Chapters 5 and 6

Chapters 5 and 6Igneous, Sedimentary, and Metamorphic Rocks..

How are Igneous Rocks formed?

Question of the Day.

Learning Targets

1). You will be able to explain how igneous rocks are formed.

2). You will understand how scientists classify igneous rocks; the difference between intrusive and extrusive igneous rocks.

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Chapter 5: Igneous RocksWHAT IS AN IGNEOUS ROCK?

Igneous Rocks: rocks that are formed from the crystallization of magma or lava

Magma = the molten rock found within the Earth’s crust.

Lava = the molten rock that flows out onto Earth’s surface.

How can Igneous Rocks look so different from each other?


Learning Targets

1). You will understand how scientists classify igneous rocks.

2). You will practice classifying igneous rocks based upon composition as well as crystal size.

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Group Challenge In your lab groups, I want you to separate these igneous rocks into 2 groups.

Take some time and carefully look at each rock for subtle similarities and differences.

Question For Thought…

1). What different types of magma may have formed these rocks?

Igneous RocksTYPES OF IGNEOUS ROCKS WHAT’S THE DIFFERENCE

Extrusive Rocks = fine-grained igneous rocks that cool quickly on Earth’s surface.

Intrusive Rocks = course-grained igneous rocks that cool slowly beneath Earth’s surface. Granite is the most common intrusive

igneous rock

Igneous RocksCOMPOSITION OF MAGMA

Magma is often a slushy mix of molten rock, gases, and mineral crystals

The elements found in magma are the same major elements found in Earth’s crust.

Silica (SiO2) is the most abundant and has the greatest effect on magma characteristics

There are 3 types of Magma 1. Basaltic

2. Rhyolitic

3. Andesitic

How do the liquids we tested in lab resemble the different types of magma?


Three Types of Magma1. Basaltic = 45-55% Silica (SiO2)

a. high in Fe, Mg, Ca, low in K, Nab. Low Viscosity = Easier for this type of magma to flow c. Gas can more easily escape = Less Violent Eruptions

2. Andesitic = 55-65% Silica (SiO2)a. intermediate. in Fe, Mg, Ca, Na, Kb. Intermediate Viscosity = Intermediate Rate of magma flow

3. Rhyolitic magma = 65-75% Silica (SiO2)a. low in Fe, Mg, Ca, high in K, Nab. High Viscosity = More Difficult for this type of magma to flow.c. Gas has a very hard time escaping = Very Violent Eruptions

Types of Magma

Basaltic Magma Made from minerals including olivine, pyroxene, and plagioclase. Basalt is erupted at temperatures between 1100 to 1250° C. Basalt is the most common rock type in the Earth's crust (the outer 10 to 50

km). In fact, most of the ocean floor is made of basalt. Huge outpourings of lava called "flood basalts" are found on many continents.

The Columbia River basalts, erupted 15 to 17 million years ago, cover most of southeastern Washington and regions of adjacent Oregon and Idaho.

Basaltic magma is commonly produced by direct melting of the Earth's mantle, the region of the Earth below the outer crust. On continents, the mantle begins at depths of 30 to 50 km.

Types of Magma

Andesitic Magma Andesite is a gray to black volcanic rock Andesites contain the minerals pyroxene and sometimes olivine. Andesite magma commonly erupts from strato-volcanoes as thick lava flows, some reaching

several km in length. Andesite magma can also generate strong explosive eruptions to form pyroclastic flows and

surges and enormous eruption columns. Andesites erupt at temperatures between 900 and 1100° C. The word andesite is derived from the Andes Mountains, located along the western edge of

South America, where andesite rock is common. Andesite was the main rock type erupted during the great Krakatau eruption of 1883.

