Mc connell 2e_ppt_ch07

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Chapter 7: Rocks and Minerals1. Earth Scientists: Nature

Detectives

2. Elements and Atoms: Basic Building Blocks

3. Minerals

4. Igneous Rocks

5. Sedimentary Rocks

6. Metamorphic Rocks

7. The Rock Cycle and Mineral Resources

Earth Scientists: Nature Detectives

The Good Earth, Chapter 7: Rocks and Minerals

Are the rocks on Mars the same as rocks on Earth?

• Understanding rocks enables scientists to• Locate mineral resources (e.g., copper, gypsum)

• Find fossil fuels (e.g., oil, gas, coal)

• Assess the risk from natural hazards such as volcanic eruptions and tsunami

• Learn about Earth processes such as plate tectonics

• Discover the history and origins of other planets

Original ideas about how rocks formed• Neptunism

• Rocks formed in a global ocean when material sank to ocean floor or was precipitated from chemical reactions

• Plutonism• Heat from Earth’s interior melted rocks or

caused them to fuse together

Examination of the production of bricks – manufactured materials with some of the same characteristics as rocks - can provide clues to rock formation processes

Bricks are made from raw materials such as shale or fireclay found at Earth’s surface

Variations in the composition of raw materials produces different brick colors. Red bricks contain more iron.

Where do bricks come from?Raw materials smashed into smaller pieces in crusher.Crushed materials ground to smaller size by grinding wheel.

Resulting particles passed through a series of screens to sort materials by size.Sugar- and flour-sized particles mixed with water and other ingredients.

Small particles mixed with water and other ingredients.Wet mixture forced through brick-shaped form.Wet “bar” cut into smaller brick-sized pieces.

Excess water removed by passing wet bricks slowly through long dryers (200oC).Final stage is “firing” of bricks in kiln at high temperatures (1,100oC).

• Brick making, like rock formation, involves:− Physical disintegration of

raw materials

− Chemical changes

− Thermal effects

And brick making is influenced by the composition of the raw materials, just like the formation of rocks

Go back to the Table of Contents

Go to the next section: Elements and Atoms: The Basic Building Blocks

Elements and Atoms: Basic Building Blocks

ATMOSPHERE HYDROSPHERE

BIOSPHERE GEOSPHERE

• The geosphere is composed of rocks and related materials

Rocks are made of minerals• ~20 common minerals

• Example: The rock granite (below) is composed of 4 key minerals - feldspar, quartz, mica, amphibole - and minor amounts of others.

quartz

feldspar

biotite mica, amphibole

Minerals are made of elements• 8 common elements compose 98% of continental

crust rocks

Minerals are made of elements• Some minerals (e.g., quartz) are composed of just

two elements

• Others (e.g., amphibole) are made up of several elements

• Some elements occur more frequently than others

Atom – smallest particle that retains the characteristics of an element

• Atoms are made up of protons, neutrons, and electrons

• Protons and neutrons in atomic nucleus

• Electrons in surrounding “cloud”

Atom – smallest particle that retains the characteristics of an element

• Atomic number – the number of protons in the nucleus

• Each element has a different number of protons in the atomic nucleus

• Example: Neon has 10 protons, Helium has 2 protons

Atoms may have negative or positive charge if they gain or lose electrons

• Ions – atoms with different numbers of protons (positive) and electrons (negative)

− Silicon may lose 4 electrons +4 (positive charge, Si4+)

− Oxygen can gain two electrons to fill vacant sites

− 8 protons, 10 electrons -2 (negative charge, O2-)

Rocks and Minerals Checkpoint 7.1

Elements bond together to form minerals

• Ionic bonds – balance of negative and positive charges of different ions (e.g., rock salt)

• Covalent bonds – sharing of electrons between elements (e.g., diamond) to achieve a stable atomic structure

• Ionic bonds – balance of negative and positive charges

Sodium atom loses extra electron to yield a positive charge (Na+)

Chlorine ion gains extra electron to produce a negative charge (Cl-)

Ionic bonds – balance of negative and positive charges

• Sodium and chlorine bond together to form rock salt (halite)

