Download The Rock and Minerals of the Earth*s Crust

The Rock and Minerals of the
Earth’s Crust
Elements of the Earth's Crust
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Minerals
A mineral is material formed when two
or more elements combine in a
crystalline structure
 The 92 elements found in the Earth’s
crust form at least 2000 different minerals

Common Minerals: Building Blocks
of the Earth’s Crust
See page 68
Rocks
A rock is any consolidated mixture of
one or more minerals
 Oxygen and Silicon combine to form the
silica tetrahedron (SiO4), the basic
building block of the Earth’s crust.
 The variety of rocks is only limited by the
various combinations of minerals that
occur in the Earth

Rocks
The composition of crustal rocks gives us
a good idea of the composition of the
crust and the interior of the earth.
 Some rocks are very old- up to 3 billion
years old, but more rocks are very young
(well for rocks)

Why do you think that most rocks are so
young??
Answer

Due to the convection currents beneath
the Earth’s surface put pressure on the
crust, which causes the rocks of the
ocean floor to move. In other portions of
the crust disappear into the mantle at
deep trenches on the ocean floor.
Therefore, the constant recycling of rocks
results in rocks no older than 2-3 million
years old. However the rocks of the
continents are much older
Answer
Second part lies in the hydrosphere.
 The movement of water and ice play a
major role in eroding older rocks and the
deposition helps account for the youthful
age of many rocks of the Earth’s crust

The Rock Cycle

The process of replacing of older rocks
with new ones is referred to as the Rock
Cycle
Rock Cycle Con’t

There are 3 rock classes:
◦ igneous (cooling/solidification)
◦ sedimentary (erosion/deposit)
◦ metamorphic (heat/pressure)
Activity

Using the chart 5.3 (pg 69) in your
textbook create your own rock cycle.
◦ Ensure that factors contributing to their
formation are present (ex. Heat/pressure)
◦ Ensure it is titled
◦ Ensure it has colored corresponding arrows
◦ Ensure it has your name on it
**When you are done complete questions 1,3, and
4 on page 70 **
Born of Fire: Igneous Rocks
Igneous Rocks
95% of the rocks on the Earth’s crust
 Formed by the cooling and solidification
of molten materials, or magma beneath
the Earth’s surface
 The term igneous comes form the Latin
word fire

◦ Which refers to the origin of these rockVOLCANIC ERUPTIONS
Major Igneous Rocks

There are two main categories of Igneous
Rocks:
◦ 1. Extrusive (Volcanic): cool on the surface
◦ 2. Intrusive (Plutonic): Cool below the Earth’s
surface
Extrusive Rocks
Rapid cooling occurs when molten magma is
erupted onto the Earth’s surface and is
exposed to the Atmosphere.
 Magma that reaches the Earth’s surface is
called Lava
 Heat is given off quickly and lava solidifies
into hard rock (or smooth volcanic glass)
 Sometimes the rocks cool so quickly that gas
does not have time to escape (ex. Pumice)

Intrusive Igneous Rocks
Where mama cools slowly below the
Earth’s surface.
 These rocks are much different in
appearance

◦ Slow cooling allows the various elements to
gather together to form crystals of pure
minerals that are visible with the eye.
 Granite is the most common rock of this category.
Examples of Igneous Rock
Born of Erosion and Deposition:
Sedimentary Rocks
The energy for the creation of
sedimentary rock comes largely from the
sun rather than the Earth’s interior
 Closely related to the movements of
water (hydrological cycle)
 Formed from sediments
 Many areas only have layers of
sedimentary rocks that are skin deep.

Born of Erosion and Deposition:
Sedimentary Rocks

These sediments have many origins and
sizes; however, they can be divided into
two types:
◦ Clastic (inorganic): gravel, sand, silt, etc.
◦ Non-Clastic (organic): solids from ocean
waters are made up of animal or plan remains
Clastic Sedimentary Rocks
Settle out of relatively calm waters, the
build up horizontal layers of the floors of
these lakes or oceans
 These sediments turn to rock by two
main processes:

◦ 1. pressure from more recent overlying
sediments
◦ 2. lithification: cementing together the
sediments by various chemicals (ex. Calcium
carbonate) that seep into the layers.
Clastic Sedimentary Rocks

Today these types of rocks are slowly
forming in many parts of the world.
However, they are most productive in
forming areas where major river deposits
sediments into the ocean, forming huge
deltas.
Non-Clastic Sedimentary Rocks

Originate from the remains of plans and animals
(usually skeletons or shells) that accummulate on
the ocean and sea floors, or from the chemical
precipitation of minerals from seawater.

These take longer to form than Clastic
Sedimentary Rocks, but make up common rocks
such as:
◦
◦
◦
◦
◦
Limestone
Dolomite
Shale,
Sandstone
Coal
Non-Clastic Sedimentary Rocks

The Great Barrier Reef of Australia and
the reefs of the Caribbean Sea and Pacific
Ocean are areas where limestone rocks
are presently being formed fromt eh
remains of sea creatures and coral reef.
Origins of Important Sedimentary
Rocks
Examples of Sedimentary Rocks
Born of Great Heat and Pressure:
Metamorphic Rocks
Name comes from the word
“metamorphosis” meaning change.
 Rocks that have been greatly altered from
their original forms through hit and
pressure fit into this category

Metamorphic Rocks

We cannot observe metamorphic rocks
forming, as with igneous and sedimentary
rocks.
◦ Often the heat and pressure that transform
these rocks are found deep with Earth’s
surface where mountain ranges are forming.
◦ Form where crustal plates collide pushing up
new mountain ranges such as the Himalayas,
Andes, Rockies, and Alps
Metamorphic Rocks
The term foliated is used to describe the
structure caused by gathering together of
different minerals into parallel bands. Do
not confuse this with the layers of
sedimentary rocks
 Common Characteristics:

◦ Hard to break (very compact)
◦ Reflection of their origins in their roots of the
mountains
Uses of Metamorphic Rocks
Slate and marble are rocks useful for
building purposes, as they are very
durable
 Seldom contain old, natural gas, or coal
because the materials would be burnt up
due to the immense heat and pressure
put on these rocks
 Metal are found in these rocks due to the
minerals that igneous rocks possess
before being exposed to the elements

Examples of Metamorphic Rocks
Oceans and Continents
The division of the Earth’s materials into
the three major rock classes is only one
way to consider them.
 A second way to classify rocks is by
dividing them into two categories: 1. those
found in the ocean, and 2. those found on
continents.

◦ These tow groups of rocks have different
densities and generally different colors
Oceans and Continents

The term sial is used to identify the
granitic rocks of the continents since they
are primarily comprised of silicon and
aluminum.
◦ These rocks are less dense than basaltic rocks
that lie in the ocean as they are comprised of
lighter elements.
Oceans and Continents

On the other hand, the term sima is used
for denser basaltic rocks of the ocean
floor, as they are primarily comprised of
silicon and magnesium.
◦ Iron is present in greater amounts in these
rocks.
◦ Usually darker in color than the granitic
continental rocks
Theory of Isostacy: Balance
Between Crust and Mantle

Isostacy: state of balance maintained by the
earths crust as it floats on the plastic layer of the
upper mantle

The difference in density between the granitic and
basaltic rocks is the key to development of
continents and ocean basins.

It is believed that the various blocks of the crust
float on the softer materials of the asthenosphere