Chapter 4Chapter 4

RocksRocks

The Rock CycleThe Rock CycleH.W. pg. 93 ques. 1-4H.W. pg. 93 ques. 1-4

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

All rocks slowly change All rocks slowly change through time, and the through time, and the model that we use to model that we use to show this slow change show this slow change is called the is called the rock cyclerock cycle..

Rock CycleRock Cycle As you can see the As you can see the

rock cycle shows 3 rock cycle shows 3 different types of rock: different types of rock:

1)1) Sedimentary Sedimentary 2)2) MetamorphicMetamorphic3)3) IgneousIgneous Also you see that all 3 Also you see that all 3

types can be formed in types can be formed in a number of ways.a number of ways.

This shows that any rock This shows that any rock can change into any of can change into any of the three major rock the three major rock types.types.

Igneous RockIgneous Rock

Igneous rockIgneous rock forms when magma cools and forms when magma cools and hardens. hardens.

At certain within the Earth, the temperature At certain within the Earth, the temperature and pressure are just right for rocks to melt and pressure are just right for rocks to melt and form magma.and form magma.

Magma can be located at depths of 150km below Magma can be located at depths of 150km below the Earths surface. The temperature of this the Earths surface. The temperature of this magma can range between 650- 1,200magma can range between 650- 1,200ooC, C, depending on their chemical compositions and depending on their chemical compositions and pressures exerted on them.pressures exerted on them.

Igneous RockIgneous Rock The reason that these rocks melt is because of heat The reason that these rocks melt is because of heat

that is formed in the Earth’s interior.that is formed in the Earth’s interior. The heat comes from the decay of radioactive The heat comes from the decay of radioactive

material inside the Earth.material inside the Earth. Another source of this heat is actually heat that is left Another source of this heat is actually heat that is left

over from the formation of the planet, which was over from the formation of the planet, which was originally molten.originally molten.

Since magma is less dense than the surrounding rocks Since magma is less dense than the surrounding rocks it is forced upward toward the surface, like in a it is forced upward toward the surface, like in a volcano.volcano.

When magma reaches the Earths surface and flows When magma reaches the Earths surface and flows from volcanoes it is then called from volcanoes it is then called lavalava

Igneous RockIgneous Rock

So So magma magma is melted rock material composed of is melted rock material composed of common elements and fluids.common elements and fluids.

As magma cools atoms and compounds rearrange As magma cools atoms and compounds rearrange themselves into new crystals called themselves into new crystals called mineral grainsmineral grains. . And rocks form as these mineral grains grow And rocks form as these mineral grains grow together.together.

So rocks that form from magma below the Earths So rocks that form from magma below the Earths surface are called intrusive.surface are called intrusive.

These intrusive rocks stay underground until the land These intrusive rocks stay underground until the land above them are removed, either by erosion of by above them are removed, either by erosion of by physical means, and exposed to the surface.physical means, and exposed to the surface.

Igneous RockIgneous Rock

Intrusive rocksIntrusive rocks form form at deep depths of the at deep depths of the Earth. This causes the Earth. This causes the rocks to cool very rocks to cool very slowly. slowly.

Slowly cooled magma Slowly cooled magma will then produce very will then produce very large mineral grains that large mineral grains that we can see, within the we can see, within the intrusive rocks.intrusive rocks.

Igneous RockIgneous Rock

Extrusive igneousExtrusive igneous rocks rocks are formed by the cooling of are formed by the cooling of lava on the surface of the lava on the surface of the Earth. Earth.

When lava cools on the When lava cools on the surface it could be exposed surface it could be exposed to water and air. This to water and air. This causes the lava to cool causes the lava to cool quickly and does not allow quickly and does not allow large mineral grains to form.large mineral grains to form.

Therefore extrusive igneous Therefore extrusive igneous rock looks fine grained.rock looks fine grained.

