Download rocks!!

The Wonders of . . .
ROCKS!!
Rocks
• All rocks are formed from minerals.
• There are three (3) main classifications of
rocks:
– 1.
– 2.
– 3.
Igneous
Sedimentary
Metamorphic
These rocks are formed under different conditions and posses certain
characteristics. The characteristics a rock has depends upon the condition
in which it formed. The rock cycle illustration below shows the process
that each rock type undergoes to form.
Igneous Rocks
Igneous: Rocks formed by the crystallization of molten
material inside (intrusive) or outside (extrusive) the surface
of the earth.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~
• Felsic rocks are light
colored and have a low
denisty.
• Mafic rocks are dark
colored and have a high
density.
Magma or Lava?
• When molten rock is
inside the earth it is
called magma
• When molten rock is
outside the earth, it is
called lava.
Intrusive/Extrusive
• Intrusive rocks have a
• Extrusive rocks have
coarse texture with large
small grains or a
mineral particles
glassy texture due to
because of slow cooling.
fast cooling.
Slow cooling =
large crystals
Fast cooling =
no crystals
• The crystallization of igneous rocks is a complex
and time consuming process The more time a
crystal has to form, the larger the crystal will be.
• If a mineral has a short amount of time to cool,
like lava that pours into water, no crystals will
form; obsidian, or volcanic glass will be the
result.
• If cooling takes more time, crystals will start to
form, but most often will cool too quickly to form
crystals large enough to see the without the help of
a magnifying glass. If given a long enough time
to cool, crystals will begin to form that are large
enough to see with the naked eye.
• Magma that is stuck underground (intrusive) will
cool very slowly, because it is insulated by the
surrounding rock. As this material cools, crystals
will form that can be very large (porphyry = large
crystals).
• Pegmatite is an igneous rock
with very coarse (porphorytic)
texture (>10mm ~ see the ESRT!)
• Igneous rocks are identified based on their texture,
density, color, grain size and mineral composition.
• Texture is the size and arrangement of mineral
crystals; NOT how it feels!!
Get a black Earth Science book
off the shelf . . .
In your lab groups:
• Open to page 68
• Answer questions 3 – 8 in complete
sentences; one sheet per group.
• NO GROUPS LARGER THAN FOUR!
Time for your
IGNEOUS ROCK
lab!!
• Go get your lab books,
– Lab 2-3
• Pages 73 – 75
• Complete your vocab
• ESRT Page 6
Sedimentary Rocks
• Sediments (broken bits of rock) are materials that
have been transported by air, water or ice. Most
sediments are rock, but some can be pieces of
animals or plants, and even molecules dissolved in
water. When these materials are deposited, they
form loose layers, and are then changed into rock
layers.
• Sedimentary rocks are
formed from a variety
of sediments.
• Sediments can range
from clay (tiny
particles) up to
cobbles (very large
particles)
• Check page 6 of your
ESRT !!
• The main difference
between clastic rocks
and chemically formed
rocks is the clastic
rocks have obvious
fragments whereas the
chemical rocks appear
to be homogenous or
monomineralic.
• Chemically formed
• Clastic sedimentary rocks
rocks (evaporates) form
form from the process of
when water containing
cementation, compaction
dissolved particles
and lithification.
evaporates, leaving the
– Sediments are deposited in
layers, compacted by pressure
precipitate behind.
and cemented by natural
processes.
Types of sedimentary rocks:
• Clastic: Made up of
fragments.
• Sediments are cemented
(glued together) and
compacted (pressed
together) by burial.
• The compacted sediments
then go through the
process of lithification
(hardened into layers)
• Organic: Contains remains of
living organisms.
• Animal or plant remains make
up organic rocks. Coal is
made of squashed plants;
fossil limestone is formed
when animal skeletons sink to
the bottom of the sea and
collect.
• Precipitate/Chemical
Evaporate: During the
process of precipitation,
water evaporates and leaves
behind solids that were
dissolved in the water.
• This process produces rock
salt, rock gypsum and some
limestones.
• Most sedimentary rocks are formed by
deposition in shallow seas, oceans and
lakes. They are laid down in flat layers (A
great identifying feature . . .) and sometimes
contain fossils.
• Some sedimentary rocks
form a veneer, which is a
thin covering or layer
caused by the products of
weathering and erosion
from higher elevations
being transported and
deposited over large
areas.
