Download What is a Rock?

What is a Rock?
 Naturally-occurring
mixtures of
minerals, mineraloids, glass or organic
matter.
What is a Rock?
 Rocks
are divided into 3 groups based
on how they were formed:
 IGNEOUS
 SEDIMENTARY
 METAMORPHIC
What is the difference
between a rock and a
mineral?
 Rocks
are made up of Two or MORE
minerals.
Once a rock is formed, does it
stay the same rock forever?
 NO!
 Rocks
are continually changed by
many processes, such as
weathering, erosion, compaction,
cementation, melting, and cooling
 Rocks
can change to and from the
three types
What is the process through
which rocks change?
 The
Rock Cycle—earth materials change
back and forth among the different
types of rocks
 No
set path a rock takes to become
another kind of rock
IGNEOUS
Weathering, Erosion,
Compaction,
Cementation
Recrystallization
Melting,
Solidification
Melting,
Solidification
Recrystallization
METAMORPHIC
SEDIMENTARY
Weathering, Erosion,
Compaction,
Cementation
How are rocks redistributed?
 The
core, mantle, & crust are one giant
rock recycling machine
1.
2.
3.
What do igneous rocks form from?
What kind of rock is sandstone?
What are metamorphic rocks formed
by?
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“Ignis” = Latin for “fire”
Formed from the cooling of either magma or
lava
The most abundant type of rock
Classified according to their origin and
composition
ORIGIN— Where rocks are formed
 Below
ground = from magma (intrusive
igneous rock)
 Usually
slowly)
have LARGE crystal grains (they cooled
Some have large & small crystals
(called porphyritic)
 Above
ground = from lava (extrusive
igneous rock)
 Usually
have SMALL or NO crystals (they
cooled too quickly)
Practice Classifying Igneous Rocks as
intrusive or extrusive—
#2 Granite: Intrusive or
Extrusive? Why?
#12 Obsidian: Intrusive or
Extrusive? Why?
COMPOSITION— What kind of
substances the rocks are made of
Basaltic Igneous Rocks
—made
from lava/magma that is low in silica, rich
in iron and magnesium. Rocks are darkcolored.
Granitic Igneous Rocks—made
from magma/lava high in silica
and oxygen. Rocks are lightcolored.
Andesitic Igneous Rocks—
have a composition between
basaltic and granitic.
 Formed
from sediments
(rock fragments, mineral
grains, animal & plant
remains) that are
pressed or cemented
together or when
sediments precipitate
out of a solution.
 These
sediments are moved by wind,
water, ice or gravity.
 Sedimentary rocks represent 7% of the
Earth’s crust, but they cover 70% of
the Earth’s surface.
 Sedimentary
rocks.
rocks are fossil-carrying
What turns sediments into solid rock?
 Water
or wind breaks down and
deposits sediment (erosion & deposition)
 The
heavy sediments press down on the
layers beneath (compaction)
 Dissolved
minerals flow between the
particles and cement them together
(cementation)
How were most of the sedimentary rocks in
the Puget Sound area deposited?
Glaciers
about 1500 years ago.
How can sedimentary layers help us
understand the age of fossils?
As sedimentary
rocks are
deposited, they
form horizontal
layers
 Scientists know
that the layers on
top (and the fossils
in the top layer) are
YOUNGER than the
fossils in lower
layers.

3 Types of Sedimentary
Rocks:
 Clastic
(also called Detrial)—made of
broken pieces of other rocks
3 Types of Sedimentary
Rocks:
Organic—remains of plants and animals are
deposited in thick layers
 Examples
 Fossil rich limestone is made from the
shells of ocean animals; used to make
chalk
3 Types of Sedimentary
Rocks:
 Chemical—minerals
dissolved in
lakes, seas, or underground water
Mineral crystals are made as the shallow water that has
flooded the bottom of Death Valley evaporates.
Click on image for full size (66K JPG)
Courtesy of Martin Miller, University of Oregon
Examples
 Limestone
made when
calcite
mineral
precipitates
from sea
water

Rock Salt—
made from
evaporation
of sea
waters
 Rocks
that have changed due to intense
temperature and pressure
 “Meta” means “change” and morphosis
means “form” in Greek
 Igneous, sedimentary and other
metamorphic rocks can change to
become metamorphic rocks
What occurs in the Earth to
change these rocks?
 Pressure
from overlying rock layers
 High heat, but not enough to melt the rock
 Rocks may be flattened or bent or atoms may
be exchanged to form new minerals.
 *You
can think of metamorphic rocks as
a squished peanut butter & jelly
sandwich in your lunch.
How are metamorphic rocks classified?
 Foliated—mineral
grains are flattened
and line up in parallel bands
 Example:
gneiss formed from
rearrangement of minerals in granite
into bands
How are metamorphic rocks classified?
 Non-Foliated—No
 Example:
bands are formed
marble formed from limestone
Where do metamorphic rocks
usually form?
Where magma intrudes relatively
cool rock
 Near colliding plates (near mountain
ranges)
 Places that are covered miles thick
with other rock causing pressure
 When hot water intrudes rock
 Where a meteorite strikes Earth
(rare)
 Where lightning bolts strike rocks
(rare)
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