Hello, my name's Mrs. Niven, and today we're going to be talking about igneous rocks as part of our unit on earth's resources.

Now, you may have some understanding of what we talk about in today's lesson from your previous learning.

But what we do in today's lesson will help us to answer that big question of how can we explain changes that we observe in the air, the oceans, and the land.

By the end of today's lesson, you should hopefully feel more confident being able to explain how igneous rocks form, and also describe features of different types of igneous rock.

Now, throughout the lesson I will be referring to some key words, and these include lava, magma, crystallisation, extrusive, and intrusive.

Now the definitions for these keywords are given in sentence form on the next slide, and you may wish to pause the video here, so you can read through these definitions, or perhaps make a note of them so you can refer back to those definitions later on in the lesson or later on in your learning.

Now, today's lesson is broken into three parts.

We'll look at melting rock, freezing rock, and then look at how that impacts the types of igneous rocks that form.

So let's get started to look at how rocks might melt.

Firstly, we need to recall that earth is a rocky, spherical planet, whose structure is divided into different layers.

So we have crust, the mantle, the outer and inner cores.

And that the crust itself is broken into different pieces known as tectonic plates.

Now a tectonic plate is composed of a portion of earth's crust, and the upper mantle that rests directly below that section of crust.

And the earth's surface has approximately 15 major tectonic plates across its surface.

We also need to remember that there are radioactive processes taking place in earth's inner core that generate energy, and this energy then transfers through earth's layer until it reaches the mantle below those tectonic plates.

Now, rock that is deep underground, so we're talking about rock that's found in the mantle, is under an enormous amount of pressure.

And as pressure increases, so does the melting point of that rock.

Now what that means then is that despite the amount of energy that's being transferred through earth's layers from that inner core, the rock in the mantle remains solid, because of the amount of pressure that it is under.

What all this means then is that there's a very fine line where the correct conditions are found for rock to melt.

Now, when I'm talking about those conditions, I'm talking about the right temperature, and the correct amount of pressure needed for that rock to melt.

Now, those specific conditions of temperature and pressure are found near tectonic plate boundaries.

So we're talking about where one tectonic plate maybe slides underneath another one, where tectonic plates might be moving away from each other, and these specific conditions of temperature and pressure can also be found at hot spots.

Now these are places where melted rock is able to push through the crust.

Let's stop here for a quick check.

True or false? The upper mantle is composed of solid rock.

Well done if you said, true.

But which of these statements best justifies that answer? Well done if you said B.

The mantle is under an immense amount of pressure, and that's what keeps the rock in the solid state.

Very well done, guys.

Great start.

Keep it up.

Now you may recall that rocks are a mixture of minerals or organic matter, and I have an example here of granite.

Now, granite contains the minerals of feldspar, quartz and mica.

And you might also recall that minerals are pure substances.

Now, because they're a pure substance, each mineral has a very specific melting point.

Now, there is a knock on effect for that, because when rocks become hot, that means that some minerals might melt, while other minerals remain in the solid state.

So if we were to take a zoomed in look of a particular rock, with say three different types of minerals shown here in the diaphragm.

If the temperature then, and the pressure gets to a point where the melting point of one mineral is reached, we could see a deformity in one of those minerals.

Now, most minerals in the rocks melt at around about 600 to 1300 degrees Celsius, and I think we can all agree that that means the melting point of rocks then is very, very high.

Time for another quick check.

Which of these do you think could melt rock? Well done If you said C, a furnace that's able to reach temperatures above 1000 degrees Celsius would be able to melt some rocks.

So very well done if you managed to get that correct, guys.

Great job.

Now, melted rock can also be described as being molten.

So molten is melted.

Now, melted or molten rock can be found both above and below earth's surface.

So if we say, look at a diagram here of a volcano, we can identify the molten rock both above and below earth's surface.

So the molten rock above earth's surface is called lava, and any molten rock, or melted rock that's found below earth's surface then is referred to as magma.

Let's stop here for another quick check.

Which of the following do you think is a correct statement about magma? Now, you may wish to pause the video so you can discuss your ideas with the people nearest to you and then come back when you're ready to check your answer.

Well done if you chose C, magma is deep underground, but it's only found in areas where conditions, so that's the temperature and pressure, are correct and can melt the rock in that location.

It's not everywhere, it's only where those conditions will allow rock to melt.

So very well done if you managed to get that correct, guys.

Well done.

Time now for the first task in today's lesson.

What I would like you to do is to use words from the box to fill in the blanks below.

So pause the video, and then come back when you're ready to check your work.

