Chapter 4- Rocks

Earth Science

Bell Work Lesson 4.1• Rock- Natural, solid mixture of minerals/grains• Grain- What mineralogists call the fragments that

make up a rock• Texture- The grain size and the way the grains fit

together• Magma- Molten or liquid rock underground• Lava- Molten rock that erupts on Earth’s surface • Sediment- Rock material that forms where rocks

are broken down into smaller pieces or dissolved in water as rocks erode

• Rock cycle- The series of processes that change one type of rock into another type of rock

Rocks

• A natural, solid mixture of minerals or grains– Grain= fragments that

make up rock• Mineral crystals, broken

bits of minerals or rock fragments

• Can contain remains of organisms or volcanic glass

How to classify rocks?

• Two important observations:– Texture– Composition

Texture

• The grain size and the way the grains for together– Look at the size of the minerals or

grains– Look at the arrangement of the minerals

or grains– What is the overall feel of the rock?

Composition

• Classified by the minerals or grains present in a rock– Can tell a geologist where the rock

formed• Certain minerals can suggest rock formed

under extreme temperature or pressure

Three major rock types

• Based on how they form– Can determine

where they formed based on the characteristics

• Three types:– Igneous– Sedimentary– Metamorphic

Igneous rock• When magma or lava

cools and crystallizes, it creates this kind of rock.– Magma= molten or liquid

rock underground– Lava= molten rock that

erupts on Earth’s surface

• The crystals that grow form the grains of the rock

• Can form in different environments:– Subduction zones, mid-

ocean ridges, hot spots (lots of volcanoes)

Igneous rock cont’d

Sedimentary rock

• Sediment: rock material that forms where rocks are broken down into smaller pieces or dissolved in water as rocks erode

• Sediment, mineral crystals, remains or plants and animals are building blocks of sedimentary rock

Sedimentary rock cont’d

• Rock forms where sediment is deposited (added to a landform)– Examples of where

sediment is deposited: Rivers/streams, deserts, valleys

• Loose sediment will someday turn into rock– Examples of where

sedimentary rocks can be found: mountain valleys, along river banks, beach etc.

Metamorphic rock

• Rocks that are exposed to extreme temperature and pressure can change to metamorphic rock– Can happen along plate boundaries– Can also happen if rock is exposed

to some chemical fluids

• Minerals change AND texture changes when the rock changes into metamorphic rock. – Grains can look bent or twisted

Metamorphic rock cont’d

• Can form from ANY rock (including other metamorphic rock)– Limestone (sedimentary

rock) metamorphoses into marble

– Granite (igneous rock) metamorphoses into gneiss.

Rock Cycle

• The series of processes that change one type of rock into another type of rock– Rocks are changing all the

time • Slowly• Because of forces within Earth

and on Earth’s surface

– Example: 1- Lava forms igneous rock; 2- the rock is exposed to Earth’s surface and is eroded by water to form sediment; 3- the sediment cements together to form sedimentary rock.

Rock cycle cont’d

• Some processes can only occur under Earth’s surface– Extreme pressure and temperature (and

melting)

• Some rocks that are made under Earth’s surface change when uplifted to Earth’s surface– What changes can happen once on surface?

• Weathering, erosion, deposition, compaction, cementation.

HOMEWORK Ch4 L.1

• Vocabulary words on flash cards– MEMORIZE THEM FOR QUIZ

• Outline Lesson 1

• Lesson Review questions– P. 116 #1-8

• QUIZ!!!!

LaunchLab p.111

• Obtain a rock sample• Examine the rock with/without a

magnifying glass• Describe rock in detail

– Color– Texture– Anything weird/cool in it?– Any minerals/grains you can see?

• WRITE YOUR NAME ON PAPER AND TURN IT IN

Ch4 L.2 Igneous Rocks

Bell Work Ch4 L.2

• Extrusive rock: When volcanic material erupts and cools and crystallizes on Earth’s surface

• Volcanic Glass: Rock that forms when lava cools too quickly to form crystals

• Intrusive Rock: Igneous rocks that form as magma cools slowly underground

Essential questions:

• How do igneous rocks form?

• What are the common types of igneous rocks?

Launch Lab p.119

• Observe what happens when I drop hot, melted sugar into your beaker of water.– One time slowly– One time quickly

• Record what happens– What is the difference between the two?

• WRITE YOUR FULL NAMES ON IT AND TURN IT IN.

• WORK IN PAIRS.

