RocksCh. 6

How Rocks Form ch. 6 sec. 1

What is a Rock?• What is a rock?– a solid made of 1 or more minerals• also can contain organic matter ex. Coal

• In which of Earth’s layers (crust, mantle, core) are rocks found?– crust & mantle

BrainPop 3 Types of Rocks

What is a Rock?• What are the 3 types of rock found in Earth’s crust?– igneous– sedimentary– metamorphic

• How do we classify these 3 types of rocks?– according to how they formed

• igneous– cooling & hardening of hot, molten rock (magma)

• sedimentary– compaction & cementing of layers of sediments (rock fragments, plant &

animal remains, minerals that settle out of solution onto lake/ocean bottoms, or water that evaporates & leaves behinds minerals)

• metamorphic– effect of heat & pressure on other rocks BrainPop 3 Types of Rocks

The Rock Cycle

• What is the rock cycle?– gradual & continuous process that causes rocks

to change from one form to another

• What causes the rock cycle?– interactions between water, air, land

Rock Cycle Movie

The Rock Cycle ESRT pg. 6

1. Heat & pressure/ “metamorphism” metamorphic rock

2. Melt to form magma which solidifies igneous rock

3. Weathering & erosion form sediments which are deposited, buried, compacted, & cemented sedimentary rock

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2

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What Can Happen to Igneous Rocks?

1. Heat & pressure/ “metamorphism” metamorphic rock

2. Melt to form magma which solidifies igneous rock

3. Weathering & erosion form sediments which are deposited, buried, compacted, & cemented sedimentary rock

1 2

3

What Can Happen to Sedimentary Rocks?

What Can Happen to Metamorphic Rocks?1. Heat & pressure/ “metamorphism” new metamorphic rock

2. Melt to form magma which solidifies igneous rock

3. Weathering & erosion form sediments which are deposited, buried, compacted, & cemented sedimentary rock

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2

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Igneous Rocks ch. 6 sec. 2

Igneous Rock Formation• How are igneous rocks classified?–By mineral composition & texture

• What do igneous rocks form from?–molten rock (magma/lava) or volcanic ash• What happens as the material cools?– crystals grow & interlock

» rate affects size of crystals

Igneous Rock Formation Movie

• How can we classify the magma/lava that forms igneous rocks?– felsic• large amounts of silica (& aluminum)

– small amounts of calcium, iron, magnesium

• thick, sticky, slow-moving (high viscosity)• low density• typically forms light-colored minerals

–mafic• large amounts of iron & magnesium

– Small amounts of silica

• thinner, runnier (less viscous)• high density• typically forms dark-colored minerals

Igneous Rock Formation

Igneous Rock Formation• What are the 2 types of igneous rocks?– intrusive & extrusive

• How do intrusive igneous rocks form?– form from magma inside Earth• cools slowly

– How does that affect the crystal texture (size)?» medium to coarse (easily seen)

• How do extrusive igneous rocks form?– form from lava (or ash) that has exited Earth• cools quickly

– How does that affect the crystal texture (size)?» glassy (no crystals) to fine (not easily seen)

• can be vesicularIgneous Rock Formation Movie

Igneous Rock Descriptions• How do we group igneous rocks into different

“families”?– according to mineral composition

• How can we recognize/ID specific igneous rocks?– color• determined by mineral composition

– texture• size & arrangement of crystals

• Granite Family/Felsic Rocks–What is the composition of felsic magmas?• silica (& aluminum)

– thick, sticky, slow-moving (high viscosity)

–What minerals are typically found in felsic rocks?• quartz, feldspar, mica, amphibole/hornblende

–What are other common characteristics of felsic rocks?• light color• low density

– Examples:• pegmatite, granite, obsidian, pumice, rhyolite

Igneous Rock Descriptions

• Gabbro Family/Mafic Rocks–What is the composition of mafic magmas?• iron and magnesium-rich (silica poor)

– thinner, runnier (less viscous)

–What minerals are typically found in mafic rocks?• pyroxene, olivine, plagioclase feldspar (amphibole &

biotite mica)–What are other common characteristics of mafic

rocks?• dark color• high density

– Examples:• gabbro, basalt, diabase, basaltic glass, scoria

Igneous Rock Descriptions

Igneous Rock Descriptions• Diorite Family/Intermediate Rocks–What is the composition of intermediate

magmas?• neither felsic or mafic… has characteristics of both

–What are other common characteristics of mafic rocks?• intermediate color–medium grays & greens

