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How Rocks Are Formed

hi guys in this video we are going to

look at how rocks are formed and the

three different types of rocks that are

formed in the different ways these types

of rocks are igneous rocks sedimentary

rocks and metamorphic rocks so firstly a

little background information on rocks

the earth is about 4.5 billion years old

okay so that's a pretty old however most

of the rocks found on earth are only

about a hundred million years old and

this 100 million years sounds like a

long time but when you're talking 4.5

billion years you can see that it's only

a fraction so therefore there must be

some process which is making and

breaking rocks down and making new ones

the first way that rocks can be made is

through the cooling of molten rock and

we call these igneous rocks and igneous

comes from the word Greek word from fire

so we have this molten rock inside the

earth in the mantle and as this gets up

to the top of the earth in the crust it

can cool down and form rocks and this

can happen either on top of the earth

where lava on the surface cools down

into extrusive rocks or it can happen

just below the surface of the earth

where the magma inside the earth cools

down to form intrusive rocks now these

rocks have different properties based on

how they formed some of the properties

of igneous rocks is that they're strong

and hard and more importantly they have

interlocking crystals the reason they

have interlocking crystals is because

when that molten rock cooled and the

crystals grew these crystals formed so

because it all formed at the same time

these crystals interlock with each other

some examples of igneous rocks include

pumice basalt obsidian and granite and

the thing that matters here is the

minerals that are in that molten rock

when it cools as well as how quickly

that molten rock cools

sedimentary rocks on the other hand are

formed when small particles of rocks or

sediment settle over time and we call

this deposition and the particles become

cemented together so basically they're

sitting there in layers and over many

many many years those rocks start to

stick together and we call this

cementation for this reason sedimentary

rocks are found in layers so they'll

have a layer that's come from one place

through erosion and then maybe the

waterways change and you get erosion

bringing the sediments from another

place into the same lake there's soft so

they can generally break apart in your

hand and they don't have interlocking

crystals the reason for this is the

crystals were not formed within the rock

they were formed in the previous rocks

that were then weathered and those

sediments formed this sedimentary rock

so those crystals were formed a long

time ago before the rock some examples

of sedimentary rocks include mud stone

shale silt stone and sandstone the

difference here between the different

types of rocks is the sediments that

make up those rocks both the size of the

sediments and the minerals found in

those sediments so sandstone has

reasonably large sediments that are

cemented together while silt stone has

very fine grains of sediment cemented

together the third type of rock is

called a metamorphic rock and this again

comes from a Greek word matter being

change and morph being form so over time

inside the earth the immense heat and

pressure causes those rocks in the earth

to change forms so it might come from an

igneous rock or it might come from a

sedimentary rock but we end up with

metamorphic rocks which have different

properties from the rocks that they've

formed from some examples of metamorphic

rocks include marble which is made when

limestone undergoes Ament immense heat

and pressure over period of time and

nice which is made when diorite

undergoes immense heat and pressure over

the time

so you can see these rocks are made from

other rocks the common thing here is

heat and pressure and the difference

between the type of rock will be the

different rock sedimentary or igneous

that it the rock is made of so in this

video we have looked at igneous rocks

coming from fire when magma from or lava

from volcanoes cools to form rocks we've

looked at sedimentary rocks which are

formed when small particles called

sediments are cemented together to form

rocks and we've looked at how these two

igneous and sedimentary rocks can

undergo immense heat and pressure to

change form into a third type of rock

called a metamorphic rock peace out guys