The Rock and Minerals of the Earth’s Crust

Oxygen

Silico

n

Aluminu

mIro

n

Calcium

Magne

sium

Sodiu

m

Other M

atter

01020304050

Elements of the Earth's Crust

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

RocksA rock is any consolidated

mixture of one or more mineralsOxygen 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

RocksThe 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??

AnswerDue 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

AnswerSecond 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 CycleThe process of replacing of older

rocks with new ones is referred to as the Rock Cycle

Rock Cycle Con’tThere are 3 rock classes:

◦igneous (cooling/solidification) ◦sedimentary (erosion/deposit) ◦metamorphic (heat/pressure)

http://www.geolsoc.org.uk/gsl/education/rockcycle/page3531.html

ActivityUsing 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 Rocks95% of the rocks on the Earth’s crustFormed 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 rock-

VOLCANIC ERUPTIONS

Major Igneous RocksThere are two main categories of

Igneous Rocks:

◦1. Extrusive (Volcanic): cool on the surface

◦2. Intrusive (Plutonic): Cool below the Earth’s surface

Extrusive RocksRapid 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 RocksWhere 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 sedimentsMany 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 RocksSettle 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 RocksToday 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 RocksWe 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 RocksThe 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 ContinentsThe 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 ContinentsThe 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 ContinentsOn 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