The Rock Cycle-Minerals form rocks

All rocks can be transformed into other rock types

Rocks are divided into 3 categories

Igneous- crystalline- forms as liquid cools

Metamorphic- crystalline-forms as rocks are

heated and squeezed

Sedimentary- non-crystalline- smaller pieces

or chemicals from other rocks

The Rock Cycle-Minerals form rocks

All rocks can be transformed into other rock types

Rocks are divided into 3 categories

Igneous- crystalline- forms as liquid cools

Metamorphic- crystalline-forms as rocks are

heated and squeezed

Sedimentary- non-crystalline- smaller pieces

or chemicals from other rocks

MagmaMagma•• molten rock below Earth's molten rock below Earth'ssurface.surface.

LLava ava •• magma on the Earth's surface. magma on the Earth's surface.

Pyroclastic materialPyroclastic material•• ( (pyro pyro = fire, = fire, clastic clastic = debris)= debris)•• Airborne lava Airborne lava

—— cools as it falls cools as it falls

Igneous formed from Magma and LavaIgneous formed from Magma and Lava

Composition of the magmaComposition of the magma• • Analogous to what makes up the “stew"Analogous to what makes up the “stew"

• • What chemical elements are presentWhat chemical elements are present• • What material has the magma moved

throughWhat material has the magma moved through

Temperature of the meltTemperature of the melt• • Not only how hot, but how long it stays that hot Not only how hot, but how long it stays that hot

• • also relates to pressure of the molten rockalso relates to pressure of the molten rock

Cooling environmentCooling environment• • fast fast vsvs slow slow• • Internal vs ExternalInternal vs External

Water contentWater content

Bowen's Reaction Series- IMPORTANT!

Olivine

Plagioclase(Na-feldspar)BiotiteBiotite

Quartz

PyroxenePyroxene

AmphiboleAmphibole

Muscovite

Plagioclase(Ca-feldspar)

Orthoclase(K-feldspar)

Discontinuous C

ontin

uous

What things might you describe when looking at an igneous rock?

What things might you describe when looking at an igneous rock?

••

Composition of Igneous rocksComposition of Igneous rocksFelsic or Sialic Felsic or Sialic magmamagma

•• Si-rich (> 65%) Si-rich (> 65%) •• rich in K, and Al rich in K, and Al•• little Ca, Fe, and Mg. little Ca, Fe, and Mg.

Intermediate magma Intermediate magma •• between the two extremes in Si between the two extremes in Si content and other atoms. content and other atoms.Mafic Mafic magma magma •• Si - poor (< 35%) Si - poor (< 35%) richer in Ca, Fe, and Mg. richer in Ca, Fe, and Mg.

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magmamagma

AssimilationAssimilation

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Crystal SettlingCrystal Settling

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Magma MixingMagma Mixing

Ways of Changing Magma Composition

Viscosity of Magma/ LavaViscosity of Magma/ Lava

• the resistance of a liquid to flow— —

Viscosity- important for volcanic activity Viscosity- important for volcanic activity

• the resistance of a liquid to flow— high viscosity = thick and stiffhigh viscosity = thick and stiff

— low viscosity = thin and "runny".low viscosity = thin and "runny".

Related to:• • • Mafic

— • Felsic

—

Related to:• amount of water (H2O) in magma• amount of silica (Si) in magma• Mafic

— thin, low viscositythin, low viscosity

• Felsic— thick, high viscosity thick, high viscosity

Igneous Rock Textures- how big are the minerals?

Igneous Rock Textures- how big are the minerals?Phaneritic TexturePhaneritic Texture

•• Visible Mineral Grains Visible Mineral Grains distinguishable as different colored interlockingdistinguishable as different colored interlocking

shapesshapes

Aphanitic TextureAphanitic Texture•• Mineral grains too small to be seen Mineral grains too small to be seen

—— microscopic microscopic

Porphyritic TexturePorphyritic Texture•• Two distinct sizes of mineral grains Two distinct sizes of mineral grains•• Large and Small Large and Small

—— Large = Phenocrysts Large = Phenocrysts—— Small = Groundmass or Matrix Small = Groundmass or Matrix

•• Groundmass Groundmass—— Grains may be either visible or not Grains may be either visible or not

Aphanitic basalt (mafic composition) constitutes the groundmass

Aphanitic basalt (mafic composition) constitutes the groundmass

Porphyritic texturePorphyritic texture

Cooling HistoriesCooling HistoriesMinerals need time and space to growMinerals need time and space to grow

