RocksRocksSection 1Section 1

The Rock CycleThe Rock Cycle

RocksRocksA rock is a coherent aggregate of A rock is a coherent aggregate of

minerals - a physical mixture.minerals - a physical mixture.Three categories of rock:Three categories of rock:

IgneousIgneousFormed from cooling and Formed from cooling and

crystallization of magma or crystallization of magma or lavalava

SedimentarySedimentaryFormed from preexisting Formed from preexisting

rocks subjected to rocks subjected to weathering and erosionweathering and erosion

MetamorphicMetamorphicFormed from preexisting Formed from preexisting

rock transformed by heat, rock transformed by heat, pressure, or chemical fluidspressure, or chemical fluids

Rock—a mixture of minerals, volcanic Rock—a mixture of minerals, volcanic glass, organic matter, or other materialglass, organic matter, or other material

The Rock Cycle—model showing processes The Rock Cycle—model showing processes that create and change rockthat create and change rock– Sedimentary rock can be changed by heat and Sedimentary rock can be changed by heat and

pressure into metamorphic rockpressure into metamorphic rock– Metamorphic rock can melt and cool to form Metamorphic rock can melt and cool to form

igneous rockigneous rock– Igneous rock can be broken into fragments that Igneous rock can be broken into fragments that

may later form sedimentary rockmay later form sedimentary rock

Rock Cycle Rock Cycle

Conservation of matter—rock cycle Conservation of matter—rock cycle never destroys elements of rocks but never destroys elements of rocks but merely redistributes themmerely redistributes them

James Hutton recognized the rock James Hutton recognized the rock cycle in 1788 by observing Siccar cycle in 1788 by observing Siccar Point, ScotlandPoint, Scotland

RocksRocksSection 2Section 2

Igneous RocksIgneous Rocks

Igneous rocks form from magma Igneous rocks form from magma found deep under Earth’s surface.found deep under Earth’s surface.– Magma reaching the surface flows from Magma reaching the surface flows from

a volcano as lavaa volcano as lava– Magma trapped below the surface forms Magma trapped below the surface forms

large-grained intrusive igneous rock large-grained intrusive igneous rock when it cools.when it cools.

– Magma cooling at or near Earth’s Magma cooling at or near Earth’s surface forms small-grained extrusive surface forms small-grained extrusive igneous rockigneous rock

Magma to Igneous RockMagma to Igneous Rock

The mineral makeup of igneous rock The mineral makeup of igneous rock is dependent on the chemical is dependent on the chemical composition of the magma from composition of the magma from which it crystallizes.which it crystallizes.

Three types of magma:Three types of magma:– BasalticBasaltic– AndesiticAndesitic– GraniticGranitic

Basaltic igneous rocks are dark-Basaltic igneous rocks are dark-colored and dense.colored and dense.– Contain iron and magnesium but very Contain iron and magnesium but very

little silicalittle silica– Basaltic lava flows freely from a volcanoBasaltic lava flows freely from a volcano

Granitic igneous rocks are lower Granitic igneous rocks are lower density and lighter color.density and lighter color.– Contain more silica and less iron and Contain more silica and less iron and

magnesiummagnesium– Granitic magma is thick and stiffGranitic magma is thick and stiff

Andesitic rocks have a more Andesitic rocks have a more balanced composition of minerals balanced composition of minerals and density than basaltic or granitic and density than basaltic or granitic rocks.rocks.

Crystal size, large or small, can help Crystal size, large or small, can help identify an igneous rock as intrusive identify an igneous rock as intrusive or extrusiveor extrusive

Volcanic glass rocks cool so quickly Volcanic glass rocks cool so quickly that few crystals formthat few crystals form

Some rocks have holes formed Some rocks have holes formed around once-trapped air and other around once-trapped air and other gasesgases

Igneous Rocks Are Classified by Igneous Rocks Are Classified by Their TextureTheir Texture

Rate of cooling determines crystal size:Rate of cooling determines crystal size: Slow rate promotes the growth of fewer Slow rate promotes the growth of fewer

but larger crystals (coarse-grained).but larger crystals (coarse-grained). Fast rate forms many small crystals Fast rate forms many small crystals

(fine-grained).(fine-grained). Very fast rate forms glass (i.e., no Very fast rate forms glass (i.e., no

crystals).crystals).

RocksRocksSection 3Section 3

Metamorphic RocksMetamorphic Rocks

Metamorphic RocksMetamorphic Rocks produced from:produced from:

Igneous rocksIgneous rocks Sedimentary rocksSedimentary rocks Other metamorphic rocksOther metamorphic rocks

Metamorphism is “changed Metamorphism is “changed rock”; the transition of one rock rock”; the transition of one rock into another by temperatures or into another by temperatures or pressures different from those in pressures different from those in which it formed.which it formed.

