ROCKS
Study Guide
Know the three types of rocks and some common descriptors
Metamorphic
 This word means "changed"
 Marble is an example; it was once limestone
 Slate is an example; it was once shale
 These rocks are formed underground from heat
and pressure
Igneous
o These rocks are originally melted
o The size of the crystals in these rocks depends on how
quickly they cooled
o This word means "fire-made"
o These rocks sometimes have large holes from gases
o The glassy black rock called obsidian is an example
o Pumice is an example
o These rocks can be cooled on land or underground
Sedimentary
o There may be fossils buried in these rocks
o These rocks are often in layers made from material that
has settled out of water
o Many of these rocks contain grains of sand
o Caves are made from this type of rock
o Sandstone is an example
o Conglomerate is an example
o Limestone is an example
o Most of these rocks were formed under water
Be able to recognize the 15 rocks studied in class
VOCAB:
Cave: An area of sedimentary rock that has been worn away by
acids
Coal:
A fossil fuel made from sediment and decomposed
plant material
Extrusive: This word means "cooled on the surface"
Geode: A rock filled with crystals
Intrusive: “cooled inside the earth”
Lava: Melted rock outside the earth
Magma: Melted rock inside the earth
Fossils
1. How is the fossilized skeleton of a dinosaur similar to the
modern skeleton of a lizard?
2. Where are prehistoric animals preserved as whole animals?
3. Why is a fossil dinosaur bone much heavier than the original
bone it was made from?
4. Why are the soft parts of a shark’s body not preserved as a
fossil?
5. If I brought a piece of sandstone to school that had some ripples
across it. What might have been preserved?
6. Which would be an example of a fossil?
7. Which rock type would be best for finding fossils?
8. How do we know different kinds of plants and animals lived in
Missouri a long time ago?
9. Which animal used to live in Missouri but does not now?
10. What do dinosaur tracks in coal beds tell us about the
environment in Utah’s past?
11. What is a common cause of plant and animal extinction?
12. What evidence shows that parts of Missouri were once the sea
floor of an ancient ocean?
13. What might a scientist tell from seashell fossils found on top of
a mountain?
14. What have scientists learned about oceans from fossils?
Minerals
PROPERTIES OF MINERALS
LUSTER
This tells the degree of shininess in the mineral. Some words
geologist use to describe them are:
Metallic
Pearly
Vitreous: glassy
Greasy
Silky
Earthy: like clay or dirt
Dull
COLOR
This is usually the first property noticed by an observer. However, it
is the least important property used in determining a mineral by geologists.
TRANSPARENCY AND LIGHT
Can you see through the mineral as you can see through glass?
Depending on how much light passes through the mineral. You can describe
it as translucent (light shines through) or opaque (no light shines through).
STREAK
This is the color of the powder that a mineral leaves behind if it is
scratched along a piece of unglazed porcelain. A particular mineral may
occur in various colors, but its streak will always be the same.
ACID TEST
Does the mineral bubble when an acid (vinegar) is placed on it?
MAGNETIC
Is it attracted to a magnet?
CLEAVAGE AND FRACTURE
Study a fragment of your specimen to see how it breaks. Write down
whether it cleaves (breaks) in a well-defined, even way and consistent
direction or directions, or whether it fractures unevenly, or does both.
Feldspar, for example cleaves evenly into block-like shapes, while agate
fractures into uneven, shell-like (conchoidal) fragments.
What type of crystal system does is seem to have? This is directly
related to its cleavage, since the mineral will usually break along its crystal
structure: Hexagonal, tetragonal, orthorhombic, monoclinic, and triclinic.
(see Peterson First Guides, Rocks and Minerals, p. 32-37
HARDNESS
Use Moh's scale to identify how hard your mineral specimen is. Use a
testing kit or the common objects noted to determine the hardness. Draw the
softest material in the table over the specimen. If it doesn't leave a scratch,
go on to the next hardest mineral, and so on, until you find the mineral that
is hard enough to scratch your specimen. Make a note of the number of the
scale.
I.
II.
III.
IV.
3.5
4.0
5.
MOH'S HARDNESS SCALE
Talc
6.
Feldspar
Gypsum
6.5
Steel Knife
Fingernail
7.
Quartz/ Glass
Calcite
8.
Topaz
Copper coin
8.5 .
Emery cloth
Fluorite
9.
Corundum
Apatite/ Nail
10.
Diamond
SPECIFIC GRAVITY
This is a measure of how dense the mineral is. The mass of a mineral
is compared to that of an equal volume of water. Then is it noted as how
much (times ?) heavier it is.