Types of Magma

Rhyolitic Magma Low temperature eruptions (750–850ºC) High gas content Very explosive Erupt from Caldera Volcanoes

Igneous RocksORIGINS OF MAGMA PARTIAL MELTING

In lab, most rocks must be heated to temps around 800 – 1200 degrees Celsius before they melt In nature these temps are found in the

upper mantle and lower crust

Not all minerals have the same melting points Because of this not all parts of the rock

melt at the same time

This explains why magma is often a slushy mix of crystals and molten rock

Partial Melting = when some minerals melt at low temps and other minerals remain solid

Igneous RocksCLASSIFYING IGNEOUS ROCKS UNIQUE FEATURES

Mineral Composition There are 3 main groups of igneous

rocks1). Felsic

Light-colored

Have high silica contents

2). Mafic

Dark-colored

Lower silica contents and are rich in iron and magnesium

3). Intermediate

Porphyritic Texture = large, well formed crystals surrounded by finer-grained crystals. Indicates a complex cooling history

where a slowly cooling magma suddenly began cooling rapidly

Group Challenge In your lab groups, I want you to separate these igneous rocks into 3 groups

based upon color.

Group 1: Light Colored Rocks = Felsic Group 2: Medium Color = Intermediate Group 3: Dark Colored Rocks = Mafic

What are the 2 ways scientists tell igneous rocks apart?


Learning Targets

1). You will practice classifying igneous rocks based upon composition as well as crystal size.

You will understand some uses of igneous rocks.

Group Challenge In your lab groups, I want you to visit each station around the room which

will give you some practice identifying characteristics of igneous rocks.

You will have approximately 3 minutes at each station to answer the question inside the box.

EVERYONE from your group must write down the answer.

1). Compare and Contrast: Extrusive and Intrusive Igneous Rocks.2). Explain how the color of igneous rocks can help us determine what they are made of.

Let’s See What You Remember

Learning Targets

1). You will understand some uses of igneous rocks.

2). You will understand how sedimentary rocks are formed.

Igneous RocksORIGINS OF MAGMA PARTIAL MELTING

In lab, most rocks must be heated to temps around 800 – 1200 degrees Celsius before they melt In nature these temps are found in the

upper mantle and lower crust

Not all minerals have the same melting points Because of this not all parts of the rock

melt at the same time

This explains why magma is often a slushy mix of crystals and molten rock

Partial Melting = when some minerals melt at low temps and other minerals remain solid

Igneous Rocks Igneous Rocks as Resources

They are useful for building materials because of their strength and resistance to weathering (granite)

Memory Clue

To show your understanding of igneous rocks and there characteristics, complete memory clues for vocab 1-8.

Cross out ultra-mafic

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Sedimentary RocksFORMATION OF SEDIMENTARY ROCKS

Sediments = pieces of solid material that have been deposited on Earth’s surface by wind, water, ice, gravity, or chemical precipitation

When these sediments get “cemented” together, they form sedimentary rocks Occurs from weathering and erosion

Classified into two groups based on how they form.

1. Clastic

2. Chemical

Clastic Sedimentary RocksClastic sedimentary rock = formed as bits of weathered rock become cemented together.

All kinds of rock are subject to weathering

Many different minerals can make up this group of rocks.

Clays and quartz are the most common.

Classification of Clastic sedimentary rocks is done according to the size of the sediments that make up the rock.

The table contains the major groups of Clastic sedimentary rocks with their characteristics

Clastic Sedimentary Rocks

Name of Rock Sediment Type Texture

Conglomerate gravel - rounded fragments

courseover 2 mm

Breccia gravel - angular fragments

courseover 2 mm

Sandstone sand medium1/16 to 2mm

Siltstone mud fine1/256 to 1/16 mm

Shale mud very fineless than 1/256 mm

Chemical Sedimentary Rocks Chemical sedimentary rocks = form

from dissolved minerals that are precipitated or separated from water. This happens most frequently when water

evaporates leaving the minerals behind.

You can see this process taking place in your own home. The white deposits that form around the faucets in your bathroom or kitchen are from minerals left behind as water evaporates.

The table contains the major groups of chemical sedimentary rocks with some of their characteristics:

Chemical Sedimentary Rocks

Name of Rock Composition Texture

Crystalline Limestone Calcite - CaCo3 corse to fine Crystalline

Fossiliferous Limestone Calcite - CaCo3 visible fragments of shells

Chalk Calcite - CaCo3 microscopic shells and clay

Chert Quartz - SiO2 very fine crystalline

Gypsum Gypsum - CaSO4-2H2O fine to course crystalline

Rock Salt Halite - NaCl fine to course crystalline

Bituinous Coal Organic Matter fine

Sedimentary Rocks

Weathering = the process where the Earth’s crust is continually getting worn away by a set of physical and chemical processes. Chemical Weathering = when minerals in a rock

are dissolved or otherwise chemically changed.

