Rocks: Mineral Rocks: Mineral MixturesMixtures

Chapter 4Chapter 4

20082008

The Rock CycleThe Rock Cyclesection 1section 1

► 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.

Rock CycleRock Cycle

The Value of RockThe 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.

Processes That Shape the Processes That Shape the EarthEarth

► 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 Processes That Shape the Earth 2Earth 2

► 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.

Processes That Shape the Processes That Shape the Earth 3Earth 3

► 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.

Processes That Shape the Processes That Shape the Earth 4Earth 4

► 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.

Processes That Shape the Processes That Shape the Earth 5Earth 5

► 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 CycleIllustrating 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.

Click below to watch the Visual Concept.

Visual Concept

Chapter 4Rock CycleRock Cycle

Rock ClassificationRock Classification

• Rock 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

Section 1 The Rock CycleChapter 4

Rock Classification 2Rock Classification 2

► 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 3Rock Classification 3

►Sedimentary and metamorphic rocks are also divided into smaller groups.

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

Rock Classification 4Rock Classification 4► Composition is the chemical makeup of a rock.

Composition can describe either the minerals or other materials in the rock.

►

Rock Classification 5Rock Classification 5►Texture is the quality of a rock that is

based on the sizes, shapes, and positions of the rock’s grains.

Rock Classification 6Rock Classification 6

Igneous RockIgneous RockObjectives section 2Objectives section 2

► 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.

Origins of Igneous RockOrigins 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.

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

►Describe the origin of sedimentary rock.

► Describe the three main categories of sedimentary rock.

► Describe three types of sedimentary structure.

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.

Section 3 Sedimentary RockChapter 4

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.

Shale

Clastic Sedimentary RockClastic Sedimentary Rock

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.

Limestone

HaliteGypsum

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.

Coal

Organic Limestone

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. Mud crack

Ripple marks

Rain drops

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.

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

► Non-foliated Metamorphic Rock

quartzite

gneiss

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.

phyllite

Texture of Metamorphic Rock, continued

► Non-foliated Metamorphic Rock The texture of metamorphic rock in which the mineral grains are not arranged in planes or band is called nonfoliated.

► Non-foliated 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.

marble

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.