CHAPTER 14
ROCKS: MINERAL MIXTURES
• Rocks change through a process called the
Rock Cycle and rocks are classified by how
they form, by what they are made of, and by
their texture.
Chapter 14 Objectives
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We will learn about the Rock Cycle
We will learn about the three types of rocks
We will learn how each type is formed
We will learn how each type is classified
Section 1: The Rock Cycle
• What we will learn in this section:
– Describe two ways in which rocks are used by
people.
– Describe the four processes that shape Earth’s
features.
– Describe how rocks move through the rock cycle.
– List two characteristics of rocks that help classify
them.
The Rock Cycle
• Rock- naturally occurring solid mixture of one or more
minerals or organic matter.
– Rocks are always changing.
• Rock Cycle- the series of processes in which a rock forms,
changes from one type to another, is destroyed, and forms
again by geological processes.
The Rock Cycle
Value of rock
• Rock has always been valuable.
• Rocks were the first form of tools.
• It has been used to make things in ancient and
modern times.
Processes That Shape the Earth
• Weathering, Erosion, and Deposition
• Weathering- breaks rocks down into fragments.
• Erosion- the process by which wind, water, ice, or
gravity transports soil and sediment from one
location to another.
• Deposition- the process in which material is laid
down.
Processes That Shape the Earth
• Heat and Pressure
– Rocks also form under high heat and pressure.
– High pressure can create sedimentary rocks.
– Add heat to those rocks and they can melt and
turn into Metamorphic rocks.
Processes That Shape the Earth
• Magma can reach the surface through
volcanoes or can cool in the ground and
create igneous rocks.
Processes That Shape the Earth
• How the cycle continues…..
– Buried rock can come to the surface by uplift and
erosion.
– Picture the Earth as a float in a pool, the land is
the float and we are “floating” on hot magma.
Round and Round It Goes
• The rock cycle is always moving very slowly.
• New rocks are created, then destroyed, just to
be created again.
• There is no set path
to the Rock Cycle,
rocks travel in all
directions.
Rock Classification
• Rocks are divided into three main classes, but
now we go further.
• Rocks are divided further on how they form.
• Scientist study rocks closely to find out how to
classify them.
• The two main characteristics are composition
and texture.
Rock Classification
• Composition- the chemical makeup of a rock;
describes either the minerals or other
materials in the rock.
– Composition means the percentage of minerals or
other materials that make up each rock.
Rock Classification
• Texture- the quality of a rock that is based on
the sizes, shapes, and positions of the rocks
grains.
– Three types of texture: fine-grained, mediumgrained, and coarse-grained.
– Texture tells us how and where the rocks were
formed.
Section 2: Igneous Rocks
• What are going to learn:
– We will describe the ways that igneous rocks form.
– We will explain how the cooling rate of magma
affects the texture of igneous rocks.
– We will be able to distinguish between igneous
rock that cools within the Earth’s crust and
igneous rock that cools at Earth’s surface.
Igneous Rocks
• Igneous is Latin for “FIRE”!
• Igneous rocks form when hot magma or lava
cools and hardens.
• Magma- INSIDE the Earth.
• Lava- OUTSIDE the Earth.
Origins of Igneous Rock
• Begins as magma.
• Three ways magma is formed:
– When rock is heated.
– When pressure is released.
– When rock changes composition.
Origins of Igneous Rock
• When water freezes, it makes ice. When magma
“freezes”, it makes igneous rock.
• Each mineral has its own melting and freezing point.
• Remember, rocks are made from many minerals put
together. This means the igneous rock freezes at
different temperatures. (Some parts freeze faster
than others.)
Composition and Texture of Igneous Rocks
• Composition
• Rocks made from light colored minerals are
called felsic rocks.
• Rocks made from dark colored minerals are
called mafic rocks.
Composition and Texture of Igneous Rocks
• Texture- Texture of igneous rocks depend on
how fast they cool.
• Faster cooling causes SMALLER crystals.
• Slower cooling causes LARGER crystals.
Igneous Rock Formations
• Igneous rocks form both inside the Earth and
outside the Earth.
• Intrusive Igneous Rock- rock formed from the
cooling and solidification of magma beneath
the Earth’s surface.
• Plutons are large intrusive bodies of igneous
rock.
– Types of plutons include: Batholiths, Stocks,
dikes, and sills.
