1.
pg.
Journal: Rocks
86
Write three words that come to mind when you think of “rocks”.
2.
What characteristics do you think a geologist observes when
Don’t write the question, but restate
the question in your answer.
studying a rock sample?
3.
Looking at the rock samples at your table, name three ways you
could classify the rocks.
4.
Do you know the names of the 3 major groups of rocks? If not ask
someone at your table.
Rock Notes
pg. 87
Classification of Rocks:
1. Rocks are mixtures of minerals, volcanic
glass, or other materials.
2. When studying rocks geologists observe a
rock’s color and texture and determine its
mineral composition.
a. Texture is the look and feel of a rock’s
surface
1.) If the grains are easy to see it is
identified as coarse-grained
2.) If the grains are too small to see if is
identified as fine-grained
b. Mineral composition – scientists study
this by taking a small sliver of rock and
looking at it under a microscope to
identify the crystal structure
Igneous Rock Notes
How Igneous Rocks Form:
1. Igneous rocks form from the cooling of
molten rock (either magma or lava)
a. The name igneous comes from the Latin
word ignis, meaning “fire”.
b. Magma is molten rock that is below the
surface
c. Lava is molten rock that reaches the
surface
How they are classified:
2. Igneous rocks are classified according to
their origin, texture, and mineral
composition.
3. Origin
a. Intrusive Igneous Rocks – form from
magma that hardens below the surface
b. Extrusive Igneous Rocks – form from
lava that has erupted to Earth’s surface
4. Texture
a. Intrusive Igneous Rocks – form large
crystals and are coarse grained because
the magma cools slowly
b. Extrusive Igneous Rocks – form small
crystals, are fine grained, even glassy;
because the lava cools quickly
c. Porphyritic – Intrusive rocks that have
large crystals scattered on a background
of smaller crystals. This shows the
magma cooled in two stages. First slow
then rapidly.
d. Volcanic Glass – rocks that cool so
quickly that few crystals form
5. Mineral Composition
a. Basaltic igneous rocks are dark colored
and dense
1.) contain iron and magnesium but very
little silica
2.) basaltic lava flows freely from a
volcano
b. Granitic igneous rocks are lower in
density and lighter in color
1.) contain more silica and less iron and
magnesium
2.) granitic magma is thick and stiff
c. Andesitic rocks have a more balanced
composition of minerals and density than
basaltic or granitic rocks
Rock Notes
pg. 87
Classification of Rocks:
1.
Rocks are mixtures of ______________, ___________________, or _____________________.
2.
When studying rocks geologists observe a rock’s _______________ and _______________ and
determine its _____________________________.
a.
Texture is the look and feel of a rock’s surface
1.)
If the grains are __________________ it is identified as ____________________
2.)
If the grains are ____________________ it is identified as __________________
b.
Mineral composition – scientists study this by taking a small sliver of rock and looking
at it under a microscope to ____________________________________________
Igneous Rock Notes
How Igneous Rocks Form:
1.
Igneous rocks ______________________________________________ (either magma or lava)
a.
The name igneous comes from the Latin word ignis, meaning “_____________”.
b.
Magma is molten rock that is _______________________________
c.
Lava is molten rock that ______________________________
How they are classified:
2.
Igneous rocks are classified according to their origin, texture, and mineral composition.
3.
Origin
a.
Intrusive Igneous Rocks – form from ___________ that hardens __________________
b.
Extrusive Igneous Rocks – form from _________ that has erupted to _______________
4.
Texture
a.
Intrusive Igneous Rocks – form ____________________ and are __________________
because the magma __________________________
b.
Extrusive Igneous Rocks – form ___________________, are _____________________,
even glassy; because the lava _________________________
c.
Porphyritic – Intrusive rocks that have large crystals scattered on a background of
smaller crystals. This shows the _________________________. First slow then rapidly.
d.
Volcanic Glass – rocks that cool so quickly that ___________________________
5.
Mineral Composition
a.
Basaltic igneous rocks are ______________________________________________
1.)
contain iron and magnesium but very little silica
2.)
basaltic lava flows freely from a volcano
b.
Granitic igneous rocks are _____________________________________________
1.)
contain more silica and less iron and magnesium
2.)
granitic magma is thick and stiff
c.
Andesitic rocks have a more _____________________________ of minerals and density
than basaltic or granitic rocks
Size of
Crystals
Colors
(none, small,
medium, large)
IGNEOUS ROCK ID
Basaltic
Texture
Intrusive
- dark colored /dense
(fine-grained or
coarse-grained)
Granitic
-light colored/low density
Andesitic
-balanced/blended
composition
- large crystals/coarse
grained
Extrusive
- small or medium
crystals/fine grained
A
B
C
D
E
F
G
Review Questions:
1. How are igneous rocks formed?
2. What is the difference between intrusive and extrusive?
3. What is the difference between basaltic, granitic, and andesitic?
Conclusion Questions:
1. Infer which rock samples are granitic based on color.
2. Infer which rocks cooled quickly. What observations led you to this inference?
3. Identify any samples that suggest gases were escaping from them as they cooled.
4. Which samples have a glassy appearance? How did these rocks form?
ROCK
NAME
pg. 73
Sedimentary Rock Notes
Form from particles deposited by water and wind. They often form as layers.
How Sedimentary Rocks Form:
1.
Sediments are eroded and moved by wind, water, ice, or gravity.
2.
Then they are deposited – settled out of the water, wind, or ice carrying it.
3.
Compaction – occurs over time. The layers can become very thick. The thicker the layers the more
they press down.
4.
Cementation – occurs during compaction. The dissolved minerals in the rock seep deep into holes and
crystallize acting like a glue
How they are classified:
1.
Detrital or Clastic
o Sedimentary rocks are made from broken pieces of other rocks.
o They have a granular texture.
o Named according to size and shape of sediments
a.
sediment size can be large like gravel or small like clay
i.)
shale is made from tiny particles of clay
ii.)
sandstone is formed form small piece of sand
b.
sediments can be well rounded or have sharp angles
i.)
Conglomerate and breccia rocks are made from various size sediment fragments
2.
Organic rocks
Rocks that form from the remains of plants and animals which are deposited in thick layers
a.
coal forms from the remains of swamp plants buried in water
b.
chalk forms form the hard shells of living things
3.
Chemical rocks
Form when minerals that are dissolved in a solution crystallize
a.
can also form when mineral deposits are left when seas or lakes evaporate.
Sedimentary Rock ID
Observations Fossils Present
Sediment
A
B
C
D
Detrital,
Chemical, or
Organic
ROCK
NAME
Metamorphic Rock Notes
The most important thing to remember is that these rocks are formed by the processes of HEAT AND
PRESSURE!
How Metamorphic Rocks Form:
o Heat and pressure result from one layer of rock on top of another layer
1.)
sometimes temperature and pressure are great enough to melt rock, forming magma
2.)
sometimes pressure flattens mineral grains in rocks without melting them
o Every metamorphic rock is a rock that has changed its form – its appearance, texture, crystal structure,
and mineral content change
o Metamorphic comes from the Greek words
1.)
meta meaning change
2.)
morphos meaning form
How they are classified:
o Metamorphic rocks are classified by composition and texture
1.
Foliated rocks – rocks that have their grains arranged in parallel layers or bands, rocks can split
along these layers
2.
Non-foliated – rocks whose grains are randomly arranged, do not split into layers
Drawing
E
F
G
H
Metamorphic Rock ID
Description
Foliated or Nonfoliated
ROCK NAME