Rocks Tell Stories Records of Geologic Past

1. Igneous rocks … from cooling and solidification of lava or magma

2. Sedimentary rocks … from compacted and cemented sediments, or chemical precipitates or evaporites

3. Metamorphic rocks … meta (change) morphic (form) … rocks changed by heat and pressure –but remain solid

Rock Classification – 3 major groups based on their methods of

formation or origin

IGNEOUS ROCKS

Formation of Igneous Rocks

COOLING AND SOLIDIFICATION OF MAGMA/LAVA

INTERGROWN OR INTERCONNECTED SILICATE CRYSTALS IN A RANDOM PATTERN – NOT ORGANIZED

INTERGROWN SILICATE CRYSTALS - RANDOM

PATTERN

Magma – molten material BELOW the surface of the Earth

Lava – molten material AT OR ABOVE earth’s surface

MAGMA VS. LAVA

MAGMA LAVAIntrusive – below the surface

Extrusive - above the surface

A pluton is a body or chamber of magma deep inside the crust.

Ejected from volcano

Rocks formed when magma cools and solidifies are called

INTRUSIVE (PLUTONIC)

Rocks formed when lava cools and solidifies are called

EXTRUSIVE (VOLCANIC)

ENVIRONMENT OF FORMATION

COOLING HISTORY

IGNEOUS ROCKS ARE CLASSIFIED BASED ON 2 MAIN CHARACTERISTICS

•TEXTURE – MINERAL GRAIN SIZE

•MINERAL COMPOSITION (COLOR)

Classification of Igneous Rocks by Texture

•WHAT IS TEXTURE? It is NOT how it feels!

It’s the SIZE OF MINERAL CRYSTALS

What controls texture?What controls texture?

How fast an igneous rock cools.

What controls how fast an What controls how fast an igneous rock cools?igneous rock cools?

Where the rock is formed.

coarser crystals

slower cooling

deep in ground

ESRT – TOP OF THE IGNEOUS ROCK SCHEME TELLS THE

TEXTURE / GRAIN SIZE

Classification of Igneous Rocks – Texture or Grain Size

Extrusive Extrusive Intrusive Intrusive

Volcanic - LAVA

Volcanic- LAVA

Plutonic - MAGMA

Plutonic - MAGMA

Extremely fast cooling

Fast Cooling

SlowCooling

Extremely slow cooling

Non-crystallineGlassy vesicular (gas pockets)

Fine-grained

Coarse-grained

Very Coarse-grained

EXTRUSIVE – VOLCANIC - LAVA• When lava cools extremely fast crystals have

no time to form – JUST FROZEN IN PLACE RANDOMLY WHEN LAVA ENTERS ATMOSPHERE OR WATER

• GLASSY – NON-CRYSTALLINE Non-vesicular Vesicular gas pockets

EXTRUSIVE – VOLCANIC - LAVALava that cools fast at or near the Earth’s surface

Produces small crystals FINE-GRAINED TEXTUREnot easily seen with the naked eye.

INTRUSIVE – PLUTONIC - MAGMA

Magma that cools slowly deep underground produces large crystals COARSE-GRAINED TEXTURE easily seen with the naked eye.

EXTREMELY SLOW COOLING HAS ABNORMALLY LARGE CRYSTALS

AND IS VERY COARSE.  

INTRUSIVE – PLUTONIC - MAGMA

IN THE MIDDLE OF THE IGNEOUS ROCK CHART ARE

CHARACTERISTICS BASED ON WHICH MINERALS ARE IN EACH

ROCK.

NOTICE 2 NEW WORDS

FELSIC AND MAFIC

CHARACTERISTICS OF IGNEOUS ROCKS

FELSIC VS. MAFICFELSIC MAFIC

“FEL” = FELDSPARS “MA” = MAGNESIUM

“SIC” = SILICA “F” = IRON

High % of quartz, feldspars, mica

“IC” = SILICAHigh % of pyroxene, feldspars, amphibole

LIGHTER IN COLOR LESS DENSE

DARKER IN COLORMORE DENSE

Continental mixed oceanic mantle

FELSIC MAFIC ULTRAMAFIC

THE BOTTOM OF THE IGNEOUS ROCK SCHEME TELLS YOU THE COMPOSITION

TEXTURE + COMPOSITION CAN NAME ROCK

FELSIC COMPOSITION COLUMN

+

COARSE TEXTURE ROW

Granite RhyoliteFigure 4.7 AMINERAL COMPOSITION THE SAME – TEXTURE ONLY DIFFERENCE