» darker than felsic, lighter than mafic

• medium density– Examples:• diorite & andesite

Identifying Igneous Rocks

Igneous IntrusionsLaccolith Volcanic neck

Sill

Volcano

Batholith

Stock

Dike

• Where are most sedimentary rocks found?– covering the surface of Earth’s crust

• In general, how do sedimentary rocks form?– compaction & cementing of layers of sediment

• How are sedimentary rocks classified?– by 3 basic formation processes

• What are the 3 major types of sedimentary rocks?– clastic– chemical– organic

Sedimentary Rocks ch. 6 sec. 3

Formation of Sedimentary Rocks

Clastic Sedimentary Rocks• How are clastic sedimentary rocks formed?–weather forms fragments of rock (sediments)• Usually eroded (transported) by running water

– sediments are deposited• layer after layer as the water slows down– sorted by largest sediments first, smallest last

» Why?

– compacted• as layers pile up• cemented together by minerals (dissolved in water)– cement influences color (silica, calcite, iron oxide, clay)

Deposition & Sorting of Sediments

•If given velocity, see where intersects w/ line on graph…. • look to left/right to find largest particle size that the water

can carry (& all sizes below)•If given particle size, see where intersects w/ line on graph….• look down to see lowest velocity at which that particle size

can be carried

• Smallest to largest– silt & clay particles shale/siltstone

– sand particles sandstone

–mixed particles conglomerate/ breccia

Clastic Sedimentary Rocks areClassified by Particle Size

• How are chemical sedimentary rocks formed?–when minerals precipitate (fall out) of water• What cause mineral precipitation?– evaporation

» sea or lake dries up leaving behind minerals that were dissolved in water

– chemical action» dissolved ions combine to form new minerals

Chemical Sedimentary Rocks

• Examples:– Rock Salt

– Rock Gypsum

– Limestone (travertine)

Chemical Sedimentary Rocks

• How are chemical sedimentary rocks formed?– from sediments consisting of the remains of

plants and animals• Examples of organic sedimentary rocks– limestone (& coquina)– coal

Organic Sedimentary Rocks

• Shells Fossil limestone

Organic Sedimentary Rocks

• Plant remains coal

anthracitebituminouspeat lignite

Organic Sedimentary Rocks

Features of Sedimentary Rocks• stratification• fossils• ripple marks• mud cracks• nodules• concretions• geodes

Identifying Sedimentary Rocks

• In general, how do metamorphic rocks form?– formed from “parent rock” that has undergone

metamorphism• pressure & heat– Earth’s internal heat–weight of overlying rock– deformation of rock as mountains build

• moisture– hot liquids (& gases) from magma that react with minerals

Metamorphic Rocks ch. 6 sec. 4

Formation of Metamorphic Rocks

• How do metamorphic rocks compare to parent rocks?–may resemble parent rock–may have a chemical composition, texture, or

internal structure that differs from parent rock• minerals may be enlarged or reformed• new minerals may appear• rock may become more dense & less porous (less

“empty” space)

Formation of Metamorphic Rocks

Metamorphic Processes• What are the 2 basic types of metamorphism?– regional– local

Metamorphic Processes• What is regional metamorphism?– Large-scale• intense heat & pressure (ex. mountain building)• pressure greater in one direction minerals align in layers

(perpendicular to force)• can cause folding of rock layers

Limestone

Marble

gneissschistphylliteslateshale

Lime

quartzite

sandstone

• What is local metamorphism?–occurs over smaller, more

distinct areas than regional– two types• contact– hot magma “bakes” rock

• deformational (dynamic)– low temperature, but high

pressure» areas of stress & friction

• ex. plate boundaries

– changes to texture & structure of minerals (not composition)

Metamorphic Processes

• description & ID usually based on texture, grain size, mineral content, & parent rock

• 2 main types– foliated• mineral alignment (due to pressure)– often different colored bands (“banding”)–may look scaly– often split along parallel layers

–non-foliated• don’t show mineral alignment or banding• look crystalline (sparkly or sugary)

Metamorphic Rock Descriptions

Foliated Metamorphic Rocks: Examples

granite gneiss

shale slate phyllite schist

(Extreme Metamorphism)

Non-foliated Metamorphic Rocks: Examples

• Limestone marble

• Sandstone quartzite

• Conglomerate metaconglomerate

Identifying Metamorphic Rocks