Rocks and the Rock Cycle

Ch 10.2Please take notes

Rocks• Rocks are made of

minerals

– Minerals are inorganic, naturally occurring solid materials (pure or compound)

– Can you think of any examples of minerals?

Rock Families

• There are three families

– Igneous– Sedimentary– Metamorphic

The word igneous comes from the Latin word ignis- meaning fire… why call them igneous?

Igneous Rock• Formed when hot

magma and hot lava cool and solidify

• 2 types are:– Intrusive: when magma

cools and solidifies in the Earth’s crust (granite)

– Extrusive: when lava cools and solidifies on the Earth’s crust

See fig 10.11, page 289Also:

Rock Hounds - Igneous Rock

Sedimentary Rock• Is made up of sediments, loose

material (rock, minerals, plants and animal remains). They become closely packed and cemented together

• Form layers called beds• Formed by compaction

Limestone is sedimentary rock made up of fossils, organic sedimentary rock

See Fig 10.14ABC, page 293

Also:Rock Hounds - Sedimentary Rock

Metamorphic Rock

• Is a rock that has changed from the parent rock (original rock) due to intense pressure or heat. Slate Schist Gneiss

(from shale)

See fig 10.16, page 294

Also:Rock Hounds - Metamorphic Rock

The Rock Cycle

• Rocks continue to change in an ongoing process called the Rock Cycle

– See fig 10.17, page 295

Weathering

• Weathering is the natural break down of rocks

Three Types Are:

• Mechanical• Chemical• Biological

Mechanical Weathering• Abrasion

– Abrasion is the wearing down of rocks by solid particles carried by wind or water.

• Frost– Freezing water can cause a lot of damage to rocks.

This happens because when water freezes it expands, or spreads out and gets larger.  When water gets into cracks in rocks and freezes, it also expands.  This expansion of water when it freezes can produce enough force to crack rocks apart.

• Gravity – Gravity is another cause of erosion because it can

pull loose materials down hills in a landslide. 

Abrasion– Rocks found in rivers are

usually very smooth and round.  The moving water carries with it loose rocks and other materials.  These pieces crash into one another and are sometimes scraped along the river bed which can break the rocks into smaller pieces. 

– The wind can also pick up sand and slam them into other rocks.  The sharp edges of the sand can have a dramatic effect on larger rocks and sometimes creates very stunning formations.

Frost/Wedging• If you've ever placed a closed

container such as a soda pop in the freezer and forgot about it you probably returned to find that the container had been split open. 

  • Potholes in roads and cracks in

rocks are often caused by the repeated freezing and expansion of water in small cracks. 

• Road crews are busiest during early spring trying to repair the potholes caused by the cold temperatures of winter.

Gravity• A landslide is a large, sudden

movement of loose rocks and soil. 

• As the rocks are falling down the hill they bump into one another and can be broken into smaller pieces. 

• The rocks on a hill can be loosened by other factors such as heavy rains or human activity.

Chemical Weathering• Chemical reactions break down

the bonds holding the rocks together, causing them to fall apart, forming smaller and smaller pieces.

• Chemical weathering is much more common in locations where there is a lot of water. This is because water is important to many of the chemical reactions that can take place. Warmer temperatures are also more friendly to chemical weathering.

Types of Chemical Weathering• Oxidation takes place when oxygen combines with

other elements in rocks to form new types of rock. These new substances are usually much softer, and thus easier for other forces to break apart.

• Hydrolysis occurs when water combines with the substances in rocks to form new types of substances, which are softer than the original rock types. These allows other forces such as mechanical weathering to more easily break them apart.

• Carbonation takes place when carbon dioxide reacts with certain types of rocks forming a solution, that can easily be carried away by water.

Biological Weathering

• The word ‘bio’ means life. Thus biotic or biological weathering is any type of weathering that is caused by living organisms.

Types of Biological Weathering• Most often the culprit of biotic weathering are plant roots.

These roots can extend downward, deep into rock cracks in search of water, and nutrients. In the process they act as a wedge, widening and extending the cracks.

• Other causes of biotic weathering are digging animals, microscopic plants and animals, algae and fungi.