EARTH SCIENCE
ROCKS
IGNEOUS, SEDIMENTARY,
AND METAMORPHIC
WHAT IS A ROCK?
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A rock is a group of minerals that are
bound together.
Rocks are MIXTURES because they have
varying percentages of different minerals
Rocks are classified according to how they
were formed.
THREE GENERAL TYPES OF
ROCKS:
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Igneous rocks—formed by the cooling and
hardening of magma from inside the earth.
Sedimentary rocks—formed by the
compaction and cementing of layers of
sediments
Metamorphic rocks—formed by the effects
of heat and pressure on other rocks
ROCK CYCLE
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Rocks form from other rocks.
The rock cycle is the repeated series of
events by which rock gradually and
continually changes from one type to
another.
“WORDY VERSION” OF ROCK
CYCLE
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Magma (hot, molten rock) beneath the earth’s
surface is the source of all rocks.
Once magma reaches the surface (lava), or cools
in the interior (as magma) igneous rocks are
formed.
Once igneous rocks are weathered and
erodedsedimentary rocks are formed.
Sedimentary rocks (and sometimes igneous
rocks) are buried and caught in Earth’s
movementsmetamorphic rocks are fomed.
“SCHEMATIC” ROCK CYCLE
“VISUAL” ROCK CYCLE
MAGMA
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Is hot, molten rock beneath Earth’s surface
Is called lava once it reaches the surface
Four types:
Felsic
Intermediate
Mafic
Ultramafic
FELSIC MAGMA
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Thick and slow moving
Large amounts of silica
Hardens into rocks of light-colored silicate
minerals
MAFIC MAGMA
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Hotter, thinner than felsic
Large amounts of iron and magnesium
Forms rocks of darker colors
INTERMEDIATE MAGMA
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Mix between felsic and mafic
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Ultramafic
Low Si
High Fe and Mg
Green in color or
green tint
Varying densities
Kimberlites are rare
ultramafic rocks
where diamonds
have been found in
Kimberly, S Africa
Peridotite
Dunite
IGNEOUS ROCKS
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Although all igneous rocks form from
magma, they are not all the same.
The differences are caused by:
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Variations in the magma’s composition
Variations in the formation process
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Formed from underground magma intrusive
Formed at Earth’s surface extrusive
TEXTURE OF IGNEOUS ROCKS
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The texture of an igneous rock is caused by
the rate of cooling.
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Cools rapidly extrusive glassy, fine-grained
texture
Cools slowly intrusive coarse texture,
crystals formed
Igneous Textures
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Fine Grained- cools fast,
small crystals form (too
small to be seen without
the use of a microscope)
Basalt
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Coarse Grained- cools
slowly, large visible
crystals (easily seen with
the eye, many colors or
patterns)
Granite
Igneous Textures
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Glassy: cools too fast for
crystals to form.
Pumice
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Obsidian
Porphyritic: mixture of
fine and coarse grains.
Fine grained ground
mass with large crystals
mixed in.
Andesite
Bowen’s Reaction Series
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A Canadian
scientist, N.L.
Bowen,
demonstrated that
as magma cools,
minerals form in
predictable
patterns.
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Each mineral
crystallizes at a
different
temperature.
SEE “Explore” of
your Discovery
Techbook, Igneous
Rocks
FAMILIES OF IGNEOUS ROCKS
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Are grouped together based solely on
mineral composition, so a family can have
rocks of all different textures and origins.