− Ionic bond – balance of positive sodium ions with negative chlorine ions (NaCl)

Covalent bonds – sharing of electrons between elements

• Hydrogen and oxygen bond together to form water (H2O)

− Covalent bond – sharing of electrons between atoms ions

Multiple bonds – silicon and oxygen join together by a combination of ionic and covalent bonding

• 4 oxygen and one silicon atom combine by covalent bonds to form a silica tetrahedron (SiO4)

− Tetrahedron has a negative charge (4-) and forms ionic bonds with atoms of other elements

Silicate minerals – contain both silicon and oxygen

• Silicon and oxygen are most common elements in crust

• Silicates are the most common mineral group

− Examples: quartz, feldspar, mica, amphibole

Different types of bonds result in minerals of different strengths

• Type of bonds determine strength of minerals, rocks

− Ionic bonds – Velcro analogy, weaker bonds

− Covalent bonds – Rope analogy, stronger bonds

• Minerals formed with covalent bonds are stronger and more resistant to destructive forces at Earth’s surface

− Silicates form more resistant rocks than most other mineral groups

Silica tetrahedra combine together in different patterns in different silicate minerals

• Minerals with low silica content have simple structures

− Olivine, amphibole

• Minerals with high silica content have more complex structures

− Quartz, feldspar

Rocks and Minerals Conceptest

Which of the following mineral formulae represents a silicate?

A. FeS2

B. KAlSi3O8

C. Fe2O3

D. CaSO4•2H2O

The total electrical charges of the ions of the elements in the mineral olivine must balance. From the data in Table 7.1, which is the most reasonable formula for the mineral?

A. MgSiO2

B. MgSiO4

C. Mg2SiO4

D. Mg4SiO2

Go to the next section: Minerals

Minerals

• Minerals: Naturally occurring, inorganic solids of one or more elements that have a definite chemical composition with an orderly internal arrangement of atoms

Quartz Muscovite Mica Orthoclase Feldspar

Galena Iron Pyrite Halite

Minerals

Mineral Characteristics• Crystal form – the

arrangement of the faces of a crystal to form a particular shape

− Common shapes arePrismsPyramidsNeedlesCubesSheets

Pyramids of calcite

Needles of tourmaline

Minerals

Mineral Characteristics• Cleavage – minerals

break along planes of weakness defined by atomic structure

− Cleavage planes more likely to occur across weak bonds between ions

− Example: mica forms sheets joined by weak ionic bonds

Mica 1 set of cleavage planes

Minerals

Mineral Characteristics• Cleavage – minerals

break along planes of weakness defined by atomic structure

− Example: feldspar has 2 cleavage planes that intersect at 90 degrees

− Example: amphibole has 2 cleavage planes that are not at 90 degrees to each other

Amphibole 2 sets of cleavage planes

Feldspar 2 sets of cleavage planes

Minerals

Mineral Characteristics• Hardness – minerals

ranked by their relative hardness using Mohs Hardness Scale

− Harder minerals can scratch softer minerals

− Softer minerals more likely to break down at Earth’s surface

− More resistant minerals more likely to be preserved (e.g., quartz sand on beaches)

Minerals

Mineral Characteristics• Color – minerals have

characteristic colors

− Dark minerals (black, brown, dark green) Olivine, amphibole,

pyroxene, biotite mica

− Light minerals (white, gray, pink) Quartz, feldspar,

muscovite mica, calcite

− Careful, some minerals have many colors

Minerals

Mineral Characteristics• Other – luster, streak

− Streak – color of mark on unglazed porcelain

− Example: brown streak of hematite (iron mineral)

− Luster: how light reflects from mineral

− Example: metallic luster of iron pyrite

Atoms to rocks: How they fit together

Fill in the concept map to assess your understanding of minerals

Go to the next section: Igneous Rocks

Igneous Rocks

Two types of igneous rocks are classified based on texture and composition

The same magma can form both rock types

1. Volcanic rocks – form when magma rises to Earth's surface• Produces

volcanoes, lava flows, tephra

• Molten rock cools rapidly

Igneous Rocks

Two types of igneous rocks are classified based on texture and composition

The same magma can form both rock types

2. Plutonic rocks – form when magma solidifies below Earth's surface• Produces plutons

that remain hidden until exposed by erosion

• Molten rock cools slowly

Examples of PlutonsBatholith, stock, sill, dike, laccolith

Igneous Rocks

• On the basis of observations only, how could you classify these objects into different groups?