Metamorphic RockMetamorphic Rock

Rocks that have changed because of changes in Rocks that have changed because of changes in temperature and pressure or the presence of hot, temperature and pressure or the presence of hot, watery fluids are called watery fluids are called Metamorphic Rock.Metamorphic Rock.

These changes can be in the form of the rock or in its These changes can be in the form of the rock or in its composition or both.composition or both.

Metamorphic rocks can form from igneous, Metamorphic rocks can form from igneous, sedimentary or from other metamorphic rocks.sedimentary or from other metamorphic rocks.

Ex: When you add heat and pressure to granite, the Ex: When you add heat and pressure to granite, the mineral grains are flattened and a metamorphic rock mineral grains are flattened and a metamorphic rock called gneiss is formed.called gneiss is formed.

Granite & GneissGranite & Gneiss

How to Classify Metamorphic RockHow to Classify Metamorphic Rock

Metamorphic rocksMetamorphic rocks can form from igneous, can form from igneous, sedimentary, or other metamorphic rocks sedimentary, or other metamorphic rocks through their interaction with heat pressure through their interaction with heat pressure and hot fluids.and hot fluids.

We classify these rocks by their We classify these rocks by their composition composition and texture.and texture.

First is First is FoliatedFoliated rocks rocks. A metamorphic rock . A metamorphic rock is said to have foliated texture when mineral is said to have foliated texture when mineral grains in the rock line up in parallel layers.grains in the rock line up in parallel layers.

Metamorphic foliated rockMetamorphic foliated rock

Two examples of Two examples of foliated rocks are slate foliated rocks are slate and gneiss.and gneiss.

Non Foliated metamorphic RockNon Foliated metamorphic Rock

In In non foliated metamorphic rocknon foliated metamorphic rock layering does not layering does not occur. The mineral grains grow and rearrange but do occur. The mineral grains grow and rearrange but do not form layers.not form layers.

This produces a non foliated texture. This produces a non foliated texture. An example is when sandstone, a sedimentary rock An example is when sandstone, a sedimentary rock

composed of mostly quartz grains, is exposed to heat composed of mostly quartz grains, is exposed to heat and pressure.and pressure.

The quartz grains here grow in size and become The quartz grains here grow in size and become interlocking like a jigsaw puzzle.interlocking like a jigsaw puzzle.

The resulting rock is called quartzite.The resulting rock is called quartzite.

Non Foliated metamorphic RockNon Foliated metamorphic Rock

Sedimentary RockSedimentary Rock

Igneous rocks are the most common rocks on Earth. Igneous rocks are the most common rocks on Earth. However we don’t see them a lot because they are However we don’t see them a lot because they are mostly beneath the Earths surface.mostly beneath the Earths surface.

75% of the rocks that are exposed at the surface are 75% of the rocks that are exposed at the surface are sedimentary rockssedimentary rocks..

Sediments are loose materials such as rock fragments, Sediments are loose materials such as rock fragments, mineral grains, and bits and pieces of shell that have mineral grains, and bits and pieces of shell that have been moved by wind, water, or icebeen moved by wind, water, or ice

These sediments come from already existing rock that These sediments come from already existing rock that were weathered or eroded. were weathered or eroded.

Sedimentary rock forms when these sediments are Sedimentary rock forms when these sediments are pressed together by great pressure, or when minerals pressed together by great pressure, or when minerals form in solution.form in solution.

Stacked RocksStacked Rocks

Sedimentary rocks often form in layers. The Sedimentary rocks often form in layers. The older layers are on the bottom layers because older layers are on the bottom layers because they were deposited first.they were deposited first.

Sometimes these layers can be disturbed by Sometimes these layers can be disturbed by the forces of nature. This will sometimes the forces of nature. This will sometimes overturn the layered sedimentary rock and the overturn the layered sedimentary rock and the oldest will no longer be on the bottom.oldest will no longer be on the bottom.

ConglomerateConglomerate

Test on chapter 3 in one Test on chapter 3 in one week!!!!!!!!!!!!!week!!!!!!!!!!!!!