The Rock Cycle

• Types of Rocks

• Forces that change rocks

• Weathering

• Erosion

• Deposition

• Heat and Pressure

Types of Rocks: IGNEOUSIgneous rocks are “made by fire” because they are

formed from magma (molten rock) or volcanic activity.

Igneous rocks include quartz, granite, obsidian, geodes, ash, pumice, lava, feldspar, mica, silica, and many minerals and crystals.

If the magma reaches the surface of the earth, it can cool quickly, leaving little time for crystals to grow. Magma that cools under the surface takes longer to cool, and the crystals have time to grow bigger. Large granite domes such as Enchanted Rock (TX) and Half Dome (Yosemite) were once magma “bulges” underground.

Igneous Rock Review

• Intrusive Igneous:• Magma that cools under

the earth’s surface, underground

• Granite (same silica content as obsidian)

• Gabbro (silica- poor)

• Extrusive Igneous:• Magma at the earth’s

surface is called lava• The more silica in the

magma, the more explosive the eruption

• Obsidian, rhyolite (silica- rich, like granite)

• Basalt (gentle flow of lava, small grains)

Write what you learned about igneous rocks

• What is magma?

• What kinds of rocks are formed from magma underground?

• What other things did you learn?

• What is the difference between magma and lava?

• What kinds of rocks are formed from lava?

Types of Rocks: Sedimentary

• Sedimentary Rocks are made from sediments, or small pieces of other types of rocks which have been broken down (weathered,) carried away (eroded,) and deposited in other places on the earth’s surface.

• Sedimentary rocks usually show layers (as in sandstone or shale) or small pieces that are cemented together to form larger rocks (such as conglomerates or aggregates.) Other sedimentary rocks are formed by buried decaying organisms such as plants and animals.

Types of Sedimentary Rocks

• Clastic Rocks: “stuck together” rocks

• Sandstone (made from sand grains)

• Siltstone/ mudstone (made from mud or silt stuck together)

• Shale (made from tiny clay particles)

• Conglomerates (pebbles and sand cemented by minerals)

• Chemical Rocks: made from minerals after the water that carried them evaporates)

• Rock Salt (Halite)• Gypsum• Limestone (from

evaporated seas/ lakes)• Chert

More Sedimentary Rocks

• Organic Rocks: formed from the remains of plants and animals

• Coal: see text p. E58-59

• Chalk (from tiny sea creatures)

• Limestone (from sea animals with shells)

• Fossils: from plants or animals buried in layers of sediments, then replaced by minerals (text p. E74-77)

• Mold: imprint, hollow “cup.” “A mold can ‘hold’.”

• Cast: the actual 3-D object turned to stone

Review

Sedimentary Rocks

Clastic:“stuck together”

Chemical:“Mineral deposits”

Organic:Decayed plants/

Animals

Write what you learned about sedimentary rocks

• How are sedimentary rocks formed? Include words such as:– Erosion– Deposits– Sediments– Cementing– Pressure– Layers– Evaporation– Dissolved

METAMORPHIC ROCKS

• The word “metamorphic” means “to change form.”

• Metamorphic rocks begin as some other type of rock (igneous or sedimentary) and then change.

• Examples: – Shale (sedimentary) Slate (metamor.)– Granite (igneous) Gneiss (metamor.)– Limestone (changes to) marble

Rocks Can Change

• Changes are seen in the texture (size of grains) and/ or composition (mineral make-up) of the rock.

• Contact metamorphism (see Heat)

• Regional Metamorphism (see Pressure)

• Burial Metamorphism (Heat & Pressure are lower)

• Causes of change are:– Heat (contact with nearby

magma changes minerals and grain sizes)

– Pressure (from weight of rocks on top causes grains to line up in the same direction = banded rocks)

– Chemicals (from magma’s liquids or gases change minerals)

Fossil FuelsPlants & Animals contain carbon

and hydrogen. They undergo changes when they die and

are quickly buried under othersediments.

Bacteria, pressurefrom more sediments,

and increased heat change organisms into

Fossil Fuels.

Swamp or bog plantsdecay and form peat. More heat & pressure

form lignite(a sedimentary rock.)

More heat & pressureform coal, which is a

rock that burns as fuel.

Fossil Fuels

• OIL AND GAS ARE FORMED FROM REMAINS OF OCEAN PLANTS AND ANIMALS THAT WERE BURIED BY SEDIMENTS.

• OVER LONG PERIODS OF TIME, BACTERIA, HEAT, AND PRESSURE CHANGED THE ORGANISMS TO OIL AND GAS.

Write what you know about fossil fuels

• Tell what specific materials make fossil fuels.

• Name as many fossil fuels as you can.• Are these sources of energy renewable?• What forces are necessary to make fossil

fuels? Explain.• Does it take a short/ long time to make

fossil fuels? Explain.• What living organisms help change the

decayed materials into fossil fuels?

THE ROCK CYCLE

• Forces that break down:

• Weathering and Erosion– Roots break rocks.– Freezing and heating

make cracks.– Glaciers scour, polish,

move, or grind rocks.– Wind (scouring, erosion)– Water (erosion)– Dissolving

• Forces that build up:• Deposition of more

sediments over time• Rising magma forms

new rocks under the earth’s surface.

• Lava flows and volcanic eruptions bring more rock material to the surface of the earth (ash, lava, obsidian, basalt, etc.)

HEAT AND PRESSURE

MELTINGWEATHERING

DEPOSITION

COOLING

ROCK CYCLE

ROCK CYCLE

COOLING

• Magma cools to form granite, gabbros, and minerals

• “Lava” (extrusive magma that reaches the surface of the earth) cools to form obsidian (volcanic glass,) pumice, basalt, lava rocks

WEATHERING

• All rocks can be broken down or “weathered.”

• The pieces of rock can be huge blocks or slabs that break off from cliffs or boulders that are moved by glaciers.

• Rocks and minerals may be ground up into grains of sand.

• Rocks may be tumbled in rivers against other rocks to form pebbles.

DEPOSITION

• Broken pieces of rock are carried and deposited (set down) in other places by:– Wind (dust storms) – Water (wave action, floods, mudslides, rivers,

rain runoff)– Evaporation leaves sediments behind

(minerals in caves or lakebeds, or in layers of sediments)

MELTING• All types of rocks can melt and become

magma again:– Igneous– Sedimentary– Metamorphic

• The cycle begins again and continues to change rocks as time goes on.

Write your explanation of the rock cycle

• Write several paragraphs to explain the steps of the rock cycle. Write a short explanation for each word:

• Melting

• Cooling

• Weathering

• Deposition

• Heat and Pressure