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Chapter 6 – Rocks
Section 6.1 – Rocks and the Rock Cycle
Section Objectives
Identify the 3 major types
of rock, and explain how
each type forms.
Summarize the steps in
the rock cycle.
Explain Bowen’s reaction
Summarize the factors
that affect the stability of
Rocks Are:
 The materials that make
up the solid part of the
 A collection of one or
more minerals, may not
be crystals (glass).
3 Major Types of Rocks
(based by the way the rocks form)
Igneous Rock
(Latin: “from fire”)
Forms when molten
rock (magma) cools
and hardens.
Magma is called lava
when it is erupted on
the Earth’s surface.
 Agents
Satellite Photograph;
Rio Tinto, Spain
of erosion
(wind, water, ice,
gravity) break down all
types of rock into small
 These fragments of
rocks, crystals, and
organic matter are
known as sediment.
Sediments Deposited
Sediments are
carried away and
deposited in another
area by wind, water,
and ice. They are
then compressed
and/or cemented
together to harden
Sedimentary Rocks
Pressure, Heat, and Chemical Processes
• Can change the form
of an existing type of
rock. The result is
an altered rock
known as………
Metamorphic Rock
Greek: “changed form”
The Rock Cycle
Any rock can be
changed into
another of the
three types of
Rock cycle video
Changed Conditions = Changed Rock
 A particular body of
rock does not always
pass through each
stage of the rock
Properties of Rocks
The physical
characteristics of
rock reflect the
composition of the
N. L. Bowen (1928)
Proposed that different
minerals form at different
times during the cooling of
magma, and that they
generally form in the same
order. The pattern of
mineral formation depends
on the chemical
composition of the magma.
Bowen’s Reaction
Zoned Plagioclase:
Ca rich core, Na rich rim
• Minerals form in one of
two ways. The first
(right-hand side) is a
gradual, continuous
formation of
plagioclase minerals
that have similar
chemical compositions.
The Second Way
• Sudden changes in
mineral types, the
reaction series of
Fe-Mg minerals
(the left-hand side
of the diagram).
Chemical Stability of Minerals
The rate at which a mineral
breaks down is dependent
on the chemical stability of
the mineral, and is a
measure of the tendency to
maintain its original
composition rather than
break down to form a
different chemical.
Depends on Chemical Bond Strength
Generally, the most
resistant minerals
have the highest
number of bonds
between silica and
oxygen. This
reflects Bowen’s
reaction series (first
formed, first
Physical Stability of Rocks
Rocks have natural
zones of weakness that
are determined by how
and where the rocks
form. Once the
surfaces of these
weaknesses are exposed
to air and water,
chemical and physical
weathering begins.
Sedimentary Rocks
Sedimentary rock video
Zones of weakness
along layers or
through fractures that
develop when
pressure is released
when the rock is
uplifted to the
Earth’s surface.
Metamorphic Rocks
Can have layering
also, which are zones
of weakness.
Metamorphic Rock video
Igneous Rocks
Can have evenly
spaced zones of
weakness, called
joints, that form as
the rock cools and
Igneous rock video
Significant Digits
 6.1 Key Terms
 Rock Cycle Directed