Download What is a Rock? - Davis School District

What is a Rock?
 Naturally-occurring
mixtures of
minerals, mineraloids (no crystals), or
organic matter.
Types of Rocks…

The three main kinds of rock are
igneous, sedimentary and
metamorphic rock.
– Igneous rock: forms when
magma/lava cools and hardens
– Sedimentary rock: forms when
sediments are buried,
compacted & cemented together
– Metamorphic rock: forms when
existing rock is subjected to
great heat & pressure over a
long period of time
What is the difference
between a rock and a
mineral?
 Rocks
are made up of ONE 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



“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
 Igneous Rocks come from magma/lava
cooling down.

ORIGIN— Where rocks are formed
 Below
ground = from magma (intrusive
igneous rock)
 Usually
have LARGE crystal grains (they cooled
slowly) Cooling could have taken hundreds of
years.
Some have large & small crystals
(called porphyritic)
 Above
ground = from lava (extrusive
igneous rock)
 Usually
have SMALL or NO crystals (they
cooled too quickly)
Granite: Intrusive or
Extrusive? Why?
Obsidian: Intrusive or
Extrusive? Why?
COMPOSITION— What kind of
substances or minerals are rocks 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.
Diorite-has course grains
Basalt-no course grains
Granite
 Formed
from sediments
(rock fragments, mineral
grains, animal & plant
remains-shells, bones,
leaves, stems) that are
pressed or cemented
together or when
sediments precipitate
out of a solution.
 These
sediments are moved by wind,
water, ice or gravity then deposited into
layers.
 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)
 Elements of Erosion are heat, cold, rain,
waves, and grinding ice.
 At
first sediments fit together loosely,
over long periods of time, thick layers
build up. Because of the heavy layers,
the upper layers press down on the
layers below them, causing Compaction.
 Dissolved
minerals flow between the
particles and cement them together
(cementation)
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. Formed
when rock fragments are squeezed
together.
Clastic-Sedimentary Rocks
Shale: Formed
from tiny particles
of clay compacted
together.
 Sandstone: Forms
from the
compaction and
cementation of
small particles of
sand.

Clastic-Sedimentary Rocks


Conglomerate:
Formed from
fragments of various
sizes of rocks and
pebbles. Fragments
are rounded because
they have been worn
along riverbeds.
Breccia: Fragments
are jagged with sharp
edges. Formed from
various size of rocks
and pebbles.
3 Types of Sedimentary
Rocks:
Organic—remains of plants and animals are
deposited in thick layers

Organic refers to substances that once
were part of living things or were made by
living things which contain calcite or
calcium carbonate. (Can be tested by
using acid)
Organic-Sedimentary Rocks


Coal: Remains of
swamp plants buried
in water or by volcanic
ash.
Limestone: Formed
by hard shells of once
living things such as
coral, clams, oysters,
and snails. When
they die their shells
pile up and are
covered by other
sediments compacting
and cementing them.
Types of Limestone


Chalk-can be
naturally occurring
and in rock form.
Coquina-made of
large fragments of
shells.
3 Types of Sedimentary
Rocks:
 Chemical—minerals
dissolved in
lakes, seas, or underground water.
Can occur when lakes evaporate.
Chemical-Sedimentary Rocks


Rock Salt: Made of
the mineral halite.
Gypsum: Formed
by evaporation in
dry climates.
 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.
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)

How are metamorphic rocks classified?
Look at Pages 162-163 in your books
 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
Rocks Transformed
Limestone
Shale
Marble
Slate
Rocks Transformed
Sandstone
Mudstone
Quartzite
Schist
or
Gneiss
Say you have an unknown rock
how do you classify it?

Color: Like with
minerals, color
alone does not
provide enough
information to
identify a rock.
Say you have an unknown rock
how do you classify it?






Texture can be very useful.
Look at and feel the rocks
surface.
Some are smooth and
glassy others are rough
and chalky.
Grain Size: Large or Small
Grain Shape: Fine Grained
or Jagged
Grain Patterns: Flat
Layers, Wavy, banded, or
random.
No Visible Grain: Some
cool to fast to have grains.
Say you have an unknown rock
how do you classify it?


Mineral composition:
By looking under a
microscope, a
geologist can identify
the minerals it
contains.
You can use acid to
check for carbonates.
(Limestone or Chalk)
Say you have an unknown rock
how do you classify it?




Origin: Where it came
from!
Metamorphic: Usually
have bigger crystals
because of increased
heat and pressure.
Igneous: Usually is
made up of very large
particles.
Sedimentary: Small
solid pieces of
material that come
from rocks or living
things. (Smoother)
Rock Cycle Animations
Rock Cycle Quiz
 Rock Cycle Animation #1
 Weathering and Erosion Quiz
 Rock Cycle Video (Made by a
Middle School Student)
 Go to the next slide to play
Jeopardy.

Jeopardy Game
The Rock Cycle
The Rock
Cycle
Igneous
Rocks
Metamorphic
Rocks
Sedimentary
Rocks
10 pts
10 pts
10 pts
10 pts
20 pts
20 pts
20 pts
20 pts
30 pts
30 pts
30 pts
30 pts
40 pts
40 pts
40 pts
40 pts
50 pts
50 pts
50 pts
50 pts
Question 1
Rock
Mixture of minerals, volcanic glass,
organic matter, or other material
Check Answer
Question 2
Rock Cycle
A model showing the processes
that create and change rock.
Check Answer
Question 3
Sedimentary Rock
_________ rock can be changed by
heat and pressure into
metamorphic rock.
Check Answer
Question 4
Igneous
__________ rock can be broken
into fragments that may later form
sedimentary rock.
Check Answer
Question 5
Metamorphic
______ rock can melt and cool to
form igneous rock.
Check Answer
Question 6
Lava
Magma reaches the surface flows
from a volcano as ____________ .
Check Answer
Question 7
Intrusive
Magma trapped below the surface
forms large – grained
______________ rock when it
cools.
Check Answer
Question 8
Extrusive
Magma cooling at or near Earth’s
surface forms small-grained
__________ igneous rock.
Check Answer
Question 9
Intrusive and extrusive
Igneous rocks are classified in 2 ways.
1. ______________
2. ______________
Check Answer
Question
10
cool
Volcanic glass rock __________ so
quickly that few crystals form.
Check Answer
Question
11
Heat and pressure
_____________ and
______________ result from one
layer of rock on top of another
layer.
Check Answer
Question
12
magma
Sometime temperature and
pressure are great enough to melt
rock, forming ______________.
Check Answer
Question
13
Foliated texture
_____________ texture – mineral
grains flatten and line up in
parallel layers or bands.
Check Answer
Question
14
Nonfoliated texture
_______ texture - mineral grains
grow and rearrange but do not
form layers.
Check Answer
Question
15
Pressure
Sometimes ____________ flattens
mineral grains in rocks without
melting them.
Check Answer
Question
16
Sedimentary Rock
Type of rock mostly found on the
exposed surface of Earth.
Check Answer
Question
17
layers
Sedimentary Rocks form in
__________ .
Check Answer
Question
18
sediments
Rock fragments, mineral grains,
and bits of plants and animal
remains moved by wind, water, ice
or gravity are called
_________________.
Check Answer
Question
19
cementation
When water and other minerals
move through open spaced
between larger sediments, gluing
them together, ____________
occurs.
Check Answer
Question
20
Organic sedimentary
_________ ___________ rocks
are made from the remains of once
– living plants or animals.
Check Answer