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ROCKS
Chapter 4 Sections 1 and 2
Rock Cycle and Igneous
Rocks
What is a rock?
A
rock is a mixture of broken rock
fragments, volcanic glass, organic
matter, and other natural materials.
Example of
Andesite
Common Rock Forming
Minerals
Quartz
 Feldspar
 Hornblende
 Mica

Example of
granite
The Rock Cycle
crystallization
The Rock Cycle



The rock cycle shows how rocks slowly change
through time.
The rock cycle shows the three types of rocksigneous, metamorphic, and sedimentary and the
processes that form them.
Example: A sedimentary rock can change by heat and
pressure to form a metamorphic rock. The
metamorphic rock can melt and cool to form and
igneous rock. The igneous rock can be broken into
sediments by weathering and eroding away. The
sediments might then compact and cement together
to form a sedimentary rock.
Example of Metamorphic Rock
Gneiss
Example of Sedimentary Rock
Conglomerate
Example of an Igneous Rock
Rock Cycle
– The main processes found in the rock
cycle are
– Melting and Cooling magma form
igneous rocks.
– Weathering and erosion break rocks into
sediments.
– Compaction and Cementation change
rocks into sedimentary rocks.
– Heat and Pressure form metamorphic
rocks
Formation of Igneous Rocks
 When
hot magma cools and hardens,
it forms igneous rocks.
 Because magma is less dense than
surrounding rocks, it is forced
upward towards the surface. When
magma reaches the Earth’s surface
and flows from volcanoes it is called
lava.
Lava Picture before solidification
Lava picture after solidification
Intrusive rocks
 Rocks
that form from magma below
the surface of Earth are called
intrusive igneous rocks.
(intrusive=inside).
 Intrusive igneous rocks take a long
time to form. Slowly cooled magma
produces large individual mineral
grains in the rocks.
Granite
Diorite
Gabbro
Extrusive Rocks
Extrusive igneous rocks are formed as
lava cools on the surface of the Earth.
(extrusive=exterior=outside).
 When lava flows on the surface it is
exposed to air and water. Under these
conditions the lava cools very quickly.
 When the lava cools quickly, the atoms in
the liquid don’t have time to arrange into
large crystals, which is why extrusive
igneous rocks are fine-grained.

Extrusive Rocks
 Pumice
and Obsidian are examples of
volcanic glass. These rocks cooled so
quickly that few or no mineral grains
formed.
 In the case of pumice gases became
trapped in the molten material as it
cools. The gases escape, but holes
are left behind where the rock
formed around the pockets of gas.
Basalt
Rhyolite
Andesite
Pumice
Obsidian
Classifying Igneous Rocks



Igneous rocks are intrusive or extrusive
depending on how they formed.
A further way is to classify these rocks is by the
magma from which they formed.
Basaltic igneous rocks are dense, dark-colored
rocks. They form from magma that is lacking
silicon.
-Basaltic lava is fluid and flows freely from
volcanoes in Hawaii.
-These rocks are also called mafic igneous rocks.
-These rocks compose the seafloor.
Classifying Igneous Rocks

Grantic igneous rocks are light-colored
rocks of lower density than basaltic rocks.
Granitic magma is think and stiff and
contains a lot of silica.
– Grantic magma is stiff and builds up a a large
amount of gas pressure which is released
explosively during a volcanic eruption.
– These rocks are called felsic igneous rocks.
– The continents are composed mainly of
granite.
Classifying Igneous Rocks.
 Andestic
igneous rocks have mineral
compositions between those of
granitic and basaltic rocks. Many
volcanoes around the rim of fire
formed from andesitic magma.