Intrusive vs. Extrusive

INTRUSIVE EXTRUSIVE

DioriteAndesite

Figure 4.7 B

MINERAL COMPOSITION THE SAME ---- TEXTURE ONLY DIFFERENCE

Intrusive vs. Extrusive

INTRUSIVE EXTRUSIVE

Gabbro BasaltMINERAL COMPOSITION THE SAME – TEXTURE ONLY DIFFERENCE

Intrusive vs. Extrusive

INTRUSIVE EXTRUSIVE

WHAT GRAPH BELOW SHOWS AS TIME INCREASES THE SIZE INCREASES?

A B

SEDIMENTARY ROCKS

Sedimentary Rocks• 80 % of Earth’s surface is covered

with sediments and Sedimentary Rocks (only a thin layer on top)

What is sediment????

Broken pieces of rocks called Sediments

Chemical precipitates ( dissolved solids come out of solution)

Organic fragments – shells, decayed plant matter – this is called BIOCLASTIC

Source of Sediment

When Igneous, Metamorphic Rocks, and Sedimentary Rocks are uncovered and exposed to the atmosphere and hydrosphere they start to break down

Weathering is the general term for all actions that break down or wear away rock

Erosion is the moving/transport of the sediment

Sedimentary Rocks form when sediments are transported to large

bodies of water and are …

Deposited in horizontal layers called beds or strata

Buried

Compacted – particles forced extremely close together because of the pressure of the overlying layers and water

Cemented – glued together

Sedimentary RocksSediments that are

eroded settle to the bottom of the rivers, lakes, and oceans

Layer after layer of eroded earth is deposited on top of each other

Most Sedimentary Rocks form under large bodies of water, such

as lakes, seas, and oceans

Horizontal layers deposited under water

Classification of Sedimentary Rocks

• We classify sedimentary rocks depending whether the sediments are

LAND DERIVED (came from)

CHEMICALLY - ORGANICALLY DERIVED

INORGANIC LAND DERIVED ROCKS NAMED BY GRAIN SIZE

Breccia

Sediments are pebbles, cobbles, and boulders

rounded

angular

Sand (0.2 to 0.006 cms.)

SANDSTONE

Silt (0.006 to 0.0004 cms.

SILTSTONE

Clay (less than 0.0004 cms.)

SHALE

2 TYPES OF TEXTURE

CRYSTALLINE FOR CHEMICALLY FORMED SEDIMENTARY ROCKS

BIOCLASTIC FOR ORGANICALLY FORMED SEDIMENTARY ROCKS

HOW USEFUL IS GRAIN SIZE????

CHEMICAL Sedimentary RocksSediment From Solution

All liquid water contains dissolved minerals.

These minerals precipitate (dissolved solids come out of solution/water)

Usually happens because of evaporation

Characteristics of Chemically Formed Sedimentary Rocks

They are monominerallic – consisting of intergrown crystals of just 1 mineral.

Form in shallow seas

ROCK SALT

DOLOSTONE

ROCK GYPSUM

Intergrown crystals of just 1 mineral

ORGANIC Sedimentary Rocks Bioclastic Sediment

LIMESTONE AND CORALS• Dissolved minerals taken out of solution by

marine organisms for their hard parts (shells) can pile up on the seafloor when they die.

• These fossil remains accumulate into a thick enough layer to form an “organic” sedimentary rock

• Cement is commonly calcite ( bubbles with acid)

COAL• Decayed plant remains

BIOCLASTIC LIMESTONE CHEMICALLY PRECIPITATED LIMESTONE

COAL

Summary

Inorganic Land-Derived Sedimentary Rocks are identified by Texture or Grain Size

Chemically and/or Organically Formed Sedimentary Rocks are identified by Composition

HIGH ENERGY

LOW ENERGY

Environment of Formation Ocean Derived Sedimentary Rocks

Sedimentary Rockshelp us understand our pastgeologic history

There is evidence of climatechange as well as lost speciesof plants and animals in Sedimentary Rocks

During the Cretaceous Period (about 120 mya) a shallow inland sea split North America.

