ROCKS: MINERAL MIXTURESChapter 4

Section 1

The Rock cycle

Introduction Rock: a naturally occurring solid mixture

of one or more minerals and organic matter

Rock cycle: the continual process by which new rock forms from old rock material

Processes that Shape the Earth Weathering, Erosion, and Deposition

Weathering: the process in which water, wind, ice, and heat break down rock

Erosion: the process by which sediment is removed from its source

Deposition: the process in which sediment moved by erosion is dropped and comes to rest Deposited in bodies of water and other low-

lying areas

Processes that Shape the Earth Heat and Pressure

Sedimentary rock made of sediment can also form when buried sediment is squeezed by the weight of overlying layers of sediment

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

The melting of rocks creates the magma that eventually cools to form igneous rock

Processes that Shape the Earth How the Cycle Continues

Uplift: movement within the Earth that causes rocks inside the Earth to be moved to the Earth’s surface When uplifted rock reaches the Earth’s surface,

weathering, erosion, and deposition begin

Weathering > Erosion > Deposition > Compaction and Cementation > Metamorphism > Melting > Cooling >

Solidification > Weathering

SEDIMENTARY ROCK

METAMORPHIC ROCK

IGNEOUS

ROCK

MAGMA!

SEDIMENT

Sedimentary Rock Grains of sand and other sediment are

eroded from hills and mountains and wash down a river to the ocean. Over time, the sediment forms thick layers on the ocean floor. Eventually, the grains of sediment are compacted and cemented together to form sedimentary rock.

Metamorphic Rock When large pieces of the Earth’s crust

collide, some of the rock is forced downward. At great depths, intense heat and pressure heat and squeeze the sedimentary rock to change it into metamorphic rock.

Magma The hot liquid that forms when rock

partially or completely melts is called magma. Where the metamorphic rock comes into contact with magma, the rock tends to melt. The material that began as a collection of sand grains now becomes part of the magma.

Igneous Rock Magma is usually less dense than the

surrounding rock, so magma tends to rise to higher levels of the Earth’s crust. Once there, the magma cools and solidifies to become igneous rock.

Sediment Uplift and erosion expose the igneous

rock at the Earth’s surface. The igneous rock then weathers and wears away into grans of sand and clay. These grains of sediment are then transported and deposited elsewhere, and the cycle begins again.

Round and Round it Goes Each rock type can

change into one of the three types of rock

As one rock is changed into another type, several variables, including time, heat, pressure, weathering, and erosion, may alter a rock’s identity

Rock Classification Scientists divide all rock into three main

classes based on how the rock is formed Igneous Sedimentary Metamorphic

Can be divided further Divisions based on differences in the way rocks

form Two important criteria for divisions—

composition and texture

Rock Classification Composition

The chemical makeup of a rock; describes either the minerals or other materials in the rock

Rock Classification Texture

The size, shape, and positions of the grains that make up a rock Sedimentary rock: fine-grained, medium-

grained, or coarse-grained texture Igneous rock: fine-grained or coarse-grained

texture Metamorphic rock: fine-grained or coarse-

grained texture

Rock Classification Texture

Can provide clues as to how and where the rock formed

Can reveal the process that formed it

Fine-grained Medium-grained Coarse-grained

Section 2

Igneous rock

Origins of Igneous Rock Forms when

magma cools and solidifies 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 rocks are less dense than the dark-colored rocks

Felsic rocks: light-colored rocks rich in elements such as aluminum, potassium, silicon, and sodium

Mafic rocks: dark-colored rocks rich in calcium, iron, and magnesium, and poor in silicon

Composition and Texture of Igneous Rock

The more time the crystals have to grow, the larger the crystals are and the coarser the texture of the resulting igneous rock is