Okay, let's see how you got on.

Now the eagle-eyed among you will notice that there were more words than were needed, so you really needed to make sure that you were using those correct words.

So what I'm gonna ask you to do is as you mark your work, please do tick it if you got it right, fix it if you got it wrong, and fill in the blanks if you left them blank so that you have this nice summary about melting rock.

So, reading them out.

A, was earth's surface is called the crust.

Rock that has been melted is described as being molten.

The mantle is solid rock.

Conditions needed to melt rock are usually found at tectonic plate boundaries.

The melting point of rock is very high.

Melted rock outside earth's surface is called lava.

And magma is melted rock found under earth's surface.

Very well done if you manage to get those all correct, guys.

Great, great job.

Next, I'd like you to label the diagram as shown below, and you may wish to refer to some of the statements from part one of task A to help you, but pause the video and come back when you're ready to check your answers.

Okay, let's see how you got on.

If you got these correct, you should have labelled A as magma, because that looks as molten rock that is below earth's surface.

B then is lava, because it's molten rock outside earth's surface.

And C then is showing us the tectonic plates.

So very done if you managed to get those correct, guys.

Great, great job.

Now that we're feeling a little more comfortable talking about how rock might melt, let's look at how rock freezes.

Now, you may recall that when substances cool past a particular temperature, they change from the liquid state into the solid state, and this particular physical change is known as freezing.

And you will be familiar with this.

For instance, dew that is found on grass is actually just liquid water.

And if the temperature outside gets below zero degrees Celsius, that water then on the grass can freeze, and what we now have is frost, or solid water on that grass.

Now, some substances actually form crystals when they freeze, and in fact, that's what water is doing when it changes from the liquid state into the solid state.

Now, when melted or molten rock freezes, it also forms crystals in a process known as crystallisation.

So igneous rocks form when molten rock, that's the magma or the lava, cools and crystallises.

And I have a video here that's showing a lava flow in Hawaii.

And brighter areas show where the lava is flowing, so that's molten rock above ground, and the darker areas that start to form around those brighter areas show where that lava is cooling, and forming crystals, or crystallising.

Let's stop here for a quick check.

Which term describes the formation of crystals when molten rock cools? Well done if you chose D, crystallisation.

That's the process of forming crystals.

Very well done, guys.

Keep it up.

Now, how quickly that molten rock, so that's the magma or the lava, how quickly that cools will impact then the size of the crystals that actually form.

So if a molten rock cools quickly, it's going to produce smaller crystals.

If that molten rock cools slowly, it manages to produce larger crystals.

Let's have another quick check.

True or false? Larger crystals form when magma cools quickly.

Well done if you said false.

But which of these statements best justifies that answer? Well done if you chose B, larger crystals form when magma cools slowly.

The key for larger crystals is cooling slowly.

Very well done if you managed to get those correct, guys.

Really impressed.

It's now time for the next task in today's lesson, and I'd like you to consider this substance known as Salol.

Now, salol melts at 42 degrees Celsius, and it can be cooled between two microscope slides.

Now, salol forms crystals as it cools, and at room temperature, medium-sized crystals will form.

I'd like you to consider what will the crystals be like if hot microscope slides are used, and I'd like you to please explain why you think this will happen.

So I'm looking for that because clause, so you may wish to pause the video here so you can discuss your ideas with your neighbours, and jot down what you might think, and then come back when you're ready to check your work.

Okay, let's see how you got on.

If I was to change the room temperature slides for hot microscope slides, I would expect the crystals that were forming to be larger and that is because the salol will cool more slowly on hotter slides.

So very well done if you manage to correctly identify that the crystals will be larger, and very well done if you managed to tell me why the fact that they're cooling a lot more slowly in those hottest slides.

Well done.

For the next part of this task, I'd like you to observe crystals forming yourself.

So, once you've collected all the apparatus listed, I want you to use the dropping pipette to put a few drops of salol onto one of the warmed microscope slides, and then immediately cover that with the other warmed microscope slide.

You'll then repeat those two steps with the cooled microscope slides.

So you'll end up with two sets of slides, each with a few drops of salol between them.

Now, once you've done that, you want to grab your magnifying glass, or your hand lens and observe any crystals that form, and then you'll record your observations for each set of slides in then a table that I'll show you in a moment.

But a few hints and tips before you get started.

First of all, remember that salol will form crystals at room temperatures, so keep it warmed in a water bath until you're ready to use it.

