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5.2.3 Moon rocks under the microscope

The video introduces the study of polished thin slices of rock – known as thin sections – under the microscope, how samples are prepared and what geologists look for when they study thin sections. It also introduces the features of the virtual microscope including panning and zooming, measurements and the rotation feature. Finally, the minerals that you will see next, when you have your first chance to use the virtual microscope, are described in more detail.

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I want to show you the Virtual Microscope. It's easy to use, and you can use it to look at Moon rocks. You can look at the lunar mare basalts, the highland rocks, meteorite impact breccias, and the soils, all of which the astronauts brought back between 1969 and 1972.
When geologists pick up rocks, they can generally tell quite a lot just from the rock - from the colours, from the weight of the rock, from the textures and the patterns in it. If you really want to understand a rock, you have to cut a thin section. Now, you can see that we've taken one from this rock already. The thin section is a very thin slice of rock glued to a glass slide like this one.
This is a sample of that meteorite. It's so thin that the light can pass through it, so that when I place it on this microscope, you can start to see the textures inside the rock. And you can see mineral grains that are just a few fractions of a millimetre across.
What we've done with the Virtual Microscope is we've digitised hundreds of rocks. Most of them are terrestrial rocks from Earth, but also we've managed to work with NASA to digitise some Moon rocks. So I want to take you through the features of the Virtual Microscope, and show you some of the minerals that you'll have to study in the first exercise.
You can do this on your smartphone, on a tablet like I've got here, or a computer. The Virtual Microscope works on almost any platform. You don't need a powerful system, you just need a good connection to the internet.
So let's look at the one on the computer here. In fact, this is the first sample you'll study. It's 14053, it's a lunar basalt, and you can see the general features of the microscope. I'm just going to click and drag on the scale at the bottom, and you'll see that we zoom in on the sample. On a tablet or a smartphone you can pinch to zoom. Already you can see the features in this rock which you simply couldn't see by holding it in your hand.
And if I zoom in a bit further, right at the top of the screen here you've got a scale ruler. And you can see that I'm looking at a scale here something like four or five millimetres across. And already I can see minerals that are tiny fractions of a millimetre.
I'm going to cross the polars. In other words, I'm going to look at the rocks between cross polars just by clicking here. You can see the microscope's pulling in the new image from the server. Very different colours that tell me a lot more about the rock. There's actually a third way of viewing, in reflected light, and this is a way of looking for metal grains.
The other feature of the microscope, which mimics the sort of thing you see in our specialist microscopes, is the rotating view. Each time you see one of these little icons here, like this little rotating red arrows, you click there and it opens up a rotating view of that point. The reason for doing that is you look here, you can see that the colours of the minerals change as I rotate them through the light.
Let's think about the first exercise that you're being asked to do. I'll show you the three minerals-- pyroxene, plagioclase, and opaques. And that will equip you to look at most Moon rocks. Pyroxene is this pink mineral here. And I can see it's slightly pinker at the edges-- has a bit of cleavage going through it.
The palest mineral here, which appears white, is plagioclase. And the other one is the opaques. Here's a big opaque in the centre here.
This is the key thing about a microscope and different types of lighting. I'm switching there to reflected light, and what was a black mineral in the centre there is now at least two different minerals. So you can learn a lot about rocks by using the Virtual Microscope. It's not just a pretty picture. You can see more Moon rocks and meteorites and terrestrial rocks on the Virtual Microscope website. So you can go and explore.
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