RocksRocks

Are made up of mineralsEx: Granite ----- > 4 minerals

Essential Minerals: always occur in the rock Accessory minerals: sometimes occur

Classify Rocks By How they Form!Classify Rocks By How they Form!

Igneous- Molten Rock cools and hardens Sedimentary – Made from sediments Metamorphic – Rocks Changed by heat and

pressure

High Silica content forms High Silica content forms light-colored rocks (FELSIC).light-colored rocks (FELSIC).

While lower (but only by about 25%) Silica content forms

darker-colored rocks (MAFIC).

THE ROCK CYCLETHE ROCK CYCLE

Rocks are naturally occurring combinations or coherent aggregates of minerals, fossils or other hard materials. They are classified by the way in which they form. The three rock types are: igneous, sedimentary and metamorphic.

All rocks on Earth are locked into a system of cycling and re-cycling known as the ROCK CYCLE. (*)

IGNEOUS ROCKSIGNEOUS ROCKSIGNEOUS ROCKS are “born of

fire”. In other words, they were once molten and upon cooling, the magma (molten rock) crystallized into solid rock. Igneous rocks may form deep inside the Earth or at the Earth’s surface when a volcano erupts. (*)(*)

magma

conduit

Anatomy of a Vol cano

vent lava

land surface

IGNEOUS ROCKS : intrusiveIGNEOUS ROCKS : intrusiveSlow cooling deep beneath the

Earth’s surface allows crystals to grow to large size. These crystals are easily visible and distinguish this group of igneous rocks as INTRUSIVE.

Large Crystals Both large and small crystals

= porphyry (some grow before others begin

Texture size or arrangement of crystals

To get Large: Cools below Earth’s surface

Igneous - IntrusiveIgneous - IntrusiveGRANITE GRANITE is a coarse to medium-is a coarse to medium-

grained rock that forms from the grained rock that forms from the cooling of magma deep within the cooling of magma deep within the Earth light color - felsicEarth light color - felsic

DIORITEDIORITE is very similar to granite, but is very similar to granite, but is distinguished in the hand specimen is distinguished in the hand specimen by the absence of visible quartz.by the absence of visible quartz.

Generally it has a salt and pepper Generally it has a salt and pepper appearance (about ½ black and ½ appearance (about ½ black and ½ white).white).

Igneous RocksIgneous Rocks Rapid cooling near or at

the Earth’s surface, produces many small crystals. This group of igneous rocks is called EXTRUSIVE

Eruption at surface Numerous holes at the

surface

Small mineral crystals Small mineral crystals ex: basaltex: basalt

No mineral crystalsNo mineral crystals ex: obsidian

Top Part of Lava- Top Part of Lava- gases trapped inside of gases trapped inside of hardened lava = scoriahardened lava = scoria

From lava thrown out From lava thrown out

ex: pumiceex: pumice

Igneous - ExtrusiveIgneous - ExtrusiveRhyoliteRhyolite is a fine grained, felsic is a fine grained, felsic

rock that forms from the cooling of rock that forms from the cooling of lava above Earth’s surface lava above Earth’s surface

BasaltBasalt a dark fine grained rock a dark fine grained rock formed from thin to massive formed from thin to massive lava flows (mafic)lava flows (mafic)

Pahoehoe is a type of basalt that forms on the surface of very fluid lava flows

Igneous ReviewIgneous ReviewLavaLava ExtrusiveExtrusive

Through VolcanoesThrough VolcanoesThrough hydrothermal ventsThrough hydrothermal vents

Magma Magma Intrusive/ Intrusive/PlutonicPlutonic- Cools and Crystalizes in Magma Chamber- Cools and Crystalizes in Magma Chamber

L I G H T C O L O R E D F e l s i c

I N T E R M E D I A T E C O L O R E D

D A R K C O L O R E D M a f i c

V E R Y D A R K C O L O R E D U l t r a m a f i c

C O A R S E - G R A I N E D

( Y o u c a n s e e d i f f e r e n t

m i n e r a l s )

G R A N I T E : C a n s e e c r y s t a l s . U s u a l l y g r a y o r p i n k . C a n s e e q u a r t z - g r a y , g l a s s y g r a i n s . C a n s e e f e l d s p a r - p i n k , b u f f , o r w h i t e .