Examine these objects

Igneous Rocks

• Size• Color• Shape• Materials• Orientation• Other?

These objects could be classified on the basis of their:

We can classify igneous rocks using similar features

Igneous Rocks

Texture• Size of crystals of

minerals in igneous rocks depends on rate of cooling of magma− Rapid cooling produces

microscopic crystals

− Slow cooling produces large, visible crystals

• Crystal size interpreted to learn where rocks formed

Slow cooling in plutonic rocks

Rapid cooling in volcanic rocks

Igneous Rocks

Color• Color varies with

silica content (composition)− Silica-rich minerals

such as quartz and feldspar are light-colored

− Silica-poor minerals such as amphibole, biotite mica are dark colored

High silica Intermediate silica Low silica

Igneous Rocks

Silica-rich rocks are composed mainly of minerals quartz and feldspar

Silica-poor rocks are composed mainly of feldspar with iron and magnesium rich minerals (e.g. amphibole, pyroxene, olivine)

Geologists sometimes find a type of igneous rock known as porphyry, which contains both large and small crystals. Which is the best explanation for the formation of this rock? The rock experienced a two-stage cooling process . .

A. . . with initial slow cooling at depth followed by rapid cooling at the surface.

B. . . with initial rapid cooling at depth followed by slow cooling at the surface.

C. . . with initial rapid cooling near the surface followed by slow cooling at depth.

D. . . with initial slow cooling near the surface followed by rapid cooling at depth.

This rock sample corresponds to . . .

A. A low silica volcanic rock.

B. A low silica plutonic rock.

C. A high silica plutonic rock.

D. A high silica volcanic rock.

Igneous Rocks

Rock Types and Magma Types

3 Magma Types• Basaltic magma –

partial melting parts of asthenosphere

• Andesitic magma – partial melting of mantle rocks (with water)

• Rhyolitic magma - melting of parts of continental crust

Each magma type may produce two rocks – one volcanic, one plutonic

Igneous Rocks

• More viscous, high silica magma likely to cool below surface to form plutonic igneous rocks (e.g., granite)

Rock Types and Magma Types

• Less viscous, low silica magma likely to reach surface to form volcanic igneous rocks (e.g., basalt)

Granite batholiths, Sierra Nevada Mountains, California

Basalt lava, Hawaii

Name these igneous rocks and explain the reasons for your choices.

Complete the table by identifying which of the characteristics are present in volcanic and/ or plutonic igneous rocks.

Crystallization of silicate minerals from magma.

Rocks and Minerals

Checkpoint 7.12Finish the partially filed in concept map for igneous rocks by filling in the blanks with appropriate terms. Three of the terms are magma, basalt and plutonic rocks.

Go to the next section: Sedimentary Rocks

Sedimentary Rocks

Sedimentary rocks form as horizontal layers (beds)− identified based on composition, thickness− oldest beds at bottom, youngest at top

Sedimentary Rocks

Three types of sedimentary rocks • Clastic, Chemical, Biochemical

− Identified by materials that make up the rock and/or the process by which they formed

Sedimentary Rocks

• Composed of rock and mineral fragments

− Most common type of sedimentary rock

Clastic Sedimentary Rocks

• 3 stages of formation− Generation

− Transportation

− Lithification

Sedimentary Rocks

1. Generation− Physical and chemical

breakdown of any rock at Earth’s surface (weathering) to form sediment

− Sediment = rock and mineral fragments

− Sediment classified by grain size Clay Silt Sand Gravel

Increasing grain size

Sediment generated by weathering of Himalayas and transported in rivers

Sedimentary Rocks

2. Transportation− Erosion Sediment

moved from place of origin by streams, wind, glaciers

− Size of transported grains depends on velocity of transport medium

− Erosion produces characteristic landscapes

Sediment (dust) transported by prevailing winds from Africa toward the Atlantic Ocean

Sedimentary Rocks

3. Lithification− Sediment deposited when

velocity of transport medium decreases

− Larger grain sizes deposited first, finest grains remain in suspension and are deposited last

− Over time, sediment is slowly compacted and grains are cemented together to form a new rock (lithification)

Deposited sediment of contrasting grain sizes.

