CHAPTER 10.2Rocks and the Rock Cycle

Rock Families

As we already learned, rocks are made from minerals and can be classified into 3 major families (or types) based on how they are formed

The 3 Families are: Igneous Rocks Sedimentary Rocks Metamorphic Rocks

Igneous Rocks

Igneous rocks are formed when magma and hot lava cool and solidify Magma – is melted rock that is found below

the Earth’s crust. Even though the Earth’s mantle is solid, magma can sometimes be found in pockets

Types of Igneous Rocks

Geologists classify igneous rocks based on where they were formed above or below the Earth’s surfce. There are 2 types of igneous rocks.

Types of Igneous Rocks: Intrusive Rock Extrusive Rock

Intrusive Rocks (Igneous Rocks)

When magma cools and hardens below the Earth’s surface a new rock is formed. Because the rock was formed in the Earth’s surface we call it an Intrusive Rock.

Granite is an example of an intrusive rock (Igneous Rock) because it is formed very slowly and deep in the Earth’s Crust.

Extrusive Rocks (Igneous Rocks)

Extrusive Rocks are formed when lava cools on the Earth’s surface. Lava is the name for magma once it breaks

through the Earth’s surface during a volcanic eruption.

Example: Basalthttp://www.youtube.com/watch?v=nuIercRAxQU&feature=related

Sedimentary Rocks

Sedimentary Rocks are made from sediments which are loose materials such as bits of minerals, rock and plant and animals remains.

The sediment becomes packed and cemented together

Sedimentary Rocks make up about 75% of the rocks on the Earth’s Surface because Igneous Rocks mostly occur below the Earth’s Surface

Formation of Sedimentary Rocks

Over many years the rock sediments begin to settle and pile up usually near lakes and oceans

As the sediment settles on top of other sediment, the rock begins to take on a layered appearance.

These layers are called beds

Formation of Sedimentary Rocks

As the layers of sediment begin to form on top of each other, their weight causes the rocks to become compacted (squeezed together)

In some rocks the minerals dissolve in the water creating a natural cement that holds the rock together

Formation of Sedimentary Rock

This process is known as Compaction

Formation of Sedimentary Rocks

Limestone is the most common type of sedimentary rock. It is a very unique rock because it is formed from large amounts of sediment and the remains of fossils (such as mussels and snails)

Fossilized limestone in North Carolina

http://www.youtube.com/watch?v=Aqy-p41VpKU&feature=related

Metamorphic Rocks

Metamorphic Rocks are created under the Earth’s surface when extremely high pressure and heat cause the rock to “change form”

Slate and Marble are two examples of metamorphic rocks

Slate Marble

Metamorphic Rocks

Videos

http://www.youtube.com/watch?v=F-h7G0h9Ip0&feature=autoplay&list=PL82758DE4FBD2555A&index=7&playnext=3

http://www.youtube.com/watch?v=rkGVE6wNAzo

The Rock Cycle

We have learned that Igneous Rocks are formed when magma or lava cools

Sedimentary Rocks are formed from sediments are compacted and cemented together

Metamorphic Rocks are formed from both igneous and sedimentary rocks which have undergone high pressure and heat

The Rock Cycle

Because rocks are continually changing on an ongoing basis we call this process “The Rock Cycle”

Mechanical Weathering

As we have learned, sediment is formed when larger rocks have broken or become worn away from a natural process known as weathering.

Mechanical Weathering is defined by rocks that are physically broken up by things such as gravity, weather and erosion. Example: When a rock falls off a cliff, gravity

pulls it to the ground and parts can become broken off.

Erosion and Deposition

Erosion is a type of mechanical weathering that “wears away” and deposition is a process that build up by blowing sediments from one place to another

Erosion Deposition

Chemical Weathering

Chemical Weathering is a breakdown of minerals due to a chemical reaction with water, chemicals dissolved in the water, or with gases in the air. Example: Acid Rain – can react with some

rocks

Photo: Limestone is weathered due to rainwater

Biological Weathering

Biological Weathering is the when rocks are broken physically or chemically due to living organisms (plants, animals, bacteria, and fungi).

And Now…Mr. Parr