Physical Weathering = when the minerals remain chemically unchanged – they just break off

Erosion = The removal and movement of surface materials from one spot to another.

http://ees.as.uky.edu/educational-materials




Types of Mechanical Weathering1. Frost Wedging Water expands when it freezes - an ice cube is about 9% larger than the volume of the

water before it froze. The expansion of water when it freezes is one of the most effective processes of mechanical weathering.

*Wedging: A fracture (crack) in a rock provides ice with a lot of leverage. When the temperature drops below freezing, the ice exerts force outward on the rock as it grows.

*Freeze/thaw: Each freezing may wedge the fracture open just a tiny amount, so it takes many cycles of freezing and thawing, with water filling the fracture each time, to break off a piece of rock.

Most effective in cold, wet climates in which there are many opportunities for freeze/thaw cycles with water present. High altitudes (mountain ranges) are particularly prone to such temperature changes

Types of Mechanical Weathering2. Exfoliation = peeling of layers

describes sheets of rock peeling off a bare rock face

*Rock type: Exfoliation is most common on rock faces of intrusive igneous rocks such as granite.

3. Thermal Expansion and Contraction Crystals of rock also expand and contract as they

heat and cool Can loosen grains of a rock enough to cause

weathering.

Most Common in Desert Regions Temperature may rise and fall as much as 50 deg

Celsius (90 deg Fahrenheit) from day to night

**Fires: Even more pronounced is the fracturing of rocks that occurs during exposure to forest fires. Under these conditions, temperatures may rise briefly by 200 deg C or more, and exposed rock will expand enough to spall many small pieces off the rock face. Similarly, campfires can cause enough thermal expansion for rocks in a campfire ring to crack loudly, startling any nearby marshmallow roasters.

Types of Mechanical Weathering4. Crystal Growth Salt crystals growing in rock fractures or in the small pores between

sedimentary grains can cause rocks to loosen up and break. Usually this happens when salty water gets into the rocks and later evaporation of the water produces crystallization in the pore or fracture space. by pushing the grains apart.

*Practical Application: For readers who live in cold, snowy climates: be careful how much salt you use to melt ice on your sidewalks, stairways, and driveways. Salt crystal growth is one of the biggest causes of road potholes in the northern United States, and the outdoor stairways leading into many public buildings are in terrible disrepair due to damage from salt crystallization.

Mechanical Weathering5. Tree Roots

Tree root tips are tiny and penetrate easily into fine fractures of rocks.

As the roots grow in diameter, they put stress on the rock that can cause the fractures to expand..

*Where: In terms of climate, this weathering mechanism can occur anywhere that sufficient precipitation exists to sustain tree growth and rocks are exposed near the surface. Tree root wedging can also occur invisibly, beneath a thin layer of soil.

Mechanical Weathering6. Abrasion Rocks breaking or wearing down by

the direct actions of other rocks. The rock falling down the cliff as it

tumbles down and breaks into pieces.

*Where: Abrasion typically is strongest in the harshest environments: cold and wet (glaciers), high elevations (steep terrains), arid regions (wind), etc

Mechanical Weathering Assignment 1). Pick 1 type of mechanical weathering.

2). Write 4 sentences explaining what it is and how it happens.

3). Bring in a real picture that shows your weathering in action.

1). What is a Sediment?


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Chemical Weathering1. Dissolution

Dissolution tears mineral grains apart and carries away the ions (electrically charged atoms or molecules) in solution.

Example: The salt in the ocean all comes from chemical reactions of water with rocks.

Example: Caves in rock are the result of dissolution, usually where the mineral calcite (CaCO3) in limestones has been dissolved by groundwater.

*Acids: Most dissolution in chemical weathering is not performed directly by the water but rather by acids contained in natural waters.