Igneous Rock Formations Located above and below the surface of

the Earth Intrusive Igneous Rock

When magma pushes into surrounding rock below the Earth’s surface and cools

Has a course-grained texture Cools very slowly

Igneous Rock Formations Masses are named for their

size and shape Plutons: large, irregular-shaped

intrusive bodies Batholiths: largest of all

igneous intrusions Stocks: intrusive bodies that

are exposed over smaller areas than batholiths

Dikes: sheet-like intrusions that cut across previous rock units

Sills: sheet-like intrusions that are oriented parallel to previous rock units

Igneous Rock Formations Extrusive Igneous Rock

Igneous rock that forms from magma that erupts onto the Earth’s surface

Common around volcanoes Cools quickly Very small crystals or no crystals

Section 3

Sedimentary Rock

Origins of Sedimentary Rock

Sandstone: sand grains that are compressed and then cemented together over time

Sediment: rock and mineral fragments Deposited in layers Dissolved minerals separate from water that

passes through the sediment to form a natural cement that binds the rock and mineral fragments together in sedimentary rock

Forms at or near Earth’s surface Forms without heat or pressure

Composition of Sedimentary Rock Classified by the way it forms

Clastic sedimentary rock: forms when rock or mineral fragments are cemented together

Chemical sedimentary rock: forms when minerals crystallize out of a solution to become rock

Organic sedimentary rock: forms from the remains of once-living plants and animals

Composition of Sedimentary Rock

Clastic Sedimentary Rock Made of fragments

of rocks cemented together by a mineral such as calcite or quartz

Have coarse-grained, medium-grained, or fine-grained textures

Composition of Sedimentary Rock Chemical Sedimentary Rock

Forms from solutions of dissolved minerals and water

Some of this dissolved material eventually crystallizes and forms the minerals that make up chemical sedimentary rock

Composition of Sedimentary Rock

Organic Sedimentary Rock Forms from the fossils of animals or plants Fossiliferous limestone: animal remains that

eventually become cemented together Made from:

Coral Clams Oysters

Coal: forms underground when partially decomposed plant material is buried beneath sediment and is changed into coal by increasing heat and pressure over millions of years

Sedimentary Rock Structures Stratification: the process in which

sedimentary rocks are arranged in layers Sedimentary rocks sometimes record the

motion of wind and water waves Ripple marks Mud cracks

Indicate the location of an ancient lake, stream, or ocean shoreline

Even rain drop impressions can be preserved

Sedimentary Rock Impressions

Section 4

Metamorphic Rock

Origins of Metamorphic Rock

Rocks in which the structure, texture, or composition of the rock have changed Metamorphosis= changed shape

Most metamorphosis takes place from 50°C to 1,000°C Some take place at more than 1,000°C

Most metamorphosis takes place at depths greater than 2 km This pressure can cause the mineral grains in

rock to align themselves in certain directions

Origins of Metamorphic Rock

Contact Metamorphism Occurs near igneous intrusions Occurs because of magma heating the rock

around it as it moves Regional Metamorphism

When pressure builds up in rock that is buried deep below other rock formations or when large pieces of Earth’s crust collide with each other

Occurs over thousands of cubic kilometers Rocks that have undergone this are found

beneath most continental rock formations

Origins of Metamorphic Rock

Composition of Metamorphic Rock Index minerals: metamorphic minerals that

form only at certain temperatures and pressures Examples:

Biotite Mica Chlorite Garnet Kyanite Muscovite mica Sillimanite Staurolite

Textures of Metamorphic Rock All metamorphic rock has one of two

textures—foliated or nonfoliated

Textures of Metamorphic Rock Foliated Metamorphic Rock

Foliated: the texture of metamorphic rock in which the mineral grains are arranged in planes or bands

Slate: when shale is exposed to slight heat and pressure, the clay minerals change into mica minerals

Textures of Metamorphic Rock Nonfoliated Metamorphic Rock

Nonfoliated: the texture of metamorphic rock in which the mineral grains are not arranged in planes or bands

Commonly made of one or only a few minerals

Recrystallization: the crystals of these minerals may change in size or the mineral may change in composition

Metamorphic Rock Structures

Deformation: 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 Bends