igneous rock –
formed from magma or lava
classified by
1. origin
2. texture
where
formed?
on or
beneath
Earth’s
surface
depends
on size
& shape
of
mineral
crystals
3. mineral
composition
Silica
content
1. Origin
• extrusive rock= formed from lava on
Earth’s surface
–ex. basalt
• intrusive rock= formed from magma
below Earth’s surface
–ex. granite
2. Texture
• depends on size & shape of mineral crystals
different textures
• small crystals or no crystals
1. fine-grained
2. coarse-grained
3. porphyritic
• rapid cooling
• large crystals
• slow cooling
• large crystals surrounded
by smaller crystals
• magma cools slowly-
then rapidly
4. glassy
• no crystals form
• extremely rapid
cooling
coarse-grained
fine-grained
porphyritic
3. Mineral Composition
• lava low in silica dark colored rocks
– Examples: basalt, scoria
• lava high in silica light colored rocks
– Examples: granite, pumice
Uses of igneous rocks
• hard, dense, & durable
• ex:
1. granite
• Used for building material
Countertops, floors
statues
2. pumice
• good abrasive for cleaning & polishing
3. basalt
• Used in making
gravel in
construction
• Cooling lava forms extrusive rock with small
or no crystals
• Cooling magma forms intrusive rock with
large crystals
Small rocks, fragments and
organic remains that have
been moved by water, wind or
other agents of erosion are
called sediment.
Sedimentary rocks are the result of
the following processes:
1. Mechanical weathering: a rock
is broken down without
changing its mineral make-up.
Ex: waves, wind, running
water, gravity
2. Chemical weathering: a rock is
broken down by chemical
reactions that change its mineral
composition.
Ex: oxidation (rusting) & acid rain
3. Erosion: the process where
weathered material (sediments)
get carried away
4. Deposition: the process by
which sediments settle down
in a NEW location
Over time, sediment
is compacted and
cemented together.
Sedimentary Rocks
• Sediments are deposited, layer upon layer
builds up.
• Pressure from the upper layers pushes
down on the lower layers.
• If the sediments are small, they can stick
together and form solid rock
Sedimentary Rocks
• If sediments are large, like sand and pebbles, pressure
alone can’t make them stick together.
• Large sediments have to be cemented together.
• As water moves through soil and rock, it picks up
dissolved minerals such as quartz and calcite. These
minerals are deposited between the sediments.
• Upon solidifying, these minerals, acting as natural
cements, hold the sediment together like glue, making
clastic
sedimentary
rock.
Sedimentary Rocks
Sedimentary rocks
often form as layers.
The older layers are
usually on the
bottom because
they were deposited
first.
Layered rock is also called
Sometimes, forces within Earth overturn
layers of rock, and the oldest are NO longer
on the bottom.
Sedimentary rocks account for 75% of
the rocks exposed at the Earth’s
surface
Label the
Oldest
layer?
intrusion
Youngest
layer?
Sedimentary Rocks
1. Clastic rock- sedimentary rock formed from rock
fragments of other rocks (mentioned above)
• Clastic rocks have granular textures, much like
sugar.
• They are named according to the shapes and size
of the sediments that form them.
From smallest to largest
Examples
Conglomerates: Conglomerate rocks are made of large rock
pieces that have been cemented together. When looking at this
rock type, you can easily see the parts that it has been made of.
Pushing hard on single rock pieces in the conglomerate may
result in these pieces being broken off of the rock.
Sandstone: Sandstone rocks are made of fine sand grains. Like
conglomerate, the grains of sand have been cemented
together. Rubbing the surface of sandstone rocks may result in
small grains of sand being rubbed off of the rock.
Shale: Shale is made up of very fine grains of clay like particles.
The texture of shale is very smooth to the touch. If you apply
pressure to the shale, it is possible to break it into pieces that
also have smooth textures.
2. Organic rocks sedimentary rocks formed from
the life processes or remains of living organisms
Fossil-rich Limestone, made from
the mineral calcite, is formed
from the shells of clams, mussels,
corals and snails.
Coal is made from plants that
died in swamps millions of
years ago.
If a rock is made completely of shell
fragments that you can see, the rock is
called coquina (koh KEE nuh).
• Chemical sedimentary rocks formed when
dissolved minerals come out of solution.
• Minerals collect when seas or lakes
evaporate. The deposits of minerals that
come out of solution form sediments and
rocks.
• Chemical sedimentary rocks are NOT made
from pieces of preexisting rocks.
Halite is an example of a rock
that formed when water
evaporated and left behind
minerals. Halite forms rock
salt. Companies mine these
deposits because rock salt is
an important resource.
Chemical limestone forms when calcite comes
out of a solution in ocean water. Limestone
can contain other minerals but must be at
least 50% calcite
• Rocks that have changed because of changes
in temperature and pressure or the
presence of hot watery fluids are called
metamorphic rocks.
• Metamorphic rocks can form from igneous,
sedimentary, or other metamorphic rocks.
• Each type of metamorphic rock can come
from several kinds of parent rocks.
1. Rocks beneath Earth’s surface are under
great pressure from rock layers above
them.
• Temperature also increases with depth in
the Earth.
• Depending upon the amount of heat
& pressure applied, one type of rock
can change into several different
metamorphic rocks.
Example of Metamorphic Transition
The sedimentary rock shale will change into slate.
Slate
Shale
As increasing pressure and temperature are applied,
the slate can change into phyllite, then schist, and
eventually gneiss.
Slate
Phyllite
Schist
Gneiss
Schist also can form when basalt is metamorphosed,
or changed, and gneiss can come from granite.
Basalt
Granite
Schist
Gneiss
2. Hot Fluids, which are mostly water with dissolved
elements and compounds, can react chemically with a
rock and change its composition.
• This is what happens when
rock surround a hot magma
plume reacts w/ these fluids
• Most fluids that transform
rocks during metamorphic
processes are hot and
mainly are comprised of
water and carbon dioxide.
• In the presence of hot, water-rich fluids, solid rock can
change in mineral composition without having to melt.
Metamorphic rocks can be classified according to
composition and texture
• Foliated (texture)- when mineral grains line up in
parallel layers (dark/light bands)
Examples: gneiss (NISE) (parent rock granite) &
slate (parent rock shale)
• Non-Foliated (texture)- when mineral grains grow
and rearrange but do NOT form layers
Examples: marble (parent rock limestone) &
quartzite (parent rock sandstone)
Development of foliation due
to directed pressure (stress)
Foliated
Nonfoliated
The Rock Cycle
• The rock cycle is a continuous cycle
and a dynamic process!
• The processes of melting, cooling,
heat & pressure, weathering,
erosion, deposition, compaction &
cementation slowly change rock
from one kind to another…the cycle
NEVER ends!