naturally occurring solid mixture of one or more minerals or organic matter.

• New rock forms from old rock material constantly.

• The series of processes in which a rock forms, changes from one type to another, is destroyed, and forms again by geological processes is called the rock cycle.



The Value of Rock• Rock has been an important natural resource for as long as humans have existed.

• Ancient and modern civilizations have used granite, limestone, marble sandstone, slate and other rocks as construction materials.

• Rock is also an important ingredient in concrete and plaster, both of which are commonly used in construction.


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Processes That Shape the Earth• Certain geological processes make and destroy rock.

• These processes shape the features of our planet.

• These processes also influence the type of rock that is found in certain areas.



Processes That Shape the Earth, continued

• Weathering, Erosion, and Deposition The process in which water, wind, ice, and heat break down rock is called weathering.

• Weathering is important because it breaks down rock into fragments of which sedimentary rock is made.




• The process by which wind, water, ice, or gravity transports soil and sediment from one location to another is called erosion.

• The process in which sediment moved by erosion is dropped and comes to rest is called deposition.




• Heat and Pressure Sedimentary rock can also form when buried sediment is squeezed by the weight of overlaying layers of sediment.

• If the temperature and pressure are high enough, the rock can change into metamorphic rock.

• If the rock gets hot enough to melt, this creates the magma that eventually cools to form igneous rock.




• How the Cycle Continues Buried rock is exposed at the Earth’s surface by a combination of uplift and erosion.

• Uplift is the movement within the Earth that causes rocks inside the Earth to be moved to the surface.

• When uplifted rock reaches the Earth’s surface, weathering, erosion, and deposition begin.



Illustrating the Rock Cycle• The rock cycle is the continual process by which new rock forms from old rock material.

Round and Round It Goes• Rocks may follow various pathways in the rock cycle. The following Visual Concepts presentation show the different ways rock may change when it goes through the rock cycle.



Rock CycleClick below to watch the Visual Concept.

Visual Concept



Rock ClassificationRock can be three main classes based on how the rock is formed:

• Igneous rock

• Sedimentary rock

• Metamorphic rock



Types of Rock

Click below to watch the Visual Concept.

Visual Concept



Rock Classification, continued• Each class of rock can be divided further, based on differences in the ways rocks form.

• Igneous rock can be divided again based on whether the magma from which it forms cools on the Earth’s surface or below ground.



Rock Classification, continued• Sedimentary and metamorphic rocks are also divided into smaller groups.

• Scientists study rocks in detail using two important criteria: composition and texture.



Rock Classification, continued• Composition is the chemical makeup of a rock. Composition can describe either the minerals or other materials in the rock.

• Texture is the quality of a rock that is based on the sizes, shapes, and positions of the rock’s grains.



Section 2 Igneous Rock

Bellringer

Do you think rocks that cooled and solidified from lava on the Earth’s surface would look different from those that cooled and solidified from magma inside the Earth? Why?

Record your response in your science journal.

Chapter 4


Section 2 Igneous RockChapter 4

• Describe three ways that igneous rock forms.

• Explain how the cooling rate of magma affects the texture of igneous rock.

• Distinguish between igneous rock that cools within the Earth’s crust and igneous rock that cools at the Earth’s surface.

Objectives



Origins of Igneous Rock• Igneous rock forms when hot, liquid rock, or magma, cools and solidifies. There are three ways magma can form:

• When rock is heated

• When pressure is released

• When rock changes composition



Composition and Texture of Igneous Rock

• Light-colored igneous rocks are called felsic rocks.

• Felsic rocks are rich in elements such as aluminum, potassium, silicon, and sodium.

• Dark-colored igneous rocks are called mafic rocks.

• Mafic rocks are rich in calcium, iron, and magnesium.



Igneous Rock Formations• When magma intrudes, or pushes, into surrounding rock below the Earth’s surface and cools, the rock that forms is called intrusive igneous rock.

• Intrusive igneous rock usually has a coarse-grained texture because it is well insulated by surrounding rocks and cools very slowly.


Chapter 4 Section 2 Igneous Rock



Igneous Rock Formations, continued• Igneous rock that forms from magma that erupts, or extrudes, on the Earth’s surface is called extrusive igneous rock.

• Extrusive igneous rock, commonly found around volcanoes, cools quickly on the surface and contains very small crystals or no crystals.


Section 3 Sedimentary Rock

BellringerTree rings are formed each year of a tree’s life cycle. Tree rings exist because the weather changes of the seasons are reflected in the tree’s bark as the tree grows.

How are layers in sedimentary rock alike or different from rings in a tree? What can geologists infer from examining sedimentary rock layers?

Record your response in your science journal.

Chapter 4


Section 3 Sedimentary RockChapter 4

• Describe the origin of sedimentary rock.

• Describe the three main categories of sedimentary rock.

• Describe three types of sedimentary structure.

Objectives



Origins of Sedimentary Rock• Wind, water, ice, sunlight, and gravity all cause rock to physically weather into fragments.

• Through erosion, these rock and mineral fragments, called sediment, are moved from one place to another.