Igneous rock formation• Lava cools to become

igneous rock– Happens quickly when

exposed to air– Darker color where already

started to crystallize

• Magma cools slowly below Earth’s surface– Can become exposed to

the Earth’s surface eventually after wind, water and other factors wear away the ground on top of it

Extrusive rocks

• When volcanic material erupts and cools and crystallizes on Earth’s surface– Lava and ash solidify to

form this– Happens fast= not

enough time for crystals to grow

– Fine-grained texture

Extrusive rocks cont’d

• Volcanic glass= rock that forms when lava cools too quickly to form crystals– Example:

Obsidian (both pictures)

Extrusive rocks cont’d• Gases can be trapped in

magma – Magma moves towards

the surface– Gases can cause

eruptions (think of carbonation in soda)

• Gas-rich lava erupts and gases escape– Forms special igneous

extrusive rocks– Example: pumice

• Why do you think pumice has all those holes?

Mini Lab p.120• I NEED 3 VOLUNTEERS• Each Volunteer will receive 1 beaker and 1 watch

glasse• Fill the three beakers with water

– One filled with HOT water– One filled with WARM water– One filled with COLD water

• Place the beakers in the back of the room • Place one watch glass on each of the beaker

– MAKE SURE THERE IS ENOUGH WATER SO IT IS TOUCHING THE WATCH GLASS

• I will come around and pour 3mL of water with dissolved Epsom salt. We will look at the crystals TOMORROW.

Intrusive rock• Igneous rocks that

form as magma cools slowly underground– Large, well-defined

crystals can form– Random arrangement

of crystals• Crystals interlock like a

jigsaw puzzle

• Typical characteristics:– Large crystals – Random arrangement

Igneous rock identification

• Texture:– Crystal size

• Small + hard to see (sometimes only with magnifying lens)= extrusive

• Large enough to see with interlocking arrangement= intrusive

Igneous rock identification

• Composition: – Silica content (estimate

based on color of minerals)• Darker colored minerals=

usually less silica and more magnesium and iron

– Examples: Perodite contains minerals olivine and pyroxene

• Lighter colored minerals= usually more silica

– Examples: rhyolite contains minerals quartz and feldspar

Igneous rock identification

Igneous rock identification

HOMEWORK Ch4 L.2

• Vocabulary words on Flash Cards– MEMORIZE FOR QUIZ

• Outline Ch4 L.2

• Lesson review questions– Page 123– Questions 1-10

• QUIZ!!!!!

Ch4 L.3 Sedimentary Rocks

Bell Work Ch4 L.3• Compaction: the weight from layers of

sediment forces out fluids and decreases space between grains

• Cementation: Minerals dissolved in water crystallize between sediment grains

• Clastic rock: Made up of broken pieces of minerals and rock fragments

• Clast: the broken pieces of minerals and rock fragments that form clastic rock.

• Chemical rock: form when minerals crystallize directly from water.

• Biochemical rock: Sedimentary rock that was formed by organisms or contains the remains of organisms

Essential questions

• How do sedimentary rocks form?

• What are the three types of sedimentary rocks?

Mini Lab Follow up• What do you think crystals will look like?• Write down your predictions. THEN go to the

back of the room and observe the crystals formed from the three environments– Hot, Warm, Cold

• Record your observations– How are the crystals different?

Prediction (hot)

Prediction (warm)

Prediction (cold)

Observation (hot)

Observation (warm)

Observation (cold)

Sedimentary rock formation• Can form in different environments

– Water and air can break down rock• Also can transport rock fragments to new locations

• Sediment deposited in layers– Gets thicker over time– Compaction: the weight from layers of sediment

forces out fluids and decreases space between grains

Sedimentary rock formation cont’d

• Compaction can lead to cementation– Minerals dissolved in

water crystallize between sediment grains

• Holds grains together• Examples of minerals

that cement: quartz, calcite, and clay

Sedimentary rock identification

• Classified according to how they form– Deposited, compacted then cemented– Evaporation when minerals crystallize

from water– When organisms remove minerals from

water to make shells or skeletons

Clastic Sedimentary Rocks• Made up of broken pieces of

minerals and rock fragments – Clasts= broken pieces

• Identify according to clast shape and size– Can’t use shape alone

• Can be as big as a car or as small as a grain of flour

• Shape helps determine environment where it formed

– Small, gritty sediment= typically in calm environments (sea floor, bottom of lake)

– Large sediment= can be moved by oceans waves, fast flowing rivers

Chemical sedimentary rock

• Dissolved minerals can be carried from rivers to the ocean (contribute to saltiness)

• Water can be saturated with dissolved mineral and minerals can crystallize out of the water

• Chemical rocks form when minerals crystallize directly from water.

