Science, Grade 6


Table Of Contents: Rocks

1. Classifying Rocks

2.1. Rock Definition
Rocks are solid, naturally occurring substances composed of one or more minerals and other matter. Rocks are classified into three groups according to how they are formed.
2.2. Igneous Rocks
Igneous rocks form when liquid rock cools and hardens.
2.3. Sedimentary Rocks
Sedimentary rocks form from weathering or layering that takes place over millions of years.
2.4. Metamorphic Rocks
Rocks that change due to intense heat or pressure in the Earth's crust are called metamorphic rocks.

2. Igneous Rocks

3.1. Formation and Classification of Igneous Rocks
Igneous rocks form from cooling magma and lava. They are classified according to their mineral origin, texture and composition.
3.2. Origin of Igneous Rocks
The origin of igneous rocks is either intrusive or extrusive. Cooling magma below the Earth's surface forms intrusive rocks, while erupting lava forms extrusive rocks.
3.3. Igneous Rock Texture
The texture of an igneous rock is related to how long it takes to cool. Slow-cooling rock forms more crystals and has coarse grain. Fast-cooling rock has fine grain.
3.4. Igneous Rock Composition
Dark igneous rocks, referred to as mafic, have high concentrations of calcium, iron and magnesium. Light igneous rocks are described as felsic, and they have high concentrations of silica, aluminum and potassium.
3.5. Basalt
Basalt is a dark igneous rock with visible crystals. It is the most common extrusive rock, forming most of the ocean's crust.
3.6. Obsidian
Obsidian is a dark, glassy, extrusive igneous rock. It cools so quickly that it does not have visible crystals.
3.7. Pumice
A lightweight rock called pumice is formed when lava froths up with gases. Pumice is the only rock that can float on water.
3.8. Granite
Granite is a light-colored, intrusive igneous rock with visible crystals. It is found at the core of most mountains.
3.9. Igneous Rock Uses
Igneous rocks have a variety of uses. Pumice is used as an abrasive, and granite is used to make porcelain. Many other types of igneous rock are used in the building industry.

3. Pause and Interact

4.1. Review
Use the whiteboard tools to complete the activity.

4. Sedimentary Rocks

5.1. Formation of Sedimentary Rocks
Sedimentary rocks form in layers, or strata, that have been deposited and cemented together over millions of years.
5.2. Sedimentary Rock Categories
There are three categories of sedimentary rock—clastic, organic and chemical.
5.3. Clastic Sedimentary Rock
Clastic sedimentary rocks are made from pieces of pre-existing rocks that are transported by wind and water and deposited in a new location. Layers of sediment accumulate and become cemented together to form solid rock.
5.4. Clastic Sedimentary Rock Examples
Sandstone, shale and conglomerate are examples of clastic sedimentary rocks.
5.5. Organic Sedimentary Rock
Organic sedimentary rocks form when shell remains fossilize and become a layer of limestone on the ocean floor. A coral reef is an example of organic limestone formed from the buildup of coral skeletons.
5.6. Chemical Sedimentary Rock
Chemical sedimentary rocks form through precipitation or crystallization of dissolved minerals. Dissolved calcite forms fine-grained limestone that shows no fossilized remains.
5.7. Sedimentary Rock Uses
Limestone is primarily used for concrete and road construction. Coal is a type of organic sedimentary rock that is used as a solid fuel to produce electricity and heat.

5. Pause and Interact

6.1. Review
Use the whiteboard tools to complete the activity: Compare and contrast the three types of sedimentary rock.

6. Metamorphic Rocks

7.1. Formation of Metamorphic Rocks
Metamorphic rocks are formed from any type of rock that changes as a result of intense heat and pressure in the Earth's crust.
7.2. Shale Metamorphism
For example, as sedimentary shale is exposed to more heat and pressure, it changes into different types of metamorphic rocks.
7.3. Contact and Regional Metamorphism
Contact metamorphism occurs when rocks come in contact with magma. Regional metamorphism occurs when intense pressure, such as mountain formation, changes large-scale areas of rocks.
7.4. Foliated Metamorphic Rock
Metamorphic rocks are classified as foliated or nonfoliated. Foliated rocks have grains arranged in thin parallel layers or bands. Slate and gneiss are examples.
7.5. Nonfoliated Metamorphic Rock
Nonfoliated metamorphic rocks have a random arrangement of crystals or grains without layers or banding. Examples include marble and quartzite.
7.6. Metamorphic Rock Uses
Metamorphic rocks are used primarily for construction purposes. Marble is used for decorative statues, columns and flooring. Slate is used for roofing and walkways.

7. The Rock Cycle

8.1. Rock Cycle Diagram
The Earth is a dynamic planet, and its rocks are constantly changing. The rock cycle shows how different natural processes transform rocks from one type to another.
8.2. Sedimentary Rock Formation
All types of rock can be weathered, transported and cemented into layers to become sedimentary rock.
8.3. Metamorphic Rock Formation
Under intense heat and pressure, any type of rock can be transformed to metamorphic rock.
8.4. Igneous Rock Formation
When metamorphic rock is heated to its melting point and then cooled, it becomes igneous rock.

8. Pause and Interact

9.1. Rock Uses
Follow the onscreen instructions.
9.2. Rock Cycle

9. Vocabulary Review

10.1. Vocabulary Matching Review
In this virtual investigation you will identify rocks by observing their physical properties. After gathering data about an unknown rock, you will refer to an identification chart to determine the rock's identity.

10. Virtual Investigation

11.1. Rock Identification

11. Assessment

12.1. Rocks