Secondly, your hands can warm or cool these microscope slides as you handle them, so try to handle them as little as possible, and when you do so, only hold them by the very edges of the microscope slides, so the thinnest part, not the large flat bits that you're going to be putting the salol on, just those outside edges.

And then finally, to observe these crystals as best you can, sometimes it helps to leave those microscope slides on some dark coloured backing, so maybe some darker coloured card paper, or perhaps a darkened desk, just to help you to observe those crystals forming a little bit better.

And the table that I'd like you to use to record your observations is shown here.

So what I'd like you to do then is to gather all your equipment, follow those instructions that were shown earlier, and observe those crystals forming, record your observations.

So pause that video, and come back when you're ready to check your work.

I hope you had a really good time doing that.

I've always liked this practical, it is a little fiddly at times, but you can really see those crystals growing, and hopefully what you've noticed then is that the cooler the microscope slides that you're using, you managed to see firstly that the crystals were forming very quickly, and that those crystals were actually quite small.

And that the warmer microscope slides, actually it took quite a while for those crystals to form, they'd be forming very slowly, but those crystals that did form would've been larger than the crystals forming on those cooler microscope slides.

So I've written my observations in words here.

Some of you may have wanted to sketch what you observed as well, just to see that different crystal sizes, but either way of how you recorded those observations, we should have seen that they were smaller crystals on the cool microscope slides, and that the larger crystals were on the warmer slides.

Very well done if you managed to have similar observations.

Now we know a little bit more about the conditions needed for rocks to melt, and also for rocks to freeze.

Let's look at how those two ideas come together to give us different types of igneous rocks.

Now, if you remember, we have melted rock that is both inside earth's surface, which is magma, and we have melted or molten rock that is found outside earth's surface, and that's known as lava.

Now, both forms of melted rock, magma and lava, can undergo crystallisation.

So that means that we can have crystallisation happening both inside and outside earth's crust.

And that process then forms two basic types of igneous rock.

Now, one type of igneous rock that forms is known as extrusive igneous rock, and they form when lava undergoes crystallisation.

Now, extrusive igneous rocks form quickly, because lava's found outside earth's surface, and therefore these will also form outside earth's surface.

And because they are outside earth's surface, they're gonna cool very quickly, and that forms then small crystals.

So extrusive igneous rocks form from lava that's crystallising quickly, forming small crystals.

Some examples then of extrusive igneous rocks include things like basalt, pumice, and rhyolite.

The other type of igneous rock then that forms is known as intrusive igneous rocks, and they form when magma undergoes crystallisation.

Now, these form very slowly and they're forming inside earth's crust, and that's because that's where magma is found.

Now because they are forming slowly, they're cooling quite slowly, that melted magma, and because it's cooling slowly, it forms large crystals.

So intrusive rocks form from magma that cools quite slowly under earth's surface forming large crystals.

Some common intrusive igneous rocks then include things like granite, gabbro, and diorite.

Let's stop for a quick check then.

Which of the following statements do you think are true about extrusive igneous rocks? Well done if you said A and D, extrusive form outside earth's surface, outside earth's crust, and because they're outside the crust they can cool quickly, which then forms small crystals.

So very well done if you've got at least one of those correct, and incredibly well done if you got both of those.

Great job, guys.

Now the other thing we need to remember about these different igneous rocks is that geological processes that take place at tectonic plate boundaries, so we're talking about things like earthquakes, volcanoes, things like that, they will be able to mix different minerals together.

Now this results then in magmas that have a varying composition of minerals within magmas at that particular position under earth surface.

What this means then is that the igneous rocks that actually form depends on not just how quickly that particular molten rock is cooling, which is affecting its crystal size, but also the mineral composition within that molten rock.

For instance, rocks then that contain a lot of silicon, tend to be usually quite pale in colour, and we're talking here about an intrusive igneous rock.

Whereas another intrusive igneous rock, this time we're looking at gabbro, contains a lot of magnesium and iron, and those particular minerals create a rock that is a lot darker in colour.

So even though we have two intrusive igneous rocks, so rocks that are forming quite slowly underground, cooling slowly, creating those large crystals, they're going to look very different from each other because of that mineral composition within that molten rock as it was cooling.

Let's stop for another quick check.

When magma cools, we know that can form different igneous rocks, but what determines the igneous rock that's formed? Well done if you chose C, both the mix of the minerals in that magma, and how quickly it cools will determine the type of rock that forms. So great job if you manage to get that correct, guys.

Fab work.

Okay, moving on to the last tasks for today's lesson.

What I'd like you to do in this first part is to match each description to the correct key word, and then each key word to the correct example.

