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R
oc
ks Chapter 3
Rocks
• Naturally occurring solid
material made of one or more
minerals
• Grouped into 3 main types,
based on the way it was formed
IGNEOUS ROCKS
• Formed from magma that
cools and hardens
• “Fire Formed”
IGNEOUS ROCKS: 2 types
• Intrusive rocks: • Extrusive rocks:
– formed deep
– formed from
within Earth
lava at Earth’s
surface
– Cools slowly,
large crystals
– Cools quickly,
small crystals
– Coarse
grained
– fine grained
IGNEOUS ROCKS: texture
• Size of crystal grains and
chemical composition are used
to classify igneous rocks
– Texture depends on time it
takes a rock to harden
(cooling rate)
IGNEOUS ROCKS: porphyry
(POR-fuh-ree)
• Igneous rock
with a mixture
of large and
small crystals
Two types of magma
• Felsic:
– Lightcolored
– Thick and
slow flowing
– Rich in silica
• Mafic:
– Dark-colored
– Very fluid
– Rich in iron
Scoria
Igneous Rock Structures
• Intrusions – • Extrusions –
underground surface
rock masses rock masses
INTRUSIONS
•Batholiths
– largest igneous intrusions
– Form when huge bodies of
magma cool underground
– Cover 1000 km
Batholith
INTRUSIONS
•Laccoliths
– Domelike masses formed from
magma bulging upward
This laccolith in Red and White Mountain, Colorado, is of
Tertiary age. Overlying layers of rock have been eroded.
INTRUSIONS
•Dike
– Sheets of igneous rocks that
cut across the rock layer
Dike
Dike
INTRUSIONS
•Sill
– Sheet of hardened magma
that forms between and
parallel to layers of rock
Sill
EXTRUSIONS
•Volcanic neck:
– The plug of hardened magma
left in the vent from which
lava flowed
Volcanic neck:
INTRUSIONS
•Stock
– Similar to batholiths but less
than 100 km
Sedimentary Rocks
•75% of Earth’s
surface is
sedimentary rock!
How Sedimentary Rocks are made:
1. Mud, sand, gravel and shells are sediments
that make up rocks
2. Sediments are moved by wind and water
3. Compaction: Pressure placed in sediment
layers cause them to change to rocks
4. Cementation: sediments are joined
together (cemented) by minerals dissolved
in water
5. This process results in the formation of
layers called strata.
The major
characteristics of
all sedimentary
rocks is that they
form layers!
"For your information,
there's a lot more to ogres
than people think...
Ogres are like sedimentary rocks!
…Sedimentary rocks have layers...
Ogres have layers!
...We both have layers."
Sedimentary rocks usually form
in water
• Ripple marks and mud cracks
Fossils often preserved in
sedimentary rocks
Sedimentary Rocks: Classified by
• Composition
• Texture
• Grain size
Types:
1.Clastic
2.Organic
3.Chemical
1. Clastic Rocks
• Formed by broken pieces
or fragments of rock
• Classified according to
size and shape of
fragments
Clastic Rocks
Conglomerates:
• Made of rounded pebbles and other
rocks of different sizes and
cemented together by clay, mud ,or
sand
• Formed when rivers deposit large
pieces of rock
• Pieces of rock rounded by water
before deposited
Conglomerate:
Clastic Rocks
Breccia:
• Similar to conglomerates, but
fragments are sharp and
angular
• Not carried far enough by
water to round the edges
Breccia:
Clastic Rocks
Sandstone:
• Made of small, sand-sized
grains
• Very common
• Resistant to wear and
decay
• Used to make buildings
Sandstone:
Clastic Rocks
Mudrock:
• Formed from small
particles of clay
• Example: shale
shale
shale
2. Organic Rock
•Formed directly or
indirectly from
material that used to
be living
Organic Rock
Fossilized Limestone:
• Shells from dead animals
(containing calcium
carbonate) that sink to
bottom of ocean floor
Limestone:
Organic Rock
Chalk:
• Composed of animals and
calcium carbonate that have
been pressed together
Chalk
Organic Rock
Coal:
• Rock formed
from plants
that lived
millions of
years ago
3. Chemical Rock
• Formed by chemical means that
do not involve any living
organisms
• Can occur through evaporation
or chemical action
Chemical Rock
Limestone:
• Formed directly from
ocean water instead
of organisms
Chemical Limestone:
Chemical Rock
Rock salt:
• Natural form of
common table salt
• Ex: Halite
Chemical Rock
Rock gypsum:
Metamorphic Rocks
Metamorphism:
• Changing of one type of rock in to
another due to 1. Tremendous heat
2. Great pressure
3. Chemical reactions ( a change in
composition of minerals)
Metamorphic Rocks
Types of Metamorphism:
1. Contact Metamorphism
•
•
Occurs when rocks are heated by contact with
magma or lava
Covers a small area
2. Regional Metamorphism
•
•
Occurs when rocks are buried deep beneath
Earth’s surface and changed by increase in
temperature and pressure
Covers a large area
Types of Metamorphic Rock:
1. Foliated Texture:
Mineral crystals arranged in parallel
layers or bands (flatten under
pressure)
Slate Schist  Gneiss
(from clay or shale)
(from granite, basalt, or slate)
(from granite)
Foliated Texture:
slate
Foliated Texture:
phyllite:
Foliated Texture:
gneiss:
Types of Metamorphic Rock:
2. Unfoliated Texture:
• No bands of crystals
• Don’t break in layers
Unfoliated Texture:
marble
Unfoliated Texture:
quartzite