Are composed of more thanone mineral

Chapter 6 Section 1

1. Igneous-formed by cooling and hardening of hot, molten rock (magma) inside Earth

2. Sedimentary-formed by the compaction and cementing of layers of sediments (rock fragments, plant and animal remains, minerals that settle out of solution onto lake and ocean bottoms)

3. Metamorphic-formed by the effects of heat and pressure on other rocks BrainPop 3 Types of Rocks

The Rock Cycle

• The continuous process that causes rocks to change from one form to another– Caused by interactions between water, air,

and land

Rock Cycle Movie

ESRT pg. 6

What happens to igneous rocks?1. Heat and pressure/ “metamorphism” metamorphic rock

2. Melt to form magma which solidifies igneous rock

3. Weathering and erosion form sediments which are deposited, buried, compacted, and cemented sedimentary rock

1

2

3

What happens to sedimentary rocks?1. Heat and pressure/ “metamorphism” metamorphic rock

2. Melt to form magma which solidifies igneous rock

3. Weathering and erosion form sediments which are deposited, buried, compacted, and cemented sedimentary rock

1 2

3

What happens to metamorphic rocks?1. Heat and pressure/ “metamorphism” metamorphic rock

2. Melt to form magma which solidifies igneous rock

3. Weathering and erosion form sediments which are deposited, buried, compacted, and cemented sedimentary rock

1

2

3

• Form from molten rock or volcanic ash

• As magma cools, crystals grow & interlock (rate affects size)

Chapter 6 Section 2Igneous Rock Formation Movie

The Starting Material• Magma may be classified as felsic, mafic, or

an intermediate form.– Felsic magma: thick and slow moving; large

amounts of silica (SiO2) and small amounts of calcium, iron, and magnesium; typically hardens into rocks containing light-colored silicate minerals (ex. quartz and orthoclase feldspar)

– Mafic magma: hotter, thinner, more fluid; large amounts of iron and magnesium and smaller amounts of silica; typically hardens into rocks containing dark-colored silicate minerals (ex. hornblende, augite, biotite)

• Form from magma which cools slowly deep inside the earth (internal)

• Crystals are medium to coarse texture (easily seen)

• Form from lava (magma that has exited the crust) that cools quickly (external)

• Crystals are very small or not seen at all

Intrusive Igneous Rocks

Extrusive Igneous Rocks

• Igneous Rocks are grouped into families according to mineral composition.

• Specific igneous rocks can be recognized by:

Color- determined by the mineral composition (makeup)Texture- the size & arrangement of crystals

Granite Family/Felsic Rocks• Form from felsic (silica and aluminum-rich)

magmas• Usually coarse-grained because their

slow-rising, “sticky” parent magmas tend to cool slowly underground

• Typically contain quartz, feldspar, mica, hornblende

• Light-colored• Low in density

Granite Family/Felsic Rocks• Granite

– one of the coarsest-grained

rocks in this family

– Intrusive

– Often contain large amounts of light-colored feldspar• color of feldspar determines color of the rock

– Usually ranges from white or gray to pink

– Very common continental rock found in many mountainous areas across the U. S.

Granite Family/Felsic Rocks• Obsidian:

– Extrusive– Glassy texture (no crystals)– Chemically similar to granitic rocks even though it is usually dark brown or black

• Pumice:– Extrusive– Forms when silica-rich lava

hardens as steam & other gases bubble out of it– Vesicular texture

• Resembles a sponge because of holes and air pockets

– Often able to float on water

Granite Family/Felsic Rocks• Felsite:

– General name for any light-colored, fine-grained rock

– Rhyolite is a common example• Fine-grained, ranges from light gray to pink

Gabbro Family/Mafic Rocks• Form from mafic (iron and

magnesium-rich/silica poor) magmas

• Dark in color

• High density

• Typically contain pyroxene, olivine, plagioclase feldspar (amphibole and biotite mica)

Gabbro Family/Mafic Rocks• Gabbro: coarse-grained

rock. very dark color

• Basalt: fine-grained, dark gray or black– Composition similar to gabbro– Most common rock in gabbro family– Makes up the ocean floor– On land, most common rock– formed from lava flows

Basalt is igneous rock formed from mafic magma.

Gabbro Family/Mafic Rocks• Diabase: texture is finer than gabbro but

coarser than basalt

• Basalt glass: resembles obsidian but is mafic

• Scoria: (like pumice) full of holes,

darker and denser than pumice, holes are usually larger, unlikely to float

Diorite Family/Intermediate Rocks

• Composition is neither felsic or mafic but has characteristics of both = intermediate

• Colors tend to be medium grays and greens (darker than granites and lighter than gabbros)

Diorite Family/Intermediate Rocks

• Diorite: coarse-grained, has less quartz than granite and less plagioclase feldspar than gabbro

• Andesite:

fine-grained

Other Igneous Rocks

• Felsic-intermediate: granodiorite

• Ultramafic: peridotite, dunite, pyroxenite– Hypothesized to be similar to rocks in Earth’s

mantle

Igneous Intrusions• Pluton: any rock mass that forms when

magma pushes into fractures (cracks) in the bedrock– Dike: vertical, in between rock layers– Sill: parallel to rock layers it intrudes