Sedimentary Rocks

Clastic Sediment and Clastic Sedimentary Rocks− Rock names reflect grain size

Mudstone, Shale made of clay, silt-sized grains Sandstone composed of sand-sized particles Conglomerate made of gravel and larger fragments

Sandstone composed of quartz grains of similar sizes.

Conglomerate composed of gravel-sized rock fragments

Sedimentary Rocks

Clastic Sediment and Clastic Sedimentary Rocks− Rock names reflect grain size (see Table 7.5)− Transportation process sorts grains so deposits may have

characteristic grain size (e.g., sand on a beach)

Sedimentary Rocks

Clastic Sediment and Clastic Sedimentary Rocks• Transportation process sorts grains so deposits

may have characteristic grain size (e.g., sand on a beach)

• Sedimentary rocks hold clues to the environment where they were formed:− Example: river channels

High velocity flow in floods - gravels (conglomerate) Moderate speed flow – sand (sandstone) Slow flow - muds (shale)

Examine the diagram. Weathering, transportation, and deposition can occur during steps:

A. 1, 2, 3

B. 3, 5, 7

C. 2, 4, 8

D. 4, 5, 6

Rocks and Minerals Checkpoint 7.14What observations can you make about the grain size and arrangement of these clastic sediments that would help determine their origin?

Sedimentary Rocks

• Form when minerals precipitate (crystallize) from a solution as a result of changing physical conditions− Solutions = fresh

water in lakes, groundwater or seawater

− Changing conditions commonly = increased temperatures (evaporation)

Chemical Sedimentary Rocks

Salt deposited on floor of ancient Lake Bonneville, Utah

Sedimentary Rocks

• Can be readily dissolved in water and transported to oceans

• Rocks are typically indicative of shallow, coastal marine conditions in geologic past− Termed evaporites

as most form by precipitation due to evaporation

Chemical Sedimentary Rocks

Salt deposited on floor of ancient Lake Bonneville, Utah

Sedimentary Rocks

• Link the biosphere and geosphere

• Form due to actions of living organisms that cause minerals to be extracted from solution

• From the remains of dead organisms

Biochemical Sedimentary Rocks

Sedimentary Rocks

• Form due to actions of living organisms that cause minerals to be extracted from solution− The mineral calcite

is present in the rock limestone formed by coral organisms that build tropical reefs

Coral reef formed in shallow, tropical sea

Sedimentary Rocks

• May form from the remains of dead organisms− Coquina limestone

formed from broken shell fragments

− Coal carbon-rich rock formed from compacted plant remains

Coal seam, Wyoming

Coquina

Sedimentary Rocks

• May form from the remains of dead organisms− Chalk formed from

billions of coccoliths, round plates of calcite from microscopic (clay-sized) coccolithophore organisms

− Chalk is a type of limestone

Sedimentary Rocks

• May form from the remains of dead organisms− Coccolithophores live

in cold oceans

− Reflect sunlight to change water color

− Chalk indicates specific marine conditions in geologic past

Use the Venn diagram to compare and contrast chemical and biochemical sedimentary rocks. Identify at least seven characteristics.

Sedimentary Rocks and Fossil Fuels

− Form from buried organic-rich sediments.

− Chemical reactions convert organics with increased pressures and temperatures of 50-100 ºC.

− Over time (Myrs), oil and gas can form.

− Oil and gas may be trapped to form hydrocarbon reservoirs.

World is heavily dependant on oil and natural gas

Sedimentary Rocks and Coal

− Form from buried plants.

