Pumice is an example of extrusive igneous rock. The word extrusive means that the magma was forced onto the earth's surface and cooled in a matter of hours. Granite is an example of intrusive ...

ISLA: That’s right. It’s also an igneous intrusive feature, just like them. The rock they’re made of is called phonolite - also called a ‘sounding stone’, it makes a metallic ...

After dealing with the constituents (minerals), and their relations (textures), he gives in summary some twenty-five systems of classification of the igneous rocks. As many of these are now of ...