So pause the video, and come back when you're ready to check your work.

Okay, let's see how you got on.

Well, molten rock that is rich in silicon tends to form light coloured rock.

And rocks that form small crystals quickly are known as extrusive rocks.

And those that form large crystals slowly are intrusive rocks.

That means then that molten rock that's rich in iron or magnesium tend to form darker coloured rock.

Now you then needed to match each of those keywords to the correct example.

And for granite I would've used, sorry, intrusive rocks and light coloured rock.

And then for basalt I would've said that it was an extrusive rock that is darker coloured.

So very well done if you managed to match those up correctly.

Now, I said in the last part that basalt was an extrusive igneous rock.

What I'd like you to do is to number the statements below into an order then that will describe how that basalt might have formed.

So, you may wish to pause the video whilst you discuss your ideas with the people next to you and then come back when you're ready to check the orders.

Okay, let's see how you got on.

So for this first statement then I would've chosen, that some rock at the edge of a tectonic plate could melt.

Now, at this point then the molten or melted rock is now known as magma, because it is under a tectonic plate.

That magma then could break through earth's surface, possibly at a volcano.

And at this point now it's known as lava, and because it's outside earth surface, it can cool quickly on that surface.

Now, as it's cooling then, it will form rock with crystals, and those crystals then tend to be very small, because that lava is cooling quickly.

So very well done if you manage to get those statements in the correct order, guys.

Great job.

That was not an easy task.

For the very last part of this task then, what I'd like you to do is to consider some of the statements that pupils have made whilst they're discussing what they've learned about igneous rocks.

Now, some of them have made some errors, and I'd like you to find and correct any errors in those statements.

And they include from Jun, which is that extrusive rocks form when magma exits earth's crust.

Aisha thought that intrusive rocks contain large crystals because they cool quickly.

Jacob reckons that granite has large crystals, meaning it formed quickly.

And Sofia said that basalt is an example of an intrusive igneous rock.

So, looking at these statements, has anyone made any errors, and if so, how might you correct them? This may take a little bit of time, and you may wish to discuss your ideas with the people nearest you, so definitely pause the video, and come back when you're ready to check your work.

Okay, let's see how you got on.

Now the thing is, when you're being asked to find an error and correct it, there tends to be a few different ways that you might have corrected those statements.

So, these are some suggestions of how these statements might have been improved and corrected.

So for Jun you could have changed magma to lava, or you could have said then, intrusive rocks form when magma cools inside earth's crust.

So talking about magma rather than the lava.

But two different ways you could have corrected Jun's statement.

Very well done if you managed to choose one or the other.

Now, Aisha had said that intrusive rocks contain large crystals, because they cool quickly.

You could have changed quickly to slowly, or you could have said that extrusive rocks contain small crystals, because they cool quickly.

So two different ways that you might have corrected Aisha's statement.

Now, Jacob had said that granite has large crystals, meaning it formed quickly.

You could have said slowly, rather than quickly, to correct Jacob's statement, or you could have said that basalt has small crystals, meaning it formed quickly.

So two different ways you could have corrected then Jacob's statement.

And finally, Sofia then had said that basalt is an example of an intrusive igneous rock.

To correct her statement, you could have said that basalt is an extrusive igneous rock, or you could have changed the example that she used, and changed basalt for either granite, gabbro or diorite as an example of an intrusive igneous rock.

So two different ways you could have corrected Sofia's statement there.

That was not an easy task of being able first to identify what the error is, and secondly then to think of a way to correct that error.

So very well done if you managed to correct even one or two of those statements.

And incredibly well done if you managed to correct all four of them.

Great, great job, guys.

Wow, we have gone through a lot in today's lessons.

So let's just take a moment to summarise what we've learned.

Well, we've learned that the melting point of rock is very high, and that some locations, and these are usually near tectonic plate boundaries, have the conditions necessary.

So that's the right temperature and pressure that's needed in order to melt rock.

We also found that on earth surface, molten or melted rock is known as lava.

And when that molten or melted rock is below the earth's surface, it's known as magma.

Now, igneous rocks form then when that molten rock cools and crystallises, and the size of the crystals formed in those rocks depends on how quickly that molten rock cools.

So extrusive rocks form quickly outside the earth's crust, while intrusive rocks form slowly inside the earth's crust.

And that a rock's mineral composition, and the crystal size will determine what type of igneous rock it actually ends up forming.

So a lot of stuff that we've learned today.

I hope you had a good time learning with me today, I certainly had a great time learning with you, and I hope to see you again soon.

Bye for now.