Three main families:
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Granite Family
Gabbro Family
Diorite Family
GRANITE FAMILY
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Form from felsic magmas
Usually coarse-grained from slow cooling
Usually made of quartz, feldspar, mica, and
hornblende
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Granite
Obsidian
Pumice
Rhyolite
GRANITE
OBSIDIAN
PUMICE
RHYOLITE
GABBRO FAMILY
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Mainly made from mafic magma
Darker in color and denser than granite
family
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Gabbro
Basalt
Scoria
GABBRO
BASALT
SCORIA
DIORITE FAMILY
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From intermediate magma (characteristics
of felsic and mafic)
Color is darker than granites and lighter
than gabbros (dark greys and greens)
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Diorite
andesite
DIORITE
ANDESITE
IGNEOUS INTRUSIONS
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Are rock masses that form when magma
cools inside Earth’s interior
Forces within the earth push magma up
into the bedrock
Igneous intrusions are also called plutons
TYPES OF IGNEOUS INTRUSIONS
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Dikes—sheet of igneous rock cuts across rock
layers vertically or at a steep angle
Sills—sheet of igneous rock that lies parallel to
the layers it intrudes
Laccoliths—from stiff magma that does not flow
easily—bulges upward to form domed masses
Batholiths—form core of mountain ranges (largest
of all intrusions)
SEDIMENTARY ROCKS
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While most of the earth’s crust is made of
igneous rock, most of the earth’s surface is
made of sedimentary rock
Formed from the compaction and
cementation of layers of sediments
FAMILIES OF SEDIMENTARY
ROCKS
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Are grouped according to their formation
process
Three general groups in text:
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Clastic
Chemical
Organic
CLASTIC ROCKS
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Are formed from the fragments of other
rocks
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Conglomerates—the coarsest clastic rocks
Sandstones—made of quartz and sand
Shales—made of silt and clay
CHEMICAL ROCKS
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Made when minerals precipitate out of a
solution
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Rock salt
Rock gypsum
Some limestones
ORGANIC ROCKS
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Form from sediments of plant or animal
remains
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Limestone
Coal
LIMESTONE
COAL
FEATURES OF SEDIMENTARY
ROCKS
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Stratification
Fossils
Ripple marks
Mud Cracks
Nodules
Concretions
geodes
STRATIFICATION
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The arrangement of visible layers
Most apparent characteristic of
sedimentary rocks
Line between layers is called bedding
plane
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Usually horizontal, but cross-bedding can occur
FOSSILS
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The remains, impression, or any other
evidence of a plant or animal preserved in
rock
RIPPLE MARKS
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Sand patterns formed by the action of
winds, streams, waves, or currents
MUD CRACKS
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Occurs where a muddy road or puddle of
water has dried out after the rain
Modern
Ancient
NODULES
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Hard lumps of silica in limestone and chalk
CONCRETIONS
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Round, solid masses of calcium carbonate
in layers of shale
GEODES
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Spheres of rocks filled with crystals that
occur in limestones
METAMORPHIC ROCKS
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Formed by the effect of heat and pressure
on other rocks
Formed from pre-existing rocks called
parent rocks
Usually resemble their parent rocks
METAMORPHISM
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Process by which a rock’s structure is
changed by heat, pressure, and moisture
Two Basic Types:
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Regional
Local
REGIONAL METAMORPHISM
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Occurs in large areas
Forms most of the metamorphic rock of
Earth’s crust
Can occur during mountain-building
process
LOCAL METAMORPHISM
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Occurs in smaller, distinct areas
Two Types:
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Contact hot magma moves into rock, heating
and changing it (can even change mineral
compostion)
Deformational occurs at lower temperatures
and is more due to pressure (composition does
not change but deforms shape and texture)
CLASSIFICATION OF
METAMORPHIC ROCKS
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Based on a variety of properties:
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Parent rock
Mineral content
Texture
Foliation—tendency to form bands of minerals or
split along parallel layers
CLASSIFICATION OF
METAMORPHIC ROCKS
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Metamorphic Rocks are also classified by their
“grade” or degree of metamorphism:
Even the
minerals in a
rock can
change with
metamorphism
(but not
always!)
EXAMPLES OF METAMORPHIC
ROCK
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Quartzite a metamorphosed sandstone
Marble a metamorphosed limestone
Slate, phyllite, schist metamorphosed
shales
Gneiss—most highly metamorphosed
from a variety of parent rocks
QUARTZITE
MARBLE
SLATE
SCHIST
GNEISS