```Name: _____________________________________________________
Rock Characteristics: Making Observations and Inferences
Learning Objective: I can use the observable characteristics of a rock to infer
Igneous Rocks
Station 1: Crystal size
Use the magnifying glass to observe the igneous rocks. Notice the size of
crystals within each rock (not the size of the rock itself, but the size of the
crystals within the rock). In the space below, describe the size of the crystals
in each rock and then determine if the rock is intrusive or extrusive.
Rock
Basalt
Crystal Size/Description
Ex. Very small crystals, you need a
magnifying glass to see them.
Intrusive/Extrusive
Granite
Obsidian
Why do extrusive rocks have smaller crystals? (Think about the temperature
above and below the earth’s surface)
Answer: Extrusive rocks form when lava cools above the Earth’s surface. Since the
temperature above the surface is cooler than the temperature below the surface, the
lava cools quicker and has less time to form large crystals
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Station 2: Types of magma
Igneous rocks can form from different kinds of magma. The type of magma
influences the chemical and physical properties of the rock, and helps in classifying
them. The three types of magma are Basaltic, Granitic, and Andesitic.
Read about the magma type of each rock in the table. Then observe and
record the color of the each rock.
Rock
Scoria
Granite
Pumice
Diorite
Magma Type
Color of Rock
Basaltic – rich in iron and
magnesium, which makes
this magma dark-colored.
Granitic – rich in silica,
which makes this magma
light-colored.
Andesitic – magma that
has a moderate amount of
iron, magnesium, and
silica. It has a composition
between basaltic and
granitic magma.
Explain in your own words why basaltic, granitic, and andesitic rocks are
different colors.
Igneous rocks can be made from magma with varying mineral composition. Basaltic
rocks are darker because they are made of magma that is rich in the dark minerals
Iron and Magnesium. Granitic magma is made largely out of the light colored mineral
Silica.
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Sedimentary Rocks
Station 3: Detrital Sedimentary Rocks
Sedimentary rocks can be made out of almost any material found in nature.
Therefore, they can be classified based on their composition (what they are made
of). The three main types are detrital, chemical, and organic.
In the table, describe the composition (what the rock is made of) and make a
hypothesis about where you might find the rock.
Rock
Example of a place you
might this rock
Conglomerate
Sandstone
Station 4: Chemical Sedimentary Rocks
Sedimentary rocks can be made out of almost any material found in nature.
Therefore, they can be classified based on their composition (what they are made
of). The three main types are detrital, chemical, and organic.
Chemical: Chemical sedimentary rocks form when dissolved minerals come out of a
liquid. Minerals usually come out when they liquid they are in evaporates, leaving
behind the mineral. The two beakers demonstrate a mineral that has come out of
solution. One has saltwater that was kept at room temperature and the other had
saltwater that was boiled until all of the water was converted to steam. In the
space below, observe what you see.
Dish with room temperature saltwater_________________________________________________________________________________________________
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Dish with saltwater that was boiled_________________________________________________________________________________________________
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Two examples of chemical sedimentary rocks are limestone and gypsum.
Make observations of these rocks.
Limestone - __________________________________________________________________________________
Gypsum- _____________________________________________________________________________________
Limestone is made of calcium carbonate (the material that shells are made of).
Where could you find limestone?
You could find it in a place where there used to be a large body of water that had
animals with calcium carbonate shells.
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Station 5: Organic Sedimentary Rocks
Sedimentary rocks can be made out of almost any material found in nature.
Therefore, they can be classified based on their composition (what they are made
of). The three main types are detrital, chemical, and organic.
Organic: Two examples of organic sedimentary rocks are coquina and coal. In the
space below, make observations of the rocks. Then, using what you know
about their composition (what they are made of), where do you think these
rocks may have formed?
Rock
Coquina
Coal
Composition
Where might have the rock
formed?
Metamorphic Rocks
Station 6: Foliated and Nonfoliated Rock Texture
Observe the arrangement of mineral grains in the following metamorphic
rocks (are there patterns in the grains of any of the rocks?). Then determine
if the rock is foliated or nonfoliated.
Rock Name
Marble
Observation
Ex. Random arrangement of grains,
all the same color
Foliated/Nonfoliated
Slate
Gneiss
Quartzite
How does a rock get a foliated texture?
When a rock is exposed to heat and pressure during metamorphism, its mineral grains
can rearrange into bands of similar composition.
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