• Ex. Palisades Sill along the Hudson River (NY/NJ)

– Laccolith: domed mass, bulge– Volcanic neck: central plug of hardened magma left

after the volcanic material around it has worn away– Batholith: largest of all plutons, cores of many

mountains• Stock: a small batholith that is exposed at the surface

Igneous IntrusionsLaccolith Volcanic neck

Sill

Volcano

Batholith

Stock

Dike

• Made of sediments

• Cover most of the crust’s surface

• 3 types

Chapter 6 Section 3

• Formed from fragments of other rock that are moved (usually by running water)

• Sediments are deposited layer after layer (as the water slows down)– Sorted by largest sediments first, smallest last

• Compacted as layers pile up or cemented together by minerals that are dissolved in the water– Type of cement influences color (silica, calcite, iron

oxide, and clay)

Smallest• Silt & Clay particlesshale/siltstone

• Sand particlessandstone

• Mixed particlesconglomerate/brecciaLargest

Classified by Particle Size

• Chemical sediments form when minerals precipitate (fall out) of water.–Two ways

• Evaporation: Form when a sea or lake dries up leaving behind minerals that were dissolved in water

• Chemical action: dissolved ions combine to form new minerals

Also referred to as crystalline sedimentary rocks

Examples:Rock Salt

Rock Gypsum

Limestone (travertine)

• Form from sediments consisting of the remains of plants and animals

• Shells

Fossil

limestone

• Plant remains coal

anthracitebituminouspeat lignite

Features of Sedimentary Rocks• Stratification

– arrangement of visible layers– result from changes in sediment

type being deposited– Bedding planes (lines between the

layers) show where the layers are separated

• Usually horizontal, but cross-bedding (angled deposits) can occur

– Occur for a number of reasons• New types of rocks picked up (from

different locations)• More of different types of rocks carried

during flooding• Sediments carried longer or shorter

distances

Features of Sedimentary Rocks

• Fossils– the remains, impression, or other evidence

of a plant or animal preserved in rock• occur when dead organism is buried by

sediments and gradually turns to rock– Usually only hard parts are preserved– Impressions occur when shell, skeleton, etc. is

pressed into soft sediments

Features of Sedimentary Rocks• Ripple marks = sand patterns formed by

the wind, streams, waves, or currents

• Mud cracks = develop when wet clay dries and contracts (shrinks)– Cracks fill with different sediments & fossilize

Features of Sedimentary Rocks• Nodules = lumps of fine-grained silica in limestone or chalk

– Ex. chert and flint

• Concretions = round, solid masses of calcium carbonate– Probably form when minerals in dissolved in water precipitate

around shell fragments or other impurities in clay sediments• Ex. oolites

• Geodes = spheres of silica rockfound in limestone– Inside lined or filled with crystals (quartz or calcite)

• Formed from “parent rock”– Often resembles “parent rock”

– Differences are the result of metamorphic processes that the “parent rock” has undergone

Metamorphic Rocks

Metamorphic Processes

Metamorphism: the process by which a rock’s structure is changed by pressure, heat, and moisture.– Pressure & heat may originate from:

• the Earth’s internal heat• the weight of overlying rock• the deformation of rock as mountains build

Metamorphic Processes

• A metamorphic rock may have a chemical composition, texture, or internal structure that differs from the parent rock.– Minerals may be enlarged or reformed– New minerals may appear– The rock may be more dense and less porous

(less “empty” space)

Metamorphic Processes: Two Basic Types of Metamorphism

• Regional– Forms most of the metamorphic rock of

Earth's crust– Often occurs over very large areas

• Local– Smaller, more distinct areas

Regional Metamorphism• Can occur during mountain building

• Large areas of rock metamorphosed– Due to intense heat and pressure

• Temperature increases with depth• Pressure increases w/ depth (more overlying rock)

– Pressure greater in 1 direction, minerals align in layers

– Hot liquids & gases speed up the process

• Different amounts of heat & pressure different amounts of metamorphism.– Can cause folding of rock layers– Higher temperature & pressure greater

metamorphism

Limestone

Marble

gneissschist

phylliteslateshaleLime

quartzite

sandstone

Local Metamorphism• Two types

– Contact:• Occurs when hot magma moves into rock, heating

and changing it.• Causes fewer changes and affects much less rock

than regional metamorphism

– Deformational:• Occurs at relatively low temperatures and high

pressure• Caused by stress and friction (often at faults where

rocks move against each other)• Mineral composition usually stays the same, but

texture and structure may change

Metamorphic Rock Descriptions

• Description and identification usually based on parent rock, mineral content, and texture

• 2 types–Foliated

–Non-foliated

• Foliated Metamorphic Rocks–Minerals flattened by pressure producing mineral alignment or (different colored) bands

–May look scaly

–Often split along parallel layers

Metamorphic Rock Descriptions

Foliated Metamorphic Rocks: Examples

Granite gneiss

Shale Slate Phyllite Schist(Extreme Metamorphism)

•Nonfoliated Metamorphic Rocks–Don’t show banding

–look crystalline (sparkles)

Metamorphic Rock Descriptions

Nonfoliated Metamorphic Rocks: Examples

• Limestone marble

• Sandstone quartzite

• Conglomerate metaconglomerate