Intrusive Igneous Rock
Extrusive Igneous Rock
• Extrusive Igneous Rock- rock that forms as a
result of volcanic activity at or near the Earth’s
surface.
• Lava cools quickly so it has small or no
crystals.
• Lava also forms in oceans to create new ocean
floor.
Extrusive Igneous Rock
Section 3: Sedimentary Rock
• What we are going to learn:
– We will describe where sedimentary rock comes
from.
– We will describe the three main categories of
sedimentary rock.
– We will describe the three types of sedimentary
structures.
Origins of Sedimentary Rock
• Weathering cause rocks to break into pieces.
• Erosion transports the pieces, called sediment,
from one place to another.
Origins of Sedimentary Rock
• Sediment is deposited in layers, over time
these layers are compacted into rock.
• The most noticeable feature of sedimentary
rock is the strata.
• Strata- layers of rock.
Composition of Sedimentary Rock
• Sedimentary rock is classified by how it forms.
• Three main categories of sedimentary rock:
– Clastic Sedimentary Rock
– Chemical Sedimentary Rock
– Organic Sedimentary Rock
Clastic Sedimentary Rock
• Made of rock fragments (chunks) that are
cemented together.
• Clastic Sedimentary Rocks have three types of
textures:
– Fine-grained
– Medium-grained
– Coarse-grained
Chemical Sedimentary Rock
• Chemical Sedimentary Rock forms from
dissolved minerals in water.
• Rain dissolves minerals in rocks and carries
them to oceans where they are deposited and
harden to form rock.
Organic Sedimentary Rock
• Organic Sedimentary Rock has fossils in them.
• These fossils become cemented together to
form fossiliferous limestone.
Sedimentary Rock Structures
• Stratification- the process in which
sedimentary rocks are arranged in layers.
• Strata differ from one another depending on
the kind, size, and color of their sediment.
Sedimentary Rock Structures
• Sedimentary rocks can record the motion of wind
and waves on lakes, oceans, rivers, and sand dunes.
• Ripple marks and mud cracks are formed in the
sediment and then hardened into rock.
• Even rain drops and foot prints can be preserved in
the mud.
Metamorphic Rock
• What we will learn:
– We will describe two ways a rock can undergo
metamorphism.
– We will explain how the minerals in rocks change
as the rocks undergo metamorphism.
– We will describe the two categories of
metamorphic rock.
Metamorphic Rock
• Rocks change through metamorphism with
heat and pressure.
• This comes from the Greek word meta,
meaning “change”, and morphos, meaning
“shape”.
• Metamorphic rocks are rocks that have
changed structure, texture, or composition.
Origins of Metamorphic Rocks
• Temperature and/or pressure surrounding a
rock can change and make a metamorphic
rock.
• Most metamorphism takes place from 132°F
and 1,832°F, and at depths deeper than
1.25miles inside the Earth.
Contact Metamorphism
• When magma flows through the Earth’s crust
it melts the rock it touches.
• The rocks then re-harden
into new, metamorphic
rocks.
Regional Metamorphism
• Pressure in the Earth causes pieces of crust to
collide with each other superheating and
melting the rock.
• This changes large
areas underneath
contiential crust.
Composition of Metamorphic Rocks
• During metamorphism the minerals in a rock
change form into more stable minerals.
• Some of these minerals form at certain
temperatures, these are called index minerals.
Composition of Metamorphic Rock
• Scientist use these index minerals to tell at what
temperature, depth, and pressure the new rocks
were formed.
• More heat and pressure can cause one metamorphic
rock to morph into another kind.
Textures of Metamorphic Rock
• All metamorphic rock have one of two
textures, foliated and non-foliated.
• Foliated- the texture of metamorphic rock in
which the mineral grains are arranged in
planes or bands.
Textures of Metamorphic Rock
• If you see “bands” on the rock then it was
formed with the highest temperature and
pressure.
Textures of Metamorphic Rock
• Non-foliated- the texture of metamorphic rock
in which the mineral grains are not arranged
in planes or bands.
• Non-foliated rock are made from only a few
minerals, these minerals melt and re-form in a
process called recrystallization.
Metamorphic Rock Structures
• Metamorphic rock structures are cause by
force placed on the rock when it is formed.
• Deformation is what the change in shape is
called.
• The rock becomes folded or bended, this can
be really small or really large.
THE END!