Rocks & the Rock Cycle
Key Concepts
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What are the 3 major groups of rocks?
How do igneous rocks form?
How are sedimentary rocks classified?
How do metamorphic rocks form?
How can one type of rock change into another?
Every rock has a story to tell….
• We pass by rocks every day….
 Never thinking of their place of origin, age, or reason for even
being here
So maybe it’s just that some people collect rocks, like stamps,
solely for habit and maybe the occasional insight?
 NO WAY!!!!
 Rocks are good story tellers….problem is, in order to know the
story, you have to be trained a bit ;)
Why study rocks?
• Geologists study rocks because they contain
clues about what the Earth was like in the past
 Can assemble a historical record of a planet
 Trace events that occurred long before humans
Helps us answer questions such as:
 Was there a lake or volcano present where the rock was found?
 Was there a mountain range or sea?
 Was it hot or cold?
 Was the atmosphere thick or thin?
Basic point is to better understand our world. This
helps us to better coexist with nature and reap the
benefits that it has to offer
Classification
• Because rocks are simply a combination of 1 or
more minerals, we must have a way to classify
them
• Properties used to identify rocks include:
• Classified into 3 major groups--
Igneous Rocks
Igneous rocks• Magma
Magma that flows out of volcanoes is called ________
How does igneous rock form?
Inside Earth:
Outside Earth:
Igneous Rocks
• Extrusive vs. Intrusive
 Differences in texture caused by differences in how
they formed
 Intrusive igneous rocks cool ________ underground
 Extrusive igneous rocks very _______ at the surface
Intrusive vs. Extrusive
Igneous Rocks
• Color
• Rock’s composition
Sedimentary Rock
• Rock that forms over time as sediment is
squeezed and “cemented” together
 Sediment:
 Formation of sedimentary rock:
 3 main groups of sedimentary rocks:
1.)
2.)
3.)
FYI: fossils are mainly found in sedimentary rocks.
Clastic Rocks
Conglomerate:
Chemical & Organic Rock
Chemical Rock
 Form when minerals precipitate out
of solution
 Rainwater dissolves many minerals
Organic Rock
 Result of organic processes
 Marine animals such as coral, clams, and
mussels extract CaCO3 from ocean water
to form their shells and skeletons
 After they die, their shells & skeletons sink
to ocean floor
 Over time, fragments compact and cement
together, forming limestone
Metamorphic Rock
• Metamorphic rock:
 Forms when a rock is transformed by heat, pressure, or
chemical reactions.
 Most form under high T & P deep underground.
Metamorphism can result in a rock with a mineral content that is
____________ from the original rock
Metamorphic Rock Formation
The Rock Cycle
• We must recognize Earth as a dynamic planet
 Constructive forces form new igneous rock
 Destructive forces break down rock, forming sediment
 Other forces push rock deep beneath surface, where heat & pressure form
metamorphic rock
• These changes form a cycle
 Rock cycle:
The Rock Cycle
As you can see, rocks don’t always form in just one specific path…
Videos to help
• The Rock Cycle
• Causes of Metamorphism