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The Rock Cycle
The Earth can be considered to be a ball of rock. Rocks are formed on and beneath the Earth’s surface by certain
geological processes both physical and chemical. The Earth is continually changing and so are the rocks it contains. The
rocks are continuously redistributed and recycled. The set of
processes by which new rocks are formed from old rock material is
called the rock cycle. This has been occurring continuously
throughout the history of the Earth.
Crystallization of Magma
Magma deep below the
Earth's crust travels
towards the surface via
an erupting volcano in the form of lava. The lava rapidly cools on exposure
at the Earth's surface forming extrusive igneous rock. Sometimes the
magma cools and crystallizes below the Earth's crust to form intrusive
igneous rock.
Weathering & Erosion
The solidified lava on the Earth's surface along with other rocks
exposed due to uplift are acted upon by the destructive power of
weathering and broken down. Erosion carries this material via various
transporting agents. This process removes old rock and exposes new
rock from within the Earth's crust.
Deposition The transported rock fragments or sediments are
laid down or deposited in a process called deposition. Most of the
sediments eventually end up being deposited in the seas and oceans
via rivers.
Compaction & Cementation (Lithification)
Overtime sediments accumulate at the bottom of the seas and oceans. As
the layers of sediment build up the rock fragments at the bottom are
compacted by the weight of the overlying layers. The particles are then
cemented together to form a solid rock called sedimentary rock.
Deformation & Metamorphism
Sedimentary rock is forced underground by movement of the
tectonic plates. The rocks are exposed to heat and immense
pressure which causes them to change chemically and for
metamorphic rocks. Uplift of the Earth's crust via Earthquakes
exposes rocks to the Earth's surface.
Melting
As the rocks get pushed further underground they are exposed to
such immense heat that they melt to form magma and so they begin
their journey through the rock cycle again.
Types of Rock: Rocks are not all the same!
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
Sedimentary rocks are formed from particles of sand, shells, pebbles, and other
fragments of material. Together, all these particles are called sediment.
Gradually, the sediment accumulates in layers and over a long period of time
hardens into rock. Generally, sedimentary rock is fairly soft and may break apart
or crumble easily. You can often see sand, pebbles, or stones in the rock and it is
usually the only type that contains fossils.
Examples of this rock type include conglomerate and limestone.
Metamorphic
Metamorphic rocks are formed under the surface of the earth from the
metamorphosis (change/ transform) that occurs due to intense heat and
pressure (squeezing). The rocks that result from these processes often have
ribbon-like layers and may have shiny crystals, formed by minerals growing
slowly over time, on their surface. Foliated (banded/ striped) versus nonfoliated
(no stripes or bands).
Examples of this rock type include gneiss and marble.
Igneous
Intrusive Igneous rocks are formed when magma (molten rock deep within the
earth) cools and hardens slowly. Sometimes the magma cools inside the earth,
and other times it erupts onto the surface from volcanoes (in this case, it is called
lava). When lava cools very quickly, no crystals form and the rock looks shiny and
glasslike, forming extrusive igneous rock. 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.
Questions:
1. What is the difference between intrusive and extrusive igneous rocks?
2. What POWERS the actual rock cycle (where does the energy come from)?
____________________ & ____________________
3. What is the difference between foliated & nonfoliated metamorphic rocks?
4. Which rock texture is formed from slow cooling?
5. What are sedimentary rocks made out of?
6. Explain weathering, erosion and deposition.
7. Explain compaction and cementation
8. What are metamorphic rocks?
9. Write your own and have partner answer.
10.
Write your own and have partner answer.
1. What is the difference between intrusive and extrusive igneous rocks?
 Intrusive: Cool Slowly from magma (inside)
 Extrusive: Cool Quickly from lava (outside)
2. What POWERS the actual rock cycle (where does the energy come from)?
 Earth’s interior and the sun
3. What is the difference between foliated & nonfoliated metamorphic rocks?
 Foliated: banded / striped/ layered
 Nonfoliated: no bands
4. Which rock texture is formed from slow cooling? Intrusive igneous rock
5. What are sedimentary rocks made out of? Sediments (fossils found here)
6. Explain weathering, erosion and deposition.
 Weathering: breaking down of materials
 Erosion: carrying away of sediments/ materials
 Deposition: materials are deposited in new area
7. Explain compaction and cementation
 Compaction: layers are pressed together over time
 Cementation: after compaction sediments are cemented together to form
rock
8. What are metamorphic rocks? Rocks that undergo changes due to heat and
pressure.