Chemical Weathering2. Oxidation Oxidation is rust Many minerals contain elements

that can undergo oxidation, although iron (Fe) is by far the most common one.

Many outcrops of iron-rich rock have reddish stains from "rusting" due to chemical weathering by reactions with air.

Learning Targets

1). You will see the process of weathering in action.

2). You will understand the differences between chemical and physical weathering.

1). Compare and Contrast (physical) mechanical and chemical weathering.


Learning Targets

1). You will see both processes, chemical and physical (mechanical), of weathering in action.

2). You will understand what happens after weathering to sediments to form sedimentary rocks: processes of deposition and lithification.

3). You will see how sedimentary rocks are grouped.

Sedimentary RocksDEPOSITION AND LITHIFICATION

ANIMATION Deposition = The process of weathered sediments settling out after being moved by erosion.

Lithification = The process that transforms sediments into sedimentary rocks. Sediments are compacted as they are buried

beneath successive layers of sediment and cemented by minerals

Evidence of Past Life During lithification, parts of organisms are

replaced by minerals and turned into rocks.

Bedding = The horizontal layering of sedimentary rocks.

http://gomyclass.com/animations2.html

http://serc.carleton.edu/NAGTWorkshops/geomorph/visualizations/erosion_deposition.html








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What are the 2 types of sedimentary rocks?


Sedimentary RocksCLASSIFICATION OF SEDIMENTARY ROCKS

Clastic Sedimentary Rocks Most common

Formed from loose sediments found on Earth’s crust

3 types

1. Coarse-Grained Clastics Sedimentary rocks consisting of gravel-sized

rock and mineral fragments.

Due to their large mass, these are transported by high-level flows of water

2. Medium-Grained Clastics Sedimentary rocks that contain sand-sized rock

and mineral fragments are medium-grained

3. Fine-Grained Clastics Sedimentary rocks that contain smaller then

sand-sized rock and mineral fragments are fine-grained

What 2 steps come next in the sedimentary rock cycle after weathering?


Metamorphic RocksCAUSES OF METAMORPHISM

Metamorphic Rocks = rocks that change form while remaining solid.

Pressure and temperature increase with depth Temperature and pressure combine to alter

texture, mineralogy, or chemical composition of a rock without melting it.

The high temps required for this ultimately are derived from Earth’s internal heat.

The high pressures are generated by pressure of overlying rocks

Typically occurs at depths between 10 to 30 km where pressure is 6 times greater and temperature is 800 °C greater than at the surface of the earth!

Types of Metamorphic Rock 1. Foliated Metamorphic Rocks –

metamorphic rocks with visible layers or elongated grains of minerals The minerals in these rocks have been

squeezed into parallel layers by intense pressure

2. Non-foliated Metamorphic Rocks – rocks that do not have distinct layers or bands The majority of these rocks are formed

by extreme heat

Examples of Metamorphism:

• Granite turns into Gneiss

• Sandstone turns into Quartzite

• Limestone turns into Marble

• Shale turns into Slate

Metamorphic Rock Cartoon

Rock CycleDEFINITION EXAMPLES

The Rock Cycle = The continuous changing and remaking of rocks.

http://www.passmyexams.co.uk/GCSE/physics/rock-cycle.html

Heat and pressure may change an igneous rock to a metamorphic rock.

Metamorphic rocks can change to other metamorphic rocks, melt and turn into an igneous rock

Metamorphic or Igneous rocks may break into sediments and be eroded, deposited, and lithified make a sedimentary rock.





ROCK CYCLE ANIMATION

http://www.classzone.com/books/earth_science/terc/content/investigations/es0602/es0602page02.cfm





Memory Clue

To show your understanding of sedimentary and metamorphic rocks, complete memory clues for vocab 9-17; aka the rest.

Pre-Lab Work Title: Rock Cycle in Chocolate Lab

Purpose 1: You will understand how one rock type can become another. Purpose 2: You will understand the processes of each rock type: melting,

crystallization, erosion, weathering, deposition, lithification, and metamorphism.

Pre-Lab Questions 1). How do you form igneous rocks?

2). How do you form sedimentary rocks?

3). How do you form metamorphic rocks?

Documents

Chapters 5 and 6