D I O R I T E : C a n s e e c r y s t a l s w i t h s o m e w h a t m o r e l i g h t c o l o r e d f e l d s p a r g r a i n s t h a n d a r k c o l o r e d m i n e r a l s . A m i x o f l i g h t a n d d a r k b u t w i t h n o q u a r t z . S a l t & p e p p e r a p p e a r a n c e .

G A B B R O : C a n s e e c r y s t a l s — l o t s o f f l a t s h i n y c l e a v a g e s u r f a c e s . U s u a l l y b l a c k t o g r e e n i s h b l a c k .

F I N E - G R A I N E D

( Y o u c a n N O T s e e c r y s t a l s , f o r

t h e m o s t p a r t )

R H Y O L I T E : U s u a l l y g r a y , p i n k , p a s t e l . M i g h t s e e s m a l l c l e a r , r e c t a n g u l a r c r y s t a l s . S o m e t i m e s b a n d e d .

A N D E S I T E : L i g h t t o d a r k g r a y . N o r m a l l y h a s s m a l l b l a c k c r y s t a l s

B A S A L T : U s u a l l y b l a c k o r r u s t r e d . M a y h a v e s o m e o r l o t s o f g a s b u b b l e h o l e s , s o m e h o l e s m a y b e f i l l e d . M a y s e e s m a l l g r e e n g r a i n s .

G L A S S Y

O B S I D I A N : B l a c k , r e d , g r e e n , G L A S S

P E R L I T E : U s u a l l y p e a r l y g r a y . M a y c o n t a i n A p a c h e T e a r s .

P U M I C E : L O T S o f g a s b u b b l e h o l e s , v e r y l i g h t w e i g h t , w i l l f l o a t o n w a t e r . A b r a s i v e .

P O R P H Y R I T I C

( 2 g r a i n s i z e s )

A L L C R Y S T A L L I N E I G N E O U S V A R I E T I E S m a y e x h i b i t p o r p h y r i t i c t e x t u r e

F R A G M E N T A L

T U F F : C o m p a c t e d v o l c a n i c f r a g m e n t s g e n e r a l l y l e s s t h a n 4 m m d i a m e t e r ( a s h )

V O L C A N I C B R E C C I A : M i x e d t u f f a n d a n g u l a r l a r g e ( > 3 2 m m d i a m e t e r ) f r a g m e n t s

A G G L O M E R A T E : M i x e d a s h a n d r o u n d e d / s u b - r o u n d e d l a r g e ( > 3 2 m m d i a m e t e r ) f r a g m e n t s

P E R I D O T I T E : C o m p o s e d o f 9 0 -1 0 0 % o l i v i n e P Y R O X E N I T E : C o m p o s e d o f p r e -d o m i n a t e l y p y r o x e n e

A M P H I B O L I T E : C o m p o s e d o f p r e -d o m i n a t e l y a m p h i b o l e s ( s u c h a s h o r n b l e n d e )

C L U E S T O I G N E O U S R O C K S

C O L O R

T E X T U R E

(*)(*)

SEDIMENTARY ROCKSSEDIMENTARY ROCKS

SEDIMENTARY ROCKS are composed of particles derived from pre-existing rocks or by the crystallization of minerals that were held in solutions

Weathering : Rocks are broken into pieces by water, wind or ice

Water – enter cracks, expands and breaks rocks downRain – acid rain dissolves mineralsMovement in Rivers – Collect on the bottom

•Formation – Build very slowly

layers will grow until environment changes

•Formation – Build very slowly

layers will grow until environment changes

Cementation – minerals acting as cement holding sediments together

Compaction – pieces compact due to weight squeezing them together

Precipitation – water evaporates and minerals are left behind

Unusual FormationUnusual FormationChemical Rocks – made up of chemical sediments or

once living thingsOrganic Rocks – made up of remains of living things

Sedimentary FeaturesSedimentary Features

• Layers• Only type of rock that contains Fossils!• Ripple Marks – Air or water sand, silt, and clay• Concretion – water comes into contact with fossils and

mineral deposits• Geode – hollow rocks with mineral crystals inside

Classifying Classifying

Clastic Rocks (pieces of other rocks):Conglomerate & Breccias: Large sedimentsSandstones: Small grainsSiltstone : Very Small grainsShale : Very Small grains Clay pressed together

