Download 31.3 Sedimentary Rocks Blanket Most of the Earth`s Surface

Rocks


Sedimentary rock: formed by pieces of
rock carried by water, wind, or ice
Warm-Up:



What was your favorite food you ate on
Thanksgiving?
How are rocks and minerals related?
What are some everyday uses for rocks?


Metamorphic rock: formed by high heat,
high pressure, or both
Warm-Up:


How could sedimentary or igneous rock change
to metamorphic?
How could igneous or metamorphic change to
sedimentary?


Shield volcanoes: broad, gently sloping
cones
Warm-Up:

List the 3 types of rocks and explain how each
forms


The Earth’s surface is constantly changing
due to the theory of plate tectonics
Earth’s rocks are classified into three
categories

Igneous rocks: formed by the cooling and
crystallization of magma
 Make up 95% of the earth’s crust
 Examples: Basalt, granite

Sedimentary rocks: formed from pieces of
other rocks carried by water, wind, or ice
 Most common on the earth’s surface
 Examples: sandstone, shale, limestone

Metamorphic rocks: formed from older rocks
that are changed by high temperature, high
pressure or both
 Examples: marble, slate

Some Igneous rocks form at the earth’s
surface
Igneous rocks that form at the earth’s surface
are called extrusive
 Magma can differ in the amount of silicon it
contains
 What does silicon determine?

 Melting temperature

Higher amounts of silicon = thick, more
viscous magma

What does viscous mean?
 Gooey, sticky

Lower amounts of silicon = thinner, faster
flowing magma


Spilled milkshake vs. spilled milk
Basaltic magma- important low-silicon, fastflowing magma

Temperature also affects magmas ability to flow
 Hotter magma flows better than cooler magma



Lava – magma that flows onto the surface of
the earth
Lava most commonly comes out of
fractures and cracks in the earth’s surface
called fissures
Can also come out of a central vent or
volcano


Lava can come up through cracks
underwater or on land
Some igneous rocks form below the earth’s
surface



These rocks are called intrusive
Large intrusive rocks are plutons
Concept check:


Why is it incorrect to say that igneous rocks
may form from the intrusion of lava?
How could you correct the statement?


Most common rock on earth’s surface
Covers 2/3 of the Earth’s surface


Volcanism constantly makes new rock and
weathering is the opposite process; it
breaks down rock
Two kinds of weathering
Mechanical– physically breaks rocks into
smaller pieces
 chemical- chemical reactions that involve
water and decompose rock into smaller pieces
Erosion- process that removes weathered rock
particles and transports them by wind, water, or
ice

•
When transportation stops, deposition and
sedimentation begin

Deposition – particle being transported stops
and is deposited



Larger grains are deposited first
Grains end up sorted by size

Sedimentation – sediment particles are
deposited one layer at a time
As sedimentation builds up it starts changing
into sedimentary rock
 Occurs in two ways:



compaction- layers are pressed together and
water is squeezed out
cementation- chemicals in the water fill the
pores and act like a glue to hold the grains
together




Clastic Sediments – sediments composed
of small fragments of other rocks
Three most abundant: shale, sandstone,
conglomerate
Limestone and evaporitesare also
sedimentary rocks
Sedimentary rock contain fossils
Why would sedimentary rock contain fossils?
Fossils are important for information about
the past
Fossil Fuels-






oil- Sediment is buried and heated over a long
period of time
Natural gas – higher temperature
coal- plants that do not completely decay

All three types of rock can undergo
change and becomes metamorphic

Example of metamorphism:
 Potter’s clay
NO MELTING OCCURS!
 Recrystallization – minerals in a rock change
because the rock is exposed to high
temperature and pressure
 Mechanical deformation- rock is subjected to
physical stress deep in earth’s crust


Two Kinds of Metamorphism

contact- occurs when a body of rock is
intruded by magma
 causes increased grain size due to recrystallization
 Near contact = low water content, larger crystal
size

regional- rocks change when subjected to
physical stress and heat over a large region
 Found a lot in mountains
 Heat and pressure can produce beautiful gems



Foliated Metamorphic Rock –
has a layeredappearance
Examples: slate, schist, gneiss
Nonfoliated metamorphic rocks
have a smoother appearance


Foliation only develops if the
pressure is high enough, if not, we
get nonfoliated rocks
Examples: marble, quartzite