• The sediment is deposited in layers, and eventually newer layers cover the older layers.



Sedimentary Rock Cycle

Click below to watch the Visual Concept.

Visual Concept



Origins of Sedimentary Rock, continued

• The most noticeable feature of sedimentary rock is its layers, or strata.

• A single, horizontal layer of rock is sometimes visible for many miles.



Composition of Sedimentary Rock• Sedimentary rock is classified by the way it forms.

• Clastic sedimentary rock is made of fragments of rocks cemented together by a mineral such as calcite or quartz.

• Clasitc sedimentary rocks can have coarse-grained, medium-grained, or fine-grained textures.



Composition of Sedimentary Rock, continued

• Chemical sedimentary rock forms from solutions of dissolved mineral and water.

• As rainwater slowly makes its way to the ocean, it dissolves some of the rock material it passes through.

• Some of this dissolved material eventually crystallized and forms the mineral that make up chemical sedimentary rock.



Composition of Sedimentary Rock, continued

• Organic sedimentary rock is made up of the skeletons and shells of sea animals. These remains collect on the ocean floor and eventually become cemented together.

• Coal is a type of organic sedimentary rock that is formed when decomposed plant material is buried beneath sediment and is changed by increasing heat and pressure.



Sedimentary Rock Structures• Many features indicate the way sedimentary rock is formed. The most important feature is stratification.

• Stratification is 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, continued

• Sedimentary rocks sometimes record the motion of wind and water waves on lakes, oceans, rivers, and sand dunes in features called ripple marks.

• Structures called mud cracks form when fine-grained sediments at the bottom of a shallow body of water are exposed to the air and dry out.

• Even raindrop impressions can be preserved in fine-grained sediments, as small pits with raised rims.


Section 4 Metamorphic Rock

Bellringer

Write a brief description of how cookies are made. How is the mixture of raw ingredients like sedimentary rock? Do the raw ingredients of a cookie look the same after they are done baking?

Describe how cookie dough metamorphoses when it is baked in an oven.

Chapter 4


Section 4 Metamorphic RockChapter 4

• Describe two ways a rock can undergo metamorphism.

• Explain how the mineral composition of rocks changes as the rocks undergo metamorphism.

• Describe the difference between foliated and non-foliated metamorphic rock.

• Explain how metamorphic rock structures are related to deformation.

Objectives



Origins of Metamorphic Rock• Metamorphic rocks are rocks in which the structure, texture, or composition of the rock have changed.All three types of rock can be changed by heat, pressure, or a combination of both.

• A rock’s texture or mineral composition can change when its surroundings change. If the temperature or pressure of the new environment is different from the one in which the rock formed, the rock will undergo metamorphism.



Origins of Metamorphic Rock, continued

• Contact Metamorphism When magma moves through the crust, the magma heats the surrounding rock and changes it.

• Some minerals in the surrounding rock are changed into other minerals by this increase in temperature.

• The greatest change occurs where magma comes into direct contact with the surrounding rock.



Origins of Metamorphic Rock, continued

• Regional metamorphism occurs when pressure builds up in rock that is buried deep below other rock formations, or when large pieces of the Earth’s curst collide with each other.

• The increased pressure and temperature causes rock to become deformed and chemically changed.


Chapter 4 Section 4 Metamorphic Rock



Composition of Metamorphic Rock• As rocks undergo metamorphism, original minerals in a rock change into new minerals that are more stable within the new pressure and temperature conditions.

• Many of these new minerals form only in meta-morphic rock. These are known as index minerals, and are used to estimate the temperature, depth, and pressure at which a rock undergoes meta-morphism.



Texture of Metamorphic Rock• All metamorphic rock has one of two textures.

• Foliated Metamorphic Rock

• Nonfoliated Metamorphic Rock



Texture of Metamorphic Rock, continued

• Foliated Metamorphic Rock The texture of metamorphic rock in which the mineral grains are arranged in planes or band is called foliated.

• Foliated metamorphic rock usually contains aligned grains of flat minerals, such as biotite mica or chlorite

• Metamorphic rocks can become other metamorphic rocks if the environment changes again.



Texture of Metamorphic Rock, continued

• Nonfoliated Metamorphic Rock The texture of metamorphic rock in which the mineral grains are not arranged in planes or band is called nonfoliated.

• Nonfoliated metamorphic rocks are commonly made of one or only a few minerals.

• During metamorphism, crystals of these minerals may change in size or the mineral may change in composition in a process called recrystallization.



Metamorphic Rock Structures• Metamorphic rock has features that indicates its history. These features are caused by deformation.

• Deformation is a change in the shape of a rock caused by a force placed on it.

• These forces may cause a rock to be squeezed or stretched. Folds, or bends, in metamorphic rock are structures that indicate a rock has been deformed.


Rocks: Mineral Mixtures

Concept MappingUse the terms below to complete the concept map on the next slide.

Chapter 4

sedimentaryclasticextrusiverocks

metamorphicregionaligneousintrusive


Rocks: Mineral MixturesChapter 4

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