ClassifyingClassifyingNon-Clastic Rocks (minerals in water or past

life):- Look at composition: calcite, halite, gypsum

or quartzLimestone - Calcite and seashellsRocks Salt - HaliteRock Gypsum - GypsumChert (flint) - QuartzCoal – Past life

METAMORPHIC ROCKSMETAMORPHIC ROCKSMETAMORPHIC ROCKS have changed (meta) their form (morphic). Under the influence of heat, pressure and fluids,

pre-existing rocks are modified in form Original rock is called the parent rockThis is done within the solid state, i.e. without melting.

3 Types of Changes that occur include: - Change in Chemistry of Rock - Englargement of crystals

- Rearrangement of mineral grains

ClassifyClassify Burial Metamorphism – weight of overlying rock, causes a reorientation

of mineral grains Regional Metamorphism – As mountains rise, large amount of magma is

forced toward the surface , it hardens into the mountain core Contact Metamorphism – Small amount of magma intrudes overlying

rockThe nearby Rock is altered by heat, solutions, and gases from the magma

*Metamorphism is the MOST intense near the core where heat and pressure cause the formation of new minerals of existing mineral grains

FeaturesFeatures Metamorphic rocks that

exhibit parallel alignments of minerals are called FOLIATED. In these rocks, the minerals all line up perpendicular to the exerted pressure.

Metamorphic rocks composed of minerals that are not elongated or flat, do not exhibit parallel alignments and are called NON-FOLIATED.

The Rock CycleThinking about relationships among

the major rock groups

2323

Major Rock Groups• Igneous

– Formed from a melt (molten rock)– Plutonic (intrusive):slow cooling and crystallization– Volcanic (extrusion): quick cooling at the surface

• Sedimentary– Formed at the Earth’s surface– Clastic (Mineral Fragments or grains, clays)– Chemical (crystalline chemical/biochemical precipitates)

• Metamorphic– Changed by pressure, temperature and fluids.

Fig. 2.9

MAGMA

2525

MAGMA

Crystallization

IGNEOUS

2626

MAGMA

IGNEOUS

Plutonic

Crystallization

2727

MAGMA

Volcanic

IGNEOUS

Plutonic

Crystallization

2828

MAGMA

Volcanic

IGNEOUS

Plutonic

Uplift

Crystallization

Weathering

2929

MAGMA

Volcanic

IGNEOUS

Plutonic

SEDIMENT

Uplift

Crystallization

Weathering SEDIMENT

3030

MAGMA

Volcanic

IGNEOUS

Plutonic

SEDIMENT

SEDIMENTARY

Uplift

Crystallization

WeatheringCompaction

Cementation

Evaporation

3131

MAGMA

Volcanic

IGNEOUS

Plutonic

SEDIMENT

SEDIMENTARY

Uplift

Crystallization

WeatheringCompaction

Cementation

Evaporation

3232

MAGMA

Volcanic

IGNEOUS

Plutonic

SEDIMENT

SEDIMENTARY

METAMORPHIC

UpliftBurial

Increased P&T

Crystallization

WeatheringCompaction

Cementation

Evaporation

3333

MAGMA

Volcanic

IGNEOUS

Plutonic

SEDIMENT

SEDIMENTARY

METAMORPHIC

UpliftBurial

Increased P&T

MeltingCrystallization

Weathering

Can you see

any shortcuts?

Compaction

Cementation

Evaporation

3434

MAGMA

Volcanic

IGNEOUS

Plutonic

SEDIMENT

SEDIMENTARY

METAMORPHIC

UpliftBurial

Increased P&T

MeltingCrystallization

WeatheringCompaction

Cementation

Evaporation