We know this by the Sedimentary Rocks deposited in the former shallow sea

SALT AND GYPSUM EVAPORATION

Bedrock of Salt and Gypsum around Buffalo

What type of environment would cause salt and/or gypsum to evaporate?

Ocean environment with hot temperatures

CHARACTERISTICS OF SEDIMENTARY ROCKS

1. Horizontal layers called beds or strata

2. Clasts are rounded and sorted because they have been moved by water

3. Ripple Marks

4. Mud Cracks

5. Fossils

6. Interconnected mineral crystals of 1 mineral (monominerallic)

HORIZONTAL LAYERS

A. SHALLOW WATER B. LOW ENERGY C. DIRECTION OF FLOW

MUDCRACKS

ALTERNATING WET AND DRY CONDITIONS

Limestone - FOSSILS

SEDIMENTARY ROCK MANTRA

1.COMPACTED AND CEMENTED SEDIMENTS

FOSSILS RIPPLE MARKSMUDCRACKS

METAMORPHIC ROCKS

METAMORPHIC ROCKSMETA = CHANGE MORPH = FORM

Start with pre-existing rock and change to another rock – but these changes occur in the SOLID STATE

METAMORPHISM

Process by which igneous, sedimentary, or another metamorphic rock called the “parent rock” undergoes changes in minerals and texture

METAMORPHISM

Occurs in rocks due to the effects of

•High temperature•High pressure

HEAT EFFECTS

Temperature increases with depth or contact with magma

Recrystallization – a process that forms new mineral crystals because the mineral is no longer stable at the new temperature

• Changes to a new (high temperature) mineral

PRESSURE EFFECTS

Pressure increases with depth – weight of overlying rock (see page 10 ESRT)

Mineral crystals grow larger Mineral crystals are more dense Mineral crystals grow

perpendicular to pressure Mineral crystals are arranged in

parallel layers – PRODUCES FOLIATION

FOLIATION

Pressure actually rearranges the minerals into parallel layers.

More pressure – minerals grow larger and recrystallize and separate into layers

Even more pressure – alternating layers of light and dark minerals called

Banding

Random arrangement of minerals

Organized arrangement of minerals - banding

METAMORPHIC ROCK MANTRA

• INTERGROWN CRYSTALS IN AN ORGANIZED PATTERN

GraniteIntergrown crystals

random pattern

GneissIntergrown crystalsOrganized Pattern

2 Types of Metamorphism

1. Regional Metamorphism – Occurs over large areas where there is active mountain building

a) Convergent plate boundaries

2. Contact Metamorphism – areas in contact with magma intrusions and/or lava extrusions

MOUNTAIN

BUILDING

Classification of Regional Metamorphic Rocks

Composition is basically the same for all foliated rocks – parent rock is usually listed in comments section.

Type of texture and grain size determined by the amount of heat and pressure

GRADES OF METAMORPHISM

LOW GRADE – LESS HEAT AND PRESSURE – SLATE

HIGH GRADE – MORE HEAT AND PRESSURE - GNEISS

Low-grade metamorphism: Occurs at about 2000 C to 5000 C. and pressure greater than 1,000 atmospheres

High-grade metamorphism:Occurs at > 5000 C

Temperature

FOLIATED METAMORPHIC ROCKS

MICA CRYSTALSBECOMELARGE AND SPANGLY

MICA SCHIST WITH GARNET

METAMORPHIC ROCKS WILL OFTEN BE DEFORMED

BECAUSE OF INTENSE HEAT AND PRESSURE

LOOK AT ROCK SYMBOL FOR GNEISS

DEFORMED GNEISS

A metamorphic rock exposed to too much heat will melt and become ???

MAGMA

CONTACT METAMORPHISM

Contact Metamorphic

• Metamorphism means "changed form".

• The Changes occur because of:

• Heat from magma intruding on the surrounding rock

• Very little pressure

Near magma chambers (plutons)

Rocks in “contact” with the magma are heated

New minerals are formed –recrystallization

Contact Metamorphism – heating the adjacent rocks

Symbol for Contact Metamorphism is a line with tick marks

When limestone undergoes contact metamorphism what rock will it metamorphose into? Sandstone??

PARENT ROCK IN THE COMMENTS

LIMESTONE METAMORPHOSES INTO MARBLE

SANDSTONE METAMORPHOSES INTO QUARTZITE