Volcanoes in our Community

Volcanic and Other Types of Rocks and What Makes Them

Science Std: Geo # 3c

There are 3 main types of rocks

Sedimentary

Metamorphic

Igneous

Mel

ting

There are 3 main types of rocksThese rocks all change from one type into another

SedimentaryRock

MetamorphicRock

IgneousRock

SedimentSilt and Dirt

SedimentSilt and Dirt

Lava andMagma

Pressure

Wea

ther

ing

Wea

ther

ing

Pressure

WeatheringWeathering

Heat a

nd P

ress

ure

Heat and Pressure

MeltingCooling

Melting

All rocks are made from….Minerals that can be described by….

A Chemical Formula

Each mineral has a unique (only one)

combination of atoms

How it Looks And Acts

•Porous (lots of tiny bubble holes called vesicles•Granular (lots of small grain parts)

•Smooth / Rough

•Hard / Soft

•Shiny / Dull•How easily it breaks

All rocks are made from….All Minerals have Crystals

Crystals are atoms and molecules that are grouped and stuck together in a neat pattern

Like toy soldiers lined up, they have a definite pattern that keeps going on and on We’ll talk more

about crystals later….

Let’s look at the 3 types of rocksHow are they formed and look

SedimentaryRock

MetamorphicRock

IgneousRock

First we will look at Igneous Rocks

Lets look at the 3 types of rocksMolten rock (magma and lava) cools and makes Igneous RockSedimentary

Rock

MetamorphicRock

IgneousRock

First we will look at Igneous Rocks

Depending on how fast it cools, it looks very different

If it cools fast, it makes small crystals that you can’t see

If it cools slowly, it has time to make big crystals that you can easily see

Lets look at the 3 types of rocksThere are 2 main types of igneous rocks Igneous

RockExtrusive or Volcanic igneous rocks

They cool quickly

Normally come to the surface

Little or no crystals seen in the rocks (Basalt)

Very few crystals makes the rock look like black glass (Obsidian)

Basalt Igneous Rock

Obsidian Igneous Rock

Lets look at the 3 types of rocksThere are 2 main types of igneous rocks Igneous

RockIntrusive or Plutonic igneous rocks

Cools slowly under the surface of the Earth

Big crystals formed easy to see with eyeSizes and shapes vary widely from boulders to whole mountain ranges

Can only see when lifted up or erosion shows them

Granite

Geode

Quartz

Diamond

Lets look at the 3 types of rocksRegardless of the type of rock…. Igneous

RockThe color of the rock depends on the minerals in the magma

Light colored rocks have high silica content

Darker colors are from iron and magnesiumMedium colored rocks have combinations of light and dark minerals

Dark colored rocks have low silica content and have more iron and magnesium

SedimentaryRock

Lets look at the 3 types of rocksThe next type of Rock is Sedimentary Igneous

RockThere are 3 types of sedimentary

SandstoneMade from sediment only

LimestoneMade from pieces of fossils and sediment

ConglomerateMade from other bits of rock and sediment

MetamorphicRock

SedimentaryRock

Lets look at the 3 types of rocksThe last type of rock is MetamorphicThese can be made by…..

Heat aloneThis is where the rocks

are heated and changed without having a lot of

pressure on them

Heat and PressureThis is where there is both heat and a large amount of pressure to change the

rocks

Limestone

Becomes

Marble

IgneousRock

MetamorphicRock

So where can these rocks form?Igneous rocks come from volcanic eventsBut you don’t have to have an eruption to make igneous rocks…..

Magma Pockets

Magma can rise up and collect in a pocket

The magma can cool and form igneous rocks

It cools slowly so it can make large crystals

Lava on the surface

Lava comes to the surface

On the surface it is quickly cooled by air or

water

So it forms small crystal rocks

MetamorphicRock

IgneousRock

So where can these rocks form?Metamorphic rocks form primarily at plate boundaries.

Convergent Plates

2 plates crush and rub together

High pressure and temperatures change the rocks

They can then work their way up or we can dig down

Transverse Plates

2 plates rub together

Harder to do here because you need heat

to have the change

Unless the transverse boundary is deep, you

won’t get the heat needed

SedimentaryRock

MetamorphicRock

So where can these rocks form?Sedimentary Rocks usually form under water

Sand and silt pile up on the ocean floor

Over time (millions of years) the silt on the top presses down on the silt on the bottom

After a long time, the silt on the bottom presses and cements together into new sedimentary rocks

SedimentaryRock

MetamorphicRock

Where do the rocks go?

All rocks erode and wear away due to water and weather and chemical action

Rocks are subducted at convergent plate boundaries and are melted back into

magma

Rocks under the surface can break apart (fracture) speeding up the erosion

IgneousRock

Eventually, all rocks are recycled into another type of rock