− Coal type (rank) depends on organic content of parent material, burial depth and heat.

− Over time (Myrs), coal can form.

− Lignite (low grade); bituminous (medium); anthracite (high).

US has some of the largest coal reserves in the world.

Go to the next section: Metamorphic Rocks

Metamorphic Rocks

Metamorphism • Changes in mineral composition and texture

that can occur in any solid rock

• Changes due to increasing temperature and/or pressure and/or the presence of fluids.− Temperatures high enough to promote chemical

reactions but not high enough to cause melting Approximately 200oC 1100oC, depending on rock

type and conditions Similar temperatures found deep in crust or near

magma chambers

Metamorphic Rocks

Two types of metamorphism1. Contact metamorphism• Changes due to

increases in temperature where rocks come in contact with heat source (e.g. magma chamber)− Example: limestone

around a magma chamber is baked by the heat to form marble

Marble (above) and limestone have similar composition but marble typically has a larger grain size

Metamorphic Rocks

Two types of metamorphism2. Regional metamorphism

Foliation is produced when tabular minerals grow perpendicular to the direction of pressure.

• Increased heat and pressure associated with associated with plate tectonic processes that form mountains− Increased pressures and

temperatures cause tabular minerals to take on a preferred orientation, foliation, perpendicular to direction of pressure

Metamorphic Rocks

foliation

Unmetamorphosed, non-foliated original rock (granite) with random distribution of minerals

Metamorphic rock (gneiss) with foliation illustrates parallel alignment of minerals

Increased pressures and temperatures cause tabular minerals to take on a preferred orientation, foliation, perpendicular to direction of pressure

Metamorphic Rocks

Two types of metamorphism

2. Regional metamorphism• Higher temperatures and

pressures yield more intense metamorphism

− Grain size increases with degree of metamorphism (metamorphic grade)

− Rock names vary with grain size

The conversion from bread to toast can be seen as an analog for the formation of a metamorphic rock by:

A.Contact metamorphism

B.Regional metamorphism

Complete the table by identifying which of the characteristics are present in rocks formed by contact and/or regional metamorphism.

Contact versus Regional Metamorphic Rocks Checkpoint 7.19

Use the Venn diagram to compare and contrast metamorphic rocks formed by contact and regional processes. Add at least eight items to the diagram.

Go to the next section: Rock Cycle and Mineral Resources

The Rock Cycle and Mineral Resources

• Rock cycle links igneous, sedimentary, and metamorphic rocks together. − Any rock can become any other rock under

the appropriate conditions.

Cooking an egg could be seen as an analog for the formation of :

A. Igneous rock.

B. Sedimentary rock.

C. Metamorphic rock.

Concrete is formed by adding cement and water to a mixture of sand and gravel. This could be seen as an analog for the formation of what type of sedimentary rock?

A. Clastic rock.

B. Chemical rock.

C. Biochemical rock.

The diagram illustrates the rock cycle. Match the letters below to the blank ovals on the diagram. (Note: some letters are used more than once.)

A. Cementation and compaction (lithification)B. Heat and PressureC. Weathering, transportation, depositionD. Cooling and solidificationE. Melting

Mineral Resources

• Mineral resources result from specific geologic processes associated with formation of rocks. − Can result from chemical reactions driven by changing

temperatures and movement of fluids through rocks.

Mineral Resources

• Mineral resources result from specific geologic processes associated with formation of rocks. − Can result when minerals crystallize at different temperatures.

platinum

Mineral Resources

• Mineral resources result from specific geologic processes associated with formation of rocks. − Can result from concentration of various types of rocks and

minerals during erosion, transportation and deposition.

View of the Stullwater Mine, Nye, MT where rocks are collected for making lunar regolith simulant.

Credit: U.S. Geological SurveyDepartment of the Interior/USGSU.S. Geological Survey/photo.

Rocks and Minerals Concept Map

Complete the concept map to evaluate your understanding of the interactions between the earth system and rocks and minerals.

Label as many interactions as you can using information from this chapter.

The End

Mc connell 2e_ppt_ch07

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