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Rocks:
Mineral
Mixtures
Chapter 4
Section 1
Understanding Rock
 Rock
= solid mixture of crystals of one or more
minerals.
 Some
types of rock, such as coal, are made of
organic materials
The Value of Rock
 Humans
• Tools,
• Rocks
have a long history with rock
weapons, buildings, roads, & monuments
hold a record of what the Earth & other
planets were like before recorded history
Section 1
The Rock Cycle
 The
way rock forms determines what type of rock
it is. There are 3 different types of rock: igneous,
sedimentary, & metamorphic.
 Rock Cycle = the process by which one rock type
changes into another. This cycle involves:
• Deposition
• Compaction &
cementation
• Metamorphism
• Melting
•
•
•
•
Cooling
Solidification
Weathering
Erosion
Section 1
The Rock Cycle: Cont.
Define the three main types of rock:
 Igneous = forms from the cooling of magma.
(melting, cooling, & solidification)
• Magma = hot liquid formed when rock partially or
completely melts. Lava = magma flowing out onto
the Earth’s surface.
 Sedimentary = forms when sediments are
compacted & cemented together. (weathering,
erosion, deposition, & compaction & cementation)
 Metamorphic = formed when the texture &
composition is changed by heat or pressure deep
underground (pressure & heat = metamorphism)
Section 1
Section 1
The Nitty-Gritty on Rock Classification

Rocks are further divided into other groups
Composition
 Composition = the minerals a rock is made of
Texture
 Texture = determined by the sizes, shapes, &
positions of the grains of which it is made
 Coarse-grained – larger grains in the rock
 Medium-grained – between fine & coarse rock
 Fine-grained – small grains such as silt or clay
Section 2
Igneous Rock

Igneous – comes from the Latin word for “fire”

Magma cools into various types of igneous rock
depending on the composition of the magma &
the amount of time it takes the magma to cool &
solidify

Like all other rock, igneous rock is classified
according to its composition & texture.
Section 2
Origins of Igneous Rock
There are three ways a rock can melt:
Temperature – Temperatures increase as you travel
deeper into the Earth. This causes minerals in
rock to melt. Different minerals melt at
different temperatures. Depending on how hot
a rock is, some of the minerals melt while
other minerals remain solid
Section 2
Origins of Igneous Rock: Cont.
Pressure – Pressure increase as you travel deeper
into the Earth. This forces minerals to stay
solid, when otherwise they would melt from
the intense heat. When hot rocks rise to
shallow depths, the pressure is finally released
& the minerals can melt.
Composition – Sometimes fluids enter a rock that is
close to its melting point. When these fluids
combine with the rock, they can lower the
melting point of the rock enough for it to melt
& form magma.
Section 2
Composition & Texture of Igneous Rock
Composition
 Felsic composition – Light-colored rocks; lighter
in weight; rich in silicon, aluminum, sodium, &
potassium
 Mafic composition – dark-colored rock; heavier;
rich in iron, magnesium, & calcium
Texture
 Longer it takes for lava to cool more time mineral
crystals have to grow & the coarser the texture of
the resulting igneous rock
Section 2
Igneous Rock Formations
Intrusive Igneous Rock
 Intrusive
= rock that results from when magma
cools beneath the Earth’s surface
 Usually
has a coarse-grained texture
• it
is well insulated by the surrounding rock &
thus cools very slowly
(plutonic rock) – large, balloon-shaped
intrusive formations that result when magma
cools at great depths
 Plutons
Section 2
Igneous Rock Formations: Cont.
Extrusive Igneous Rock
 Extrusive = Igneous rock that forms on the
Earth’s surface. Most volcanic rock is extrusive.
 Contains either very small crystals or none at all
because it cools quickly
 3 examples of Extrusive Igneous Rocks are
Pumice; Obsidian; Basalt
 Fissures – long cracks in the Earth’s surface form
which lava sometimes flows
 Lava plateau – when a large amount of lava flows
out a fissure and covers a vast area
Section 3
Sedimentary Rock

Wind, water, ice, sunlight, & gravity all cause
rock to weather into fragments.

Through the process of erosion, rock fragments,
called sediment, are transported from one place
to another.

Eventually the sediment is deposited in layers.

Sedimentary rock then forms as sediments
become compacted & cemented together.
Section 3
Origins of Sedimentary Rock

As sediment is deposited, the layers eventually
become compressed. Dissolved minerals separate
out of water to form a natural glue that binds the
sediments together into sedimentary rock.

Sedimentary rock forms at or near the Earth’s
surface, without the heat & pressure involved in
the formation of igneous & metamorphic rocks.

physical features of sedimentary rock tell a part
of history. The most notable feature is the strata.

Strata = the layers found in sedimentary rock.
Section 3
Composition of Sedimentary Rock
Two main categories of sedimentary rock:
Clastic Sedimentary Rock

Formed from rock or mineral fragments
Chemical Sedimentary Rock

Formed from solutions of minerals & water.
(when minerals crystallize out of a solution, such
as sea water, to become rock)

The remains of animals can become part of
sedimentary rock as well. They form fossils.
Section 3
Sedimentary Rock Structures

Rock features can tell you how the rock was
formed

Stratification = layering

Strata differ from one another depending on the
kind, size & color of their sediment.

The rate of deposition can affect the thickness of
the layers

This rock can record the motion of wind & waves
on lakes, seas, rivers, & sand dunes.
Section 4
Metamorphic Rock
Metamorphic – “changed shape”
 All rock can change into metamorphic rock
Origins of Metamorphic Rock
 Texture or mineral composition of a rock can
change when its surroundings change
 Most metamorphic change is caused by increased
pressure that takes place at depths greater that 2
km.
 Temperature at which metamorphism occurs
ranges from 50oC to 1,000oC

Section 4
Origins of Metamorphic Rock: Cont.
 Contact
•
Metamorphism
Only happens to igneous intrusive rock
 When magma flows through the crust, its
heat flows into the surrounding rock &
“cooks” it.
 The greatest changes occur where the magma
comes into direct contact with the rock & the
effect lessens the further you travel away
from that contact.
 The heat & fluids in the magma changes the
minerals present into other minerals
Section 4
Origins of Metamorphic Rock: Cont.
 Regional
•
Metamorphism
This kind of metamorphic rock is underneath
most continental rock formations.

Enormous pressure builds up in rock that is
deeply buried under other rock formations or
when pieces of the Earth’s crust collide.

The pressure & increased temperature that
exist under these conditions cause rock to
become deformed & chemically changed.
Section 4
Composition of Metamorphic Rock

Metamorphism can occur in many different
environments. Temperature & pressure
conditions, as well as the composition of the rock
determine which metamorphic minerals will
form.

When scientists observe metamorphic minerals in
a rock, they can estimate the temperature & depth
(pressure) at which recently exposed rock under
went metamorphism.
Section 4
Texture of Metamorphic Rock
Just like all other rock metamorphic rock is
classified by composition & texture. Metamorphic
rock has one of two textures:

Foliate = consists of minerals that are aligned &
look almost like pages in a book

Nonfoliate = does not appear to have any regular
pattern
Section 4
Texture of Metamorphic Rock: Cont.
Foliated Metamorphic Rock
 Contains mineral grains that are aligned by
pressure
 Metamorphic rocks can change again if their
environment changes
Nonfoliated Metamorphic Rock
 Commonly made up of only one, or just a few,
minerals but none of the crystals are aligned.