Download Rocks and the Rock Cycle

Rocks and the Rock Cycle


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 are formed when magma and
hot lava cool and solidify

Magma – is melted rock that is found inside and
below the Earth’s crust in the Mantle. The Mantle is
mostly solid. Extreme heat causes the Mantle to
move in currents
The Mantle

Convection currents in the magma drive plate
tectonics. Heat generated from pressure and the
radioactive decay of elements deep in the interior of
the Earth creates magma


Geologists classify igneous rocks based on
where they were formed above or below the
Earth’s surface. There are 2 types of igneous
rocks.
Types of Igneous Rocks:


Intrusive Rock
Extrusive Rock


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 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: Basalt
http://www.youtube.com/watch?v=nuIercRAxQU&feature=related



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



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


As the layers of sediment begin to form on top
of each other, their weight causes the rocks to
become compacted (squeezed together) or
Lithification
In some rocks the minerals dissolve in the
water creating a natural cement that holds the
rock together

This process is known as Compaction
Lithification

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 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



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

Because rocks are continually changing on an
ongoing basis we call this process “The Rock
Cycle”


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 is a type of mechanical weathering
that “wears away” and deposition is a process
that build up by blowing or “depositing”
sediments from one place to another
Erosion
Deposition
Grand Canyon
Arizona
Devils Tower
Wyoming

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
Amphibolite
Metamorphic Rock (from Basalt)
Gneiss
Metamorphic Rock (from Granite)
Limestone
Sedimentary Rock
Shale
Sedimentary Rock
Slate
Metamorphic Rock ( from Shale)