ROCKSROCKSChapter 4 Sections 1 and 2Chapter 4 Sections 1 and 2

Rock Cycle and Igneous RocksRock Cycle and Igneous Rocks

What is a rock?What is a rock?

A rock is a mixture of broken rock fragments, volcanic glass, organic matter, and other natural materials.A rock is a mixture of broken rock fragments, volcanic glass, organic matter, and other natural materials.

Example ofExample ofAndesiteAndesite

Common Rock Forming Common Rock Forming MineralsMinerals

QuartzQuartz FeldsparFeldspar HornblendeHornblende MicaMica

Example of Example of

granitegranite

The Rock CycleThe Rock Cycle

crystallization

The Rock CycleThe Rock Cycle The rock cycle shows how rocks slowly change The rock cycle shows how rocks slowly change

through time.through time. The rock cycle shows the three types of rocks-The rock cycle shows the three types of rocks-

igneous, metamorphic, and sedimentary and the igneous, metamorphic, and sedimentary and the processes that form them.processes that form them.

Example: A sedimentary rock can change by heat Example: A sedimentary rock can change by heat and pressure to form a metamorphic rock. The and pressure to form a metamorphic rock. The metamorphic rock can melt and cool to form and metamorphic rock can melt and cool to form and igneous rock. The igneous rock can be broken igneous rock. The igneous rock can be broken into sediments by weathering and eroding away. into sediments by weathering and eroding away. The sediments might then compact and cement The sediments might then compact and cement together to form a sedimentary rocktogether to form a sedimentary rock..

Example of Metamorphic RockExample of Metamorphic RockGneissGneiss

Example of Sedimentary RockExample of Sedimentary RockConglomerateConglomerate

Example of an Igneous RockExample of an Igneous Rock

Rock CycleRock Cycle

– The main processes found in the rock The main processes found in the rock cycle arecycle are

– Melting and Cooling magma form Melting and Cooling magma form igneous rocks.igneous rocks.

– Weathering and erosion break rocks into Weathering and erosion break rocks into sediments.sediments.

– Compaction and Cementation change Compaction and Cementation change rocks into sedimentary rocks.rocks into sedimentary rocks.

– Heat and Pressure form metamorphic Heat and Pressure form metamorphic rocksrocks

Formation of Igneous RocksFormation of Igneous Rocks

When hot magma cools and hardens, When hot magma cools and hardens, it forms igneous rocks.it forms igneous rocks.

Because magma is less dense than Because magma is less dense than surrounding rocks, it is forced surrounding rocks, it is forced upward towards the surface. When upward towards the surface. When magma reaches the Earth’s surface magma reaches the Earth’s surface and flows from volcanoes it is called and flows from volcanoes it is called lava.lava.

Lava Picture before solidificationLava Picture before solidification

Lava picture after solidificationLava picture after solidification

Intrusive rocksIntrusive rocks

Rocks that form from magma below Rocks that form from magma below the surface of Earth are called the surface of Earth are called intrusive igneous rocks. intrusive igneous rocks. (intrusive=inside).(intrusive=inside).

Intrusive igneous rocks take a long Intrusive igneous rocks take a long time to form. Slowly cooled magma time to form. Slowly cooled magma produces large individual mineral produces large individual mineral grains in the rocks.grains in the rocks.

GraniteGranite

DioriteDiorite

GabbroGabbro

Extrusive RocksExtrusive Rocks

Extrusive igneous rocks are formed as lava Extrusive igneous rocks are formed as lava cools on the surface of the Earth. cools on the surface of the Earth. (extrusive=exterior=outside).(extrusive=exterior=outside).

When lava flows on the surface it is When lava flows on the surface it is exposed to air and water. Under these exposed to air and water. Under these conditions the lava cools very quickly.conditions the lava cools very quickly.

When the lava cools quickly, the atoms in When the lava cools quickly, the atoms in the liquid don’t have time to arrange into the liquid don’t have time to arrange into large crystals, which is why extrusive large crystals, which is why extrusive igneous rocks are fine-grained.igneous rocks are fine-grained.

Extrusive RocksExtrusive Rocks

Pumice and Obsidian are examples Pumice and Obsidian are examples of volcanic glass. These rocks cooled of volcanic glass. These rocks cooled so quickly that few or no mineral so quickly that few or no mineral grains formed.grains formed.

In the case of pumice gases became In the case of pumice gases became trapped in the molten material as it trapped in the molten material as it cools. The gases escape, but holes cools. The gases escape, but holes are left behind where the rock are left behind where the rock formed around the pockets of gas.formed around the pockets of gas.

BasaltBasalt

RhyoliteRhyolite

AndesiteAndesite

PumicePumice

ObsidianObsidian

Classifying Igneous RocksClassifying Igneous Rocks Igneous rocks are intrusive or extrusive Igneous rocks are intrusive or extrusive

depending on how they formed.depending on how they formed. A further way is to classify these rocks is by the A further way is to classify these rocks is by the

magma from which they formed.magma from which they formed. Basaltic igneous rocks are dense, dark-colored Basaltic igneous rocks are dense, dark-colored

rocks. They form from magma that is lacking rocks. They form from magma that is lacking silicon.silicon.-Basaltic lava is fluid and flows freely from -Basaltic lava is fluid and flows freely from volcanoes in Hawaii.volcanoes in Hawaii.-These rocks are also called mafic igneous rocks.-These rocks are also called mafic igneous rocks.-These rocks compose the seafloor.-These rocks compose the seafloor.

Classifying Igneous RocksClassifying Igneous Rocks

Grantic igneous rocks are light-colored Grantic igneous rocks are light-colored rocks of lower density than basaltic rocks. rocks of lower density than basaltic rocks. Granitic magma is think and stiff and Granitic magma is think and stiff and contains a lot of silica.contains a lot of silica.– Grantic magma is stiff and builds up a a large Grantic magma is stiff and builds up a a large

amount of gas pressure which is released amount of gas pressure which is released explosively during a volcanic eruption.explosively during a volcanic eruption.

– These rocks are called felsic igneous rocks.These rocks are called felsic igneous rocks.– The continents are composed mainly of The continents are composed mainly of

granite.granite.

Classifying Igneous Rocks.Classifying Igneous Rocks.

Andestic igneous rocks have mineral Andestic igneous rocks have mineral compositions between those of compositions between those of granitic and basaltic rocks. Many granitic and basaltic rocks. Many volcanoes around the rim of fire volcanoes around the rim of fire formed from andesitic magma.formed from andesitic magma.