Three Types of Rocks --Notes from Discovery Education Site Videos/Text
Answer Key
How they are formed
Description
Name _______________ Date ______
Notes from Mrs. Best’s discussion in class
Metamorphic Think “heat &
pressure”
Formed when heat and
pressure cause older rock to
change into new types
Intrusive-cools slowly
- Any type of rock can
Forms deep within earth, so undergo geologic processes
heat cannot escape fast.
such as faulting which can
(Think of a baked potato that bury rock deep within the
you have heaped blankets
earth and change it.
over—would it cool quickly?) - Making a rock
metamorphic is like baking a
→ rocks formed here have
large-sized crystals
batch of cookies in a superExtrusive-cools quickly
oven with one or more
Forms on surface as lava
concrete blocks on top of
cools, so heat escapes easily.
them!
Crystals do NOT have time to - If the original rock had lines
grow large, so rocks formed
of visible layers, those lines
like this have smaller crystals. get twisted, angled on
Some, like obsidian, cooled so themselves as they change.
quickly they have NO crystal The metamorphic rock may
structure at all!
have wavy, tilted lines that
can even loop!
Igneous
Think “melting”
Formed when molten rock
cools and becomes solid
Contains bubble-like cavities
Like your teeth, rock cavities
are holes. These holes form
when gases dissolved in the
liquid magma/lava come out
of solution and leave as the
rock is becoming solid,
leaving a hole behind.
Fine texture
Made of quartz or calcite
Foliated – has bands
In this case, there are visible
lines (different colors,
sometimes of texture, as well)
Non-foliated – no bands
Sedimentary Think
“weathering & erosion*”
Formed when rocks, plants, and
loose material get pressed
together into layers
It takes 5 different processes
that must happen to form a
sedimentary rock!
(involves weathering &
erosion) * but also involves
deposition (depositing),
compaction and cementation.
- Weathering softens the
rock.
- Erosion moves the rock
- Deposition (depositing) lays
the loose sediment down
when whatever is carrying it
can’t do it anymore (water,
wind, etc.)
- Compaction makes the
molecules closer together
- Cementation (cementing)
glues the mineral particles
together!
Has layering features
Since water or wind carries
different amounts of
sediments in them at any
time, they deposit different
amounts at different times.
One deposit creates a layer,
and so on, and so on…
Three Types of Rocks --Notes from Discovery Education Site Videos/Text
Examples
The more dissolved gases the
magma/lava has, the more
cavities are formed.
Pumice has so many cavities
that it floats!
Bubbly texture
Hard
Could be lined with minerals
We talked about the fact that
parts of cooling rocks get
dissolved in hot water, then
deposited elsewhere on other
rocks—like gold, silver, or
tin. Miners look for the veins
of valuable minerals along
the other rocks!
Rocks of this type have a
uniform look with no visible
lines
Granite- comes from magma
(intrusive)
Since granite cools deep
within the earth, it has coarse
texture—larger crystals
Marble- comes from limestone
Used in buildings
(Washington monument) &
statues, countertops
Basalt- comes from magma
(extrusive)
Since basalt cools after it is
lava on the surface, it has fine
texture –small crystals hard
to see without magnifying
glass
-This is the rock that forms at
mid-ocean ridges and rift
valleys!
Pumice- comes from volcano
(extrusive)
Name _______________ Date ______
Slate- comes from shale
Imagine a scene from a TV
show or movie inside an oldtime one-room schoolhouse.
Children of all ages sat on
benches with a “chalkboard”
and chalk to write with. That
board was actually a piece of
slate rock! Slate is also a
common roof material.
Quartzite- comes from
sandstone
Quartzite – slightly harder
Very soft (easily scratched)
Because all 5 processes that
make a sedimentary rock
happen right at the Earth’s
surface, low pressure and low
temperatures are the rule.
Soft rocks are the result.
Contains fossils
If you find an animal
footprint in a rock, that rock
was mud when the animal
stepped in it and left its print.
The mud went through the
compaction and cementation
processes with the imprint
still there, forming a fossil!
Made of particles cemented
together
Limestone- made of seashells
- Mainly calcium carbonite
- Very soluble in water
- This is the rock from which
water carved out caves and
caverns
Shale- made from mud
Most common sedimentary
rock
Made up of many thin layers
of material
Hydraulic “fracking”
removes oil and gas particles
from tiny pores in shale
Sandstone- made from sand
Rock made from beach or
river sands
“Brownstones” are buildings
Three Types of Rocks --Notes from Discovery Education Site Videos/Text
The lava from which pumice
comes has a lot of dissolved
gases in it which evaporate
out as the rock is cooling,
leaving LOTS of spaces in the
rock. Pumice is the ONLY
rock that has a density lower
than that of water—it
FLOATS!
than granite, but is gaining
popularity as countertop
material
Name _______________ Date ______
made from one type of this
rock
The White House and Capitol
buildings in Washington, DC
are made from this rock.