• Other sedimentary rocks
are fossiliferous;
meaning they contain a
lot of fossils.
• Sedimentary rocks are identified based on:
– How they are formed (clastic or chemical)
– Grain size (clay  cobbles)
– Mineral composition
ESRT ~ Page 7
Get a black Earth Science book
off the shelf . . .
In your lab groups:
• Open to page 74
• Answer the following questions in complete
sentences; one sheet per group.
–
–
–
–
9a
10a
11 a & b
13 – 16
• NO GROUPS LARGER THAN FOUR!
Time for your
SEDIMENTARY ROCK
lab!!
• Go get your lab books,
– Lab 2-4
• Pages 77 – 79
• Complete your vocab
Rocks
Metamorphic Rocks
• Metamorphic rocks are formed by changing any
pre-existing rock by exposure to heat and/or
pressure.
• When heat and/or pressure is applied,
recrystallization occurs.
• Recrystallization is the formation of new mineral
crystals from pre-existing mineral crystals.
(Breaking bonds and reforming new bonds – often
creating new minerals)
Slate
• Foliation is banding of
mineral concentrations and
can take on several different
forms.
• Slaty Foliation:
– Microscopic layers
Schist
• Schistose Foliation:
– Macroscopic layers with
needle-like crystals.
• Gneissic Foliation/Texture:
– Macroscopic bands of
minerals
Gneiss
• Heat: When heat is
applied to rock, it causes
the minerals in the rock to
expand and move apart. If
heated enough, it may
break the bonds and begin
to form new minerals.
• Pressure: Pressure has the
opposite effect of heat; it
pushes the atoms of rocks
together.
• Together, this heat and
pressure will result in
some sort of deformation.
Often, rocks seem to have
bands that are twisted and
turned, resulting from
metamorphosis of
sedimentary rocks.
• Therefore, during metamorphosis (adding
heat and/or pressure), the size, spacing, and
shape of the grains are changed. They may
fuse due to heating and create brand new,
exotic crystals.
• Increased density;
• Pressure, which forces
the grains closer
together, can cause the
volume to decrease,
while the mass
remains the same. The
density of the rock
increases.
Shale + pressure = Slate
Types of metamorphism:
• Regional:
Regional metamorphism
results in metamorphism
by primarily pressure
spread over broad areas
of Earth’s crust; usually
resulting in higher density
rocks like slate, phylite,
schist and gneiss.
• Contact:
Contact metamorphism
results in metamorphism
by primarily heat over
small, concentrated areas
(generally as a result of
contact with magma).
Rocks tend to have a
lower density due to
expansion from heat.
• Fossils are rarely found in metamorphic rock
because of the heat and/or pressure they
undergo.
• If fossils are present, they appear distorted and
squished.
• Some metamorphic rocks are very similar; like
marble and quartzite. The only way to
differentiate between them is to perform and acid
test to see if calcite is present.
– If calcite is present, it’s marble, if not, it’s
quartzite.
• The minerals in metamorphic rocks will rearrange
in layers because they tend to sort by density when
they are heated.
• Quartzite forms from the metamorphism of its
parent rock, quartz sandstone. When heat and/or
pressure is applied, it causes the parent rock to
become more dense and resistant to weathering.
• Metamorphic rocks are
identified based on
foliation, mineral
composition and type of
metamorphism.
Time for your
METAMORPHIC ROCK
lab!!
• Go get your lab books,
– Lab 2-5
• Pages 81 – 83
• Complete your vocab
• ESRT Page 7
A few more key terms:
• Aggregate: Composed • Weathering: The
of a mixture of
process of breaking
minerals.
down rock into
fragments/sediments.
• Erosion: The process
of transporting
weathered materials.
• Vesicular: Contains
gas pockets.
• Stratification: Formed
and/or deposited in
layers.
Rock Summary:
• Rocks vary in color and type based on how they are
formed and their mineral composition.
• A rock’s texture indicates the size of the mineral grains –
NOT how it feels.
• Igneous rocks are identified based on grain size. Igneous
rocks form from the solidification of molten rock,
therefore, there will be no fossils.
• Sedimentary rocks are identified based on grain size and
shape. Fossils are found in sedimentary rocks.
• Metamorphic rocks form from changing existing rock by
heat and/or pressure. They exhibit banding or appear
folded and/or layered. Any fossils present will appear
distorted.
Which brings us full circle back
to the rock cycle . . .