Transcript

MARCUS BADGER:

So here we have the three fundamental types of rock. We’ve got a sedimentary rock, an igneous rock, and this metamorphic rock.

GAIL:

And how do I tell the difference?

MARCUS BADGER:

Well, the easiest place to start is to tell the difference between the sedimentary rock and the other two. And the way we can do that is look really carefully at the grains, the little bits that were in the rocks. So if you look at this one, it looks kind of like lots of little bits of stuff stuck together, and that’s because that’s basically what a sedimentary rock is, whereas if we look at the other two, they both look like they’ve got crystals – individual crystals which look like they’ve kind of grown together, and they’re all interlocking.

The next thing is, how do we tell the difference between the igneous rock and this metamorphic? And in these two examples, I hope it’s pretty obvious that here, in the metamorphic rock, we’ve got this banding. We’ve got really obvious layering, whereas in this igneous rock, there’s no obvious orientation of the grains. There’s no layering or banding that we can see.

GAIL:

And how did those differences come about?

MARCUS BADGER:

Well, the difference between these two is the banding that we see here in this metamorphic rock. And that difference has come about because when this one was formed, it was exposed to some kind of pressure. And in this case, the pressure probably came from the sides like this – that kind of direction. And that causes the alignment of the minerals and that banding that we see.

GAIL:

Cool.

ANNE JAY:

Learning how to differentiate between these three different types of rock is a key skill for geologists. And you’re going to learn how to do that in the next part of the course.