•• More time = Bigger crystals More time = Bigger crystals —— visible mineral grains visible mineral grains

P & T control cooling rates of magmaP & T control cooling rates of magma•• Temp Temp

—— Earth is a good insulator Earth is a good insulator»» holds in heat holds in heat»» keeps out cool keeps out cool

—— Atmosphere is a relatively bad insulator Atmosphere is a relatively bad insulator»» transfers heat easily transfers heat easily

•• Earth has pressure Earth has pressure—— Weight of overlying rocks Weight of overlying rocks—— Magma trying to push up (density) Magma trying to push up (density)—— water vapor (steam), wants to expand water vapor (steam), wants to expand

Intrusive rocksIntrusive rocks•• cool beneath Earth's surface cool beneath Earth's surface•• cool very slowly cool very slowly•• higher P & T higher P & T

—— Phaneritic textures Phaneritic textures

Extrusive rocksExtrusive rocks•• cool on the Earth's Surface cool on the Earth's Surface•• cool relatively fast cool relatively fast•• lower T & P lower T & P

—— Aphanitic textures Aphanitic textures—— Pyroclastic textures Pyroclastic textures

ComplexComplex••

—— Porphyritic textures Porphyritic textures

Categories of Igneous EOFCategories of Igneous EOF

Partially cools below and above Partially cools below and above

GraniteGranite

Basalt porphyryBasalt porphyry

RhyoliteRhyolite

Igneous rock namesIgneous rock names• • determined by texturedetermined by texture

— — size and arrangement of mineral grainssize and arrangement of mineral grains• • AND by mineral compositionAND by mineral composition

— — minerals affect rock color and indicate temperature of creationminerals affect rock color and indicate temperature of creation

A Pegmatite is a very coarse-grained igneous rock.A Pegmatite is a very coarse-grained igneous rock.Crystals are >2 cm, often larger.Crystals are >2 cm, often larger.

Most are granitic, although mafic pegmatites can form.Most are granitic, although mafic pegmatites can form.

PegmatitePegmatite

Feldspar Feldspar mineral mineral graingrain

Quartz mineral Quartz mineral graingrain

Biotite mineralgrainBiotite mineralgrain

Granite & RhyoliteGranite & Rhyolite

RhyoliteRhyolite

GraniteGranite

Phaneritic TexturePhaneritic TextureFelsic magmaFelsic magma

Aphanitic TextureAphanitic TextureFelsic magmaFelsic magma

What are the textures in these two rocks ?What are the textures in these two rocks ?

Andesite & DioriteAndesite & Diorite Phaneritic texture Phaneritic texture-forms from intermediate composition magma-forms from intermediate composition magma

Aphanitic texture Aphanitic texture forms from intermediate composition magma forms from intermediate composition magma

What are the textures in these two rocks ?What are the textures in these two rocks ?

Basalt & Gabbro

»

aphanitic texture aphanitic texture forms from mafic magma forms from mafic magma

phaneritic texture phaneritic texture forms from mafic magma forms from mafic magma

BasaltBasalt

GabbroGabbro

Peridotite- the abundance of Olivine crystals (more than 40%) makes the rock take on a green appearance

VolcanicGlass

Obsidian- a popular rock among paleopeople for tool makingObsidian- a popular rock among paleopeople for tool making

Tuffs & BrecciasTuffs & Breccias- look like sedimentary rock

But they are not….it is volcanic ash that is lithifiedBut they are not….it is volcanic ash that is lithified

How do we tell where the igneous rocks formed and what can we derive from the rocks about the conditions of formation?

BatholithBatholith

Volcanic neckVolcanic neck

Igneous dikeIgneous dike

Igneous SillIgneous Sill

Lava flow

Pyroclastics

Sierra Nevada Batholith- Home to Yosemite National Park and a lot of Granites and Grano-diorites

Sierra Nevada Batholith

Areal extent of the Idaho Batholith- a huge (15,400 square miles) intrusive body of primarily felsic composition (granites) igneous rocks

An igneous dike-

Discordant with surrounding rock

It cuts across other rocks

An igneous dike-

Discordant with surrounding rock

It cuts across other rocks

An igneous sill-

Concordant with surrounding rock

It runs parallel to other rocks

An igneous sill-

Concordant with surrounding rock

It runs parallel to other rocks

Neck

Dike

igneous sillIgneous sill

Necks & Ig DikesNecks & Ig Dikes