Rocks formation and cycle

3 types of rocks

Igneous rocks - produced when magma from the mantle cools and solidifies.

Sedimentary rocks - formed by burial, compression, and chemical modification of deposited weathered rock debris or sediments at the earth's surface.

Metamorphic rocks - created when existing rock is chemically or physically modified by intense heat or pressure.

•Where rocks come from.•Importance of rocks.•Types of rocks.•Formation of rocks.

The crust is like a thin skin, with an

averagethickness of about 30

kilometres. Beneath the crust is the mantle—about

3000 kmthick. It consists of

solid rock, but under certain

conditions it can bend and flow like a

thick paste

The crust and the top of the mantle is called the lithosphere which means ‘rocky sphere’.

Below the lithosphere the rocks are under immense pressure.

They are very hot, and in parts molten. This molten rock is called

magma. It also contains dissolved

gases.

A rock is a solid substance that occurs naturally because of the effects of three basic geological processes;

Magma Solidification;Sedimentation of weathered rock

debris;Metamorphism.

3 types of rock formations




Rocks can tell us many stories;

Where the rock was formed;The general water depth (if marine or fresh water)The relative age of the rock (using fossils)Or it’s absolute age (if radioactive materials are present)Its original position and orientation on the surface of the earth

Igneous rocks – 2 types

Intrusive (Plutonic) rock the magma has cooled and solidified within the earths crust

Extrusive (Volcanic) rock the magma cools and solidifies on the earth’s surface.

Rate of cooling & temperature changes determine the texture & degree of crystallization

The composition of the magma will determine the composition of the igneous rock

Volcanoes form through weak spots in the earth’s crust.These may crack and allow magma to flow from the mantle to the surface. When this happens a volcano forms. The pressure inside the Earth pushes the magma upwards. Sometimes the molten rock oozes out steadily. At other times it blasts out with incredible force. Usually have no or small crystals

The longer Magma has to cool down the larger the crystals will form in the rock.

The size of the crystals demonstrates where it came from

What rock can float on water?A)AeroliteB)PumiceC)ChalkD)Eolianite

Pumice is a type of lava full of gas bubbles. It can be as light as Styrofoam, or nearly as dense as normal rock.

Aerolite is an old name for meteorites, and Eolianite is any rock type that is made of windblown sediment. Chalk is a lightweight rock, but not that light.

There are sometimes weak spots in the Earth’s crust that may crack and allow the magma to flow from the mantle to the surface. When this happens a volcano forms. The pressure inside the Earth pushes the magma upwards. Sometimes the molten rock oozes out steadily. At other times it blasts out with incredible force.

Above ground = from lava (extrusive igneous rock)

Usually have SMALL or NO crystals (they cooled too quickly)

Granite

1. Light color2. Low specific gravity

3. Coarse grained

4. Forms on the continents deep underground

Basalt

1. Dark color2. High specific gravity3. Fine grained

4. Forms at the surface, principally in the ocean basins, but also in isolated "hot spots" on the continents.

Why do we see intrusive

igneous rocks at the surface of the earth?

Once a rock is formed, does it stay the same rock forever?

3 types of rocks




How many main types of Rocks are there?Igneous rocks are formed sediments?Rocks can break down from rain?The Majority of rocks found on the surface of the planet are Metamorphic rocks.2 Types of Igneous Rocks are?How are extrusive (plutonic) rocks exposed?

Igneous rocks – 2 types


Extrusive (Volcanic) rock the magma cools and solidifies on the earth’s surface.

Do you know the Rock Cycle?How are sedimentary rocks formed?What can sedimentary rock tell us?How are Metamorphic rock formed?What change occurs to the mineral grains when a Sedimentary or Igneous rock changes to metamorphic rock?

Formed from sediments (rock fragments, mineral grains, animal & plant remains) that are pressed or cemented together or when sediments precipitate out of a solution.

These sediments are moved by wind, water, ice or gravity.Sedimentary rocks represent 7% of the Earth’s crust, but they cover 70% of the Earth’s surface.

Sedimentary rocks arefossil-carrying rocks.

As sedimentary rocks are

deposited, they form horizontal

layersScientists know

that the layers on top (and the fossils in the top layer) are YOUNGER than the

fossils in lower layers.

Water or wind breaks down and deposits sediment (erosion & deposition)

The heavy sediments press down on the layers beneath (compaction)

Dissolved minerals flow between the particles and cement them together (cementation)

Clastic (also called Detrial)—made of broken pieces of other rocks

Organic—remains of plants and animals are deposited in thick layers

Examples Fossil rich limestone is made from

the shells of ocean animals; used to make chalk

Chemical—minerals dissolved in lakes, seas, or underground water

Mineral crystals are made as the shallow water that has flooded the bottom of Death Valley evaporates. Click on image for full size (66K JPG)

Courtesy of Martin Miller, University of Oregon

Examples Limestone

made when calcite mineral precipitates from sea water

Rock Salt—made from evaporation of sea waters

Rocks that have changed due to intense temperature and pressure

Igneous, sedimentary and other metamorphic rocks can change to become metamorphic rocks

Meta” means “change” andmorphosis means “form” in Greek

Places that are covered miles thick with other rock causing pressure

Near colliding plates (near mountain ranges)

Where magma intrudes relatively cool rock

When hot water intrudes rock

Where a meteorite strikes Earth (rare)

Where lightning bolts strike rocks (rare)

Pressure from overlying rock layers High heat, but not enough to melt the rock Rocks may be flattened or bent or atoms

may be exchanged to form new minerals.

The minerals grains in rocks subjected to extreme pressure often rearrange themselves in a parallel fashion, creating a foliated texture (Image A - before metamorphism; Image B - after metamorphism).

Foliated—mineral grains are flattened and line up in parallel bands

Example: gneiss formed from rearrangement of minerals in granite into bands

Non-Foliated—No bands are formed

Example: marble formed from limestone

Write down what type of rock you think it might be.

Based on what reason have you suggested what type of rock it is? Hint: Explain what features you observe for each rock

Draw a simple picture of each rock

No. Type of rock Rational Diagram

1 Sediment Has a grain appearance – looks like compressed grains

2 Igneous - Plutonic Has medium sized crystals. Coarse grained

• No set path a rock takes to become another kind of rock

http://www.classzone.com/books/earth_science/terc/content/investigations/es0602/es0602page02.cfm

1

2 3

Weathering, Erosion, Compaction, Cementation

Recrystallization

Weathering, Erosion, Compaction, Cementation

Recrystallization

Melting, Solidification Melting,

Solidification

IGNEOUS

SEDIMENTARY METAMORPHIC

P226 – Q1, 2, 3, 5, 8P232 – Q1 – 12P240 – Q1 - 8

Rocks are continually changed by many processes, such as weathering, erosion, compaction, cementation, melting, and cooling

Rocks formation and cycle

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