Banded Iron Formation

Rocks and the Rock Cycle

Rocks

Big rocks into pebbles,

Pebbles into sand.

I really hold a million, million

Rocks here in my hand. Florence Parry Heide

How are rocks formed?

How do rocks change?

How are rocks treasured?

Volcanoes

Earthquakes

Heat and earth’s movement change what rocks

look like and change landforms. What landforms

do volcanoes and earthquakes form?

Earthquakes

Water Wind

Ice Erosion and weathering change rocks and

land formations. What changes do you see?

Water

Wind

Ice

What are the main parts of the rock cycle

that you should know?

Man changes rocks

in many ways. Look for

ways that rocks are used.

Rocks

A rock is a naturally occurring, solid mixture of minerals.

Fig 4.1

Three Classes of Rocks

• Igneous (made by “fire”) - Solidified from

molten rock (magma & lava).

• Sedimentary - Deposited and buried at Earth’s

surface.

• Metamorphic (“changed form”) - Transformed

from pre-existing rocks under high pressure

and temperature.

Three Classes of Rocks

Fig 4.2

Igneous Rock

Igneous rock comes from cooled magma

and lava. What are some names of igneous

rock?

Sedimentary Rock

Pieces of rock erode and pile up in layers

to create sedimentary rocks. This is where

you can find fossils. What other types of

rock are sedimentary rocks?

Metamorphic Rocks

Metamorphic rock are sedimentary or igneous

rocks that have been changed under pressure

while deep in the crust of the earth. What kinds

of rocks are metamorphic rock?

Distinguishing Characteristics

• Mineralogy – The different minerals that make

up the rock and their relative proportions

• Texture - Sizes, shapes, and arrangements of

minerals within the rock:

– Course-grained

– Fine-grained

– Foliated (layered)

All are clues to a rock’s origin and history.

Igneous Rocks

• Minerals crystallize out of melted rock from deep within Earth’s crust or mantle

– High temperatures, up to 700 C or more!!

– Crystal size depends on cooling rate.

• Intrusive rocks cool slowly within deep magma chambers:

– Large, coarse crystals form

• Extrusive rocks cool rapidly at (or near) the surface of the earth:

– Fine-grained, often “glassy”

Igneous Rocks

Common in volcanic areas & plate boundaries

Igneous

High melting temperatures

- Abundance of silicon and

oxygen

Sedimentary Rocks

• Loose particles (sand, silt, ocean shells) accumulate on shorelines, basins, rivers, etc.,

– Clastic Sediments

• Minerals precipitate from dissolved chemicals in water

– Chemical & Biochemical Sediments

• All are the products of Weathering - that breaks up and decays rocks, and Erosion - that transports from source to point of deposition

Weathering & Erosion

Transport

Deposition

Basement Rocks

Chemical: Limestone

Common along passive margins

(and other basins)

Clastic: Sandstone

Sedimentary

Silicates (esp. Clays)

Carbonates

Sulfates & Halides

(Precipitates)

Metamorphic Rocks

• High temperatures and pressures deep inside the Earth cause changes in mineralogy, texture, and composition

– Changes take place in Solid State by recrystallization and chemical reactions

– Temperatures greater than 250 , less than 700

Metamorphic Rocks Common at collisional plate

boundaries

Metamorphic Rocks

Fig 4.6 • Foliated - Layers defined by

– Alignment of minerals (micas & clays)

– Alternating bands of mineral types

• Indicative of high pressures and deformation during formation

• Not Foliated

• Distinct low- pressure minerals

Metamorphic

Silicates predominate

-Due to silicate

source rocks

Characteristic Metamorphic Minerals

For more images: http://skywalker.cochise.edu/wellerr/mineral/

kyanite

andalusite

sillimanite

staurolite garnet

Rock Types

Sedimentary rocks are most abundant near Earth’s surface

- poor preservation

Igneous and

Metamorphic rocks make up

most of the crustal volume

- limited exposure!

Outcrops

Sediments make up only 5% by

volume

Sediments make up

75% surface area

Outcrop

Exposures

-Measure orientation & thickness

- Record regional

patterns on geologic

maps

- Infer what lies below

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Rock Types

How can we sample what lies below the

surface? Ocean

Drilling

Continental Drilling

Outcrops

Sediments make up only 5% by

volume

Sediments make up

75% surface area

By drilling: e.g., Oceans - all over, - passive margins - rifting & spreading - convergent - hot spots Continents - San Andreas Fault - Chelungpu Fault - Hawaii

The Rock

Cycle

-Melting & Intrusion

-Solidification of melt

-Mountain Building

-Uplift & Exposure

-Weathering

-Erosion & Transport

-Deposition & Burial

-Metamorphism

-Melting & Intrusion

(a) The Rock Cycle

Convergent Plate

Boundary

-Subducting slab

-Mantle melting

-Buoyant rise of melt

(b) The Rock Cycle

Convergent Plate

Boundary

-Solidification of melt

-Mountain building

(c) The Rock Cycle Precipitation &

Weathering

-Moisture laden air

-Precipitation and run-off

-Freezing & thawing

(d) The Rock Cycle

Sediment Transport

to Oceans

-Deposition

-Burial & lithification

-Chemical precipitation

(e) The Rock Cycle

Deformation & Metamorphism

-Continental collision (i.e., orogeny)

-Burial & deformation

-Increased pressure & temperature

(a) The Rock Cycle

Convergent Plate

Boundary

-Subducting slab

-Mantle melting

-Buoyant rise of melt

Plate Tectonics & Climate

-Plate tectonics

drives uplift &

subsidence

-Climatic processes

weather & transport

sediment

-Interactions control

the rock cycle