Download Chapter 4 Rocks: Mixtures of Minerals

Chapter 4
Rocks: Mixtures of Minerals
Rocks – A naturally occurring solid mixture of one or
more minerals and organic matter.
The Rock Cycle – The continuous process by which
new rock forms from pre-existing rock material. Rocks
will actually change their chemical composition.
Weathering – The process in which wind, water,
gravity and heat break down rocks to form fragments
called sediment.
Erosion – The process in which sediments are
washed or blown away from their source.
Deposition – The process in which eroded material is
dropped and comes to rest.
The Rock Cycle Activity
• Write a humorous story in your group about what
it would be like to be a rock particle traveling
through the rock cycle. Think of this as a story
like “The Little Grain That Could”. Then you will
present this as a group in class. The winning
group gets 20 extra credit points!
• Magma – partially or completely melted rock that
forms igneous rock when it cools.
The Classification of Rocks
• Composition – The chemical make up of a
rock. This describes the mineral composition of
the rock.
• Texture – The size, shape and position of the
grains that make up the rock and determines it’s
quality.
Coarse – Large grains
Medium – Smaller grains
Fine – Smallest grains. Almost cannot be seen.
Igneous Rocks
• Igneous – Formed when magma cools and solidifies. The type
of texture is determined by the composition of the magma and
the time it took to cool. Magma contains many different types of
minerals in it that will solidify at different rates. Magma forms if
either the pressure or temperature increases or the mineral
composition changes.
Glassy – The magma was shock cooled (very rapid cooling)
Ex.: Obsidian
Fine Grained – The magma cooled quickly.
Ex. : Basalt
Coarse Grained – The magma took a long time to cool.
Ex. : Granite
Igneous Rock Formations
• Intrusive Igneous Rock – Formed when
magma cools under the surface. The grains are
large (coarse) because the upper rocks insulate
the magma.
• Extrusive Igneous Rock – Formed when lava
cools and solidifies on the surface. They usually
are formed in or around volcanoes and are fine
grained or glassy (no crystals)
• Activity: Draw the intrusive igneous bodies on
p. 100 of your book for bonus points.
Sedimentary Rock
• Formed by the cementing of sediments that was laid down in
layers.
• Strata – Layers of sedimentary rock. This makes it easy to
identify sedimentary rock.
• The classification of sedimentary rock is based on the way the
rock was formed:
A. Clastic – Fragments of rock cemented together.
Ex. : Conglomerate (Coarse Grained).
B. Chemical – Formed from solutions of dissolved minerals &
water.
Ex. : Halite (salt).
C. Organic – Formed from the remains of living organisms.
Exs. : Coral (tiny sea animals), Limestone (skeletal remains of
sea animals) & Coal (partially decomposed plant matter).
Sedimentary Rock Structures
• Stratification – The layering of
sedimentary rocks.
• Ripple Marks – The preserved movement
of wind or waves in sedimentary rock.
• Mud Cracks – Sediments that were
exposed to the air and dried out indicating
the location of ancient lake beds.
Metamorphic Rock
• Metamorphic – means “changed shape”. These are
rocks in which the structure, texture or composition
has been changed. Metamorphic change occurs when
the temperature or pressure or both have changed.
A. Contact Metamorphism – Occurs when the
magma is close by the rock formation and heats the
surrounding rocks. This usually is limited to a small
area.
B. Regional Metamorphism – Occurs when
pressure builds up deep within the Earth or large
pieces of crust collide. This occurs over a very large
area.
Composition of Metamorphic Rock
• When temperature and pressure change, the minerals
within a rock will change to a more stable mineral
structure.
Index Minerals – Certain metamorphic rocks that are
used to estimate the temperature, depth or pressure at
which the rock went through metamorphism.
Textures of metamorphic rocks – under heat and
pressure, the mineral grains are rearranged and a
metamorphic rock can be changed into another type of
metamorphic rock.
A. Foliated – The grains are arranged in bands.
Ex. : Shale turns into Slate.
Composition of Metamorphic Rocks
(cont.)
B. Unfoliated – The grains are NOT arranged in
bands. These are usually made up of only one
or two minerals.
Recrystallization – Occurs when the minerals
change in size or composition and change the
type of metamorphic rock.
Deformation – A change in the shape of a rock
due to the force placed on causing it to squeeze
or stretch and may create folds or bends in the
rock layers.