Properties and the Three Types of
Rocks
Minerals
 Geologist- A scientist
that studies the
properties of rocks to tell how they may have
formed.
 Mineral- A naturally occurring substance that
is not a plant or animal
 Rocks are made of at least one type of
mineral, sometimes many. Minerals are the
building blocks of all rocks.
 Geologist study different properties of
minerals in order to identify and classify
rocks.
Properties of Minerals

 Color-
This is
not always
useful
because many
rocks are the
same color.
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•
Texture- the way
the rock feels.
This property helps,
BUT many rocks
have the same
textures and feel the
same.
Texture examples:
rough, smooth,
gritty, coarse

•
Luster-The way a
mineral reflects light.
EX: Shiny, metallic,
glassy, greasy, dull.

•
Diamonds have
a glassy luster.
Galena has a
metallic luster.
Streak- The line left
when a mineral is
rubbed on a piece of
unglazed tile.
For example, gold
leaves a gold streak,
but pyrite (fool’s gold)
leaves a black streak.
 Hardness-
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•
The ability of one mineral
to scratch another. Can be tested
with a fingernail, penny, or an iron
nail.
For example, talc is the softest
mineral. Diamond is the hardest.
Mohs’ Scale- A rating that indicates a
mineral’s hardness.
Talc is the softest.
Diamonds are a 10 on Mohs’ Scale.
This means they can scratch any other
rock.

•
•
Another property is
how a rock breaks.
Most break into
chunks, but some
break into flat sheets.
This property is called
cleavage.

•
•
Mica looks like a normal rock, but
it breaks into flat, foil-like sheets.
•
A last property is
density.
Density- how much
something weighs
compared to how
much space it takes
up
Think of a golf ball
and a ping-pong
ball: same size, but
totally different
weights.
A golf ball is more
dense.
3 Types of Rocks
1. Igneous (“Ring of Fire”)
2. Sedimentary (“Come Together”)
3. Metamorphic (“Changes”)
Igneous Rocks- “fire-made” rock
formed from melted rock material.


Magma- melted rock beneath the
Earth’s surface.
Lava- magma that reaches the
Earth’s surface.
Ring of Fire
1. Igneous Rock- “fire-made”
rock formed from melted rock
material.
 Can form under the
ground (magma cools) or
above ground (volcano
erupts, lava cools)
 If the lava cools slowly,
the rock feels more rough
or coarse. (Under ground)
 If it cools fast, the rock
feels smoother. (Above
ground)
Obsidian formed when lava
cooled down fast above Earth’s
surface.
Granite formed when magma
under the ground cooled
slowly.
Come Together
2. Sedimentary RocksRock formed from bits
or layers of rocks
cemented together.
 Sediment- Deposited
rock particles and
other materials that
settle in a liquid.
These sediments will be pushed
together over time to form new rock
like this sandstone.
Coming Together

Weathering- The wearing away of rock. This
process turns any type of rock into sediment.

Cementation- Process that causes sediments to
stick together.

Compaction- Process that presses sediments
together.

These two processes turn sediments into
sedimentary rock.
More Sedimentary Rocks
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Relative Age- the
age of something
compared to the
age of another
thing.
The sediments of
a sedimentary
rock are all
different ages.
Fossils are found
in sedimentary
rocks.
The oldest
layers are at
the bottom.
The farther
down, the
older because
the new layers
pile on top.
Ch, Ch, Ch, Ch, Changes
3. Metamorphic Rock- a rock whose form has
been changed by heat and pressure.
+ heat and =
pressure
Limestone
Marble
HINT: Metamorphosis means change in form, so Metamorphic
rocks have been changed by heat and pressure.
Ch, Ch, Ch, Ch, Changes
The heat comes from the Earth’s core
(which is all magma)
 The pressure comes from all the soil,
rocks, and everything else pressing
down on the rock!!!
 Before the change the rock may have
been any kind of rock, even another
metamorphic rock.
