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The Rock Cycle
Ag Earth Science – Chapter 3.1
mineral
 A natural occurring,
inorganic crystalline
material with a unique
chemical composition.
rock
 A consolidated mixture
of minerals
igneous rock
 A rock formed by the
crystallization of molten
magma
sedimentary rock
 Rock formed by from
weathered products of
preexisting rocks that
have been transported,
deposited, compacted,
and cemented.
metamorphic rock
Rock formed by the
alteration of preexisting
rock deep within the Earth
by heat, pressure, and/or
chemically active fluids.
rock cycle
A model that illustrates the
origin of the three basic rock
types and the
interrelatedness of Earth
materials and processes.
magma
A body of molten rock found
at depth including any
dissolved gases and crystals.
lava
Magma that reaches the
Earth’s surface.
weathering
The disintegration and
decomposition of rock at or
near the Earth’s surface.
sediments
Loose particles created by
weathering and erosion of
rock, by chemical
precipitation from solution
in water, or from the
secretions of organisms and
transported by water, wind,
or glaciers.
That’s Random
Rocks
 A rock is any solid mass of
mineral or mineral-like
matter that occurs
naturally as part of our
planet.
 Rocks are classified into 3
major types

Igneous Rocks

Sedimentary Rocks

Metamorphic Rocks
The Rock Cycle

Interactions among the Earth’s
water, air, and land can cause
rocks to change from one type to
another

The continuous processes that
cause rocks to change make up
the rock cycle

When magma (molten material
beneath the Earth’s surface) cools
and hardens, igneous rocks form.
Magma that reaches the surface is
called lava.

When weathered (process by which
rocks are physically and chemically
broken down into small pieces
called sediments) sediments are
compacted and cemented together,
they form sedimentary rocks.

When sedimentary rocks are
subjected to extreme pressure and
heat, they change in metamorphic
rock.
The Rock Cycle
Powers of the Earth’s Rock Cycle
 Heat from the Earth’s
interior are responsible
for forming both igneous
and metamorphic rocks
 Weathering and the
movement of weathered
materials are generated
by the sun’s energy and
produce sedimentary
rock.
Another Dam Photo …..
Ag Earth Science – Chapter 3.2
ignis
 Latin word for “fire”
intrusive igneous rock
 Igneous rock that formed
below the Earth’s surface
extrusive igneous rock
 Igneous rock that has
formed on the Earth’s
surface
porphyritic texture
 An igneous texture
consisting of large
crystals embedded in a
matrix of much smaller
crystals
granitic composition
 A compositional group of
igneous rocks that
indicate a rock is
composed entirely of
light-colored silicates,
mainly quartz and
feldspar
basaltic composition
 A compositional group of
igneous rocks indicating
that the rock contains
substantial dark silicate
minerals and calciumrich plagioclase feldspar
andesitic composition
 A composition of igneous
rock rocks lying between
felsic and mafic
ultramafic
 Igneous rock composed
mainly of iron and
magnesium-rich
minerals
That’s Random
Formation of Igneous Rocks
 Igneous – Comes from
the Latin word “ignis”
which means “fire”
Formation of Igneous Rocks
 Intrusive Igneous Rocks
– rocks that form when
magma hardens (cools)
beneath the Earth’s
surface.

Example – Granite
Formation of Igneous Rocks
 Extrusive Igneous Rocks
– rocks that form when
lava hardens (cools)
above the Earth’s
surface.

Example – Rhyolite
Classification of Igneous Rocks
 Texture and composition
are two characteristics
used to classify igneous
rocks.
Classification of Igneous Rocks
 Course Grained Texture
– Slow cooling = large
crystals. Large crystals
exhibit “course-grained”
texture.
Classification of Igneous Rocks
 Fine Grained Texture –
Rapid cooling = small
mineral grains. Small
grains are said to have
“fine-grained” texture.
Classification of Igneous Rocks
 Glassy Texture – Lava
spews on surface = may
not be time for ions to
arrange themselves into
crystals. Random
distributed ions = glassy
texture.
Classification of Igneous Rocks
 Porphyritic Texture –
Large body of magma
may take thousands of
years to harden. Variety
of temperature/cooling
within large mass = large
crystals and fine-grained
minerals.
Classification of Igneous Rocks
 Granite Composition –
Made almost entirely of
light colored silicate
minerals quartz and
feldspar.
Classification of Igneous Rocks
 Basaltic Composition –
Rocks that contain many
dark silicate minerals
and plagioclase.
Classification of Igneous Rocks
 Andesitic Composition –
In-between granite
(light) and basaltic
(dark) compositions.
Classification of Igneous Rocks
 Ultramafic – Composed
almost entirely of dark
silicate minerals
(peridotite).
Classification of Igneous Rocks
That’s Random
Ag Earth Science – Chapter 3.3
erosion
 The incorporation
and transportation
of material by a
mobile agent such
as water, wind, or
ice.
deposition
 The process by
which an agent of
erosion loses its
energy and drops
the sediment it is
carrying.
compaction
 Process by which
sediments are
squeezed together
by the weight of
overlying materials
driving out water.
cementation
 Solidification of
sediments by
deposition of
dissolved minerals
clastic sedimentary rock
 A sedimentary rock
made of broken
fragments of
existing rock
chemical sedimentary rock
 Sedimentary rock
consisting of
material that was
precipitated from
water by either
inorganic or
organic means
Formation of Sedimentary Rocks
 Sedimentary – Comes
from the Latin word
“sedimentum” which
means “settling”
Formation of Sedimentary Rocks
 Weathering, Erosion, and
Deposition