Chemical sedimentary rock cont’d

• Examples: rock salt (halite), rock gypsum, limestone

• Interlocking crystalline texture (similar to igneous rocks)

• Generally composed of one dominant mineral= uniform in color– Different from igneous

rocks (generally many minerals)= multi-colored

Biochemical sedimentary rocks

• Sedimentary rock that was formed by organisms or contains the remains of organisms– Most common=

limestone• Organisms make shells

from dissolved minerals– Organism dies and

shells settle on the floor= forms part of rock

• If contains fossils= fossiliferous

Biochemical sedimentary rocks

• Carbonate rock= contains carbon and oxygen– Will fizz when add

hydrochloric acid• Limestone is an example

– Not all biochemical rocks are carbonates

• Diatomite looks like limestone but doesn’t fizz with HCl

• Coal– Composed of remains of

plants and animals • Buried and compressed to

eventually form sedimentary rock

Common Chemical and Biochemical Rocks

Mini Lab p. 128• Use grains of sedimentary rocks to identify the

environment where they likely formed• What to look for? (Write this down for each)

– Grain size– Grain shape– Have you seen something similar before?

• Guess: in what environment was each formed?

Grain Size? Grain Shape? Seen this before? Environment guess

#1

#2

#3

#4

HOMEWORK

• Vocabulary words on Flash Cards– Memorize for quiz

• Ch4 L.3 Outline

• Lesson review questions– Page 130– Questions 1-10

• QUIZ

Ch4 L.4 Metamorphic Rock

Bell Work Ch4 L.4• Metamorphism: any process that affects the

structure or composition of a rock in a solid state as a result of changes in temperature, pressure or the addition of chemical fluids

• Plastic deformation: permanent change in shape by bending and folding

• Foliated rock: metamorphic rock that contains parallel layers of flat and elongated minerals

• Contact metamorphism: Magma comes in contact with existing rock, its thermal energy and gases interact with the surrounding rock, forming new rock.

• Regional metamorphism: Formation of metamorphic rock bodies that are hundreds of square kilometers in size

Essential questions

• How do metamorphic rocks form?

• How do types of metamorphic rocks differ?

Metamorphic rock formation• Metamorphism: any

process that affects the structure or composition of a rock in a solid state as a result of changes in temperature, pressure or the addition of chemical fluids.

• Most metamorphic rocks form deep within the Earth’s crust.– Why?

Metamorphic rock formation

• Do not crystallize from magma– Different from igneous rocks

• Do not result from erosion and deposition– Different from sedimentary

rocks

• Rocks change shape because of extreme temperature and pressure– Bend and twist into wrinkly

layers

Temperature and Pressure• Under high temperature

and pressure, rocks behave like bendable plastic, they can bend or fold– Plastic deformation:

permanent change in shape by bending and folding

• Occurs during uplifting events when techtonic plates collide and form mountains

– This is how the texture changes

Temperature and Pressure

• Parent rock: rock that changes during metamorphism. – Temperature depends on composition,

between 150-200 degrees Celcius

Metamorphic rock identification• Classified into two

groups based on texture (foliated and nonfoliated)– Changes in pressure can

align minerals to form layers

• Can look like clastic sedimentary rock

– BUT presence of crystalline minerals in metamorphic rock differentiate it from sedimentary rock

– Rock can also have blocky, interlocking crystals that are uniform in color

Foliated rocks

• Contain parallel layers of flat and elongated minerals

• Layering is because of uneven distribution of pressure during metamorphism

• Examples: phyllite and gneiss

Nonfoliated rocks• Metamorphic rocks that

have mineral grins with a random, interlocking texture– No obvious alignment– Individual crystals look

blocky and approximately equal in size

• Minerals are generally uniform in color

– Different from igneous rock that is generally multicolored (like granite)

• Examples: amphibolite and quartzine

Contact metamorphism

• Magma comes in contact with existing rock, and its thermal energy and gases interact with the surrounding rock, forming new metamorphic rock.

• Can increase crystal size or form new minerals and change rock

Regional metamorphism• Formation of metamorphic rock bodies that are

hundreds of square kilometers in size• Changes in temperature and pressure and

presence of chemical fluids– Can create entire mountain range of metamorphic rock

• Examples: Himalayas (Asia), Appalachian Mountains (US)

– Act on large volumes of rock

Metamorphic rocks

Rock identification lab

Crystals visible?

Single color or multi-colored?

Uniform size grains?

Layers? What kind of rock?

Rock Identification?

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#2

#3

#4

Crystal size? Color? Arrangement? Special?

Igneous Small (extrusive), large (intrusive)

Multi-colored Interlocking (intrusive)

Light (silica), dark (Fe3+,Mg2+)

Sedimentary See pebbles or grains but not really crystals

Uniform color Varies, can have layering

Fossils?

Carbonate?

Metamorphic Yes Varies, can be uniform

Nonfoliated (blocky, interlocking crystals=uniform color)

Folliated (parallel layers of elongated minerals)

HOMEWORK Ch4 L.4

• Vocabulary words on Flash Cards– MEMORIZE FOR QUIZ

• Outline Ch4 L.4

• Lesson review questions– Page 137– Questions 1-8

• QUIZ!!!!