Metamorphic rocks—changed by Metamorphic rocks—changed by temperature, pressure, and hot fluidstemperature, pressure, and hot fluids– Heat and pressure result from one Heat and pressure result from one

layer of rock on top of another layer of rock on top of another layer.layer.Sometimes temperature and pressure Sometimes temperature and pressure

are great enough to melt rock, are great enough to melt rock, forming magmaforming magma

Sometimes pressure flattens mineral Sometimes pressure flattens mineral grains in rocks without melting themgrains in rocks without melting them

Agents of MetamorphismAgents of Metamorphism Heat is the most important agent.Heat is the most important agent.

— Recrystallization results in new, Recrystallization results in new, stable mineralsstable minerals

Two sources of heat:Two sources of heat:— Heat from magma (contact Heat from magma (contact

metamorphism) metamorphism) — An increase in temperature with An increase in temperature with

depth due to the geothermal depth due to the geothermal gradient (burial metamorphismgradient (burial metamorphism))

Agents of MetamorphismAgents of Metamorphism Pressure (stress):Pressure (stress):

—Increases with depthIncreases with depth—Confining pressure applies Confining pressure applies

forces equally in all directionsforces equally in all directions—Rocks may also be subjected to Rocks may also be subjected to

differential stressdifferential stress——unequal unequal stress in different directionsstress in different directionsLeads to foliationLeads to foliation

As pressure and temperature continue to As pressure and temperature continue to increase over time, one type of rock can increase over time, one type of rock can change into several different metamorphic change into several different metamorphic rocks.rocks.

– Hot, water-rich fluids can move through Hot, water-rich fluids can move through rock, chemically changing it.rock, chemically changing it.

Classification of metaphoric rocks—by Classification of metaphoric rocks—by composition and texturecomposition and texture– Foliated texture – minerals grains flatten and Foliated texture – minerals grains flatten and

line up in parallel layers or bands.line up in parallel layers or bands.– Non foliated texture – mineral grains grow and Non foliated texture – mineral grains grow and

rearrange but do not form layers.rearrange but do not form layers.

RocksRocksSection 4Section 4

Sedimentary RocksSedimentary Rocks

Sedimentary rocks—mostly found on Sedimentary rocks—mostly found on the exposed surface of the Earththe exposed surface of the Earth– Rock fragments, mineral grains, and bits Rock fragments, mineral grains, and bits

of plants and animal remains moved by of plants and animal remains moved by wind, water, ice or gravity are called wind, water, ice or gravity are called sedimentssediments

– Sedimentary rocks form in layersSedimentary rocks form in layers Sedimentary rocks—classified by Sedimentary rocks—classified by

what they were made of and how what they were made of and how they were formedthey were formed

Detrital sedimentary rocks—made Detrital sedimentary rocks—made from broken fragments of other rocksfrom broken fragments of other rocks– When layers of small sediments stick When layers of small sediments stick

together because of pressure, together because of pressure, compaction occurscompaction occurs

– When water and other minerals move When water and other minerals move through open spaces between larger through open spaces between larger sediments, gluing them together, sediments, gluing them together, cementation occurs.cementation occurs.

– Detrital rocks often have a granular Detrital rocks often have a granular texturetexture

– Rocks are named according to size and Rocks are named according to size and shape of sedimentsshape of sedimentsSediment size can be large like gravel or Sediment size can be large like gravel or

small like claysmall like claySediments can be well-rounded or have Sediments can be well-rounded or have

sharp edgessharp edges Chemical sedimentary rocks—non-Chemical sedimentary rocks—non-

clastic rocks formed when dissolved clastic rocks formed when dissolved minerals came out of the solutionminerals came out of the solution– Limestone forms from calcite, which was Limestone forms from calcite, which was

calcium carbonate in solutioncalcium carbonate in solution– Rock salt forms from halite, which was Rock salt forms from halite, which was

salt in solutionsalt in solution

Organic sedimentary rocks—made Organic sedimentary rocks—made from remains of once-living plants or from remains of once-living plants or animalsanimals– Chalk—made of microscopic calcite-shell Chalk—made of microscopic calcite-shell

remains of animalsremains of animals– Coal—made of plant remains, chemically Coal—made of plant remains, chemically

changed by microorganisms and changed by microorganisms and compacted over millions of yearscompacted over millions of years

Rock cycle—a continuous and Rock cycle—a continuous and dynamic processdynamic process