Rocks and the Rock Cycle

Mr. Silva

Three Major Types of Rocks

• Igneous Rocks: “meaning from fire”

– Formed when magma cools and hardens.

– Magma is called lava when it reaches the earth’s surface.

Three Major Types of Rocks

• Sedimentary Rock:

– All types of rock, minerals, and organic matter that have been broken into fragments by forces.• Wind, water, ice

– Deposits harden after being compressed together.

Three Major Types of Rocks

• Metamorphic Rock: “changed form”

– When an existing rock undergoes extreme forces it changes form.• Tremendous pressure• Extreme heat• Chemical processes

The Rock Cycle• A cycle is a series of changes

– Geological forces and processes cause rock to change from one type to another and back again.

– Rocks in the crust have passes through the cycle many times.

The Rock Cycle

Formation of Igneous Rock

Formation of Igneous Rock• When lava cools and hardens it forms

igneous rock.

• The rock has two categories and is based on how the lava cools.

– Intrusive igneous rock– Extrusive igneous rock

Intrusive Igneous• The cooling of magma deep below

the earth’s surface.

• Called intrusive because the lava that forms them intrudes other rocks.

• The magma then slowly cools to form rock.

• The slow cooling allows minerals to collect and form large crystals.

Extrusive Igneous• Formed when there is a rapid

cooling of lava or melting of rocks on the earth’s surface.

• The rapid cooling does not give crystals time to form.

• The main difference between the two types of igneous rock is the size of the crystal when the rock is forming.

Texture of the Rocks• The larger the crystals, the more rough the

rock will be.

• When rapid cooling occurs and crystal are not allowed the opportunity to form, the rock will appear extremely smooth.

• Crystal formation will be so small that they are not seen by the unaided eye.

Texture of the Rocks• An igneous rock with both large and small

crystals is called porphyritic.

• The porphyritic texture is created when lava cools slowly and is then sped up.

Texture of Rock• When thick lava cools rapidly no crystals

form at all.

• Usually thicker lava has an increased amount of trapped gases and this will cause the igneous rock to become full of holes.

Composition of Rock• The mineral make of the lava determines

the chemical make-up of the rock.

• There are 3 different types of families:– Felsic– Mafic – Intermediate

Formation of Sedimentary Rock

Formation of Sedimentary Rock

• Made up of an accumulation of various types of sediment.

• Compaction or cementation are two process that form sedimentary rock.– Compaction- when all air and water is

squeezed out of sediment– Cementation- when minerals are left

between the fragments of sediment.

3 Types of Sedimentary Rocks

• Clastic Sedimentary Rock- rock is made up of rock fragments that have been moved by water, wind or ice.

• Chemical Sedimentary Rock- forms from minerals that precipitate from water.

• Organic Sedimentary Rock- forms from the remains of organisms.

Clastic Sedimentary rocks• Rocks are classified by the sediments size.

• Conglmerates- rocks composed of rounded gravel size fragments or pebbles.– Individual pieces are easily seen.

• The sandstone group is made up of sand size grains that have been cemented together.

• The third group is shale, which consists of clay size particles the easily flake or break apart.

Conglomerates

Sandstone

Shale

Chemical Sedimentary Rocks

• Rocks that form from minerals that were once dissolved by water.

• These rocks are called evaporates.

Organic Sedimentary Rock

• Formed out of the remains of living things.

• Coal is a prime example of this.

Sedimentary Rock Features

• Easily identifiable– Layering– Ripples marks– Mud– Cracks– Fossils– Concretion

Formation of Sedimentary Rock

Formation of Metamorphic Rock

• Changed from one type of rock into another by heat, pressure, and chemical processes.

• Form deep beneath the earth’s surface.

• ALL metamorphic rocks are formed from existing igneous, sediment or metamorphic rocks.

Formation

• Minerals may change in size or shape or separate into parallel bands.

• Metamorphic formation happens two different ways– Contact metamorphism– Regional metamorphism

Contact Metamorphism

• Formed when magma pushes through existing rock.

• Changes the structure and mineral composition of surrounding rock.

Regional Metamorphism• Metamorphism sometimes occurs with

tectonic plate movement.• Tremendous heat and pressure is

created at plates edge. • This heat and pressure will cause

chemical changes in the rocks.• Most metamorphic rock is created be regional metamorphism.

Classification of Rocks

• Rocks can be classified into two different types based on their texture:– Foliated– Nonfoliated