Rocks, what do they mean
to you?
• Some rock formations are famous
and when they disappear, their
legends don’t
Rocks
• The ones
found
in the
Earth, not
in some
of your
heads!!!!
Igneous Rocks
• Also known as “fire rocks”
• They are formed by the
crystallization of magma or
lava
• Magma is the molten
material found underground
• Lava is the molten material
found above ground
Composition of Magma
• Magma is a slushy mix of molten
rock, gases, and mineral crystals
• It has the same major elements
that are found in the earth’s crust:
O2, Si, Al, Fe, Mg, Ca, K, and Na
• Magma is classified according to
the amount of Si it contains
• Rhyolitic (70%), Andesitic (60%),
and Basaltic (50%)
Classification of Igneous
Rocks
• Igneous rocks are classified
according to their composition
and texture
• Texture refers to the minerals of
which rocks are formed, the
shape, size, arrangement, and
distribution of the minerals
• Ex: light colored rocks are rich in
quartz, dark colored rocks might
be rich in olivine
There are two types of
igneous rocks:
- extrusive are
fine grained
(small crystals)
that cool on the
surface of the
Earth
- (obsidian,
pumice, basalt)
- intrusive are
coarse
grained (large
crystals) that
cool slowly
underground
from plutons
(granite)
Mineral Composition
• Felsic rocks
are high in
silicon and
light colored.
Ex: granite
• Intermediate
rocks have less
silicon and are
darker. Ex:
Diorite
• Mafic rocks are
low in silicon
and dark in
color. Ex:
gabbro
• Ultramafic rocks
are very low in
silicon and very
dark in color. Ex:
peridotite and
dunite
Texture of Igneous
Rocks
• Glassy
igneous rocks
look like
glass and do
not have their
minerals
arranged in
crystalline
formation
• Aphanitic or
fined
grained
igneous
rocks have
crystals
present, but
they are too
small to be
seen with
the naked
eye
• Phaneritic
or coarse
grained
igneous
rocks have
crystals
that are
about the
same size
and easily
seen
• Porphyritic
or mixed
grained
texture
igneous
rocks, large
crystals
embedded in
a field of
smaller
crystals
Veins of Igneous Rocks
• Pegmatite contains
very large grained
minerals such as
lithium and
beryllium, as will as
some of the most
beautiful crystals
• Kimberlites are rare
and can contain
diamonds
And on we
gooooooooo!
Sedimentary Rocks
Slowly Built Layers
• Sedimentary rocks are
classified according to the
origin of the material that
they are made from
• Clastic
• Organic
• Chemical
Clastic
• Clastic
sedimentary
rocks are made
from the
fragments of
existing rocks
• They are further
classified
according to the
size and shape of
the fragments
they are made of
Conglomerates
• These are made from pebbles
cemented together with mud,
clay, or sand
• Over one third is made of pebbles
Sandstones
• Made from
particles the size
of sand
• At least half of the
material must be
sand to be
classified as
sandstone
• Grains are
cemented
together by
minerals
• Most common
sedimentary rock
Shales
• Made from
particles smaller
than sand
• Made from small
particles of mud
and clay
• Most can be split
into flat pieces
Organic Rocks
• Organic
sedimentary
rocks are
made either
directly or
indirectly
from
material that
was once
living
Limestones
• May be
produced by
the shells of
once living
organisms
• Living
organisms may
produce
limestone
directly as in
coral reefs
Chalk
• Fine grained limestone made
from microscopic shells
Coal
• Formed
from the
remains of
plants that
lived
millions of
years ago
Chemical Rocks
• Formed when
a sea or lake
dries up
leaving behind
large amounts
of minerals
• This includes
rock salt,
gypsum, and
some
limestone
The Making of Sedimentary
Rocks
• Erosion and weathering of parent
rock
• Transportation of sediments
• Deposition of sediments
• Compaction and cementation of
sediments
• Lithification which turns the
sediments into sedimentary
rocks
Interesting sedimentary rock
structures
Had enough yet?
Metamorphic Rocks
Metamorphic Rocks
• Rocks that are caused by high pressure
and/or heat
• They are not completely melted
• High temperature and pressure combine
to change the texture, mineralogy, and
chemical composition of igneous,
sedimentary, and metamorphic rocks
Regional Metamorphic Rocks
• Large areas of metamorphism
Contact Metamorphic Rocks
• Contact with an igneous intrusion
Hydrothermal Metamorphism
• Contact with very hot water
Textures of Metamorphic
Rocks
• Foliated have wavy layers and bands of minerals
Non-foliated have minerals with blocky crystals
shapes
Changes to Parent Rocks
• Mineral changes- one mineral changes to another due to the
high heat and pressure
• Compositional changes- most of the composition of original
rocks doesn’t change, hot liquid can alter the mineral and
texture which can form valuable ore deposits like Au, Cu, Zn,
W, and Pb
Granite
Limestone
Shale
Sandstone
Basalt
Shale
Gneiss
Marble
Slate
Quartzite
Schist
Mica Schist
Rock Humor
1.
2.
3.
4.
5.
6.
7.
8.
What does a rock want to be when it gets older?
What do you call a dog who collects rocks?
What do you do to a baby rock?
What is a rock’s favorite kind of music?
Where do rocks sleep?
How do rocks wash their clothes?
What is a rock’s favorite transportation?
What is a rock’s favorite cereal?
Answers
1.
2.
3.
4.
5.
6.
7.
8.
A Rock star
A Rockhound
Rock it
Rock ‘n Roll
Bedrock
On the rock cycle
A rocket
Cocoa pebbles
The Grand Finale