The rock cycle

The Rock Cycle
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stAIR Project

By: Sarah Barnes


How Rocks Change

 Introduction
All rocks change slowly from one type to another, again and again.
The changes form a cycle, called "the rock cycle."
The way rocks change depends on various processes that are
always taking place on and under the earth's surface. Now let's take
a closer look at each of these processes.


Heat & Pressure

 Heat
Deep below the earth's surface, temperatures are hot enough to
melt most rocks. However, before the melting point is reached, a
rock can undergo many changes while in a solid state — changing
from one type to another without melting.

 Pressure
An additional factor that can transform rocks is the pressure caused
by tons of other rocks pressing down on it from above.

Heat and pressure usually work together to alter the rocks under
the earth's surface. This kind of change is called metamorphism
which results in a metamorphic rock.

 Click here to see the heat and pressure video:
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Melting & Cooling
Melting
The high temperatures required to melt a rock are generally found only deep within the
earth. It takes temperatures between 600 and 1,300 degrees Celsius (1,100 and 2,400
degrees Fahrenheit) to melt a rock, turning it into a substance called magma (molten
rock).

Cooling
Liquid magma also turns into a solid — a rock — when it is cooled. Any rock that forms
from the cooling of magma is an igneous rock. Magma that cools quickly forms one kind
of igneous rock, and magma that cools slowly forms another kind.
Extrusive Igneous
When magma rises from deep within the earth and explodes out of a volcano, it is called
lava, and it cools quickly on the surface. Rock formed in this way is called extrusive
igneous rock. It is extruded, or pushed, out of the earth's interior and cools outside of or
very near the earth's surface.
Intrusive Igneous
Magma that gets pushed up toward the earth’s surface cools at a much slower rate than
lava. The kind of rock formed in this way is called intrusive igneous rock. It intrudes, or
pushes, into the earth's interior and cools beneath the surface.
Click here to see the melting and cooling video:
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Weathering & Compacting

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Weathering

Weathering, such as rain or wind, cause rocks to get eroded or broken down into smaller
pieces. These small pieces of rock form the sediment that creates sedimentary rock.

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Compacting

As these little pieces of sediment get compacted together, they eventually for a
sedimentary rock.

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Click here to see the weathering and compacting video:

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The Rock Cycle

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Types of Rocks
Rocks are not all the same!
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The three main types, or classes, of rock are sedimentary, metamorphic, and igneous

and the

differences among them have to do with how they are formed.

Sedimentary
Formed from particles of sand, shells, pebbles, and other fragments of material.
These particles or sediments accumulate and harden into rock.
You can often see sand, pebbles, fossils or stones in the rock.

Examples of this rock type include conglomerate and limestone.
Metamorphic
Formed under the surface of the earth
Go through metamorphosis (change) that occurs due to intense heat and pressure (squeezing).
Usually have ribbon like layers and may have shiny crystals.

Examples of this rock type include gneiss and marble.
Igneous
Formed when magma or lava cools and hardens.
When lava cools very quickly, no crystals form and the rock looks shiny and glasslike.
Sometimes gas bubbles are trapped in the rock during the cooling process,
leaving tiny holes and spaces in the rock.

Examples of this rock type include basalt and obsidian.


What to Look For:
 Here's a chart of some of the key characteristics that can help
you identify the rocks within these three main classes.

Sand or pebbles

Fossils

Gas bubbles

Glassy surface

Ribbonlike layers

Individual stones,

Imprints of leaves, shells,

"Holes," like Swiss cheese,

A shiny and smooth

Straight or wavy stripes of Small, flat surfaces that

pebbles, or sand grains

insects, or other items in

in the rock.

surface, like colored glass.

different colors in the

are shiny or sparkly, like

visible in the rock.

the rock.

rock.

tiny mirrors

Sedimentary

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Igneous

Crystals

Metamorphic

.


Let’s Review
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To take the quiz hit the start button. If you don’t feel ready to take the quiz and need to look over the
information more, press the back arrow.

 Which type of rock is this?
metamorphic
sedimentary
igneous


WRONG!
Click this button to try again:


Correct!
You can tell that this rock is igneous because of
its shiny, glasslike surface.


 Which type of rock is this?
metamorphic
sedimentary
igneous


WRONG!
Click this button to try again:


Correct!
You can tell that this rock is sedimentary
because it has large chunks of other rocks in

it.


 Which type of rock is this?
metamorphic
sedimentary
igneous


WRONG!
Click this button to try again:


Correct!
You can tell that this rock is metamorphic
because of the rippled layers.


 Which type of rock is this?
metamorphic
sedimentary
igneous


WRONG!
Click this button to try again:


Correct!
You can tell that this rock is sedimentary because you

can see fossils embedded in the rock.


The End!
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Hopefully you have learned a lot about the rock cycle!

Information and videos from: />