 Welcome back to our series on the rock cycle. In this video we'll be looking at igneous rocks and in particular how they fit into the rock cycle. We'll be looking at the processes involved in their formation and the controls in particular on texture. So let's start this video with a feel for texture. Igneous rocks are either intrusive, plutonic rocks or extrusive volcanic rocks. The plutonic igneous rocks have a coarse interlocking texture and you can see that these minerals are easily seen with your naked eye. Now these minerals would have cooled over thousands to millions of years so they've had a long time to form these large crystal sizes that you can see. Whereas when we compare that to a volcanic extrusive igneous rock it has a very fine texture. The minerals are still interlocking however you can't see them with your naked eye and this is because they cool very quickly on the surface so they just don't have enough time to grow as large. The really cool thing with this sample is you can see its flow patterns. So this was a basaltic lava flow and you can even see it has a slightly vesicular texture and by that I mean there are little vesicles where the gas bubbles would have been trying to escape as it cooled. So in summary igneous rock textures are controlled by the rate at which it's cooled from the molten rock. Extrusive igneous rocks cool fast so they have a very fine crystal texture. Conversely intrusive igneous rocks cool much slower so they've got time to grow much larger crystals. In our next video we'll be talking about the composition of igneous rocks and the processes that control this.