Erosion – involves
weathering and the removal
of rock

When an agent (wind, ice,
water, or gravity) loses
energy, it drops the
sediments.

Deposition – the process of
erosion losing energy and
dropping sediment.
Formation of Sedimentary Rocks
 Compaction and
Cementation

Compaction – process of
“squeezing” or compacting
sediments

Cementation – dissolved
minerals are deposited in
the tiny spaces among
sediments.
Formation of Sedimentary Rocks
 The 5 Main Processes
that Form Sedimentary
Rocks





weathering
erosion
deposition
compaction
cementation
Classification of Sedimentary Rocks
 Clastic Sedimentary
Rocks – Made up of
weathered bits of rocks
and minerals
Classification of Sedimentary Rocks
 Classified according to
particle size

Conglomerate –(gravel)
rounded, large gravel-size or
larger pebbles cemented
together

Breccia – (gravel) angular
particles

Sandstone – sediments are
sand-sized grains

Siltstone – fine-grained
sediments
Classification of Sedimentary Rocks
 Chemical and
Biochemical
Sedimentary Rocks –
form when dissolved
substances precipitate, or
separate, from water
solution.

Examples – limestones,
rock salt, chert, flint, and
rock gypsum.
Features of Some Sedimentary Rocks
 The many unique
features of sedimentary
rocks are clues to how,
when, and where the
rocks formed.
 Each layer is a “time
period”
 Fossils are unique in
sedimentary rocks
That’s Random
Ag Earth Science – Chapter 3.4
metamorphism
 The changes in mineral
composition and texture
of a rock subjected to
high temperatures and
pressure within the Earth
contact metamorphism
 Changes in rock caused
by the heat from a nearby
magma body
regional metamorphism
 Metamorphism
associated with largescale mountain building
hydrothermal solution
 The hot, watery solution
that escapes from the
mass of magma during
later stages of
crystallization
Another Dam Photo …..
Formation of Metamorphic Rocks
 Metamorphism – “to
change form”
 Formation of Metamorphic
Rocks

Most metamorphic changes
occur at elevated
temperatures and pressures.

These conditions are found a
few kilometers below the
earth’s surface and extend
into the upper mantle
Formation of Metamorphic Rocks
 Types of Metamorphism

Contact Metamorphism –
Hot magma moves into
rock

Regional Metamorphism
– large scale deformation
and high-grade
metamorphism due to
extreme pressures and
temperatures. (Example –
mountain building)
Agents of Metamorphism
 Agents of Metamorphism

The agents of
metamorphism are heat,
pressure, and
hydrothermal solutions
Agents of Metamorphism
 Heat – Most important
agent of metamorphism.
Provides energy for
chemical reactions. Heat
comes from magma and
change in temperature
with depth.
Agents of Metamorphism
 Pressure (Stress) –
Increases with depth
(example – bottom of
swimming pool).
Pressure causes spaces
between minerals to
close = greater density.
Agents of Metamorphism
 Reactions to Solutions –
solutions that surround
mineral grains aid in
recrystallization by
making it easier for ions
to move. When hot,
water-based solutions
escape from magma, they
are called hydrothermal
solutions. These hot
fluids promote
recrystallization.
Classification of Metamorphic Rocks
 The texture of
metamorphic rocks can
be foliated or nonfoliated
Classification of Metamorphic Rocks
 Foliated Metamorphic
Rocks – a texture that
gives the rock a layered
appearance
Classification of Metamorphic Rocks
 Nonfoliated
Metamorphic Rocks – a
texture that does not
exhibit a banded or
layered appearance.
THE END ….. for this unit.